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A hash function converts any input into a fixed-length output (the hash). The same input always produces the same hash, but it is computationally infeasible to reverse the process. Even a single character change produces a completely different hash — this is called the avalanche effect.
Hash algorithm comparison
| Algorithm | Output size | Security | Best used for |
|---|---|---|---|
| MD5 | 128-bit (32 hex) | Broken — collisions possible | Checksums, cache keys (not security) |
| SHA-1 | 160-bit (40 hex) | Weak — avoid for new systems | Legacy systems, Git commit IDs |
| SHA-256 | 256-bit (64 hex) | Secure | Integrity checks, JWT, TLS, Bitcoin |
| SHA-512 | 512-bit (128 hex) | Secure (higher margin) | High-security signatures, HMAC |
When to use each algorithm
- MD5 — Fast, 32-character hex output. Cryptographically broken (collisions are possible). Use only for checksums, cache keys, or non-security purposes.
- SHA-1 — 40-character hex output. Also considered weak for security. Still used in Git commit IDs and some legacy systems.
- SHA-256 — 64-character hex output. The standard choice for security. Used in TLS, Bitcoin, JWT, and most modern cryptography.
- SHA-512 — 128-character hex output. Provides higher security margin. Preferred for password hashing alongside a salt (e.g. with bcrypt/Argon2).
Never hash passwords with MD5 or SHA-256 directly. Use a dedicated password hashing function like bcrypt, Argon2, or PBKDF2 which include salting and work factors.
How hashing works
A hash function takes any input text and produces a fixed-length output. The same input always produces the same hash, but it is computationally infeasible to reverse the hash back to the original input. Even a single character change in the input produces a completely different hash (the avalanche effect).
Frequently Asked Questions
What is the difference between MD5 and SHA-256?
MD5 produces a 128-bit (32 hex characters) hash and is fast but cryptographically broken — intentional collisions can be generated. SHA-256 produces a 256-bit (64 hex characters) hash and is part of the SHA-2 family, considered secure for digital signatures, integrity checks, and most cryptographic purposes.
Which algorithm should I use?
Use SHA-256 for integrity checks, API signatures, JWTs, and general security. Use SHA-512 for maximum security margin. Use MD5 only for non-security purposes like cache keys or checksums where collision resistance is not required. Never use MD5 or SHA-1 for passwords or any security-sensitive purpose.
Is my text sent to a server when hashing?
No. SHA-1, SHA-256, and SHA-512 use the browser's built-in WebCrypto API (crypto.subtle.digest). MD5 uses a JavaScript library running entirely in your browser tab. Your text never leaves your device.
Can I reverse a hash to get the original text?
No. Hash functions are one-way — there is no algorithm to derive the input from the hash output. For common short inputs, attackers use precomputed rainbow tables, which is why passwords must always be salted and why dedicated password hashing functions (bcrypt, Argon2, PBKDF2) should be used instead of raw SHA-256.
What is a hash collision?
A collision is when two different inputs produce the same hash output. MD5 and SHA-1 are considered broken because researchers have demonstrated practical collision attacks against them. SHA-256 and SHA-512 have no known practical collisions.
Should I use hashing for passwords?
Not with a general-purpose hash like SHA-256 directly. Password hashing requires a function specifically designed to be slow and to include a unique salt per password — use bcrypt, Argon2, or PBKDF2. These prevent brute-force and rainbow table attacks. SHA-256 is too fast for passwords on its own.
Last updated: May 2026