2005-12-17 17:00:52 +01:00
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This is Encrypted MAC (EMAC), formerly known as Double MAC (DMAC).
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Unlike HMAC, which reuses an existing one-way hash function, such as
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MD5, SHA-1 or RIPEMD-160, EMAC reuses an existing block cipher to
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produce a secure message authentication code (MAC).
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Using the block cipher, a message is encrypted in CBC mode. The last
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block is taken as the MAC of the message. For fixed-length messages,
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this method is provably secure. In reality, however, messages have
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arbitrary lengths, and this method is not secure. To make secure MACs
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for variable length messages, the last block is encrypted once again
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with a different key. The security of this construction has been proved
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in the paper, ``CBC MAC for Real-Time Data Sources'' by Erez Petrank
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and Charles Rackoff. The security can be proved on the assumption that
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the underlying block cipher is pseudo-random.
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The performance and key-agility of EMAC are reasonable. EMAC is
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preferable for short messages because the block length is smaller
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compared to the schemes based on a hash function. EMAC is also chosen
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as one of the NESSIE winners for Message Authentication Codes, along
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with UMAC, TTMAC and HMAC. The current NESSIE specification chooses the
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AES as block cipher.
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2006-02-20 21:50:22 +01:00
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WWW: http://search.cpan.org/dist/Digest-EMAC/
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