Question 1

When should I use SHA-512 over SHA-256?

Accepted Answer

Use SHA-512 when you need 256+ bits of collision resistance (SHA-256 only offers 128 bits). Practical scenarios: cryptographic protocols requiring long-term security against future quantum attacks, applications hashing very large amounts of data where the SHA-2 birthday bound matters, derive-once material that feeds into PBKDF2 or HKDF, /etc/shadow $6$ Linux passwords. For general-purpose use (file checksums, content addressing, TLS), SHA-256 is the standard and SHA-512 offers no practical advantage.

Question 2

Is SHA-512 faster or slower than SHA-256?

Accepted Answer

On 64-bit CPUs, SHA-512 is often slightly faster than SHA-256 because it operates on 64-bit words natively. SHA-256 uses 32-bit operations that don't fully utilize 64-bit registers. On 32-bit ARM (older mobile, embedded), SHA-256 is faster because 64-bit math gets decomposed. For most desktop/server use cases in 2026, the two algorithms are comparable in speed — typically within 20% of each other. Pick based on output size, not performance.

Question 3

What is SHA-512/256?

Accepted Answer

SHA-512/256 is a truncated variant defined in FIPS 180-4: compute SHA-512 with different initial hash values, then truncate to 256 bits. It produces a 256-bit output (like SHA-256) but is often faster than SHA-256 on 64-bit CPUs. Less widely supported — most languages provide SHA-256 directly but require explicit configuration for SHA-512/256. This tool offers full SHA-512 only; for SHA-512/256 specifically, you'd need a more specialized library.

Question 4

Where is SHA-512 actually used in the wild?

Accepted Answer

Linux /etc/shadow $6$ password hashes (the default since glibc 2.7), OpenPGP signatures, some TLS 1.3 cipher suites, BLAKE2b derivatives, Sodium/libsodium's default hash, OpenSSH's host key signatures, and certain Bitcoin-derived cryptocurrencies that wanted SHA-256's properties at a larger digest size.

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