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Validation Process

Certified Cryptographic Devices

Advanced Narrowband Digital Voice Terminal (ANDVT) Family


Secure Telephone Unit-Third Generation (STU-III) / Secure Terminal Equipment (STE)


Secure Telephone Unit Third Generation (STU-III)
/ Secure Terminal Equipment (STE)


Description | Characteristics | Life Cycle Support | Life Cycle Documentation |
Repair/Maintenance | Aquisition Authority | Contract Information |


STE/STU-lll Dial-Up Networking Configuration Support

STUMP Y2K Compliant Software


The Secure Telephone Unit - Third Generation (STU-III) is a low-cost, user-friendly, secure telephone device. The terminals are designed to operate reliably, with high voice quality, as both ordinary telephones and secure instruments over the dial-up public switch telephone network. STU-III operates in full-duplex over a single telephone circuit using echo canceling modem technology. STU-IIIs come equipped with 2.4 and 4.8 kbps code-excited linear prediction (CELP) secure voice. Secure data can be transmitted at speeds of 2.4, 4.8, and 9.6 kbps. There are many manufacturers each having different maximum throughput rates. The data throughput between two STU-IIIs can only be as great as the slowest STU-III connected. After, 31 March 1998, General Dynamics (Formerly AT&T) became the only producer of STU-III terminals, and will continue to produce terminals until December 1999.

The STU-III Family consists of some of the following devices:

  • The STU-III/Low Cost Terminal (LCT) was designed for use in the office environment among a broad spectrum of military, civil, government, and selected private sector users. It is compatible with standard modular or multiline (key system) connectors and operates full-duplex over a single telephone circuit.
  • The STU-III/Cellular Telephone is interoperable with all other versions of the STU-III Family. It combines cellular mobile radiotelephone technology with advanced secure voice/data communications. The unit includes a message center that is integrated with the standard cellular handset; it can be conveniently mounted inside a vehicle and provides all STU-III functions, including authentication/classification display.
  • The STU-III/Allied (A) is a specialized version of the STU-III/LCT that is compatible with the STU-II. It retains all basic STU-III functions and capabilities and incorporates STU-II BELLFIELD Key Distribution Center (KDC), STU-II net, and STU-II multipoint modes of operation.
  • The STU-III/Remote Control Interface (RCU) provides RED enclave subscribers with STU-III compatible secure communications in a rack-mounted remotely controlled line encrypting unit. When used in conjunction with a RED switch or conferencing director, the STU-III/R allows STU-III users to confer with multiple STU-III users or others who have secure functions. It is capable of encrypting/decrypting voice or data over two-wire or four-wire telephone systems and incorporating a 2.4 kbps BLACK digital (external modem) interface.
  • The MultiMedia Terminal (MMT) 1500 is a diversified STU-III capable of clear or secure voice and data communications over both analog and digital mediums. The MMT interfaces to the commercial telephone system via a standard RJ-11 telephone jack and to digital systems through a Black Digital Interface (BDI). The BDI port will support both half-and full-duplex communications, precedence dialing, black digital network signaling, and multiple satellite hopsWhen unattended the MMT can automatically answer an inbound call without operator intervention and establish a secure link with any user on a preprogrammed Access Control List (ACL).
  • The Inter Working Function (IWF) is the shore gateway device that provides the digital to analog conversion between the MMT and the analog STU-III. The IWF supports half and full duplex voice and data communications with rates of 2.4, 4.8, and 9.6Kbps. The IWF improves secure voice and data synchronization over multiple satellite hops with programmable extended time-outs and pre-staging of STU-III call information. The IWF supports all necessary network-signaling functions to enable call setup and status messages including canned voice messaging to the analog user.
  • The STU-III Secure Data Device (SDD) is designed with the same capabilities as other members of the STU-III family including Secure Access Control System (SACS), remote authentication (RA), remote control, auto-answer secure data, and capable of operating in both attended and unattended environments. The SDD provides protection for facsimiles, e-mail, and computer communications.
  • The Motorola CipherTAC 2000 (CTAC) STU-III family compatible secure voice communications via cellular phone. CTAC without an inserted CipherTAC 2000 security module is unclassified and functions as a non-secure commercial off the shelf (COTS) telephone product. The CTAC CiphterTAC security module is certified for all levels of classified discussions up to and including SECRET in an adequate operating/security environment.

