MD5 algorithm was developed by Professor Ronald L. Rivest in 1991. According to RFC 1321, “MD5 message-digest algorithm takes as input a message of arbitrary length and produces as output a 128-bit “fingerprint” or “message digest” of the input.
The MD5 algorithm is intended for digital signature applications, where a large file must be “compressed” in a secure manner before being encrypted with a private (secret) key under a public-key cryptosystem such as RSA.”
- Input message must be < 264 bits
- Not really a problem.
- Message is processed in 512-bit blocks sequentially
- Message digest is 160 bits
MD5 Algorithms steps:
Step2: Appending length as 64 bit unsigned
Step3: Initialize MD buffer 5 32-bit words
Store in big endian format, most significant bit in low address
A = 67452301
B = efcdab89
C = 98badcfe
D = 10325476
E = c3d2e1f0
Step 4: the 80-step processing of 512-bit blocks – 4 rounds, 20 steps each.
Each step t (0 <= t <= 79):
Wt. – a 32-bit word from the message
Kt – a constant.
ABCDE: current MD.
ABCDE: new MD.
Only 4 per-round distinctive additive constants
0 <=t<= 19 Kt = 5A827999
20<=t<=39 Kt = 6ED9EBA1
40<=t<=59 Kt = 8F1BBCDC
60<=t<=79 Kt = CA62C1D6