What is MD5?
MD5 (Message Digest Algorithm 5) produces a fixed 128-bit output—shown as a 32-char hexadecimal string—from any length input. Designed by Ron Rivest and published in RFC 1321 (1991), it became the de-facto checksum for downloads and legacy systems.
Security note: MD5 is broken for cryptographic use—choose SHA-256, BLAKE3, or Argon2 for anything security-critical.
How does MD5 work?
- Pad the message so its length ≡ 448 (mod 512) bits
- Append the original length (64-bit little-endian)
- Initialize four 32-bit words (A, B, C, D)
- Process the data in 16-word blocks through 4 non-linear rounds
- Produce the final 128-bit digest
MD5 vs. other hash functions
| Algorithm | Output | Current security | Relative speed* |
|---|---|---|---|
| MD5 | 128 bits | ❌ Broken | ⚡ Very fast |
| SHA-1 | 160 bits | ❌ Broken | ⚡ Fast |
| SHA-256 | 256 bits | ✅ Secure | 🚀 Moderate |
| SHA-512 | 512 bits | ✅ Very secure | 🚀 Moderate-slow |
| BLAKE3 | 256 bits | ✅ Secure | ⚡ Blazing |
Example hashes
| Input | MD5 Hash |
|---|---|
Hello, World! | 65a8e27d8879283831b664bd8b7f0ad4 |
password | 5f4dcc3b5aa765d61d8327deb882cf99 |
123456789 | 25f9e794323b453885f5181f1b624d0b |
| (empty) | d41d8cd98f00b204e9800998ecf8427e |
Frequently Asked Questions
Is any data sent to your server?
No. The JavaScript library runs entirely in your browser. Text and files never leave your device.
Can I verify a downloaded ISO with MD5?
Yes. Drop the ISO file into the tool to compute its MD5 checksum, then compare it with the hash published by the distributor.
Is MD5 safe for passwords?
No. Use dedicated password-hashing algorithms such as bcrypt, Argon2, or PBKDF2 instead.
Security considerations
- Collisions: Different inputs can yield identical MD5 outputs.
- Length-extension: Attackers can append data without knowing the original message.
- Speed: MD5's very speed aids brute-force attacks.
Rule of thumb: Use MD5 only for non-security purposes like duplicate-file detection or quick checksums.