A cryptographic algorithm, also called a cipher, is the mathematical function used for encryption and decryption. If the security of an algorithm is based on keeping the way that algorithm works a secret, it is a restricted algorithm. Restricted algorithms are woefully inadequate by today�s standards. A large or changing group of users cannot use them, because every time a user leaves the group, everyone else must switch to a different algorithm. If someone accidentally reveals the secret, everyone must change their algorithm.