Password Hashing

1. Password Hashing Dan Johnson

2. What is a hashing function? • Fingerprint for a given piece of data • Typically generated by a mathematical algorithm • Produces a fixed length string as its output • Hashes are sometimes called a checksum or message digests

3. Cryptographic hashing functions • Have four major properties: • It is impossible for any given output to determine the original input. • This does not mean we can’t use inference to find input that is likely correct • It is easy to compute the hash of any given input. • Easy means that it does not require a lot of system resources or time to compute the hash of a given input.

4. (cont…) • It is infeasible to determine two inputs that produce the same output. • It is infeasible to change an input and produce the same output. • Infeasible means that a solution cannot be found in less time than by brute force.

5. Cryptographic Strength • Determined by output length and ability to resist cryptanalytic attack • Output length expressed in number of bits • Attacks attempt to break one of the cryptographic properties.

6. Preimage Attacks • Two types, “first-preimage” and “second-preimage” • Both attempt to break the one way property of the hashing function • Both are similar in nature • If a hashing function is vulnerable to one form of preimage attack, it is likely vulnerable to the other form of attack • Successful attack executes in less that brute force time

7. Collision Attack • A collision occurs when two pieces of input produce the same output. • Collision attacks take advantage of a property of probability theory called the birthday paradox or birthday problem. • Collision attacks attempt to find a collision in less than O(2n/2)

8. MD5 • Published by Ronald Rivest in 1994. • Produces 128-bit output, represented by 32bit hexadecimal number. • Vulnerable to collision attacks. • Now mostly used for creating checksums of large files.

9. SHA-1 • Created by the National Security Agency • Creates a 160-bit message digest represented by a 20 character string • More secure than MD5 • Widely popular and used in many applications • In 2005, a group of Chinese researches discovered mathematical errors that could lead to a preimage attack in less than brute force time. • No known attacks based on these findings have surfaced.

10. SHA-256 • Also created by NSA as a part of the SHA2 family which includes SHA224, SHA256 and SHA512. • Creates a 256bit output, hence its name. • Considered to be more secure than SHA1 because of increased bit size. • Mathematical problems found in SHA1 are not present in SHA256. • Less popular than SHA1.

11. Hash Based Authentication • Works the same way as password authentication • Store hashed value of password in database instead of password itself • When a user attempts to authenticate, hashes input value and compares it with value stored in database • “password” => [ﾪaäɹ??ﾂ%lø3~æﾏØ

12. Example implementation • Consider the following PHP code snippet. • From this we can clearly see that adding hash based authentication does not add a much code.

13. What an attacker sees… • Without encryption: • With just SHA-1 encryption:

14. Cont… • Can this be improved? • Better solution: sha1( username + password) • Even better solution: • sha1( sha1(username) + sha1(password) )

15. Microsoft Store India • Earlier this year, the Microsoft Store web site for India was breached. • Attackers stole hundreds of thousands of usernames and passwords. • All passwords were stored in plaintext. • Credit Card information was also not encrypted in any from. • Many users had their identity compromised and fraudulent purchases charged to their credit card.

16. Sony • Playstation Network and Sony Pictures customer databases were both breached in 2011. • Credit card information was encrypted, but several reports indicate that encryption may have been compromised. • User data was not encrypted in any way. • Class action lawsuit filed over negligence.

17. Other protection methods • Hashing not good for everything. • Credit card information could be stored using symmetric key encryption. • This allows for the input to be determined at a later date. • BE SUPER CAREFUL!

18. Questions?

19. References • Agarwal, A. (2012, February 27). Not just email addresses, credit card numbers also stolen from microsoftindia store. Retrieved from http://www.labnol.org/india/microsoft-india-store-hacked/20891/ • Gallagher, S. (2012, February 14). Microsoft's store site in india defaced; hackers find plain text passwords. Retrieved from http://arstechnica.com/business/news/2012/02/microsofts-store-site-in-india-defaced-hackers-find-plain-text-passwords.ars • McGlinn, J. (2005, March 20). Password hashing. Retrieved from http://phpsec.org/articles/2005/password-hashing.html • Silva, J. (2003). An overview of cryptographic hash functions and their uses. Retrieved from http://www.sans.org/reading_room/whitepapers/vpns/overview-cryptographic-hash-functions_879 • Schneier, B., & Hoffman, P. (2005). attacks on cryptographic hashes in internet protocols. Retrieved from http://www.ietf.org/rfc/rfc4270.txt • Schwartz, M. (2011, June 3). Sony hacked again, 1 million passwords exposed. Retrieved from http://www.informationweek.com/news/security/attacks/229900111 • Stallings, W., Brown, L., & Howard, M. (2008). Computer security, principles and practice. Upper Sadddle River, NJ: Pearson Education. • Ullrich, J. (2011, June 28). Hashing passwords. Retrieved from http://www.dshield.org/diary.html?storyid=11110