Cryptography
Block Cipher
Definition
A symmetric cipher that encrypts fixed-size blocks of plaintext with a secret key, usually combined with a mode of operation to handle data of arbitrary length.
Examples
- AES is a 128-bit-block cipher used in modes like GCM, CBC, and XTS.
- DES is a 64-bit-block cipher, now obsolete due to its small key size.
Related terms
AES (Advanced Encryption Standard)
A NIST-standardized 128-bit block cipher with 128-, 192- or 256-bit keys, designed by Daemen and Rijmen and used as the dominant symmetric cipher worldwide.
DES (Data Encryption Standard)
An obsolete 64-bit block cipher with a 56-bit key, standardized by NBS in 1977 and now considered broken because its key space can be exhausted in hours.
Stream Cipher
A symmetric cipher that encrypts data one bit or byte at a time by XORing it with a pseudorandom keystream derived from a key and nonce.
Symmetric Encryption
An encryption scheme in which the same secret key is used for both encryption and decryption, offering high speed and strong confidentiality when the key is shared securely.
Encryption
The cryptographic transformation of plaintext into ciphertext using an algorithm and key so that only authorized parties can recover the original data.
Initialization Vector (IV)
A randomized starting value for a block-cipher mode of operation that ensures identical plaintexts encrypted under the same key yield different ciphertexts.