← Entropy Atlas
Fresh or unique
Initialization vectors
An IV makes repeated encryption of similar data behave differently, but each mode defines different rules.
Evaluation card
What “plenty” means here.
- Required property
- The exact property required by the encryption mode: unpredictable, unique, or both.
- If it fails
- Applying one mode’s IV advice to another can leak patterns or enable chosen-plaintext attacks.
- Relevant attacker
- An observer or active sender who can compare ciphertexts or influence plaintext.
- The Plenty Line
- Read the mode specification, allocate the full IV width, and generate or count as that specification requires.
- Why more is not automatically better
- A longer random IV cannot rescue a mode that requires non-repetition but is allowed to collide.
Where it appears
Recognize the pattern.
- 01CBC initialization vectors
- 02CTR initial counters
- 03storage-encryption tweaks
The Plentropy rule
Protect the requirement, then stop.
Read the mode specification, allocate the full IV width, and generate or count as that specification requires.
Once that claim has comfortable evidence and margin, improve the next limiting factor instead of worshipping a larger entropy number.