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Length extension attack The reason why $H(k || m)$ is insecure with most older hashes is that they use the Merkle–Damgård construction which suffers from length extensions. When length extensions are available it's possible to compute $H(k || m || m^\prime)$ knowing only $H(k || m)$ but not $k$. This violates the security requirements of a MAC. Like all ...

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There are two parts to this proposal: the use of a code book and a scheme to send short confidential and authenticated messages utilising an existing shared symmetric key. A code book can be used alone to provide a degree of confidentiality, or can be used to ascribe specific pre-agreed meanings to short messages, in combination with any scheme for sending ...

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Is there any advantage – other than potential memory or speed performance reasons – of picking a state size different from 512? If, what would the advantage(s) be? Yes. With 256-bit state, the main advantages are memory use and hardware implementation area. With 1024-bit state, a hardware implementation can be faster, but there are also security ...

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