MD5 is a secure hash algorithm. It takes a string as input, and produces a 128-bit number, the hash. The same string always produces the same hash, but given a hash, it is not generally possible to determine the original string. Secure hash algorithms are useful for protecting passwords and ensuring data integrity.
This site has a JavaScript implementation of MD5, and some other secure hash algorithms. This allows web sites to perform simple cryptography on clients, enabling some useful applications:
| Input | |
|---|---|
| Calculate | |
| Result |
hex_md5("message digest") = "f96b697d7cb7938d525a2f31aaf161d0"hex_sha1("160-bit hash") = "90d925d853c3d35cd54070bb75280fefad9de9e7"
| MD5 | Source |  |
|---|---|---|
| RIPEMD-160 | Source | |
| SHA-1 | Source | |
| SHA-256 | Source | |
| SHA-512 | Source | |
| HMAC | |
In 2004, a cryptographic weakness was discovered in both the MD5 and SHA-1 algorithms. One of the design goals of secure hash algorithms is "collision resistance". In others words, someone can't find two strings that hash to the same value. Because MD5 is 128-bit, by random chance you will find a collision by producing 264 hashes. The weakness in MD5 is that a way has been found to produce such collisions with only 242 hashes. This makes producing collisions practical and I have seen an example of 100 different collisions.
Most uses of JavaScript hashing (e.g. protecting passwords) do not rely on the collision resistance property. These weaknesses do not create any vulnerability in such web sites. I recommend continuing to use these algorithms for JavaScript hashing.
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