CMPSC 497 Password Authentication Trent Jaeger Systems and - - PowerPoint PPT Presentation

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CMPSC 497 Password Authentication Trent Jaeger Systems and - - PowerPoint PPT Presentation

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Systems and Internet Infrastructure Security Network and Security Research Center Department of Computer Science and Engineering Pennsylvania State University, University Park PA CMPSC 497 Password Authentication Trent Jaeger Systems and

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page

Systems and Internet Infrastructure Security

Network and Security Research Center Department of Computer Science and Engineering Pennsylvania State University, University Park PA

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CMPSC 497 Password Authentication

Trent Jaeger Systems and Internet Infrastructure Security (SIIS) Lab Computer Science and Engineering Department Pennsylvania State University

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 2

Security Model - E-voting

  • Who are the principals?
  • Voters, Admins, Counters, Others
  • Who are adversaries?
  • Which commands may be threatened (attack surface)?
  • Start the application
  • Process the vote
  • Count the votes
  • Who must the application trust? To do what?
  • Of principals above
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 3

Principals

CSE543 - Introduction to Computer and Network Security Page

Principals

  • Principals are expected system subjects
  • Computers, agents, people, enterprises, …
  • Depending on context referred to as: servers, clients, users,

entities, hosts, routers, … - and some may be adversarial

  • Security is defined with respect to these subjects
  • Implication: every principal may have unique view
  • A trusted third party
  • Trusted by all principals for some set of actions
  • Often used as introducer or arbiter

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 4

Challenges

  • Distinguish adversaries from trusted principals
  • Suppose the e-voting application receives a command
  • How do we know whether the command may be from an

adversary or a trusted principal?

  • The security mechanism for identifying principals is
  • Authentication
  • The act of confirming the truth of an attribute of a single

piece of data claimed true by an entity

  • For an identity, authentication is the process of actually

confirming a claimed identity

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 5

Authentication

  • Several mechanisms for performing authentication

CSE543 - Introduction to Computer and Network Security Page

What is Authentication?

  • Short answer: establishes identity
  • Answers the question: To whom am I speaking?
  • Long answer: evaluates the authenticity of

identity by proving credentials

  • Credential – is proof of identity
  • Evaluation – process that assesses the correctness
  • f the association between credential and claimed

identity

  • for some purpose
  • under some policy (what constitutes a good cred.?)

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 6

E-Voting Application

  • Suppose you are building an e-voting application
  • How do you ensure your application satisfies security

requirements?

  • What does the e-voting application do?
  • Process vote commands
  • Store votes
  • Retrieve/count votes
  • What are its security requirements?
  • Let’s see how we reason about security

CSE543 - Introduction to Computer and Network Security Page

Why authentication?

  • Well, we live in a world of rights, permissions, and

duties

  • Authentication establishes our identity so that we can
  • btain the set of rights
  • E.g., we establish our identity with Tiffany’s by providing

a valid credit card which gives us rights to purchase goods ~ physical authentication system

  • Q: How does this relate to security?

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page

Risk

  • What’s at risk in the e-voting application?

7 CSE543 - Introduction to Computer and Network Security Page

Why authentication (cont.)?

  • Same in online world, just different constraints
  • Vendor/customer are not physically co-located, so we

must find other ways of providing identity

  • e.g., by providing credit card number ~ electronic

authentication system

  • Risks (for customer and vendor) are different
  • Q: How so?
  • Computer security is crucially dependent on the

proper design, management, and application of authentication systems.

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page

Security Requirements

  • Usually security requirements are described in three

categories

  • Secrecy
  • Prevent risk that sensitive data may be leaked to an adversary (e.g.,

votes)

  • Integrity
  • Prevent risk that adversaries may modified data that others depend
  • n (e.g., vote instances, tallies, database)
  • Availability
  • Prevent risk that adversaries block use of critical services (e.g.,

disable the processing of votes)

8 CSE543 - Introduction to Computer and Network Security Page

What is Identity?

  • That which gives you access … which is largely

determined by context

  • We all have lots of identities
  • Pseudo-identities
  • Really, determined by who is evaluating credential
  • Driver’s License, Passport, SSN prove …
  • Credit cards prove …
  • Signature proves …
  • Password proves …
  • Voice proves …
  • Exercise: Give an example of bad mapping between

identity and the purpose for which it was used.

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page

Exercise

  • Classify each of the following as a violation of

confidentiality, of integrity, of availability, or of some combination.

  • Carol changes the amount of Angelo's check from $100 to

$1000

  • John copies Mary's homework
  • Eve registers the domain name “psu.edu" and refuses to

let Penn State buy or use that domain name.

9 CSE543 - Introduction to Computer and Network Security Page

Credentials

  • … are evidence used to prove identity
  • Credentials can be
  • Something I am
  • Something I have
  • Something I know

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 10

Passwords

  • An example of “something you know”
  • Client users must remember passwords to

access their data on servers

  • Passwords have a checkered history
  • People have often chosen poor passwords
  • Why is that an issue?
  • We (security community) assumed (in the

1990s) that passwords would be replaced with another technology to enable users to authenticate

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 11

Lateness Policy

  • Assignments and project milestones are

assessed a 20% per-day late penalty, up to a maximum of 4 days. Unless the problem is apocalyptic, don’t give me excuses. Students with legitimate reasons who contact the professor before the deadline may apply for an extension.

