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Example of a Key Derivation Function chain as used in the Signal Protocol.The output of one KDF function is the input to the next KDF function in the chain. In cryptography, a key derivation function (KDF) is a cryptographic algorithm that derives one or more secret keys from a secret value such as a master key, a password, or a passphrase using a pseudorandom function (which typically uses a ...
P i are blocks of the input string, Z i are hashed output blocks. In cryptography, a sponge function or sponge construction is any of a class of algorithms with finite internal state that take an input bit stream of any length and produce an output bit stream of any desired length. Sponge functions have both theoretical and practical uses.
Key stretching algorithms depend on an algorithm which receives an input key and then expends considerable effort to generate a stretched cipher (called an enhanced key [citation needed]) mimicking randomness and longer key length. The algorithm must have no known shortcut, so the most efficient way to relate the input and cipher is to repeat ...
One well-known example of a zero-knowledge proof is the "Where's Waldo" example. In this example, the prover wants to prove to the verifier that they know where Waldo is on a page in a Where's Waldo? book, without revealing his location to the verifier. [9] The prover starts by taking a large black board with a small hole in it, the size of Waldo.
C n−1 = Encrypt (K, D n). Encrypt D n to create C n−1. For the first M bits, this is equivalent to what would happen in ECB mode (other than the ciphertext ordering). For the last B−M bits, this is the second time that these data have been encrypted under this key (It was already encrypted in the production of E n−1 in step 2).
As above, let be the length of the string to be decrypted and let be the number of rails used during encryption. We will add two variables, x {\displaystyle x} and y {\displaystyle y} , where x + 1 {\displaystyle x+1} = the number of diagonals in the decrypted Rail Fence, and y {\displaystyle y} = the number of empty spaces in the last diagonal.
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. With a key that is truly random, the result is a one-time pad, which is unbreakable in theory.
The encryption input also includes a public nonce N, the output - authentication tag T, size of the ciphertext C is the same as that of P. The decryption uses N, A, C, and T as inputs and produces either P or signals verification failure if the message has been altered. Nonce and tag have the same size as the key K (k bits). [6]