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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Partial-matching Meet-in-the-Middle attack ： ウィキペディア英語版 Partial-matching Meet-in-the-Middle attack Partial-matching is a technique that can be used with a MITM attack. Partial-matching is where the intermediate values of the MITM attack, $i$ and $j$, computed from the plaintext and ciphertext, are matched on only a few select bits, instead of on the complete state. == Uses == A limitation with MITM attacks is the amount of intermediate values that needs to be stored. In order to compare the intermediate values $i$ and $j$, all $i$'s need to be computed and stored first, before each computed $j$ can be compared against them. If the two subciphers identified by the MITM attack both has a sufficiently large subkey, then an unfeasible amount of intermediate values need to be stored. While there are techniques such as cycle detection algorithms〔Cycle detection〕 that allows one to perform a MITM attack without storing either all values of $i$ or $j$, these techniques requires that the subciphers of the MITM attack are symmetric. Thus it is a solution that allows one to perform a MITM attack in a situation, where the subkeys are of a cardinality just large enough to make the amount of temporary values that need to be stored infeasible. While this allows one to store more temporary values, its use is still limited, as it only allows one to perform a MITM attack on a subcipher with a few more bits. As an example: If only 1/8 of the intermediate value is stored, then the subkey needs only be 3 bits larger, before the same amount of memory is required anyway, since $2^\; =\; 1/8$ A in most cases far more useful feature provided by partial-matching in MITM attacks, is the ability to compare intermediate values computed at different rounds in the attacked cipher. If the diffusion in each round of the cipher is low enough, it might be possible over a span of rounds to find bits in the intermediate states that has not changed with a probability of 1. These bits in the intermediate states can still be compared. The disadvantage for both of these uses, is that there will be more false positives for key candidates, which needs to be tested. As a rule, the chance for a false positive is given by the probability $2^$, where $|i|$ is the amount of matched bits. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Partial-matching Meet-in-the-Middle attack」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.