The Secure Terminal Equipment (STE)

The Secure Terminal Equipment (STE)/Office is the evolutionary successor to the STU-III. The STE program will improve shore secure voice communications as well as shipboard communications by changing out the analog STU-III products with digital-based STE products. The STE cryptographic engine is on a removable Fortezza Plus KRYPTON Personal Computer Memory Card International Association (PCMCIA) Card, which is provided separately. The STE Data Terminal provides a reliable, secure, high rate digital data modem for applications where only data transfer (FAX, PC files, Video Teleconferencing, etc.) is required. All STE products will be STU-III secure mode compatible with the following enhanced capabilities:

  • Voice-recognition quality secure voice communication.
  • High-speed secure data transfers (up to 38.4 Kbps for asynchronous or 128Kbps for synchronous).

STE terminal products can use Integrated Services Digital Network (ISDN), analog PSTN, TRI-TAC, or direct connection to Radio Frequency (RF) assets via RS-530A/232E ports. Maximum STE performance may be attained only by those commands employing ISDN service with two Bearer Channels (2B+D ISDN Service). When connected to a PSTN (Analog Telephone) service, the STE/Office units will only support current STU-III voice and data capabilities.

A tactical version, STE/Tactical is a replacement for MMT 1500 with a Digital Non-secure Voice Terminal (DNVT) adapter. Though not a direct replacement for the KY-68, the STE/Tactical can serve as a DNVT replacement with secure voice communication capabilities in STU-III modes over TRI-TAC/Mobile Subscriber Equipment (MSE). STE/Tactical is not secure mode compatible with the Digital Secure Voice Terminal DSVT KY-68.

A STE Direct Dial capability, comprised of the STE/C2 Tactical terminal and/or associated STE/Interworking Function(s) will improve on the existing Navy "Direct Dial" secure voice ship to shore dial-up operations. STE Direct Dial improves secure mode connectivity, provides operational flexibility support for both plain text and cipher text voice modes, and provides a standardized secure ship digital telephone system solution and Joint CINC interoperability with forces at sea and ashore.

Individual STE Product Capabilities:

  • STE/Office provides enhanced STE capabilities over digital ISDN and STU-III over analog PSTN.
  • STE/Data provides STE and STU-III data capabilities only.
  • STE/Tactical with Wedge supports STU-III Black Digital Interface (BDI) over TRI-TAC/MSE or RF asset.
  • STE Direct Dial:
    • STE/C2 Tactical with Wedge supports STU-III BDI over ISDN or RF asset.
    • STE/IWF provides interface with PSTN (Analog) and ISDN (Digital).

STE products without an inserted Fortezza Plus KRYPTON Card are unclassified and function as non-secure COTS telephone products. The Fortezza Plus KRYPTON Card is currently designated as an Accounting Legend Code 1 (ALC-1) item by the NSA. Even though STE's are unclassified items, they should still be treated as high-value Government property (e.g., such as an office computer). Certification of STE will provide security for all levels of traffic, up to and including TOP SECRET Special Compartmented Information (TS-SCI). When a Fortezza Plus KRYPTON Card is inserted into a STE, secure storage must be provided to the extent required by Operational Navy Instruction (OPNAVINST) 5510.1 (series) for the maximum classification level of the key used. Fortezza Plus KRYPTON Card is considered classified to the maximum level of key classification until it is associated with a STE terminal. Once associated with a STE terminal, the card is considered unclassified when not inserted in the associated STE terminal.


National Security Agency (NSA) has determined that the key order processes are under development for compliance with Year 2000; NSA memo of 12 Jun 98 applies.