  • You decide what you turn in

CSE543 - Introduction to Computer and Network Security Page

Password Use

  • Naively: Retrieve password for ID from database and check

against that supplied password

  • Baravelli: ...you can't come in unless you give the password.
  • Professor Wagstaff: Well, what is the password?
  • Baravelli: Aw, no.

You gotta tell me. Hey, I tell what I do. I give you three guesses. It's the name of a fish.

  • …….
  • [Slams door. Professor Wagstaff knocks again. Baravelli opens peephole again.] Hey, what's-a matter, you no

understand English? You can't come in here unless you say, "Swordfish." Now I'll give you one more guess.

  • Professor Wagstaff: ...swordfish, swordfish... I think I got it. Is it "swordfish"?
  • Baravelli: Hah. That's-a it.

You guess it.

  • Professor Wagstaff: Pretty good, eh?

[Marx Brothers, Horse Feathers]

  • How should you store passwords to protect them?
  • Just storing them in a file gives anyone with access to the file

your password

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 12

Password Storage

  • Instead of storing passwords, we store
  • A value that can be computed from the password
  • F(password) = value
  • That is highly unlikely to be the same as the value

computed from another password (collision-free)

  • From which it is difficult to extract (reverse) the

password (one-way)

  • What kind of function provides such properties?
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 13

Cryptographic Hash Functions

  • A challenge is to determine how a program may

be threatened by adversaries

  • In what ways may an adversary impact CIA?
  • Adversaries may be able to control the resources

used by the program and inputs to the program

  • Obtained via system calls – later researchers

described the system calls that may receive adversary- controlled input as a program’s attack surface

CSE543 - Introduction to Computer and Network Security Page

Hash Algorithms

  • Hash algorithm
  • Compression of data into a hash value
  • E.g., h(d) = parity(d)
  • Such algorithms are generally useful in algorithms (speed/

space optimization)

  • … as used in cryptosystems
  • One-way - (computationally) hard to invert h() , i.e.,

compute h-1(y), where y=h(d)

  • Collision resistant hard to find two data x1 and x2 such that

h(x1) == h(x2)

  • Q: What can you do with these constructs?

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page

Password Storage

  • Hosts store password hashes in a file
  • Originally, /etc/passwd for UNIX systems
  • Now /etc/shadow
  • Server programs can also store their own users’

password hashes in a file

  • For Apache can store in /usr/local/apache/passwd
  • What if an adversary can gain access to a password

storage file?

14

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 15

Ethics Statement

  • This course considers topics involving personal and public

privacy and security. As part of this investigation we will cover technologies whose abuse may infringe on the rights of

  • thers. As an instructor, I rely on the ethical use of these
  • technologies. Unethical use may include circumvention of

existing security or privacy measurements for any purpose, or the dissemination, promotion, or exploitation of vulnerabilities

  • f these services. Exceptions to these guidelines may occur

in the process of reporting vulnerabilities through public and authoritative channels. Any activity outside the letter or spirit

  • f these guidelines will be reported to the proper authorities

and may result in dismissal from the class.

  • When in doubt, please contact the instructor for advice. Do not

undertake any action which could be perceived as technology misuse anywhere and/or under any circumstances unless you have received explicit permission from Professor Jaeger.

CSE543 - Introduction to Computer and Network Security Page

Password Cracking

  • Attacker can access the hashed password
  • Can guess and test passwords offline
  • Called “password cracking”
  • Lots of help
  • John the Ripper
  • How well do these work?

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page

Password Cracking

  • Identify which of the following that are program

vulnerabilities

  • A program flaw (e.g., buffer overflow)
  • A program flaw in writing user input to a program variable
  • A program flaw in writing user input to a program variable

containing a function pointer

  • Writing untrusted input to a log file
  • Executing log files

16 CSE543 - Introduction to Computer and Network Security Page

Cracking Passwords

  • How hard are passwords to crack?
  • How many 8-character passwords are there given that

128 characters are available?

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 17

Road Map

  • Introduction
  • 1. Today
  • Software Vulnerabilities
  • 1. Information Flow
  • 2. Memory Errors
  • Defensive Programming
  • 1. Techniques
  • 2. Attack Surfaces
  • Finding Program Flaws
  • 1. Runtime Testing
  • 2. Static Analysis
  • 3. Symbolic Execution
  • Security Mechanisms
  • 1. Authorization
  • 2. Privilege Separation
  • 3. Auditing
  • 4. CFI
  • Safe Programming Environments
  • 1. Memory Safe
  • 2. Information Flow-Safe
  • Retrofitting Software for Security
  • 1. Authorization
  • 2. Privilege Separation

CSE543 - Introduction to Computer and Network Security Page

Cracking Passwords

  • How hard are passwords to crack?
  • How many 8-character passwords given that 128

characters are available?

