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:

Protecting Passwords
Without protection, passwords are vulnerable to network sniffing. An attacker could be monitoring an open wireless access point, or using a tool like tcpdump on an ethernet network. JavaScript MD5 provides basic protection of passwords, for sites that do not use SSL.

Generating Passwords
Most people have accounts on many different web sites. It isn’t possible to remember so many passwords, so most people use the same password everywhere. If one web site suffers a security breach, or has a malicious operator, all your online accounts are at risk. Password generators help solve this problem.

Self-Decrypting Pages
Internet email messages are vulnerable to interception and generally considered unsuitable for confidential communication. A self-decrypting page is unreadable until the correct password is entered. Pages can be attached to emails to support confidential communication.

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