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cipher block chaining message authentication code
Sign in to saveIn cryptography, a cipher block chaining message authentication code (CBC-MAC) is a technique for constructing a message authentication code (MAC) from a block cipher. The message is encrypted with some block cipher algorithm in cipher block chaining (CBC) mode to create a chain of blocks such that each block depends on the proper encryption of the previous block. This interdependence ensures that a change to any of the plaintext bits will cause the final encrypted block to change in a way that cannot be predicted or counteracted without knowing the key to the block cipher. thumb|400px|CBC-MAC
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12 sectionsContents
- Use in standards
- Standards that define the algorithm
- Security with fixed and variable-length messages
- Length prepending
- Encrypt-last-block
- Attack methods against incorrect use
- Using the same key for encryption and authentication
- Allowing the initialization vector to vary in value
- Using predictable initialization vector
- See also
- References
- Sources
In cryptography, a cipher block chaining message authentication code (CBC-MAC) is a technique for constructing a message authentication code (MAC) from a block cipher. The message is encrypted with some block cipher algorithm in cipher block chaining (CBC) mode to create a chain of blocks such that each block depends on the proper encryption of the previous block. This interdependence ensures that a change to any of the plaintext bits will cause the final encrypted block to change in a way that cannot be predicted or counteracted without knowing the key to the block cipher. thumb|400px|CBC-MAC construction To calculate the CBC-MAC of message , one encrypts in CBC mode with zero initialization vector and keeps the last block. The following figure sketches the computation of the CBC-MAC of a message comprising blocks m_1\|m_2\|\cdots\|m_x using a secret key and a block cipher :
CBC-MAC on its own is not secure for variable-length messages (see the discussion below) and is currently used to construct a pseudorandom function family and as a component of the CCM mode.