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Re: Which encryption algorithm used?
From: exon <exon () home se>
Date: Sun, 30 May 2004 04:46:12 +0200
John Borwick wrote:
Pitts, Christopher C. wrote:
With a proper algorithm, it should be nearly impossible. That being
said, many implementations, stick a header or footer that can be used
to identify the method used. Take a look at mcrypt and it's bare
function, you can use it to compare the stripped (--base IIRC) ouput
of the different algorithms.
What do you mean, "with a proper algorithm"? Cryptographic algorithms
are supposed to be secure *even when the methods used are known*. The
only thing that has to be secret is the key.
And that's about exactly what he means. You can't determine what cipher
was used to encrypt a message by looking at the encrypted message if the
output is secure when the methods used are known. That's because the
encrypted message would consist of a bunch of pseudo-random characters
with no appearent coherence what so ever.
In this sense, rotation-, simple-hash and XOR-ciphers don't use "proper
algorithms" because it's fairly simple to conclude that one of the three
was used to encrypt a message by looking at the encrypted text ("hello"
would look something like "ifmmp" with a rotation cipher and a key of 1).