One-way compression function: Difference between revisions

Revision as of 19:57, 13 September 2006

Revision as of 13:58, 21 September 2006

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It feeds each block of the message (m_i) as the cleartext to be encrypted. The output ciphertext is then also XORed (<math>\oplus</math>) with the same message block (m_i) to produce the next hash value (H_i). The previous hash value (H_i-1) is fed as the key to the block cipher. In the first round when there is no previous hash value it uses a constant pre-specified initial value (H₀).

If the block cipher havehas different block and key sizesizes the hash value (H_i-1) will have the wrong size for use as the key. The cipher might also have other special requirements on the key. Then the hash value is first fed through the function g( ) to be converted/padded to fit as key for the cipher.

<math>H_i = E_{g(H_{i-1})}(m_i)\oplus m_i</math>

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== Miyaguchi-Preneel ==

[[Image:Miyaguchi-Preneel hash.svg|thumb|230px|right|The Miyaguchi-Preneel hash construction]]