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TEMPEST Cisco 7962 VoIP Phone

DTD-7962-T2 is a TEMPEST certified version of the Cisco 7962G Unified VoIP telephone set, introduced in 2011 by CIS Secure in Ashburn (Virginia, USA). It is based on a standard Cisco 7962G, to which fibre optic interfaces have been added, as well as shielding against unwanted emanations, to military standards (TEMPEST). The price for a single unit in 2011 was US$ 1999.

The image on the right shows a typical unit. The original Cisco 7962G IP Phone is embedded in a larger black plastic vacuum-molded enclosure that extends the unit at the top and at the back.

At the top right is a red push-button with LED indicator. The black blob at the rear contains a double optic fibre interface — one for the
and one for a personal computer — that replace the original ethernet interfaces. It uses separate fibres for TX and RX, and is suitable for 10, 100 and 1000 Mbit/s networks. The basic operation is identical to the standard Cisco 7962G Phone.
DTD-7962-T2 Tempest phone

There are several modifications however. The internal speaker is disabled in hands-free mode, as this is a requirement of the TEMPEST standard. As a result it can not be used to play the ring­tone(s) on incoming calls, which is why an alternative ringer has been fitted. Furthermore, the handset and the external power supply unit have been modified to meet TEMPEST requirements.

The original Cisco 7962G Unified IP Phone was introduced on 27 July 2007 and was sold until 1 February 2016 [1]. 1 The TEMPEST version, made by CIS Secure (DTD-7962-T2), was approved for critical applications on 17 May 2011 [2]. It was succeeded by the CIS TEMPEST Cisco 8841.

  1. No support will be available from Cisco after 31 January 2021.

DTD-7962-T2 Tempest phone DTD-7962 with handset off-hook Front view Rear view Rear side Push-button with indicator light Connections at the rear Fibre optic sockets at the rear
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DTD-7962-T2 Tempest phone
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DTD-7962 with handset off-hook
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Front view
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Rear view
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Rear side
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Push-button with indicator light
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Connections at the rear
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Fibre optic sockets at the rear

Controls and connections
The diagrams below provide an overview of the controls and connections on the DTD-7962. The front panel is identical to that of the Cisco 7962G on which it is based, and so is its operation, with the exception of the use of the built-in speaker whilst the handset is on-hook. On the DTD-7962 it is disabled, as this is a security requirement for TSG/TEMPEST approval. Instead, a new ringer-device has been added. At the top right, a red indicator/push-button has also been added.

All connections are at the rear of the device. At the left is a 4-pin LEMO socket for connection of the external power supply unit (which is also TEMPEST approved). At the right is a DE9 socket for connection of the (modified) handset. At the centre are the terminals for the optic fibres: one for connection to the local area network (LAN) and one for an (optional) personal computer (PC).

The enclosure and the handset cable are shielded against unwanted emanations. Note that the power supply unit (PSU), which is included with the kit, has to be connected to the mains network (100-240V AC) by means of the supplied shielded cable, in order to meet TEMPEST requirements.

DTD-7962-T2 telephone (modified Cisco 7962D Unified IP phone) Modified handset Power supply unit
Mains power cord
Phone   DTD-7962-T2
The DTD-7962 is based on a regular Cisco 7962G desktop telephone set, that has been modified to meet TEMPEST requirements.

The most obvious (visual) modification is the black plastic enclosure that has been added at the rear. It houses the optic fibre interfaces, and fills two gaps in the front panel of the 7962G: at the top right (where the red indicator is) and in between the handset cradle and the display.
DTD-7962-T2 Tempest phone

Modified handset
The original handset of the Cisco 7962 phone was modified to meet TEMPEST requirements. It connects to the base unit via a shielded coiled cable with a female 9-pin sub-D plug (DE9/F).

The handset can be placed in the cradle – as before – but is connected to the DE9/M socket marked HANDSET at the rear of the base unit.
Handset with shielded connector

Power supply unit   DTD-7962-PWR
A standard Cisco 7962G telephone set can be powered via the Ethernet line – using power-over-ethernet (PoE) – or by means of a simple wall socket power adapter, neither of which meets the stringent TEMPEST requirements.

As the device uses optical interfaces, it can not be powered over the optic fibres. For this reason, the special TEMPEST shielded power supply unit (PSU) shown here, is supplied with the set.
Power supply unit (PSU)

Mains power cord   DTD-7962-PWR
The power supply unit (shown above) has a standard 3-pin socket for connection to the mains AC network. Although it can be used with any regular power cable, it was recommended to use the shielded one that was supplied with the set, in order to meet TEMPEST requirements.

The cable has two large (black) ferite beads that are clamped on at either end, to reduce any residual leakage of radio frequency (RF) signals, that might appear on the power line.
Shielded mains cable

Power supply unit (PSU) Shielded mains cable Handset with shielded connector
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Power supply unit (PSU)
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Shielded mains cable
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Handset with shielded connector

The DTD07962 is well-constructed. Getting access to its interior, requires the removal of quite a few screws, as one would expect from a TEMPEST approved device. First, the vacuum-molded black plastic cover has to be removed. This involves the removal of the 4 rubber feet and three recessed screws around the edges of the case. Note that this breakes the two warranty seals.

The original PCB of the Cisco 7962 telephone, has been encapsuled in a metal frame, to which a trapezium-shaped aluminium case is bolted. This case contains the interfaces that convert the phone's 100BaseT interfaces to optic fibres.

The case also holds a PCB with relays that cut the wiring to the handset and the (optional) headset, and the socket for connection of the external power supply unit (PSU). The power socket is contined in a metal box that contains appropriate filtering by means of ferrite beads. Surprisingly, the handset wiring is not filtered.
100BaseT to optic converters

Apparently, the fact that the wiring is shielded (and disconnected when the handset is on-hook) was enough to obtain TEMPEST approval. The 100BaseT interfaces of the original Cisco set, are still visible at the bottom. They are wired to the fibre converters by means of short

DTD-7962 with rear cover removed Bolted-on interface Inside the optic interface Additional PCBs and wiring 100BaseT to optic converters
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DTD-7962 with rear cover removed
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Bolted-on interface
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Inside the optic interface
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Additional PCBs and wiring
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100BaseT to optic converters

  • IPc6
  • SCCP
  • SIP
CTP II TEMPEST certifications
  1. Type A device, which means it does not required or rely on external device(s).

LAN   Local Area Network
Typically an in-house or in-office computer network.
LED   Light Emitting Diode
In this case, the red indicator at the top right is an example of an LED.
RX   Receive (reception)
This line carries the incoming traffic.
TEMPEST   Codename, referring to (the study of) unwanted compromising emanations. This includes the emission of unintentional and unwanted intelligence-bearing signals. If such signals were intercepted and analyzed, they might disclose sensitive information. In cryptography, the interceptor might be able to reconstruct (part of) the plain text.
TX   Transmit (transmission)
This line carries the outgoing traffic.
  1. Fiber Ready Cisco VoIP Phones
    CIS Secure, 2017.
  1. Cisco, Cisco Unified IP Phone 7962G
    Retrieved January 2020.

  2. TSG Standard 6 — TSG Approved Telephones
    August 2018. Unclassified.
Further information
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Crypto Museum. Created: Tuesday 28 January 2020. Last changed: Saturday, 08 February 2020 - 13:15 CET.
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