| Meet-in-the-middle Attack |
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Information AboutMeet-in-the-middle Attack |
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| cryptographic attacks | |
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It was first developed as an attack on an attempted expansion of a Block Cipher by Diffie and Hellman in 1977. When trying to improve the security of a block cipher, one might get the idea to simply use two independent Key s to encrypt the data twice. Naively, one might think that this would square the security of the double-encryption scheme. Certainly, an exhaustive search of all possible combination of keys would take attempts if each key is n bits long, compared to the attempts required for a single key. Diffie and Hellman, however, devised a time-memory tradeoff that could break the scheme in only double the time to break the single-encryption scheme. The attack works by encrypting from one end and decrypting from the other end, thus meeting in the middle. Assume the attacker knows a set of plaintext and ciphertext: ''P'' and ''C''. That is, : , where ''K''1 and ''K''2 are the two keys. The attacker can then compute ''EK''(''P'') for all possible keys ''K'' and store the results in memory. Afterwards he can compute ''DK''(''C'') for each ''K'' and compare with the table in memory. If he gets a match it is likely that he has discovered the two keys and he can verify it with a second set of plaintext and ciphertext. If the keysize is ''n'', this attack uses only encryptions (and space) in contrast to the naive attack, which needs encryptions (but only space). SEE ALSO
REFERENCES |
Author |
W Diffie and M E Hellman |
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Date |
June 1977 |
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Title |
Exhaustive Cryptanalysis of the NBS Data Encryption Standard |
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Journal |
Computer |
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Volume |
10 |
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Issue |
6 |
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Pages |
74-84 |
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