Various embodiments of a system and method for a single request—single response protocol with mutual replay attack protection are described. Embodiments may include a system that receives multiple single request messages, each of which may include a respective nonce, timestamp, and digital signature. The system may create a record of previously received nonces that, at any given time, may include multiple message nonces received within a valid period of time prior to that given time. To validate a given single request message the system may verify the digital signature of the that message, determine that the timestamp of that message indicates a time within the valid period of time prior to the current time, and determine the nonce of the that message is not present within the record of previously received nonces. The system may send a single response message that includes the same nonce as the validated message.