SHA-256 vs SHA-512
A rare comparison where both answers are right. Neither is broken; pick by compatibility, output size and hardware — here's how.
| SHA-256 | SHA-512 | |
|---|---|---|
| output | 256 bits · 64 hex | 512 bits · 128 hex |
| word size / block | 32-bit · 512-bit blocks | 64-bit · 1024-bit blocks |
| security status | unbroken | unbroken, larger margin |
| hardware acceleration | widespread (x86 SHA-NI, ARMv8) | rarer |
| speed, plain software (64-bit CPU) | good | often ~1.5× faster on large inputs |
| speed, with SHA instructions | clearly faster | unchanged |
| ecosystem default for checksums | yes | no — seen, but rarer |
Security: margin, not survival
SHA-256 offers 128-bit collision resistance — already beyond any conceivable brute force; SHA-512 raises the ceiling further and its bigger internal state shrugs off multi-target scenarios. No known attack threatens either, and none on the horizon distinguishes them. Choosing SHA-512 "for security" over SHA-256 is buying flood insurance for a house on a hill: defensible, rarely decisive. (Passwords are the exception where neither belongs — they're too fast by design; that job wants Argon2 or bcrypt.)
Speed: it's about the silicon
SHA-512 does more work per round but eats twice the data per block, so on a 64-bit CPU running plain software it usually wins on throughput. Then hardware tips the table: most current x86 and ARM chips accelerate SHA-256 natively, making it the faster one in practice on laptops and phones. For file checksums, your disk often outweighs both. If you're picking a hash because of speed, the honest answer is BLAKE3 — this pair should be chosen on compatibility.
The middle children
SHA-384 and SHA-512/256 run SHA-512's engine truncated — 64-bit speed, shorter output, and immunity to length extension (a quirk both plain siblings share; it matters for naive keyed hashing, which is HMAC's job anyway). TLS leans on SHA-384; SHA-512/256 is elegant and rare.
Bottom line
Publishing checksums or matching the ecosystem: SHA-256. Told to use SHA-512, or standardized on 64-bit-heavy backends: SHA-512, with no apology. Verifying someone else's hash: length decides for you — 64 vs 128 characters — and the verify tool reads that automatically.
questions
Is SHA-512 more secure than SHA-256?
It has more margin — 512-bit output, larger internal state — but both are unbroken and SHA-256's 128-bit collision resistance is already beyond any conceivable brute force. No real-world attack distinguishes them today; pick by ecosystem and output-size needs, not fear.
Which one is faster?
It depends on the hardware. On 64-bit CPUs without SHA extensions, SHA-512 processes more data per round and often wins on large inputs. On CPUs with SHA-256 instructions — most laptops and phones now — SHA-256 wins clearly. For file verification, disk speed usually dominates either way.
What is SHA-512/256?
SHA-512 run with different initial values and truncated to 256 bits: 64-bit speed with a SHA-256-sized output, plus immunity to length-extension attacks. Elegant, standardized, and rarely seen next to downloads — publishers overwhelmingly stick with plain SHA-256.
Should I use SHA-512 for password storage?
Neither SHA-256 nor SHA-512, on their own — they're too fast, which helps attackers guess. Passwords belong in a dedicated slow scheme (Argon2, bcrypt, scrypt). Fast hashes are for integrity: checksums, signatures, content addressing.