MD5 and SHA-256 are both cryptographic hash functions that turn arbitrary input into a fixed-size fingerprint, but their security properties diverge sharply. MD5 has been demonstrably broken since 2004 — collision attacks are fast enough to run on a single phone. SHA-256, part of the SHA-2 family, remains unbroken and is the default choice for any security-sensitive context. The question is rarely "which is better" — it is "are you sure MD5 is acceptable here?"
Side-by-Side Comparison
SHA-256
Pros
- Cryptographically secure — no practical collision or preimage attack exists as of today
- Required by TLS, Bitcoin, PGP, DKIM, and most modern security standards
- 256-bit output makes brute-force and rainbow-table attacks infeasible
- Part of the SHA-2 family, broadly certified by NIST and FIPS 180-4
- Hardware-accelerated on modern CPUs (Intel SHA-NI, ARMv8) for fast, constant-time hashing
- Saltable and compatible with HMAC for keyed message authentication
Cons
- Slower than MD5 on older hardware without SHA-NI acceleration
- 256-bit (64 hex char) output is longer and more verbose in logs and URLs
- Still vulnerable to length-extension attacks in its raw form — use HMAC-SHA256 for MACs
- Not password-hash-optimized — use bcrypt, scrypt, or Argon2 for storing passwords
MD5
Pros
- Extremely fast — historically useful for non-security checksums on slow hardware
- 128-bit output (32 hex chars) is compact and easy to eyeball in logs
- Universally implemented — every language has a built-in MD5 function
- Useful for change detection in non-adversarial contexts (cache keys, dedup hints)
- Lowest CPU cost of any common hash — sometimes matters at extreme throughput
Cons
- Broken against collisions since 2004 — chosen-prefix attacks run in seconds on a laptop
- Unsafe for any digital signature, certificate, or integrity check where attackers exist
- Vulnerable to length-extension attacks in its raw form
- 128-bit output is well within reach of distributed brute force for short inputs
- Deprecated by every modern security standard (PCI-DSS, NIST, OWASP)
- Banned from TLS since 2010 and from code-signing certificates since 2012
The Verdict
For any security-sensitive use — file integrity against tampering, digital signatures, password storage (combined with a slow KDF), API request signing, or anything where an attacker might benefit from a collision — use SHA-256 or stronger. MD5 is acceptable only for non-adversarial change detection: cache keys, deduplication, ETag generation where you trust the input. If you are unsure whether your use case is adversarial, default to SHA-256. The performance gap is negligible on modern hardware.
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