SHA-256 vs MD5 — Hash Function Comparison
SHA-256 and MD5 are both cryptographic hash functions that take arbitrary input and produce a fixed-size digest, but they are not interchangeable for security purposes. MD5 was designed in 1992 and is fast but has known collision vulnerabilities. SHA-256 (part of the SHA-2 family) was designed in 2001 with these weaknesses in mind and is the current standard for cryptographic use. Understanding when each is appropriate prevents security mistakes.
Comparison Table
| Aspect | SHA-256 | MD5 |
|---|---|---|
| Output size | 256 bits (32 bytes, 64 hex characters) | 128 bits (16 bytes, 32 hex characters) |
| Speed | Slower than MD5 (by design for security) | Very fast; originally optimized for speed |
| Security status | Cryptographically secure; no known attacks | Collision-vulnerable; do not use for security |
| Collision resistance | 128-bit security margin; no practical collision attack | Practical collision attacks demonstrated (2004+) |
| HMAC usage | HMAC-SHA256 is the standard for API authentication | HMAC-MD5 is weak; avoid for security |
| Password hashing | Do not use bare SHA-256; use bcrypt or Argon2 | Never use for passwords; trivially crackable with GPUs |
| Checksum use | Overkill but fine for integrity verification | Acceptable for non-security checksums (deduplication) |
When to Use SHA-256
Use SHA-256 for all security-relevant hashing: HMAC signatures, TLS certificate fingerprints, code signing, API authentication signatures, and data integrity verification where security matters. SHA-256 is the minimum acceptable hash function for new cryptographic systems. For even stronger security, SHA-3 (Keccak) or BLAKE3 are alternatives, though SHA-256 hardware acceleration makes it the practical standard.
When to Use MD5
MD5 is only appropriate for non-security checksums where speed matters and collision resistance is irrelevant: deduplication based on content hash, generating cache keys, identifying duplicate files, or comparing large data sets for equality. For these use cases, MD5's speed advantage is relevant and its collision vulnerability does not matter because there is no adversary trying to craft collisions.
Convert Between SHA-256 and MD5
Generate SHA-1, SHA-256, SHA-384, and SHA-512 cryptographic hashes from any text.
Generate an MD5 hash from any text. Pure JavaScript implementation, runs client-side.
Upload a file and calculate its MD5, SHA-1, SHA-256, and SHA-512 checksums.
Generate HMAC-SHA-256/384/512 message authentication codes using a secret key.
FAQ
- Can MD5 be used for password storage?
- Absolutely not. MD5 (even salted) is crackable in milliseconds using GPU-based dictionary and brute-force attacks. Modern rigs can compute billions of MD5 hashes per second. For passwords, use bcrypt (cost factor 12+), Argon2id, or scrypt — algorithms specifically designed to be slow and memory-intensive.
- What does "collision-vulnerable" mean for MD5?
- A collision is two different inputs that produce the same hash. MD5 collision attacks have been practically demonstrated — two different PDF files with the same MD5 hash were created in 2008. This means an attacker could craft a malicious file that has the same MD5 as a legitimate file, defeating any MD5-based integrity check.
- Is SHA-1 also broken?
- Yes. SHA-1 is also cryptographically broken — the first practical SHA-1 collision (SHAttered) was published in 2017. Google's Chrome and other browsers no longer trust SSL certificates signed with SHA-1. Like MD5, SHA-1 should only be used for non-security checksums, and even then SHA-256 or BLAKE3 are preferable.