MD5 Generator

What is MD5?

MD5 (Message-Digest algorithm 5) is a hash function designed by Ronald Rivest and published in 1992 as RFC 1321, as the successor to MD4. It reads a message of any length and produces a fixed 128-bit value, written as 32 hexadecimal characters. The same input always gives the same digest, and the process only runs one way: you cannot recover the text from its hash.

Internally MD5 pads the message to a multiple of 64 bytes, then processes it in 64-byte blocks. Each block is mixed into four 32-bit state words through 64 steps of bitwise operations, additions and rotations. The four words, written out one after another, are the digest.

These reference values, from the RFC and from common test suites, are handy for checking any MD5 tool:

The empty message has a well-defined digest, but this tool needs at least one character, so an empty box shows no result.

How to use the MD5 generator

1. Type or paste your text into the String box.
2. Press Calculate. The hash appears in the results table with a button to copy it.
3. Compare it with the checksum you were given, or keep it as a fingerprint of that exact text.

What is hashed. The tool hashes the UTF-8 bytes of the text exactly as you typed it. Nothing is trimmed, normalised or added, and the digest is shown in lower-case hexadecimal.

• Every character counts. Leading and trailing spaces, tabs, capital letters and blank lines all change the digest.
• UTF-8 encoding. A plain ASCII character is one byte, é is two (c3 a9), 日 is three (e6 97 a5) and an emoji such as 😀 is four (f0 9f 98 80).
• Line breaks are kept as they arrive. A browser text box stores each line break as a single line-feed character (LF, byte 0a), and text pasted with Windows CR LF line endings normally arrives as LF too. The tool does not convert it to anything else, so the digest equals what printf piped into md5sum gives for the same text.
• A final line break counts. Pressing Enter after the last word adds one more byte, which is why printf hello | md5sum and printf 'hello\n' | md5sum differ.

To get the digest of a file that uses Windows CR LF line endings, hash the file itself with a command-line tool. This page can only hash text the way a browser text box holds it.

A tiny change gives a completely different hash

A good hash function changes about half of its output bits when a single character of the input changes. MD5 still behaves this way for ordinary inputs:

Adding a full stop changes 69 of the 128 bits and swapping dog for cog changes 71, close to the 64 you would expect from two unrelated values. Nothing in the first line hints at the others.

Is MD5 secure?

No. A hash function is meant to make it infeasible to find two different inputs with the same digest (a collision). In 2004 and 2005 researchers led by Xiaoyun Wang showed how to produce MD5 collisions with modest computing power, and the attacks have only become cheaper since. In 2008 a team used a collision to build a forged certificate authority certificate, and the Flame malware abused an MD5 weakness in 2012 to fake Microsoft code-signing certificates. Browsers and certificate authorities no longer accept MD5-signed certificates.

• Do not use MD5 for digital signatures, certificates or anything where an attacker might choose the input.
• Never use MD5 to store passwords, with or without a salt. MD5 is built to be fast, and a single graphics card can test many billions of MD5 guesses per second. Passwords need a deliberately slow, salted, purpose-built function such as Argon2, scrypt or bcrypt (PBKDF2 with a high iteration count if those are unavailable).
• For new general-purpose hashing choose the SHA-256 or SHA-512 hash instead. These are faster than a password hash should be, so the warning about passwords applies to them too.

If you need a strong password for an account, our random password generator creates one. How a service stores that password is a separate question, and the answer is never plain MD5.

Where MD5 is still used

MD5 remains common as a checksum. Download pages often publish an MD5 value next to a file; you hash your copy and compare. A match tells you the file was not damaged by a transfer error. It does not prove the file is safe: someone who can swap the file can usually swap the published checksum too, and a deliberate attacker can craft a different file with the same MD5.

Other legitimate uses are non-security ones: spotting duplicate files, building cache keys, and generating short stable identifiers where nobody is trying to forge a collision. Older systems also use MD5 in ETag headers and in legacy protocols. If you are comparing several algorithms, the SHA-1 generator is another legacy hash with the same caveats.