History and Principles of Steganography CSM25 Secure Information - - PowerPoint PPT Presentation

History and Principles of Steganography

CSM25 Secure Information Hiding Dr Hans Georg Schaathun

University of Surrey

Spring 2009 – Week 6

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 1 / 31

Outline

1

Secret writing in the past

2

Cryptography versus Steganography

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 2 / 31

Objectives

After this session, you should know Kerckhoffs’ principle, and understand how it applies to steganography as well as to cryptography understand the relationship between cryptography and steganography

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 3 / 31

Secret writing in the past

Outline

1

Secret writing in the past Francis Bacon 1605 The Antique

2

Cryptography versus Steganography

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 4 / 31

Secret writing in the past Francis Bacon 1605

Outline

1

Secret writing in the past Francis Bacon 1605 The Antique

2

Cryptography versus Steganography

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 5 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

3

(in some cases) that they be without suspicion. Hidden i.e. steganography

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

3

(in some cases) that they be without suspicion. Hidden i.e. steganography

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane For CYPHARS; they are commonly in Letters or Alphabets, but may bee in

• Wordes. The kindes of CYPHARS, (besides the SIMPLE CYPHARS with

Changes, and intermixtures of NVLLES, and NONSIGNIFICANTS) are many, according to the Nature or Rule of the infoulding: WHEELE-CYPHARS, KAY-CYPHARS, DOVBLES, &c. But the vertues of them, whereby they are to be preferred, are three; that they be not laborious to write and reade; that they bee impossible to discypher; and in some cases, that they bee without suspition. The highest Degree whereof, is to write OMNIA PER OMNIA; which is vndoubtedly possible, with a proportion Quintuple at most, of the writing infoulding, to the writing infoulded, and no other restrainte whatsoever. This Arte of Cypheringe, hath for Relatiue, an Art of Discypheringe; by supposition vnprofitable; but, as things are, of great vse. For suppose that Cyphars were well mannaged, there bee Multitudes of them which exclude the Discypherer. But in regarde of the rawnesse and Vnskilfulnesse of the handes, through which they passe, the greatest Matters, are many times carryed in the weakest CYPHARS.

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

3

(in some cases) that they be without suspicion. Hidden i.e. steganography

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

3

(in some cases) that they be without suspicion. Hidden i.e. steganography

No distinction between stego-systems and ciphers

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past Francis Bacon 1605

Francis Bacon 1605

Of the Proficience and Advancement of Learning Divine and Humane

Bacon’s three cryptographic principles

1

that they be not laborious to write and read; User-friendly

2

that they be impossible to discipher; Secure

3

(in some cases) that they be without suspicion. Hidden i.e. steganography

No distinction between stego-systems and ciphers Defined by purpose: keeping secrets.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 6 / 31

Secret writing in the past The Antique

Outline

1

Secret writing in the past Francis Bacon 1605 The Antique

2

Cryptography versus Steganography

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 7 / 31

Secret writing in the past The Antique

Secret Writing in the Antique

(Egypt) Tomb of Khnumethotep II c. 1900 B.C. Menet Khufu

Rebuses obscure writing. Brain exercises – adds mystery same principles in Norse Runes (Orkneys and Scandinavia)

(Mesopotamia) Seleucia 1500 B.C.: 3"x2" tablets

Protect trade secrets. Earliest known formula for glazes for pottery.

(India) K¯ ama-s¯ utra by V¯ atsy¯ ana (legendary erotics)

64 arts (yogas) women should know and practice mlecchita-vikalp¯ a (secret writing) is no. 45.

