Cosc 4765

1. Cosc 4765 Authentication

2. Interesting Fact • Following the second world war, the now famous pair, Julius and Ethel Rosenberg were convicted and executed for spying on the U.S. bomb project for the Soviet Union in 1953. • At one point they improvised a clever password system: a cardboard Jell-O box was torn in two and one half given to a contact whom they later would need to identify. • The complex edge shape and color matching made a complex key quite impossible to forge. • Without matching secrets it is impossible to prove someone's identity

3. Orange Book • The only risk to computers is the people who come into contact with them: networked users. To minimize the effects of users on the system, we introduce security mechanisms. • The Trusted Computer Security Evaluation Criteria (TSEC) Orange book was the first attempt to try to specify a standard for security management in the US in 1967. • Although concentrated on national security issues, the recommendations were also of general applicability.

4. Orange Book (2) • Trusted Computing Base (TCB) • The totality of protection mechanisms within an OS including software, hardware and firmware. • Four basic divisions • A, B, C and D. • With A highest degree of security and D lowest (no requirements!). • Complete set of ratings • D, C1, C2, B1, B2, B3 and A1

5. Authentication • “Authentication binding of an identity to a subject.” • What information can be used to establish this binding? • What the subject knows (secrets) • What the entity has (smart cards) • What the entity is (retinal prints) • Where the entity is (current location)

6. Secrets: A Password • Simple and natural mechanism. Widely used. • How do we store passwords? • Fixed messages encrypted with passwords • Hash of password • We'll look at *nix first, then Windows password system. • On both systems the users are identified by usernames and authenticated by passwords

7. *nix authentication • The passwords are used as key to encrypt the all zero word using crypt • which uses a modified version of DES repeated 25 times. • Result stored in /etc/passwd file • The user name is usually 6 to 8 characters • represented internally by 16 bit number (UID) • Example: • jdoe:987hggw2fd435:103:1001:John Doe: /home/jdoe:/bin/csh

8. *nix Password algorithm

9. Passwords and crypt • First eight characters password used as the DES key to encrypt constant 64-bit block (consisting of all zero bits) via DES 25 times • the result of each encryption is used to feed the next round. • The resultant 64-bits is converted into a string of 11 printable ASCII characters by encoding every six bits into a printable ASCII character and zero padding the 11th character.

10. The "Salt" • When a password is first selected, the password encryption program selects a random 12-bit number as the salt. • Salt and the result is stored in password file. • Later on, when the user attempts to login the salt is extracted from the password file and is used • The effect of salting is to allow for 4096 possible encryptions of same password string. • With Salt two users may have the same password but the “encrypted” versions would look different.

11. Brute force attack • Known as the dictionary attack • To find a user’s password from the encrypted password • Search through all passwords is better then all the possible keys • Password can be found by encrypting dictionary of possible passwords with all possible salts and comparing the result. • Total number of passwords can be large (708) • Set of typical passwords is surprisingly small! • Why?

12. md5 passwords • md5-crypt • salt 8 to 48 bits • 1000 iterations • passwords can be 256 in length. • Doesn't slow down dictionary attacks as much as needed. • Some security experts even recommend not using it!

13. Improvements? • Keep encryption algorithm secret • Security by obscurity rarely works, see Windows. • Keep password file hidden from non-privileged users • Widely used. Shadow file in Unix. • Only works on local machines, see perl stuff, even then doesn't "hide" passwords. • Enforce better passwords?!

14. Windows • NT, W2k, and WXP • Passwords stored in encrypted form in SAM database which is effectively part of the registry. • Can be accessed separately with tools • There are actually two encrypted passwords • LAN Manager and NT password

15. LAN Manager Password • Developed by Microsoft for OS/2 • Algorithm: • Truncate/Pad password to 14 characters and upper case everything • Split the password into two 7-byte halves • using DES, build {c}k1 + {c}k2 , c a constant • Very weak and easily broken!!!!!!!!! • They are in the registry, boot dos/linux disk then read the file, and/or capture passwords over the network (wincrack).

