A single passcode can be used for validation by a user of several entities in a system without compromising security. The source of the entity providing validation credentials, along with the passcode, is considered when determining validity. A one-time password system validates credentials if a validation credentials, such as a user's valid passcode and the source of the credentials, have not been used previously. In a one-time passcode system, a validation processor receives validation credentials from a client processor. If the client processor has not previously sent the validation credentials to the validation processor, and the credentials are valid, the validation processor will validate the credentials. Otherwise, the credentials are invalid. Other client processors can utilize the same passcode and their respective source identifiers, and as long as the other client processors have not previously utilized the credentials, the credentials are declared valid.