(India) Artha´ s¯ astra 321-300BC

but first political mention of cryptography Ambassadors should use cryptanalysis to gather intelligence.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 8 / 31

Secret writing in the past The Antique

China: No cryptography

Only great civilisation using ideogrammatic writing

... and only one with little interest in cryptography but steganograhy was used:

Thin silk, covered in wax, rolled into balls (la wan)

11th century: Wu-ching tsung-yao (Essentials from Military Classics)

List of 40 plaintext items (victory reports, requests for arrows, etc.) Assign to 40 first ideograms of a poem. Write appropriate ideogram in an ordinary dispatch, Mark by seal stamp over it.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 9 / 31

Secret writing in the past The Antique

China: No cryptography

Only great civilisation using ideogrammatic writing

... and only one with little interest in cryptography but steganograhy was used:

Thin silk, covered in wax, rolled into balls (la wan)

11th century: Wu-ching tsung-yao (Essentials from Military Classics)

List of 40 plaintext items (victory reports, requests for arrows, etc.) Assign to 40 first ideograms of a poem. Write appropriate ideogram in an ordinary dispatch, Mark by seal stamp over it.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 9 / 31

Secret writing in the past The Antique

Elementary Steganography à la greque

Reported in Histories by Herodotus (c. 486-425 B.C) Histæus 440 B.C.

1

Shave the head of a slave

2

Tattoo the messages on his head

3

Wait until the hair grows back

4

Dispatch the Slave

(also used by Germany in the early 20th century) Wax tablets

1

Remove the wax

2

Write the message on the wood

3

Recover with wax to make a blank tablet.

(Demeratus used it to warn Sparta of a Persian invasion)

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 10 / 31

Secret writing in the past The Antique

Elementary Steganography à la greque

Reported in Histories by Herodotus (c. 486-425 B.C) Histæus 440 B.C.

1

Shave the head of a slave

2

Tattoo the messages on his head

3

Wait until the hair grows back

4

Dispatch the Slave

(also used by Germany in the early 20th century) Wax tablets

1

Remove the wax

2

Write the message on the wood

3

Recover with wax to make a blank tablet.

(Demeratus used it to warn Sparta of a Persian invasion)

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 10 / 31

Secret writing in the past The Antique

Elementary Steganography anno 18..

Pin holes in news papers

Mark individual letters in a news paper

make pin wholes

• verwrite with a pencil

Invisible ink Quite a few methods

Invisible to a casual observers Easy to spot when you know what to look for

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 11 / 31

Cryptography versus Steganography

Outline

1

Secret writing in the past

2

Cryptography versus Steganography Kerckhoff’s principles Steganography versus Kerckhoffs

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 12 / 31

Cryptography versus Steganography Kerckhoff’s principles

Outline

1

Secret writing in the past

2

Cryptography versus Steganography Kerckhoff’s principles Steganography versus Kerckhoffs

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 13 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

The Advent of Modern Cryptography

Auguste Kerckhoff 1883

« La cryptographie militaire » Journal des sciences militaires 1883 Principles of military cryptography Defines the security paradigm

Claude Shannon 1948

Defines Information ... and Entropy to measure Information quantitatively Enables mathematical proofs of security of information

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 14 / 31

Cryptography versus Steganography Kerckhoff’s principles

Modern Cryptography

Modern cryptography has mainly been shaped by Auguste Kerckhoff 1883 : The security paradigm Claude Shannon 1948 : Mathematical theory of information and Diffie & Hellman 1976 (Public Key Cryptography) The consequence of Modern day cryptography is

Theoretically mature Reliable Highly trusted technology

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 15 / 31

Cryptography versus Steganography Kerckhoff’s principles

Modern Cryptography

Modern cryptography has mainly been shaped by Auguste Kerckhoff 1883 : The security paradigm Claude Shannon 1948 : Mathematical theory of information and Diffie & Hellman 1976 (Public Key Cryptography) The consequence of Modern day cryptography is

Theoretically mature Reliable Highly trusted technology

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 15 / 31

Cryptography versus Steganography Kerckhoff’s principles

Modern Cryptography

Modern cryptography has mainly been shaped by Auguste Kerckhoff 1883 : The security paradigm Claude Shannon 1948 : Mathematical theory of information and Diffie & Hellman 1976 (Public Key Cryptography) The consequence of Modern day cryptography is

