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如何为 hash 制造病理钥匙？

[英]How can I manufacture pathological keys for a hash?

原文 2011-07-17 13:25:17 0 1 perl/ hash

I am trying to trigger the hash randomization feature in Perl 5.8.2 and later.我正在尝试在 Perl 5.8.2 及更高版本中触发 hash 随机化功能。 To do this, I need a set of keys that would be pathological but for the randomization feature.为此，我需要一组可能是病态的但用于随机化功能的键。 I tried using MJD's code , but that didn't work.我尝试使用MJD's code ，但没有奏效。 And, now that I look at it, I shouldn't be surprised.而且，现在我看着它，我不应该感到惊讶。 It comes from 1997, and we have switched hashing functions since then.它来自 1997 年，从那时起我们就切换了散列函数。

Does anyone know of a set of pathological keys, or how to generate them?有谁知道一组病理键，或者如何生成它们？ I guess I should just go look at the hash function and reverse engineer a solution, but I am lazy.我想我应该只是 go 看看 hash function 并逆向工程解决方案，但我很懒。

1 个解决方案

Note: this information is valid for perl between 5.8.2 and 5.17.x.注意：此信息对 5.8.2 和 5.17.x 之间的 perl 有效。 Beginning with perl 5.18, perl uses a new hash algorithm, hash randomization occurs on every startup (instead of only when a pathological hash is detected), and PERL_HASH_SEED is interpreted differently. Beginning with perl 5.18, perl uses a new hash algorithm, hash randomization occurs on every startup (instead of only when a pathological hash is detected), and PERL_HASH_SEED is interpreted differently. As perl now uses a 128-bit hash seed, the "pathological hash" condition should be almost impossible to trigger intentionally.由于 perl 现在使用 128 位 hash 种子，因此几乎不可能故意触发“病态哈希”条件。

Original answer: If you force the hash seed to 0 by putting PERL_HASH_SEED=0 in the environment before perl starts, the collection of keys "\0" , "\0\0" , "\0\0\0" , etc. will cause every key to land in hash bucket 0 with current perls.原始答案：如果在 perl 开始之前将PERL_HASH_SEED=0放入环境中，强制 hash 种子为 0，则键的集合"\0" 、 "\0\0" 、 "\0\0\0"等。将导致每个密钥都以当前的 perls 降落在 hash 存储桶 0 中。