Editing XOR cipher (section)

== Use and security ==
The XOR operator is extremely common as a component in more complex ciphers. By itself, using a constant repeating key, a simple XOR cipher can trivially be broken using [[frequency analysis]]. If the content of any message can be guessed or otherwise known then the key can be revealed. Its primary merit is that it is simple to implement, and that the XOR operation is computationally inexpensive. A simple repeating XOR (i.e. using the same key for xor operation on the whole data) cipher is therefore sometimes used for hiding information in cases where no particular security is required. The XOR cipher is often used in computer [[malware]] to make reverse engineering more difficult.

If the key is random and is at least as long as the message, the XOR cipher is much more secure than when there is key repetition within a message.<ref>{{Harvnb|Churchhouse|2002|p=68}}</ref> When the keystream is generated by a [[pseudo-random number generator]], the result is a [[stream cipher]]. With a key that is [[Hardware random number generator|truly random]], the result is a [[one-time pad]], which is [[Information-theoretic security|unbreakable in theory]].

The XOR operator in any of these ciphers is vulnerable to a [[known-plaintext attack]], since ''plaintext'' <math>\oplus</math> ''ciphertext'' = ''key''.
It is also trivial to flip arbitrary bits in the decrypted plaintext by manipulating the ciphertext.
This is called [[Malleability (cryptography)|malleability]].