Theoretically mature Reliable Highly trusted technology

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 15 / 31

Cryptography versus Steganography Kerckhoff’s principles

Modern Cryptography

Modern cryptography has mainly been shaped by Auguste Kerckhoff 1883 : The security paradigm Claude Shannon 1948 : Mathematical theory of information and Diffie & Hellman 1976 (Public Key Cryptography) The consequence of Modern day cryptography is

Theoretically mature Reliable Highly trusted technology

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 15 / 31

Cryptography versus Steganography Kerckhoff’s principles

Modern Cryptography

Modern cryptography has mainly been shaped by Auguste Kerckhoff 1883 : The security paradigm Claude Shannon 1948 : Mathematical theory of information and Diffie & Hellman 1976 (Public Key Cryptography) The consequence of Modern day cryptography is

Theoretically mature Reliable Highly trusted technology

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 15 / 31

Cryptography versus Steganography Kerckhoff’s principles

Auguste Kerckhoffs (1835–1903)

1

Le système doit être matériellement, sinon mathématiquement, indéchiffrable ;

2

Il faut qu’il n’exige pas le secret, et qu’il puisse sans inconvénient tomber entre les mains de l’ennemi ;

3

La clef doit pouvoir en être communiquée et retenue sans le secours de notes écrites, et être changée ou modifiée au gré des correspondants ;

4

Il faut qu’il soit applicable à la correspondance télégraphique ;

5

Il faut qu’il soit portatif, et que son maniement ou son fonctionnement n’exige pas le concours de plusieurs personnes ;

6

Enfin, il est nécessaire, vu les circonstances qui en commandent l’application, que le système soit d’un usage facile, ne demandant ni tension d’esprit, ni la connaissance d’une longue série de règles à observer.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 16 / 31

Cryptography versus Steganography Kerckhoff’s principles

Auguste Kerckhoffs (1835–1903)

Translation from Wikipedia

The system should be, if not theoretically unbreakable, unbreakable in practice. The design of a system should not require secrecy and compromise of the system should not inconvenience the correspondents The key should be rememberable without notes and should be easily changeable The cryptograms should be transmittable by telegraph The apparatus or documents should be portable and operable by a single person The system should be easy, neither requiring knowledge of a long list of rules nor involving mental strain

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 17 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Bacon said: that they be not laborious to write and reade Why? Security depends on correct use. If it is difficult, users make mistakes.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Bacon said: that they be not laborious to write and reade Why? Security depends on correct use. If it is difficult, users make mistakes.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Bacon said: that they be not laborious to write and reade Why? Security depends on correct use. If it is difficult, users make mistakes.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Bacon said: that they be not laborious to write and reade Why? Security depends on correct use. If it is difficult, users make mistakes.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Bacon said: that they be not laborious to write and reade Why? Security depends on correct use. If it is difficult, users make mistakes.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Kerckhoffs also says:

• 5. The apparatus or documents should be portable and oper-

able by a single person

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Kerckhoffs also says:

• 5. The apparatus or documents should be portable and oper-

able by a single person and

• 3. The key should be rememberable without notes and should

be easily changeable

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s first principle

User-friendliness

Kerckhoffs says:

• 6. The system should be easy, neither requiring knowledge of

a long list of rules nor involving mental strain Kerckhoffs also says:

• 5. The apparatus or documents should be portable and oper-

able by a single person and

• 3. The key should be rememberable without notes and should

be easily changeable (We will return to #3 in when we discuss keys.)

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 18 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s second principle

Security

Kerckhoffs says: The system should be, if not theoretically unbreakable, unbreakable in practice. Bacon said: that they bee impossible to discypher Security still essential. Bacon did not clarify the meaning of «impossible». Kerckhoffs allows theoretically breakable ciphers.

