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In cryptography, the simple XOR cipher is a type of additive cipher, [1] an encryption algorithm that operates according to the principles: A ⊕ {\displaystyle \oplus } 0 = A, A ⊕ {\displaystyle \oplus } A = 0,
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 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)
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.
Encrypt (K, data): use the underlying block cipher in encrypt mode on the 'data' string using the key K. Decrypt (K, data): use the underlying block cipher in decrypt mode on the 'data' string using the key K. XOR: Bitwise Exclusive-OR. Equivalent to bitwise addition without use of a carry bit. ||: Concatenation operator.
Internally, the cipher uses bitwise addition ⊕ (exclusive OR), 32-bit addition mod 2 32 ⊞, and constant-distance rotation operations <<< on an internal state of sixteen 32-bit words. Using only add-rotate-xor operations avoids the possibility of timing attacks in software implementations. The internal state is made of sixteen 32-bit words ...
The most common form of key whitening is xor-encrypt-xor-- using a simple XOR before the first round and after the last round of encryption. 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 .
In cryptography, XOR is sometimes used as a simple, self-inverse mixing function, such as in one-time pad or Feistel network systems. [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).