SHA-256 vs SHA-512: which hash function should you choose?
SHA-256 and SHA-512 both belong to the SHA-2 family, designed by the NSA and standardised by NIST. They produce a fixed-size digest from any data and are today considered secure. The difference lies in the digest size, the performance depending on the architecture and a few security details. Here is which to choose and why.
The SHA-2 family
SHA-2 gathers several variants (SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256) that share the same structure but differ in the size of the words and the digest. The number indicates the digest size in bits: SHA-256 produces 256 bits (64 hexadecimal characters), SHA-512 produces 512 (128 characters).
You can compute these digests with our hash generator, or recognise an algorithm from a digest with the hash identifier. Not to be confused with MD5, obsolete for security (see our MD5 vs SHA-256 comparison).
SHA-256
SHA-256 works on 32-bit words and produces a 256-bit digest. It is the most widespread hash function in the world: TLS certificates, Bitcoin signatures, file integrity verification, git. Its shorter digest makes it convenient to store, display and transmit.
- Digest: 256 bits, 64 hexadecimal characters
- Words: 32 bits, optimal on 32-bit platforms and embedded systems
- Adoption: the widest, universal support
SHA-512
SHA-512 works on 64-bit words and produces a 512-bit digest. Counter-intuitively, on a modern 64-bit processor, it is often faster than SHA-256 for large volumes, because it processes more data per round. Its longer digest also offers a higher security margin.
- Digest: 512 bits, 128 hexadecimal characters
- Words: 64 bits, optimal on 64-bit architectures
- Native resistance: SHA-512 is not vulnerable to the length-extension attack when using its truncated variants (SHA-512/256)
Comparison table
| Criterion | SHA-256 | SHA-512 |
|---|---|---|
| Digest size | 256 bits (64 hex) | 512 bits (128 hex) |
| Word size | 32 bits | 64 bits |
| Speed on 64-bit CPU | Good | Often higher |
| Speed on 32-bit / embedded | Higher | Slower |
| Security margin | Very high | Even higher |
| Length extension | Vulnerable | Vulnerable (except truncated variants) |
| Adoption | Universal | Wide |
Performance
Performance depends on the architecture. On a 64-bit server or laptop, SHA-512 can outperform SHA-256 by 20 to 50 % on large files, because it processes larger blocks per iteration. On a 32-bit microcontroller or a constrained environment, SHA-256 regains the advantage.
In practice, for small inputs (a password, an identifier), the difference is negligible. It only becomes measurable on significant volumes or high throughput.
When to choose one or the other
Choose SHA-256 when
- You aim for maximum compatibility and a compact format
- You target embedded systems, IoT or 32-bit platforms
- You verify file integrity or sign certificates
- A short digest makes display and storage easier
Choose SHA-512 when
- You hash large volumes on 64-bit servers
- You want the widest possible security margin
- You use SHA-512/256 to resist length extension while keeping 256 bits
Important: neither of the two is suitable for hashing passwords. For that, use bcrypt or Argon2, designed to be slow and salted.
Recommendation
For general use, SHA-256 is the default choice: universally supported, compact, amply secure. Opt for SHA-512 if you hash large volumes on 64-bit hardware or if you want an extra security margin. And to store passwords, turn to a dedicated function such as Argon2id, never to SHA-2 alone.
Frequently asked questions
Is SHA-512 safer than SHA-256?
SHA-512 offers a higher theoretical security margin thanks to its longer digest, but SHA-256 is already well out of reach of current attacks. For almost all uses, both are considered secure.
Why can SHA-512 be faster than SHA-256?
Because it handles 64-bit words and processes larger blocks per round. On a native 64-bit processor, this offsets the overhead and often makes it faster on large volumes. On 32 bits, it is the opposite.
Can I hash passwords with SHA-256 or SHA-512?
No, that would be a mistake. These functions are fast, hence easy to attack by brute force. Use bcrypt or Argon2id, which are deliberately slow and incorporate a salt.
What is SHA-512/256?
It is SHA-512 whose digest is truncated to 256 bits, with different initialisation values. You obtain a 256-bit digest, the speed of SHA-512 on 64 bits and native resistance to the length-extension attack.