Why? Are theoretically unbreakable cipers at all possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 19 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s third principle

Steganography

Bacon said: that they bee without suspition. Not mentioned by Kerckhoffs. Why not?

He addressed military communications. You already know who the enemies are.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 20 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s third principle

Steganography

Bacon said: that they bee without suspition. Not mentioned by Kerckhoffs. Why not?

He addressed military communications. You already know who the enemies are.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 20 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s third principle

Steganography

Bacon said: that they bee without suspition. Not mentioned by Kerckhoffs. Why not?

He addressed military communications. You already know who the enemies are.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 20 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s third principle

Steganography

Bacon said: that they bee without suspition. Not mentioned by Kerckhoffs. Why not?

He addressed military communications. You already know who the enemies are.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 20 / 31

Cryptography versus Steganography Kerckhoff’s principles

Bacon’s third principle

Steganography

Bacon said: that they bee without suspition. Not mentioned by Kerckhoffs. Why not?

He addressed military communications. You already know who the enemies are.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 20 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ fourth principle

Telegraph

«The cryptograms should be transmittable by telegraph.» Why does he require this? What do we require today?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 21 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ fourth principle

Telegraph

«The cryptograms should be transmittable by telegraph.» Why does he require this? What do we require today?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 21 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ fourth principle

Telegraph

«The cryptograms should be transmittable by telegraph.» Why does he require this? What do we require today?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 21 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ principle

The key principle

• 2. The design of a system should not require secrecy and

compromise of the system should not inconvenience the correspondents This is the one known as Kerckhoffs’ principle. Foundation of all modern cryptography. All modern cryptographic algorithms are published in detail. Available to Eve as well as Alice and Bob. How is secrecy possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 22 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ principle

The key principle

• 2. The design of a system should not require secrecy and

compromise of the system should not inconvenience the correspondents This is the one known as Kerckhoffs’ principle. Foundation of all modern cryptography. All modern cryptographic algorithms are published in detail. Available to Eve as well as Alice and Bob. How is secrecy possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 22 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ principle

The key principle

• 2. The design of a system should not require secrecy and

compromise of the system should not inconvenience the correspondents This is the one known as Kerckhoffs’ principle. Foundation of all modern cryptography. All modern cryptographic algorithms are published in detail. Available to Eve as well as Alice and Bob. How is secrecy possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 22 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ principle

The key principle

• 2. The design of a system should not require secrecy and

compromise of the system should not inconvenience the correspondents This is the one known as Kerckhoffs’ principle. Foundation of all modern cryptography. All modern cryptographic algorithms are published in detail. Available to Eve as well as Alice and Bob. How is secrecy possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 22 / 31

Cryptography versus Steganography Kerckhoff’s principles

Kerckhoffs’ principle

The key principle

• 2. The design of a system should not require secrecy and

compromise of the system should not inconvenience the correspondents This is the one known as Kerckhoffs’ principle. Foundation of all modern cryptography. All modern cryptographic algorithms are published in detail. Available to Eve as well as Alice and Bob. How is secrecy possible?

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 22 / 31

Cryptography versus Steganography Kerckhoff’s principles

The key

The use of a key is crucial for Kerckhoffs’ principle.

• 3. The key should be rememberable without notes and should

be easily changeable. So, we have Public algorithm

Difficult (expensive) to develop few good choices

Secret key

Easy (cheap) to change Many possibilities

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 23 / 31

Cryptography versus Steganography Kerckhoff’s principles

The key

The use of a key is crucial for Kerckhoffs’ principle.

• 3. The key should be rememberable without notes and should

be easily changeable. So, we have Public algorithm

Difficult (expensive) to develop few good choices

Secret key

Easy (cheap) to change Many possibilities

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 23 / 31

Cryptography versus Steganography Kerckhoff’s principles

The key

The use of a key is crucial for Kerckhoffs’ principle.

