security - 什么是字典攻击？

Question

当我们说字典攻击时，我们并不是真正指真正的字典，不是吗？我的猜测是我们指的是黑客词典，即 rainbow tables ，对吗？

我的观点是，我们不是在谈论某人在登录框中输入不同的密码，我们谈论的是对您的数据库具有完全访问权限的人(具有散列密码，而不是纯密码)，并且此人正在逆转哈希值，对吗？

Answer 1

由于密码通常是密码学中最容易受到攻击的部分，因此它实际上是一本真正的字典。假设人们很懒，会选择适当的单词作为密码或从中构造密码短语。不过，字典可以包含其他内容，例如常用的非单词或字母/数字组合。基本上所有可能都是选择不当的密码。

有一些程序会占用整个硬盘驱动器，并根据其上的每个可输入字符串构建一个字典，假设用户的密码在某个时间点以明文形式放入内存中(然后放入页面文件中) )或者如果文本存储在驱动器上，则它仅存在于语料库中¹:

Even so, none of this might actually matter. AccessData sells another program, Forensic Toolkit, that, among other things, scans a hard drive for every printable character string. It looks in documents, in the Registry, in e-mail, in swap files, in deleted space on the hard drive ... everywhere. And it creates a dictionary from that, and feeds it into PRTK.

And PRTK breaks more than 50 percent of passwords from this dictionary alone.

实际上，即使您包含人们通常如何构建密码的知识，您也可以使词典更加有效。 Schneier 对此进行了详细的讨论¹:

• Common word dictionary: 5,000 entries
• Names dictionary: 10,000 entries
• Comprehensive dictionary: 100,000 entries
• Phonetic pattern dictionary: 1/10,000 of an exhaustive character search

The phonetic pattern dictionary is interesting. It's not really a dictionary; it's a Markov-chain routine that generates pronounceable English-language strings of a given length. For example, PRTK can generate and test a dictionary of very pronounceable six-character strings, or just-barely pronounceable seven-character strings. They're working on generation routines for other languages.

PRTK also runs a four-character-string exhaustive search. It runs the dictionaries with lowercase (the most common), initial uppercase (the second most common), all uppercase and final uppercase. It runs the dictionaries with common substitutions: "$" for "s," "@" for "a," "1" for "l" and so on. Anything that's "leet speak" is included here, like "3" for "e."

The appendage dictionaries include things like:

• All two-digit combinations
• All dates from 1900 to 2006
• All three-digit combinations
• All single symbols
• All single digit, plus single symbol
• All two-symbol combinations

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¹ Bruce Schneier:选择安全密码。见:Schneier 谈安全性。 (URL)