MD5 Sha - Message Digest tutorial
MD5 (Message Digest Algorithm 5)
Message integrity algorithms ensure data has not been changed in transit. They use one way hash functions to detect if data has been changed.
The MD algorithms consist of a family of one way hash functions. MD2, created by Ron Rivest produces a 128 message digest hash. MD2 was considered slow, and so the creation of MD4 was developed. MD4 was faster, however found to be vulnerable to some attacks, and so finally the MD5 was developed.
MD5 is a cryptographic one way hashing algorithm which uses a 128 bit hash value just like its predecessors. Although it still uses the same hash value, the algorithm is more complex and difficult to break than the others. MD5 is used by to provide data integrity and authentication, ensuring data has not been altered in transit. However sha-1 is a stronger hash function than MD5, and ideally should be used if the option is available. MD5 will ensure data has not been tampered with and achieves this by converting plain data into unreadable ciphertext known as a hash. If any data during transit has changed, even slightly the hash will look completely different, and it would be assumed data has been tampered with.
In a nutshell MD5 will ensure data has not been changed when in transit. MD5 is a symmetric key algorithm. MD5 consists of a key size of 128 bits. A hash is appended to the original message.
Other common integrity algorithms include Sha1, Sha256, Sha384, Sha512, Haval and Tiger.
Further Reading
Wikipedia's guide to MD5