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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. [4] When the keystream is generated by a pseudo-random number generator, the result is a stream cipher.
On July 22, 1919, U.S. Patent 1,310,719 was issued to Gilbert Vernam for the XOR operation used for the encryption of a one-time pad. [7] Derived from his Vernam cipher, the system was a cipher that combined a message with a key read from a punched tape. In its original form, Vernam's system was vulnerable because the key tape was a loop, which ...
The xor–encrypt–xor (XEX) is a (tweakable) mode of operation of a block cipher. In tweaked-codebook mode with ciphertext stealing , it is one of the more popular modes of operation for whole-disk encryption. XEX is also a common form of key whitening, and part of some smart card proposals. [1] [2]
The stream cipher produces a string of bits C(K) the same length as the messages. The encrypted versions of the messages then are: E(A) = A xor C E(B) = B xor C. where xor is performed bit by bit. Say an adversary has intercepted E(A) and E(B). They can easily compute: E(A) xor E(B)
The first block cipher to use a form of key whitening is DES-X, which simply uses two extra 64-bit keys for whitening, beyond the normal 56-bit key of DES. This is intended to increase the complexity of a brute force attack , increasing the effective size of the key without major changes in the algorithm.
[citation needed] XOR is also heavily used in block ciphers such as AES (Rijndael) or Serpent and in block cipher implementation (CBC, CFB, OFB or CTR). In simple threshold-activated artificial neural networks , modeling the XOR function requires a second layer because XOR is not a linearly separable function.
The propagating cipher block chaining [25] or plaintext cipher-block chaining [26] mode was designed to cause small changes in the ciphertext to propagate indefinitely when decrypting, as well as when encrypting. In PCBC mode, each block of plaintext is XORed with both the previous plaintext block and the previous ciphertext block before being ...
Since encryption of each digit is dependent on the current state of the cipher, it is also known as state cipher. In practice, a digit is typically a bit and the combining operation is an exclusive-or (XOR). The pseudorandom keystream is typically generated serially from a random seed value using digital shift registers.