Equipment Height (in) Width (in) Depth (in) Weight (lb)
STU-III/Low Cost Terminal (LCT) 4.0 10.0 9.0 8.0
STU-III/Cellular Terminal (SCT) 3.0 10.0 15.0 12.0
STU-III/Allied (A) 2.5 9.0 10.0 8.0
STU-III/Remote Control Interface (R) 3.2 10.5 12.75 12.5
MultiMedia Terminal (MMT) 1500 3.0 9.7 8.5 6.5
Inter Working Function (IWF) 7.0 19.0 22.0 6.5
STU-III Secure Data Device (SDD) 2.5 8.0 9.5 7.0
Motorola CipherTAC 2000 (CTAC)* 5.23 2.33 0.6 0.25
Motorola CipherTAC 2000 (CTAC)** 6.16 2.33 0.99 0.30
STE/Office w/Wedge 10 9.5 4.6 6.0
STE/Office w/o Wedge 10 9.5 2.57 6.0
STE/Data 10 9.5 2.4 6.0
STE/Tactical 10 9.5 4.6 6.0
STE Direct Dial (GW/IWF Module) 9.2 11.0 32.0
STE Direct Dial (VME Enclosure) 17.0 14.0 19.3
*Without security module
**With security module

Data Rates:
STU-III/Low Cost Terminal (LCT) Supports voice/data rates of 2.4, 4.8, 9.6, and 14.4 Kbps
STU-III/Cellular Terminal (SCT) Synchronous (sync): 2.4, 4.8, 9.6 Kbps
Asynchronous (async): 300, 1.2, 2.4 Kbps
STU-III/Allied (A) Data: 300, 1200, 2400 bps async & 2400 bps sync
STU-III/Remote Control Interface (R) Voice: 2.4, 4.8, 9.6 Kbps full-duplex synch/async 2.4 Kbps half-duplex
Data: 2.4, 4.8, 9.6 Kbps full-duplex sync/async 75, 110, 300, 600, 2400, 4800, 9600 bps full-duplex async 2.4 Kbps (or slower rates) half-duplex async
MultiMedia Terminal (MMT) 1500 BDI Voice: 2.4, 4.8, 9.6 Kbps secure full duplex, 2.4 Kbps half-duplex
Analog Voice: 2.4, 4.8, 9.6 Kbps secure full/half-duplex
Data: 4.8, 9.6 Kbps secure full-duplex sync & async
Simultaneous Voice/Data: 2.4 Kbps secure full-duplex (voice/data)
Inter Working Function (IWF) Data: 2.4, 4.8, 9.6 Kbps full & half-duplex
STU-III Secure Data Device (SDD) 2.4, 4.8, 9.6 and 14.4 Kbps full-duplex sync & async w/2.4 Kbps half-duplex sync secure data communications link
Motorola CipherTAC 2000 (CTAC) Voice: up to 4.8 Kbps
STE/Office Synchronous Secure: 2.4 to 128 Kbps
Asynchronous Secure: 2.4 to 38.4 Kbps
STE/Data Synchronous Secure: 2.4 to 128 Kbps
Asynchronous Secure: 2.4 to 38.4 Kbps
STE/Tactical Synchronous Secure: 2.4 to 128 Kbps
Asynchronous Secure: 2.4 to 38.4 Kbps
SSTE Direct Dial (GW/IWF Module) Voice and Data: Narrowband: 2.4, 4.8, 9.6 Kbps
Wideband: 64, 128 Kbps
STU-III/Low Cost Terminal (LCT) 20 Watts (nominal), 115 or 230 VAC, 50-60 Hz
STU-III/Cellular Terminal (SCT) Volts: +10 to +14 Vdc negative ground, Amps: 3.5 maximum
STU-III/Allied (A) 90 Vac to 265 Vac, 50 Hz to 60Hz
STU-III/Remote Control Interface (R) 90-265 Vac, 117V. 305 nominal
MultiMedia Terminal (MMT) 1500 90-270 Vac, 47-63 Hz (Auto-ranging)
Motorola CipherTAC 2000 (CTAC) Less than 2.0 watts in secure with 1.75 hours talk time on a 3-hour battery in secure mode. Less than 0.8 watts in clear with 2.75 hours talk time on a 3-hour battery in clear mode. Less than 0.2 watts in power down with 24 hours standby time on 3-hour battery
STE/Office External Power Supply 90-253 Vac, 47-63 Hz, Autoranging 20 watts maximum
STE/Data External Power Supply 90-253 Vac, 47-63 Hz, Autoranging 20 watts maximum
STE/Tactical External Power Supply 90-253 Vac, 47-63 Hz, Autoranging
20 watts maximum
Standard EOC Connector
Portable Uninterruptible Power Supply (PUP)
SSTE Direct Dial (GW/IWF Module) External Power Supply 90-253 Vac, 47-63 Hz, Autoranging
STU-III/Low Cost Terminal (LCT)
STU-III/Cellular Terminal (SCT)
STU-III/Allied (A)
Storage Temperature: -40C to 70C
Operating Temperature: 0C to 50C
Motorola CipherTAC 2000 (CTAC) Operating Temperature: 0C to 50C
Storage Temperature: -40C to 70C
STE/Office Operating Temperature: 0C to 40C
Operating Rel Humidty: 10% to 90% Noncondensing
Storage Temperature: -20C to 60C
STE/Data Operating Temperature: 0C to 40C
Operating Rel Humidty: 10% to 90% Noncondensing
Storage Temperature: -20C to 60C
STE/Tactical Operating Temperature: 0C to 40C
Operating Rel Humidty: 10% to 90% Noncondensing
Storage Temperature: -20C to 60C
STE Direct Dial (GW/IWF Module) Operating Temperature: 0C to 50C
Operating Rel Humidty: 10% to 90% Noncondensing
Storage Temperature: -20C to 60C


