Final answer:
SIPRNET tokens are physical devices used with alphanumeric PINs to access the Secret Internet Protocol Router Network, ensuring secure transmission of classified information by U.S. government agencies.
Step-by-step explanation:
The SIPRNET, or Secret Internet Protocol Router Network, is a system of interconnected computer networks used by the U.S. Department of Defense and the U.S. Department of State to transmit classified information. Access to SIPRNET is secured with various mechanisms, including the use of tokens. A SIPRNET token is a physical device used in conjunction with a Personal Identification Number or PIN to authenticate users accessing the network. The PINs associated with SIPRNET tokens can consist of both numbers and letters, providing an added layer of security through complexity. It is essential for users with access to SIPRNET to follow strict guidelines for creating and protecting their PINs to maintain the confidentiality and integrity of sensitive information.