• 3. The key should be rememberable without notes and should

be easily changeable. So, we have Public algorithm

Difficult (expensive) to develop few good choices

Secret key

Easy (cheap) to change Many possibilities

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 23 / 31

Cryptography versus Steganography Kerckhoff’s principles

The key

The use of a key is crucial for Kerckhoffs’ principle.

• 3. The key should be rememberable without notes and should

be easily changeable. So, we have Public algorithm

Difficult (expensive) to develop few good choices

Secret key

Easy (cheap) to change Many possibilities

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 23 / 31

Cryptography versus Steganography Kerckhoff’s principles

The key

The use of a key is crucial for Kerckhoffs’ principle.

• 3. The key should be rememberable without notes and should

be easily changeable. So, we have Public algorithm

Difficult (expensive) to develop few good choices

Secret key

Easy (cheap) to change Many possibilities

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 23 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Consequences

We need not trust the developers.

The key can be changed by the user Security assessment by independent experts.

Mass-produced crypto-software off the shelf.

Eve buys the same software; it does not matter.

No new costly development is required when secrets are lost

Changing the key is easy (cheap)

All new crypto-systems are published in detail

scrutinised by independent researchers world-wide

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 24 / 31

Cryptography versus Steganography Kerckhoff’s principles

Summary

Kerckhoffs’ Principles in Four Keywords

User-friendly Secure in practice (not necessarily in theory) Public algorithm – secret key Telegraph

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 25 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

Outline

1

Secret writing in the past

2

Cryptography versus Steganography Kerckhoff’s principles Steganography versus Kerckhoffs

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 26 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

Kerckhooffs’ principle and classic steganography

Recall tattooed slaves and wax tablets How does Kerckhoffs’ principle apply? It worked once – because it was unexpected Now the technique is known. Eve is going to shave all slaves passing by. ... and scrutinise every wax tablet. No key : when the algorithm is known there is no security

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 27 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

Kerckhooffs’ principle and classic steganography

Recall tattooed slaves and wax tablets How does Kerckhoffs’ principle apply? It worked once – because it was unexpected Now the technique is known. Eve is going to shave all slaves passing by. ... and scrutinise every wax tablet. No key : when the algorithm is known there is no security

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 27 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

Kerckhooffs’ principle and classic steganography

Recall tattooed slaves and wax tablets How does Kerckhoffs’ principle apply? It worked once – because it was unexpected Now the technique is known. Eve is going to shave all slaves passing by. ... and scrutinise every wax tablet. No key : when the algorithm is known there is no security

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 27 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

What about modern steganography?

Many computer programs became available during the 90-s.

Many free of charge. Hiding messages in images. For instance, using Least Significant Bit (LSB)

Most are as banale as the ancient techniques. It is relatively easy to detect the changes,

you only have to think of it.

Many solutions rely on the secrecy of the algorithm

I.e. not Kerckhoffs-compliant Not Modern Cryptography.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 28 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

Three disciplines

A conclusion

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Hiding

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Steganography

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cryptography

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 29 / 31

Cryptography versus Steganography Steganography versus Kerckhoffs

Three disciplines

A conclusion

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Hiding

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Steganography

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cryptography

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 29 / 31

Exercise

Outline

1

Secret writing in the past

2

Cryptography versus Steganography

3

Exercise

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 30 / 31

Exercise

Weekly exercise 1

Kerckhoffs’ principles

Make a list of principles, which you consider important for confidential communications systems (cryptography and/or steganography) in our

• time. You may prioritise if appropriate.

1

Give reasons for your principles.

2

Compare Kerckhoffs’ principles to your own, and justify any differences. Your principles may be general and universal, or restricted to some application which interests you (as Kerckhoff was considering military cryptography). State any assumptions you make.

Dr Hans Georg Schaathun History and Principles of Steganography Spring 2009 – Week 6 31 / 31