Reciprocal cipher
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A reciprocal cipher means, just as one enters the cleartext into the cryptography system to get the ciphertext, one could enter the ciphertext into the same place in the system to get the cleartext. Sometimes also referred as self-reciprocal cipher.
The Enigma machine was a reciprocal cipher machine. ROT13 is a reciprocal encryption algorithm. The Beaufort cipher is a reciprocal encryption algorithm.