← Entropy Atlas
Fresh or unique
AEAD nonces
Authenticated-encryption modes often require a nonce that never repeats under one key.
Evaluation card
What “plenty” means here.
- Required property
- Uniqueness under the same key according to the mode’s contract; some modes permit random nonces, others prefer counters.
- If it fails
- Nonce reuse can reveal plaintext relationships, enable forgery, or catastrophically expose authentication state.
- Relevant attacker
- A network observer who collects ciphertexts and notices repeated key–nonce pairs.
- The Plenty Line
- Use the protocol’s specified nonce construction and enforce the per-key message limit; counters are often better than chance.
- Why more is not automatically better
- More entropy does not beat guaranteed uniqueness when uniqueness is the actual requirement.
Where it appears
Recognize the pattern.
- 01AES-GCM nonces
- 02ChaCha20-Poly1305 nonces
- 03record-layer sequence values
The Plentropy rule
Protect the requirement, then stop.
Use the protocol’s specified nonce construction and enforce the per-key message limit; counters are often better than chance.
Once that claim has comfortable evidence and margin, improve the next limiting factor instead of worshipping a larger entropy number.