Finding encryption algorithm from source and resulting string

Question

If we have a source string and encrypted string, can we find out algorithm/forumla used in encrypting that source string?

EDIT

Here are a couple of such strings.

string, encrypted string
avtacarguy,c0e54a662e8d7adbf26e2515dcb2bfde
burris212,0c9fe74ce3abb1507108dba1f04497e5
directert,96336189003e59a2d4a3fdbb2cf02707

Do you know if it's a modern algorithm(DES, AES,...) or a history one(Caesar, letter substitution,...)? — CodesInChaos
– CodesInChaos, Commented Mar 24, 2012 at 9:40
Create a bunch of example ciphertext-plaintext pairs. Some of them should have related plaintext (replace a single letter for example). If it's a historic cipher you might discover a structure. If it's a modern cipher, you're out of luck. You'll need to find the algorithm and key by reversing the software in question. — CodesInChaos
– CodesInChaos, Commented Mar 24, 2012 at 9:52

Simeon Visser · Accepted Answer · 2012-03-24 09:39:07Z

3

In general, no. There can be numerous algorithms that turn the source string into the encrypted string, based on what public and/or private keys are used.

In simple cases, such as the Caesar cipher it may be possible to figure out how it was done but even then you've only provided a 'most likely' explanation as to what encryption algorithm was used.

answered Mar 24, 2012 at 9:39

Simeon Visser

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Simeon Visser Over a year ago

Sorry, we just don't know enough. Even with some samples it's going to be tough.

aioobe · Accepted Answer · 2012-03-24 09:38:30Z

3

Technically (mathematically) speaking, no. Several encryption schemes could yield the same crypto text for some particular input.

If you had had the encryption key, you could of course try out all popular encryption schemes and see if you got some exact match in which case you could be pretty sure you found the algorithm.

answered Mar 24, 2012 at 9:38

aioobe

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