On Wed, 6 Feb 2002, fooyu wrote: > I want to know if encryption algorithm has footprint. Is there any > technica to find which encryption algorithm it used? <nb: i'm not a cryptographer, i just enjoy reading about this a bit. this is a question i faced last year in a project which we dropped.> none that i know of, aside from very minor odd cases (ie the RC4 second bit in the key being zero) or bad algorithms or implementations. the best you can do is to look at the entropy of the output, which will typically approach random for decent algorithms, not allowing you to differentiate the algorithms. other indicators may be useful, though, like the output size of the cihpertext (ie is it a regular boundary, or not), which can help you start to determine if its a block cipher in chaining mode or a stream cipher. secondly, look at typical applications used in that field and that location, you can probably tackle a few algorithms first that are likely to be in use rather than not. ie lotus notes wont use AES or other advanced ciphers, typically, at this time. in short, you have a difficult problem ahead of you. but you can start to narrow it down based on probabilities and some basic detective work. > Thank you all and Happy Chinese New year! happy lunar new year to you, as well. ____________________________ jose nazario joseat_private PGP: 89 B0 81 DA 5B FD 7E 00 99 C3 B2 CD 48 A0 07 80 PGP key ID 0xFD37F4E5 (pgp.mit.edu)
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