keyless ciphers of ROT13/47 ilk

Question

Do you know of any other ciphers that performs like the ROT47 family ? My major requirement is that it'd be keyless. Thanks.

Answer 1

Sounds like you might be looking for some "classical cryptography" solutions.

SUBSTITUTION CIPHERS are encodings where one character is substituted with another. E.g. A->Y, B->Q, C->P, and so on. The "Caesar Cipher" is a special case where the order is preserved, and the "key" is the offset. In the rot13/47 case, the "key" is 13 or 47, respectively, though it could be something like 3 (A->D, B->E, C->F, ...).

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TRANSPOSITION CIPHERS are ones that don't substitute letters, but ones that rearrange letters in a pre-defined way. For example:

CRYPTOGRAPHY

may be written as

C Y T G A H
 R P O R P Y

So the ciphered output is created by reading the two lines left to right

CYTGAHRPORPY

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Another property of rot13/47 is that it's REVERSABLE:

encode(encode(plaintext)) == plaintext

If this is the property you want, you could simply XOR the message with a known (previously decided) XOR value. Then, XOR-ing the ciphertext with the same value will return the original plaintext. An example of this would be the memfrob function, which just XORs a buffer with the binary representation of the number 42.

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You also might check out other forms of ENCODINGS, such as Base64 if that's closer to what you're looking for.

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!! Disclaimer - if you have data that you're actually trying to protect from anyone, don't use any of these methods. While entertaining, all of these methods are trivial to break.