Custom security tokens

A sending computer system generates a message and creates one or more security tokens to encrypt portions of the message. The computer system includes in the message a markup language identifier for the one or more security tokens used for encryption, and includes identification of the value type used to create the tokens. The computer system then serializes at least the portion of the message that identifies the one or more security tokens, without serializing other portions of the message that aid relaying of the message to a receiving computer system. A receiving computer system deserializes at least the portion of the message that identifies the one or more security tokens, and then uses deserialized token data to decrypt encrypted portions of the message. Each created security token can be made with customized data and fields, and can be made with a customized value type.