16. Cracking LAN Manager Passwords • This hashing implementation means that an attacker needs only to complete the trivial task of cracking two seven-character, upper-case passwords to gain authenticated access to your system. • Since the complexity of cracking hashes increases geometrically with the length of the hash, each seven-character string is at least an order of magnitude simpler to attack by brute-force than would a combined fourteen-character string. • Since all strings are exactly seven characters (including spaces) and entirely upper-case, a dictionary-style attack is also simplified.

17. Network Login • Using LAN Manager passwords for remote logon is even weaker. • susceptible to replay and man-in-middle attacks • Need a challenge system, so the information changes.

18. NT Remote Login Challenge-Response Mechanism • User enters password, client calculates its 16 byte hash (LM and NT) and remembers for future use. • When client connects to server, the server generates an 8-byte random value which it sends to the client. • Client pads 16-byte hash with 5 null bytes to get 3 56-bit DES keys. 8-byte random challenge DES encrypted with each DES key, generating a 24-byte response. • Server compares response to that generated by user's hash values from it's password database. • Someone sniffing only sees 8-byte challenge and 24-byte response. To obtain original hash attacker must perform three brute force DES attacks. • Not really

19. Brute forcing NT Remote Login • NOTE: • Hashed password (uncracked) is the password equivalent! • Client does not actually need to know the clear text password. It only needs to know the hashed password! The regular client software has the end user input his/her password and calculates the hashed password from the manually entered original password. • If you have a modified client which has access to a stolen copy of uncracked Windows/NT password database, • Then the client can look up hash value to use to calculate response. The client can get authenticated without knowing the original (clear text) password! • This means that even a good password (dictionary attack resistant) can be misused!

20. CHAP • Challenge Handshake Authentication Protocol (RFC 1334 and 1994). • Without going into the ugly details, it suffers many of the same problems of NT and LAN Hashes. • Stronger, but still pretty easy to break.

21. CHAP v2 • much stronger version and harder to break. • Except! • Version Rollback Attack • Since Microsoft has attempted to retain some backwards compatibility with MS-CHAPv1, it is possible for an attacker to mount a "version rollback attack" • In this attack, the attacker convinces both the Client and the Server not to negotiate the more secure MS-CHAPv2 protocol, but to use the less secure MS-CHAPv1 protocol.

22. Windows 7 • Server side of LAN manager removed • Client can still be as used as fall back • Kerberos authentication protocol used. • Research project: • Windows 7 password authentication • How does it work, weakness and strengths.

23. References and tools • John the Ripper http://www.openwall.com/john/ (crack for windows and *nix) • LC6 (L0phtcrack version 5) http://www.atstake.com/products/lc/index.html • L0pht Heavy Industries http://www.l0pht.com/ (NT password security and cracker) • Unix password security http://www.ja.net/CERT/Belgers/NIX-password-security.html

24. Authentication Tokens • What you have • Smart cards: • Challenge/response • Cryptographic calculator: • Interaction through a user (typing ...)

25. Biometrics • Accuracy: • False acceptance rate. • False rejection rate. • Can adversary select imposters? • Identical twins, family members, etc. • Retinal scanner, fingerprint reader, handprint reader, voiceprint, keystroke timing, signature.

26. Fingerprints • Vulnerability: • Dummy fingers and dead fingers • Suitability and stability: • Not for people with high probability of damaged fingerprints • Not for kids growing up

27. Voice Recognition • Single phrase: • Can use tape recorder to fake • Stability: • Background noise • Any sickness/thing that effects your voice. • Use in public

28. Keystroke Timing • Each person has a distinct typing timing/style • Hand/finger movements • Suitability: • Best done for “local” authentication • Avoid network traffic delay

29. Signatures • Machines can’t match human experts in recognizing shapes of signatures • Add information of timing (dynamics) of movements • Signing or an electronic tablet • It should be noted that people very rarely sign their name the same way. • There are numerous environmental factors that change how people write at any given point. • The signature is the same, then most consider it to be a fake!

30. Q A &