Question

The concept is pretty simple actually, and involves finding out the hash function from known input and output.

Is there a tool (I’m on linux) that can find out this information quickly?

Example:

secret – fc683cd9ed1990ca2ea10b84e5e6fba048c24929

Knowing the two values above, this hypothetical machine would print out sha1sum.

And excuse my beginner mindset, I’m new and learning about this topic in my free time.

Answer 1

Assuming that an input string X is guaranteed to produce output hash Y, you can build a program which makes use of each encoding type.

Pseudocode:

hash = "fc683cd9ed1990ca2ea10b84e5e6fba048c24929";
input = "secret"

if (md5(input) == hash)
    return "md5";
else if (sha1(input) == hash)
    return "sha1";
//etc...
else
    return "Unknown"

Edit: See How come MD5 hash values are not reversible? for more information on why you can’t “reverse” a hash such as md5.

Edit 2: I did some searches and found this: http://code.google.com/p/hash-identifier/ – It looks pretty comprehensive, so take a look.