Both digital signatures and encryption are based on encryption technology. Encryption scrambles (encrypts) a message so it can't be read until it's unscrambled (decrypted) by the intended recipient. This process of encrypting and decrypting messages is called cryptography.
Microsoft Outlook can scramble a message or convert a scrambled message back to its plaintext format by applying a mathematical formula, called an algorithm, to the message. The algorithm is used with a key, which is a random string of bits used to lock and unlock (encrypt and decrypt) the message. Only the user who has the correct key can encrypt and decrypt the message.
Microsoft Outlook advanced security is a hybrid encryption system. It takes advantage of two different encryption technologies: public key cryptography and secret key cryptography (sometimes called symmetric key cryptography). Microsoft Outlook uses complementary elements of these technologies to digitally sign and encrypt messages. For example, Microsoft Outlook takes advantage of the strengths of public key cryptography to securely distribute keys between people. However, it relies on secret key cryptography to encrypt the content of messages because this technology is best suited to bulk data encryption.