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Understanding Cryptographic Hashing
A cryptographic hash function is a one-way mathematical algorithm that converts input data into a fixed-size string of bytes (the hash or digest). The same input always produces the same hash, but even the tiniest change produces a completely different output.
Hash Algorithm Comparison
- MD5 (128-bit): BROKEN ❌ | 32 hex characters | Fast but insecure (collision attacks since 2004)
- SHA-1 (160-bit): DEPRECATED ⚠️ | 40 hex characters | Google broke it in 2017, don't use for security
- SHA-256 (256-bit): SECURE ✅ | 64 hex characters | Part of SHA-2 family, widely used (Bitcoin, SSL)
- SHA-3: Next-gen secure | Different design from SHA-2 | Use for new high-security applications
Common Use Cases
- File Integrity: Verify downloads (check SHA-256 checksums)
- Password Storage: Store hashes, not plaintext (but use bcrypt/Argon2, not plain SHA)
- Digital Signatures: Sign PDFs, emails for authenticity
- Blockchain: Bitcoin uses SHA-256 for proof-of-work mining
- Git Commits: Git uses SHA-1 for version control (being migrated to SHA-256)
💡 Expert Tip: NEVER Hash Passwords Directly!
Don't use MD5 or SHA-256 for password storage—they're too fast and vulnerable to rainbow table attacks. Use bcrypt, Argon2, or scrypt instead. These are "slow" by design (with cost factors) and include automatic salting, making brute-force attacks infeasible. Example: bcrypt with cost=12 takes ~300ms per hash, while SHA-256 computes millions per second.
⚠️ Common Mistake: Using MD5 for Security
MD5 is BROKEN and has been since 2004. It's vulnerable to collision attacks where two different inputs produce the same hash. Never use MD5 for security purposes—not for passwords, certificates, or file integrity in untrusted environments. It's acceptable ONLY for non-cryptographic uses like checksums in trusted internal systems. Use SHA-256 minimum, or better yet, SHA-3 or BLAKE2.
Sarah Martinez
Security Engineer | Updated November 2025
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Frequently Asked Questions
What is a cryptographic hash function?
A one-way algorithm that converts any data into a fixed-size string. The same input always produces the same hash, but you can't reverse it to get the original data.
What is the difference between MD5, SHA-1, and SHA-256?
MD5 (128-bit) is broken—don't use. SHA-1 (160-bit) is deprecated. SHA-256 (256-bit) is secure and recommended for current use.
Can you reverse a hash?
No, you cannot mathematically reverse a hash. However, weak hashes can be cracked via brute force or rainbow tables.
What are hashes used for?
Password storage, file integrity checks, digital signatures, blockchain (Bitcoin uses SHA-256), data deduplication, and checksums.