  • 1288 = 256
  • How many guesses to find one specific user’s

password?

  • 256/2 = 255

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 18

Trusted Computing Base

  • To execute a program that obeys security

requirements, you must trust something

CSE543 - Introduction to Computer and Network Security Page

Cracking w/ Dictionaries

  • How hard are passwords to crack?
  • How many 8-character passwords are there given that

128 characters are available?

  • 1288 = 256
  • Suppose we use a dictionary where there is a 25%

chance that that user’s password appears in that password dictionary. How many guesses then? (Assume 1 million dictionary entries)

  • 1/4(219) + 3/4 (255) ~ 254.6
  • However, you probably simply apply the dictionary and

accept a 25% chance of recovery

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 19

Trusted Computing Base

  • To execute a program that obeys security

requirements, you must trust something

  • Hardware
  • Operating Systems
  • Libraries
  • Critical input files (configuration)
  • Other programs (system services running with full

privilege)

  • Program installers

CSE543 - Introduction to Computer and Network Security Page

Cracking w/ Dictionaries

  • How hard are passwords to crack?
  • How many 8-character passwords are there given that

128 characters are available?

  • 1288 = 256
  • But, in practice the attacker just needs one password

from a set of users - rather than a specific user

  • If there are 1024 users, the basic work effort is now
  • 255/210 = 245
  • However, given a dictionary, we can simply see if one of

the 1024 passwords are in the dictionary

  • About equal to size of dictionary/prob. in dictionary

X

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 20

Password Guessing

  • Research in password cracking can improve the

cracker’s ability

  • Markov Chains
  • Guess the next character in order of the probability

that it next character to follow

  • Guess the highest probability first character – ‘s’
  • Guess the highest probability character to follow ‘s’
  • Grammars
  • Guess by most popular password structure
  • Then, fill in characters as above
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 21

Password Guessing

  • How can you make your password hard to guess?
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 22

Password Guessing

  • How can you make your password hard to guess?
  • Limited by memorability though
  • Suppose computers get faster and faster
  • Ever make password storage obsolete?
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 23

Password Guessing

  • How can you make your password hard to guess?
  • Limited by memorability though
  • Suppose computers get faster and faster
  • Ever make password storage obsolete?
  • Can slow down by hashing many times – h100(password)
  • Discussed in CMPSC 443…
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 24

Common Passwords

  • What if two users have the same password?
  • How will that appear in the password database?
  • How is the problem addressed?
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 25

Security Model - E-voting

  • Who are the principals?
  • Voters, Admins, Counters, Others
  • Who are adversaries?
  • Which commands may be threatened (attack surface)?
  • Start the application
  • Process the vote
  • Count the votes
  • Who must the application trust? To do what?
  • Of principals above

CSE543 - Introduction to Computer and Network Security Page

“Salt”ing passwords

  • Suppose you want to avoid a offline dictionary attack
  • bad guy precomputing popular passwords and looking at the

password file

  • A salt is a random number added to the password

differentiate passwords when stored in /etc/shadow

  • consequence: guesses each password independently

X

...

salt1, h(salt1, pw1) salti, h(salt2, pw2) salti, h(salt3, pw3) saltn, h(saltn, pwn)

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 26

Project #1

  • Store passwords for your server’s users
  • On “set” enter username and password
  • Store pair on first entry of username (unknown_user returns “1”)
  • Compute a salt from OpenSSL random number

generator functions

  • Concatenate salt (16 bytes) + password (16 bytes,

padded) into input to hash function (32 bytes)

  • Compute a hash using digest_message (cmpsc497-ssl.c)
  • Store in key-value store provided indexed by username
  • Key: username; Value: hash; Tag: salt
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 27

Project #1

  • Verify a username-password for a later command
  • How do you do that?
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 28

Project #1

  • Verify a username-password for a later command
  • How do you do that?
  • Lookup salt and password hash for user
  • Create hash input as before using input password
  • Check that this results in expected password hash
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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 29

Use OpenSSL Library

  • The file cmpsc497-ssl.c has a set of functions to

access the OpenSSL library API

  • OpenSSL is a crypto library for implementing the

SSL protocol

  • Includes code for encryption, hashing, random

number generation

  • Only need to use digest_message from that file, but
  • thers may be useful at some point
  • Will use OpenSSL to collect salt values also from

its random number generator (engine)

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 30

Use OpenSSL Library

  • Random number generation in OpenSSL
  • Uses engine_init provided to initialize RNG – in

main already

  • Then, need to extract a random number
  • For guidance
  • https://wiki.openssl.org/index.php/Manual:Rand(3)
  • How random does the salt need to be?
  • Just different for everyone ideally, but the salt is not a

secret

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Systems and Internet Infrastructure Security (SIIS) Laboratory Page 31

Take Away

  • Security depends on differentiating friend from foe
  • These are called principals
  • Mechanism to identify principals is called authentication
  • Authentication mechanisms depend on validating

the possession of a secret (credential)

  • Something you have, know, are
  • Passwords are an authentication mechanism that

validates something you know

  • Passwords are stored as a hash of a combination of the

password and a salt value to make cracking harder