  • Software Support Activity (SSA): Not applicable
  • Primary Inventory Control Activity (PICA): Commercial Supply Support / U. S. Army
  • Depot: Cryptographic Repair Facility (CRF) San Diego, CA / Motorola Inc.
  • In-Service Engineering Agent (ISEA): SPAWARSYSCEN Charleston
  • Material Support Date (MSD): Not applicable


  • Operational Requirements Document (ORD): 063-094-87, 10 Jan 86
  • Test and Evaluation Master Plan (TEMP): Aug 89
  • Navy Training System Plan (NTSP): Not required
  • Integrated Logistics Support Plan (ILSP): National Security Agency (NSA) document, 31 Aug 92
  • Technical Manuals (TMs): Manufacturer User's Manuals and Handbooks


  • Contact Director COMSEC Material Systems (DCMS) in accordance with CMS 5A "The policies and Procedures for issuing accounting, handling, safeguarding, and disposing of COMSEC Communications Security Manual: artical 410 for repair/disposition instructions.

Motorola SECTEL 1500 User's Manual 68-P35279D002
Security-Plus AT&T STU-III Communications Terminal User's Manual ON416007-1
Operators Guide for the RCA/STU-III Terminal (Type 1) F001-R1
GE Operating Guide for the GE 9600 STU-III Terminal (Type 1) 10038631
STU-III Secure Voice/Data Terminal Model 1100/1150 User's Manual ON-49306
Operators Guide for the GE 9600 STU-III Terminal (Type 1) 10038631 Rev. A
STU-III Celluar:
STU-III DYNASEC Secure Cellular Telephone User's Manual 68-P333623C001
STU-III DYNASEC Secure Cellular Telephone Installation and Service Manual 68-P33624C
DYNA T-A-C 6000XL Cellular Mobile Telephone User's Manual 68-P81116E58-B
Motorola Ins. Cellular Mobile Telephone Installation and Programming 69-P81119E99-A
Installation Instructions for Mobile Antennas None
Installation Instructions for DYNA T-A-C Cellular Mobile Telephone None
Programming Guide for Cellular telephone None
STU-III/A SECTEL User's manual 68-P33236C001
STU-III/R Remote Controllable Secure Voice/Data Terminal 68-P39024D001
STU-III/R Interface Control Document 5983-B0004-001
AT&T STU-III Secure Data Device Model 1900 User' Manual None
SECTEL MMT 1500 Multimedia Terminal User's Manual 6844083D02 P/N 5DGA14X
BDI Black Digital Interface User's Manual 6844085D02
User Logistics Support Summary (ULSS): SPAWARSYSCOM, Sep 95 (P4110.969) (Draft)
Computer Resources Life Cycle Management Plan (CRLCMP): Not required




Developing Agency:   NSA
  • L3 Communications (STE)
  • General Dynamics
  • Lockheed Martin Corporation
  • AT&T Corporation
  • Motorola Corporation

Administration provided by the
SPAWAR Systems Center
in Charleston, South Carolina, USA.