Cryptography
Nonce
Also known as: Number used once, Cryptographic nonce
Definition
A "number used once" supplied to a cryptographic algorithm to guarantee freshness and prevent replay or key/IV reuse.
Examples
- TLS 1.3 derives per-record AEAD nonces by XOR-ing a sequence number with the per-direction IV.
- The 2010 PlayStation 3 ECDSA private-key recovery happened because Sony reused the signature nonce.
Related terms
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.
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.
ChaCha20
A modern stream cipher designed by Daniel J. Bernstein, using a 256-bit key and 96-bit nonce, widely deployed alongside Poly1305 as the AEAD ChaCha20-Poly1305.
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.
Replay Attack
An attack that captures legitimate network traffic — typically authentication tokens or transactions — and retransmits it later to impersonate the original sender.
ECDSA
The elliptic-curve variant of the Digital Signature Algorithm, standardized in FIPS 186, producing compact signatures whose security relies on the elliptic-curve discrete logarithm problem.