Enigma was such an algorithm, but not realy secure.
Using a block cipher would be a problem, and I dont know any block cipher where the encryption also the decryption methode is.
But every (or most?) stream cipher has this property. E.g. you can use RC4, where the encryption routine also the decryption routine is, but RC4 is not recommended for new applications (it's realy hard to use the algorithm so that it is secure).
An other possibility is using a block cipher (e.g. AES) in OFB or CTR mode, which would be my choice.
Stream cipher has the following characterization:
Plaintext ^ Keystream = Ciphertext (Encryption)
Plaintext = Ciphertext ^ Keystream (Decryption)
^ means XOR, and the keystream has to be the same for encryption/decryption.
Replaced chiffre by cipher
Last edited by Elderan on Tue Jun 12, 2007 1:36 pm; edited 1 time in total
This is a block cipher where the encryption and decryption routine is the same in most cases.
Normaly, for encryption you have to use the encryption routine reverse, means e.g. for decryption you add first the last round key and so on.
But I think, Irfan Ahmed, wanted the following:
C = E(P);
P = E(C);
P = E(E(P));
This is, afaik, only with a stream cipher possible (or a block cipher in stream mode), resp. I don't know a block cipher where the encryption routine also the decryption routine is (although the routines are very simular).
PS: Sry, for chiffre and cipher, I'm not a native speaker, and so it's realy hard to change (or avoid) some habits, because the German word for 'block cipher' is 'Blockchiffre'.
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