A digest, also called a hash, is a fairly big number that summarizes the contents of a file. This can be used for determining a file's integrity: if the digest of your copy is the same as the digest of the original file, then your copy is probably correct, but if the digests are different, then you know that the contents are different (which probably means that your copy of the file is damaged).
EasyHash is a simple application that provides an easy way to compute the MD5 and SHA-1 digests for a file. Simply drop the file onto the application; it will present a window showing the MD5 and SHA-1 digests for its contents. You can then copy either digest for pasting elsewhere, such as into an email message or an HTML file.
EasyHash does not compute the digests itself. Instead, it uses OpenSSL, an open-source library that provides both the MD5 and SHA-1 hash functions, among many other features. OpenSSL comes with Mac OS X; you don't need to install it.
MD5 and SHA1 hashes for version 2.0b1 and later were created using EasyHash.
If you want to contribute bug-fixes or enhancements to EasyHash, the easiest way to do that is to clone the Mercurial repository for EasyHash. To do this, type this command into a terminal:
hg clone http://bitbucket.org/boredzo/easyhash
I provide EasyHash—the application, and its source code—under a three-clause BSD license. For more information, see the file named LICENSE.txt that comes with it.