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Message Digest 2 is a hash function used in cryptography. Developed in 1989 by Ronald Rivest, it is byte-oriented, producing a 128-bit hash value with the help of an arbitrary length message. It is optimized for 8-bit computers. Message Digest 2 was developed mainly to be used for digital signature applications, which required a secured and compressed large file to be signed with a private key. Although it remains in use in public key infrastructures, it is rarely used as it takes a long time to compute and is no longer considered secure.
Message Digest 2 depends on the random permutation of bytes. Thirty-two-digit hexadecimal numbers are used for representing the 128-bit Message Digest 2 hashes. The Message Digest 2 algorithm makes use of a message of any length and produces an output of a 128-bit message digest of the input. It is assumed that it is impossible to produce two messages with same message digest or to obtain a prespecified target message digest from a given message. The process of the Message Digest 2 algorithm involves the following steps: appending padding bytes, appending checksum, initializing the message digest buffer for computing the message digest, processing the message in 16-byte blocks and finally producing the output.
One of the biggest benefits of Message Digest 2 is its simplicity in implementation. However, Message Digest 2 is slower when compared to Message Digest 4 or 5. This is because it was optimized for 8-bit computers, whereas Message Digest 4 and 5 were optimized for 32-bit machines. Again, comparing secure hash algorithms such as SHA-1 or SHA-256, Message Digest 2 algorithms are slower in performance. However, it was discovered that message digest 2 could leak information of the keys with collision attacks, which is why it is no longer favored.