Crime relies on compression --- the "CR" stands for "Compression Ratio" The idea is that the DEFLATE compression algorithm used in the TLS compression mode CRI

Crime relies on compression --- the "CR" stands for "Compression Ratio" The idea is that the DEFLATE compression algorithm used in the TLS compression mode CRIME attacks will build and index of repeated strings and compress by providing keys to that index. Here's a beautiful demonstration of another similar compression algorithm: http://jvns.ca/blog/2013/10/24/day-16-gzip-plus-poetry-equals-awesome/ http://jvns.ca/blog/2013/10/24/day-16-gzip-plus-poetry-equal... So, if you control some subset of the plaintext you can make guesses as to what the secret you're trying to get at is, and if the size changes after compression you know that you got two hits to that bucket in the index, so your guess is right. You can use this technique to guess some string character by character -- reducing your seach space to n*m instead of n^m for a string of length m with character set of length n.