On 11/9/2015 11:15 AM, Dimitry Sibiryakov wrote: > 09.11.2015 16:49, Jim Starkey wrote: >> For CBC mode, the initialization vector is XORed into the first block of >> plaintext. Without this (or something like it), the first 16 bytes of >> every page would have the same encryption, allowing a mapping from >> cryptotext to presumed plaintext, possibly leaking useful information. > XORing of two known values (or doing whatever similar) won't add more > problem for > attacker because the result also will be a known plaintext. To make plaintext > unknown, > initialization vector also must be unknown. > But all this doesn't matter as AES is considered to be practically > invulnerable to > known-plaintext attacks. > It matters because if every page is encrypted with the same key and initial state, information can be learned by building a table of first blocks. If two pages have the same encryption, then an attacker knows that those pages have common prologs. This isn't a known plaintext attack, but an analysis of cryptotext. It doesn't do anything towards breaking the key, only to extract "leaked" information.
Read about how Enigma and RC4 were broken. Each was the victim of sloppy crypto procedures, not plaintext attacks. ------------------------------------------------------------------------------ Presto, an open source distributed SQL query engine for big data, initially developed by Facebook, enables you to easily query your data on Hadoop in a more interactive manner. Teradata is also now providing full enterprise support for Presto. Download a free open source copy now. http://pubads.g.doubleclick.net/gampad/clk?id=250295911&iu=/4140 Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel