[07] Cipher Feedback (CFB) Mode
By:
Prasanna
|
📘 Topic: Cipher Feedback (CFB) Mode
Domain: D6 – Security Engineering
Tags: #cissp
🧾 Definition
Cipher Feedback Mode is a block cipher mode of operation that turns a block cipher into a self-synchronizing stream-like mechanism. It uses previous ciphertext to produce the next keystream block.
🔑 Key Points
- CFB is a block cipher mode used for encryption.
- It can operate like a stream cipher and is useful for real-time data.
- It propagates errors from earlier ciphertext blocks.
- It is a legacy mode; modern systems usually prefer AEAD modes such as GCM or ChaCha20-Poly1305.
⚠️ CISSP Insight
- CISSP candidates should understand that encryption mode choice affects security properties, performance, and error behavior.
- Modern design should prefer authenticated encryption over legacy modes where possible.
⚔️ Key Difference / Trap
- CFB vs ECB
- ECB encrypts identical plaintext blocks to identical ciphertext blocks
- CFB avoids that pattern by chaining previous ciphertext
- CFB vs CTR
- CFB is feedback-based
- CTR uses a counter value for keystream generation
🏗️ Example
CFB may be used in legacy protocols where a block cipher is required in a stream-like fashion, but modern implementations usually prefer authenticated encryption.
📚 References
- NIST SP 800-38A, Recommendation for Block Cipher Modes of Operation
- NIST SP 800-57, Recommendation for Key Management
🔁 Quick Recall
- CFB = Feedback-based block cipher mode
- Modern choice = AEAD