MD2 (cryptography)
| General | |
|---|---|
| Designers | Ronald Rivest |
| First published | August 1989 |
| Series | MD2, MD4, MD5, MD6 |
| Detail | |
| Digest sizes | 128 bits |
| Rounds | 18 |
The MD2 Message-Digest Algorithm is a cryptographic hash function developed by Ronald Rivest in 1989. The algorithm is optimized for 8-bit computers. MD2 is specified in RFC 1319. Although MD2 is no longer considered secure, even as of 2014[update], it remains in use in public key infrastructures as part of certificates generated with MD2 and RSA. The MD2 hash function receives its acronym MD from its structure using Merkle–Damgård construction.
The 128-bit hash value of any message is formed by padding it to a multiple of the block length (128 bits or 16 bytes) and adding a 16-byte checksum to it. For the actual calculation, a 48-byte auxiliary block and a 256-byte S-table generated indirectly from the digits of the fractional part of pi are used (see nothing up my sleeve number). The algorithm runs through a loop where it permutes each byte in the auxiliary block 18 times for every 16 input bytes processed. Once all of the blocks of the (lengthened) message have been processed, the first partial block of the auxiliary block becomes the hash value of the message.
The S-table's values are derived from Pi, and in hex are:
The 128-bit (16-byte) MD2 hashes (also termed message digests) are typically represented as 32-digit hexadecimal numbers. The following demonstrates a 43-byte ASCII input and the corresponding MD2 hash:
As the result of the avalanche effect in MD2, even a small change in the input message will (with overwhelming probability) result in a completely different hash. For example, changing the letter d to c in the message results in:
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