[PPT] - E-commerce Systems security / /2 13 IASBS 1 Security Function of PowerPoint Presentation

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E-commerce Systems security

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Security Function of Network

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Goals of Security

!

!
!

"

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Cryptography Algorithms

Symmetric Algorithm (Secret Key Algorithm)
Public Key Algorithm
Message Digest

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Cryptography: Basic Terminology

#$%$&

' !( ' )#(

*%&

' *( ' *(

"$

' *( ' "(

%&

' $ ' (

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Encryption and Decryption

E D M C M The following identity must hold true: D(C) = M, where C = E(M)

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Cryptography: Algorithms and Keys

+, -

(

(
(
(
*..(

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Key Based Encryption/Decryption

E D M C M . ( . ( K1 K2

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Symmetric Encryption Symmetric Encryption

“An introduction An introduction to cryptography” to cryptography”

“AxCvGsmWe# “AxCvGsmWe#4^, ^, sdgfMwir sdgfMwir3:dkJeTs :dkJeTs Y8R\s@!q s@!q3%” %” “An introduction “An introduction to cryptography” to cryptography”

Clear Clear-text input text input Clear Clear-text output text output Cipher Cipher-text text

Same key Same key

(shared secret) (shared secret)

Encryption Encryption Decryption Decryption

DES DES DES DES 13 /راو/29 IASBS

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Asymmetric Encryption Asymmetric Encryption

“An introduction “An introduction to cryptography” to cryptography” “Py “Py75 75c%bn&*) c%bn&*)9|f |f De^bDzjF@g De^bDzjF@g5=& =& nmdFgegMs” nmdFgegMs” “An “An introduction to introduction to cryptography” cryptography”

Clear Clear-text Input text Input Clear Clear-text Output text Output Cipher Cipher-text text

Different keys Different keys

Encryption Encryption Decryption Decryption

RSA RSA RSA RSA 13 /راو/210 IASBS

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Symmetric Algorithm

.(

' -( ' /.-.%01&

Sender and Receiver Use Same Secret Key
Advantage :simple, Fast Encryption and Decryption
Disadvantage: key exchange, key management
Algorithms : RC4, DES, IDEA, etc

Encryption Decryption PlainText CipherText Original PlainText K K

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Symmetric Key - Issues

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EMTM 553 13

Symmetric Key - Issues

Key management, keys required = (p*(p-1))/2 or:

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DES (Data Encryption Standard)

#23442343(
5-016789:0.

' *8 (

0101(
*01:0.

DES Encryption 64 bit M 64 bit C 56 bits

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DES: Top-Down View

Permutation Permutation Swap Round 1 Round 2 Round 16 Generate keys Initial Permutation 48-bit K1 48-bit K2 48-bit K16 Swap 32-bit halves Final Permutation 64-bit Output 48-bit K1 64-bit Input 56-bit Key

…...

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2. Public Key Cryptography

E D M C M 5;%& ;<.5;%& ;<.( KR(pub) KR(pri) S R

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Asymmetric Encryption Asymmetric Encryption

“An introduction An introduction to cryptography” to cryptography” “Py “Py75 75c%bn&*) c%bn&*)9|f |f De^bDzjF@g De^bDzjF@g5=& =& nmdFgegMs” nmdFgegMs” “An An introduction to introduction to cryptography” cryptography”

Clear Clear-text Input text Input Clear Clear-text Output text Output Cipher Cipher-text text

Different keys Different keys

Encryption Encryption Decryption Decryption

RSA RSA RSA RSA 13 /راو/217 IASBS

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Establishing Shared Secrete

Internet

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Simplified Math Tricks

#.

(

),,

6%((4$2472&

,,

2%((=$42>72&

.(
*$

' )1 ' !1?=2>7@ ' !@$42>71

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Asymmetric Algorithms

.(
*..(
A(
*.

.(

.(
,$(
*$-; B*+(

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Public Key Cryptosystem

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RSA Public Keys

C;; D 2348( ),.,. (

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RSA Key Generation

#.6( DE67 β7%2&%62&( " -2FFβ %β&72(%& "6 2FFβ E≡ 2%β&( %& !.GH .GH( !6.(

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Encryption and Decryption

, /( 7 ,GH/< .( /( !/7, GH/<.( ! , /( /.,(

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RSA - Authentication

,/

(

7 ,%& <

.(

/(
!/%&

7 .(

; ,.

%((*&(

; ,

(

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RSA Example - Key Setup

2(

p=17 & q=11

@( " n = pq =17 x 11=187 =( " I(n)=(p–1)(q-1)=16 x 10=160 1( e- gcd(e,160)=1; e=7 :( d- de=1 mod 160 d < 160 d=23 23x7=161= 1x160+1 0( #.PU={7,187} 4( 5.PR={23,187}

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Example: Confidentiality Example: Confidentiality

Different keys Different keys

Recipient’s Recipient’s public key public key Recipient’s Recipient’s private key private key

private private public public

Encryption Encryption Decryption Decryption

“An An introduction to introduction to cryptography” cryptography” “Py Py75 75c%bn&*) c%bn&*)9|f |f De^bDzjF@g De^bDzjF@g5=& =& nmdFgegMs” nmdFgegMs” “An An introduction to introduction to cryptography” cryptography”

Clear Clear-text Input text Input Clear Clear-text Output text Output Cipher Cipher-text text

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Diffie-Hellman Key Exchange

J5*$ CJ!* KB2340 $ . L#" #

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Global Public Elements

6 # α α F6

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User A Key Generation

? ? F6 "M M 7α ?

6

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User B Key Generation

?/ ?/ F6 "M/ M/ 7α ?

/ 6

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Generation of Secret Key by User A

57%M/&?

6

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Generation of Secret Key by User B

57%M &?

/ 6

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Diffie-Hellman Key Exchange

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Diffie-Hellman Key Exchange

/ / /

Public Parameters:

large prime q primitive root a

Choose a secret XA Compute YA = aXA mod q Send YA Choose a secret XB Compute YB = a

XB

mod q Send YB Shared Key KAB = YB

XA

= a X

BXA mod q

Shared Key KAB = YA

XB

= a X

AXB mod q

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Diffie-Hellman Example

K/,,,.- q=353 α=3 .-

' xA=97, /xB=233

.-

– yA==

97 mod 353 = 40

% & – yB==

233 mod 353 = 248 %/&

.-

KAB= yB

xA mod 353 = @18 97 = 160

% & KAB= yA

xB mod 353 = 1> 233 = 160

%/&

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ELGAMAL CRYPTOGRAPHIC

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ELGAMAL CRYPTOGRAPHIC

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ELGAMAL CRYPTOGRAPHIC

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Alice generates a key pair as follows:

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ELGAMAL CRYPTOGRAPHIC

Suppose Bob wants to send the message with the value M =17

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ELGAMAL CRYPTOGRAPHIC

For decryption:

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نر

مروا ن یار ن یور; ؟دھد و ؟ت و د د لور! ن یار ور B ؟دھد و دراد دو"و مروا=* زا ار ؟ دھد وار@* ؟دو هد%ا یو & یراذ(زر*"" ؟دھد حر ل روط ار

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E-commerce Systems security / /2 13 IASBS 1 Security Function of - - PowerPoint PPT Presentation

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