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The DSN's non-secure dial-up voice service may be made secure by the use of STU-III/STE devices. CJCSI 6215.01C, Policy for DoD Voice Networks, specifically states:

[The] DSN permits, through the use of secure instruments, protection of classified and sensitive information being passed, to ensure its confidentiality, integrity, and authentication. Where possible, the DSN is configured to minimize attacks on the system that could result in denial or disruption of service.

The STU-III/STE family provides a secure voice capability over the non-secure switched voice network. Secure voice terminals are managed as Customer Premises Equipment similar to the non-secure telephone instruments, but in accordance with national, CINC, and service or agency procedures.

Securing Transmissions with an STU-III/STE Device

The STU-III/STE is the primary device for enabling secure communications over the DSN. It may be used for secure voice, data, video, or facsimile.

Approval under provisions of this instruction is not required for conversion of a non-secure telephone instrument to a STU-III/STE on DSN.

A STU-III/STE connected to DSN must have the preempt feature enabled at all times.

When a STU-III/STE is used to transmit secure data or facsimile, the instrument must meet the following requirements:
- The STU-III/STE preempt feature must be enabled at all times.
- National guidance for use of STU-III/STE in secure data transmission, including access control TEMPEST, must be implemented.

The DRSN, the STU-III/STE family of equipment that provides end-to-end encryption over the DSN, and Condor, the NSA's program to secure wireless communications, are the three subservices that together provide the foundation for the DoD secure voice services.

When the STU-III reaches End-of-Life, it will no longer be supported.