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Message Digest (MD5) Algorithm and Secure Hash Algorithm (SHA)

algorithms bit computation standard

Definition: Message Digest and Secure Cash are the standard algorithms to provide data security for multimedia authentication.

The MD5 algorithm takes as input a message of arbitrary length and produces as output a 128-bit “fingerprint” or “message digest” of the input message. MD5 is currently a standard, Internet Engineering Task Force (IETF) Request for Comments (RFC) 1321. In comparison, MD5 is not quite as fast as the MD4 algorithm, but offers much more assurance of data security.

SHA is considered to be the successor to MD5. The Federal Information Processing Standard (FIPS 180-2) specifies four secure hash algorithms (SHA) – SHA-1, SHA-256, SHA-384, and SHA-512 . As shown in Table 1, all four of the algorithms are iterative, one-way hash functions that can process a message with a maximum length of 2 64 – to 2 128 bits to produce a 160 to 512-bit condensed representation called a message digest. The input message is processed in 512- to 1024-bit blocks. The four algorithms differ most significantly in the number of bits of security that are provided for the data being hashed – this is directly related to the message digest length. Different message will, with a very high probability, result in a different message digest.

Each SHA algorithm processes a message in two stages: preprocessing and hash computation. Preprocessing involves padding a message, parsing the padded message into 512- or 1024-bit blocks, and setting initialization values to be used in the hash computation. The hash computation generates a message schedule from the padded message and uses that schedule, along with functions, constants, and word operations to iteratively generate a series of hash values. The final hash value generated by the hash computation is used to determine the message digest.

Due to the fact that SHA produces larger message digest size than MD5, SHA is considered more secure than MD5.

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