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SHA-256 vs MD5

One is cryptographically broken. The other is the modern default.

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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.

Frequently Asked Questions

Is MD5 still safe for checksums?
Only for non-adversarial checksums — detecting accidental file corruption from disk errors or network noise, where no one is trying to forge a collision. If an attacker could craft a file with the same MD5 as a legitimate one (trivial today), MD5 gives you a false sense of integrity. For any tamper-resistance, use SHA-256.
Why is MD5 not suitable for passwords?
Two reasons: MD5 is fast, so an attacker with a GPU can brute-force billions of guesses per second, and MD5 has no built-in salt or work factor. Even salted MD5 falls to GPU brute force in seconds. For password storage, use a slow, memory-hard KDF like Argon2id, bcrypt, or scrypt — never raw MD5 or SHA-256.
Can two different files have the same SHA-256?
Theoretically yes — any fixed-output hash has collisions by the pigeonhole principle. Practically no — finding a SHA-256 collision would require ~2^128 operations, which is billions of years on every computer on Earth combined. No SHA-256 collision has ever been published. Treat collisions as impossible for engineering purposes.

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