Quiz Entry - updated: 2026.07.14
Summarize the key differences between stream ciphers and block ciphers.
Stream ciphers encrypt bit by bit with a keystream (fast, no padding, no integrity), while block ciphers encrypt fixed-size blocks (more versatile, can provide integrity via MAC).
| Property | Stream Cipher | Block Cipher |
|---|---|---|
| Unit of encryption | Bit/byte | Fixed-size block (e.g., 128 bits) |
| Speed | Very fast | Fast (with AES-NI) |
| Padding needed | No | Depends on mode (ECB/CBC: yes, CTR/OFB: no) |
| Integrity | No (must add MAC) | Can provide via CBC-MAC |
| Key reuse | Fatal (keystream reuse) | Safe with proper mode + IV |
| Examples | ChaCha20, RC4 | AES, DES, 3DES |
| Hardware | Simple | More complex |
The modern reality:
- Block ciphers in CTR/OFB mode act as stream ciphers
- Authenticated encryption (AES-GCM) combines both worlds
- The distinction is becoming less important as AE modes dominate
Best practice today: Use AES-GCM or ChaCha20-Poly1305 — both provide encryption + integrity + authenticity in a single, efficient construction.