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Symmetric-key encryption can use either stream ciphers or block ciphers. [8] Stream ciphers encrypt the digits (typically bytes), or letters (in substitution ciphers) of a message one at a time. An example is ChaCha20. Substitution ciphers are well-known ciphers, but can be easily decrypted using a frequency table. [9]
This increases the difficulty for an adversary attempting to compute the discrete logarithm and compromise the shared secret. These two values are chosen in this way to ensure that the resulting shared secret can take on any value from 1 to p − 1. Here is an example of the protocol, with non-secret values in blue, and secret values in red.
In cryptography, a shared secret is a piece of data, known only to the parties involved, in a secure communication. This usually refers to the key of a symmetric cryptosystem . The shared secret can be a PIN code , a password , a passphrase , a big number, or an array of randomly chosen bytes.
The shared secret can be used, for instance, as the key for a symmetric cipher, which will be, in essentially all cases, much faster. In an asymmetric key encryption scheme, anyone can encrypt messages using a public key, but only the holder of the paired private key can decrypt such a message.
[1] [2] [3] This shared secret may be directly used as a key, or to derive another key. The key, or the derived key, can then be used to encrypt subsequent communications using a symmetric-key cipher. It is a variant of the Diffie–Hellman protocol using elliptic-curve cryptography.
The secret is split into multiple shares, which individually do not give any information about the secret. To reconstruct a secret secured by SSS, a number of shares is needed, called the threshold. No information about the secret can be gained from any number of shares below the threshold (a property called perfect secrecy).
This design makes it easy to reuse Ascon in multiple ways (as a cipher, hash, or a MAC). [4] As of February 2023, the Ascon suite contained seven ciphers, [3] including: [5] Ascon-128 and Ascon-128a authenticated ciphers; Ascon-Hash cryptographic hash; Ascon-Xof extendable-output function; Ascon-80pq cipher with an "increased" 160-bit key.
Careful choice must be made in selecting the mode of operation of the cipher. The simplest mode encrypts and decrypts each 128-bit block separately. In this mode, called electronic code book (ECB), blocks that are identical will be encrypted identically; this is entirely insecure. It makes some of the plaintext structure visible in the ciphertext.