…And if you want to implement such tool by yourself, as a Web or desktop application, this is quite easy, in particular, with .NET. Please see:
http://msdn.microsoft.com/en-us/library/system.security.cryptography.hashalgorithm.aspx[
^].
Besides, if you want to publish a checksum by yourself, keep in mind that both MD5 and SHA1 are found broken, so a malicious artist can potentially fake it along with software itself (turning it to a malicious software, with a virus or a spy agent). Instead, I would advise using one of the cryptographic hash functions from the SHA-2 family. Please see:
http://en.wikipedia.org/wiki/Cryptographic_hash_function[
^],
http://en.wikipedia.org/wiki/MD5[
^],
http://en.wikipedia.org/wiki/SHA-1[
^],
http://en.wikipedia.org/wiki/SHA-2[
^].
Please don't blame me for answering a wrong question. Here is the thing: you did not ask a question about programming, did not tag platform, language, etc. But if the question is not about programming, it should be removed as off-topic. This forum is not for computer users who need to check up the checksum of downloaded software, it is for the developers.
—SA