Re: Cracking Strings from URLs

Computer Nerd Kev <[email protected]> wrote:
> I've got long strings like this from URLs (percent-encoded
> characters have been decoded):
> 
> SdADygkIiM8ED8ZK/ZfkxwbHEgOXnsgKzQcYtq2j3L1HN6OYvET8PwvO2gpCCv4Bp4vIGLwLFN3dDQABOjWT0gVI/EtBlNUIObwLFNnU90IK/gCs2QQzBzhEz8sNAAdBPpmM+T0KRgudx88HxzsFnpjGQs8PBp+fEAvQCgCZnsdKzQz+lpbIBPj7CQ==
> 
> I believe they might be encrypted strings containing one or more
> known fields, probably including a known ten digit number
> (1409518286 in that case). They might also be hashes, but I think
> it's unlikely.

I got a copy of the PHP code. Turns out it's a "transposition
cipher" which adds different numbers to the ASCII value of each
character in sequence.

To decrypt, first the string is base64 decoded. Then the first
character's ASCII value has the ASCII value of the first character
in the password subtracted from it, as well as fixed value. Then
for the next encrypted string character the next password character
is subtracted along with the fixed value, and so on, with the
password characters repeating from the start when they run out.
Sure enough that decrypted string contains "1409518286" and other
info.

Very simple, but I still wonder what tools are available to
brute-force that without knowing what sort of encryption method has
been used?

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