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FILL devices
Electronic transfer devices

A key transfer device is an electronic device that is used (most commonly by the military) for the distribution of cryptographic variables, such as crypto keys and frequency hopping tables. Key fillers often use a standard data protocol, such as DS-102 or DS-101 — both endorsed by the US National Security Agency (NSA) — but devices with proprietary protocols are also common.

FILL devices are known under different names:
  • Electronic Transfer Device
  • Key Transfer Device
  • Key Fill Device (KFD)
  • Common Fill Device (CFD)
  • Data Transfer Device (DTD)
  • Key Fill Gun
  • Key Filler
  • Key Loader
  • Fill Device
  • Fill Gun
  • Filler
  • FILL

Fill units that follow the DS-101/102 protocol, are generally equipped with a U-283 connector — the 6-pin version of the U-229 — allowing them to be connected directly to crypto devices and standard US radio sets, such as HAVE QUICK and SINCGARS. The same standard is also used on devices from a wide variety of other manufacturers, including Philips, Siemens, ANT and Harris.

Fill devices on this website
AN/KOI-18 Key Tape Reader
AN/KYK-13 Key Transfer Device
AN/CYZ-10 Data Transfer Device
ECCM Fill Device (Frequency Hopping tables)
Key fill device
Philips DS-102 compatible key loader
ANT/Siemens/R&S DS-102 key tape reader
ANT/Siemens/R&S DS-102 key transfer device
Marconi SCIMITAR Fill Gun
Slave Key Programmer (SKP) for the Philips PFX-PM mobile radio
Motorola Key Variable Loader for DVP
Motorola Key Variable Loader for DES and DES-XL
Motorola Key Variable Loader for DVP-XL
Motorola Key Variable Loader for DES
Motorola universal Key Variable Loader KVL-3000 and KVL-300a
Key Storage Device (Token)
Key Storage Device (Token)
1Kb Key Storage Device with Microwire interface, as used with the KIV-7
Keyloader for the KSD-64 and PK-64 key storage devices (STU-III)
Racal MA-4073 programmer and key filler
Racal MA-4083C fill gun
Racal MA-4778 Cougar DS-102 key filler
Vericrypt 1100 key loader
Key entry device for the HC-3400 CRYPTOVOX embedded encryption unit
Siemens Key Gun
Thales DTD-II - Data Transfer Device 2
Datakey (ATEK Access Technologies)

Key fillers are commonly used for the distribution of the Transmission Encryption Keys (TEK) and Transmission Security Keys (TSK), such as Frequency Hopping (FH) tables. The latter is also known as Electronic Counter Counter-Measures (ECCM). Fill devices are also used for the distribution of Key Encryption Keys (KEK). Fill devices are used for:

  • Crypto keys
  • FH (Frequency Hopping) tables
  • GPS (Global Positioning System) keys
  • IFF (Identification Friend or Foe)
  • Software updates
Known fill devices
Below is a non-exhaustive list of known transfer devices:

Designator Description Protocol NSN
KYK-13 Electronic Transfer Device DS-102 5810-01-026-9618
KYX-15 Net Control Device DS-102 5895-01-026-9619
KOI-18 Paper Tape Reader DS-102 5810-01-026-9650
CYZ-10 Data Transfer Device DS-101 5810-01-343-1194
PYQ-10 Simple Key Loader DS-101 5810-01-517-3587
KIK-20 Secure DTD2000 System (SDS) DS-101 5810-01-543-5943
KIK-30 Really Simple Key Loader (RASKL) DS-101 5810-01-580-4662
UP-2001 Philips Key Filler DS-102 -
UP-2101 Philips Key Filler DS-102 -
MA-4073 Programmer and filler for Racal Cougar radios Gougar -
MA-4083 Fill gun for MA-4720 and Cougar radios Gougar -
MA-4778 DS-102 fill gun for Cougar radio with SAVILLE DS-102 -
MX-10579 ECCM Fill Device DS-102 5895-01-188-8816
MX-18290 ECCM Fill Device DS-102 5895-01-270-3935
KSD-64A Key Storage Device (Token) STU-III -
PK-64KC Key Storage Device (Token) STU-III -
PKS-703 Keyloader for KSD-64 and PK-64 STU-III 7025-01-534-7164
DK-1000 Key Storage Device (Token) KIV-7 -
CFD-900 Fill Gun (for MASS SDT-500) DS-102 -
SCIMITAR Fill Gun for Marconi SCIMITAR V Radios Proprietary -
PFX-SKP Slave Key Programmer for Philips PFX-PM Proprietary -
KVL-3000 Keyloader for Motorola radios Proprietary 5963-01-532-7248
1102 Keyloader for BBC Vericrypt 1100 Proprietary -
KED-3400 Key generator/loader for HC-3400 devices HC-3400 -
Key Gun Siemens Key Gun for MSC-2001 and others C-200 -
T-3010 Motorola key variable loader DVP Proprietary -
T-3011 Motorola key variable loader DES/DES-XL Proprietary -
T-3020 Motorola key variable loader DES Proprietary -
U-229 connector
Most devices that support the NSA's DS-101 or DS-102 protocol, use the same 5-pin or 6-pin AUDIO connector, commonly referred to as U-229/U or simply U-229. It has a standard pinout, but is different for each protocol. Click the image below for more information.  More

Key Storage Device
As an alternative to key fill devices in the shape of an external box, modern electronic cipher machines sometimes use a Key Storage Device (KSD) in the shape of a plastic toy key.

One example is the NSA-developed KSD-64, that is used with the Motorola SECTEL STU-III phones. The KSD-64 can be configured for use as Fill Key (FK) and many other key types.

 More information


  • DS-101
    This is the most recent transfer protocol that is used with the current generation of FILL devices, radio sets and encryption equipment. It superceedes DS-102 and can be used for transferring crypto keys, frequency hopping data, software updates, etc.  More

  • DS-102
    This is a synchronous serial protocol that was used with the first generation of Key Fill Devices, such as the KYK-13. It is the predecessor of the DS-101 protocol, and can be used for the distribution of key material and frequency hopping tables.  More

  • C-200
    This is a proprietary protocol used by Siemens for its MSC-2001 voice encryption unit and the CHX-200 radio system. It is supported by the Siemens Fill Gun and is fully described in the technical manual of the MSC-2001.  More
Further information
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