Cryptographic hash function md5
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This document discusses the MD5 cryptographic hash function. It provides an introduction to hash functions and describes MD5, including its features, applications, algorithm, analysis, and drawbacks. MD5 produces a 128-bit hash value from a message of any size through a multi-step process involving padding, appending a length, initializing buffers, and processing in 16-word blocks. While once widely used, MD5 is now considered broken due to vulnerabilities found in its compression function and preimage resistance.
Cryptographic hash function md5
- 1. Cryptographic Hash Function: MD5 1 1 Md. Shahidul Islam CSE, KU [email protected]
- 3. Introduction A cryptographic hash function is a kind of algorithm that can be run on a piece of data, like an individual file or a password, producing a value called a checksum. MD5 (Message-Digest algorithm 5) is a widely used cryptographic hash function designed by Ronald L. Rivest in 1991. It is one in a series of message digest algorithms. 3 3
- 4. Features of a hash function Fixed Length Output (Hash Value) Efficiency in computing Collision Resistance, two different message should not have the same hash value Deterministic so the same message always results in the same hash Infeasible to generate a message from its hash value except by trying all possible messages 4 4
- 5. Application There are two types of application of hash function: 1. Password Storage 2. Data Integrity Check 5 5
- 6. Application (Cont.) MD5 is used to store hash passwords and verify when user login. An intruder can only see the hashes of passwords, even if he accessed the password. 6 6
- 8. Application (Cont.) The integrity check helps the user to detect any changes made to original file. 8 8
- 9. Algorithm 9 9 Step 1: Append padded bits: • The message is padded so that, length mod 512 = 448 • A single “1” bit is appended to the message, and then “0” bits are appended so that the length in bits equals 448 modulo 512. Message 1 0 0 0 0 0 (Message length + padded bits) % 512 = 448
- 10. Algorithm (Cont.) 10 10 Step 2: Append length: • A 64 bit integer representation of message is appended to the result of the previous step. • The resulting message has a length that is an exact multiple of 512 bits. Message 1 0 0 0 0 0 64bits (Message length + padded bits + 64 bits ) % 512 = 0
- 11. Algorithm (Cont.) 11 Step 3: Initialize MD Buffer: • A four-word buffer (A,B,C,D) is used to compute the message digest. • These are initialized to the following values in hexadecimal: A: 01 23 45 67 B: 89 ab cd ef C: fe dc ba 98 D: 76 54 32 10
- 12. Algorithm (Cont.) 12 Step 4: Process message in 16-word blocks: • Four auxiliary functions that take as input three 32-bit words and produce as output one 32-bit word. F(X, Y, Z) = (X ˄ Y) ˅ (¬ X ˄ Z) G(X, Y, Z) = (X ˄ Z) ˅ (Y ˄ ¬ Z) H(X, Y, Z) = X Y Z I(X, Y, Z) = Y (X ˅ ¬Z)
- 13. Algorithm (Cont.) 13 Step 5: Output: • The message digest produced as output is A, B, C, D. • That is, output begins with the low-order byte of A, and end with the high-order byte of D. A1 A2 . . . . . . . . . . . . . . . . . . . . D3 128 bits = 32 hexadecimal digits A1, A2 are bytes
- 14. Hash analysis 14 • A small change in original message and the output digest is completely different
- 15. Hash analysis (Cont.) 15 • Arbitrary message length to fixed length digest • For MD5 128 bits = 32bits hexadecimal
- 16. Drawbacks In 1993 a hash collision was found in MD5 compression function. In 2009 a preimage attack against MD5 was published that breaks MD5’s preimage resistance. In 2012, the most infamous attack happened by the Flame Malware. The CMU Software Engineering Institute considers MD5 "cryptographically broken and unsuitable for further use". 16 16
- 17. Drawbacks (Cont.) For cracking password crackers use rainbow table Salting process can make rainbow table ineffective 17 17
- 18. Thank You 18