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New answers tagged ecb

8

No, the proposed construction is not secure, unless the block size $b$ of the block cipher is unusually large, or much wider than the MAC. Assuming $p$ known distinct message/MAC pairs $(m_i,h_i)$ with $b$-bit message $m_i$ and $h_i$ at least $b$-bit, there's a simple attack of expected cost dominated by $2^b/p$ hashes and searches among the $h_i$. The ...

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