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Citadel II
Type 4 cryptographic engine - this page is a stub

Citadel II is a military-grade cryptographic engine for non-Type 1 applications 1 developed in 2004 by the RF Communications Division of Harris Corporation (now: L3Harris) in Rochester (NY,USA). It is the successor to the popular and widely accepted Citadel I encryption engine.

Citadel II is provided as a chip that can be embedded in customer's equipments. It uses a Harris-proprietary encryption algorithm that is known as MK-256. Three variants of it are available to the user. Some aspects of the algorithm were presented on the IEEE MILCOM conference in 2004 [A].

The image on the right shows the Citadel II chip on the crypto board inside the Falcon II military handheld radio of the US Army, as photographed by Bryan Fields (W9CR) in 2019. Visit his wiki for more detailed pictures of the Falcon II [2].

 Read the description of the algorithm
Citadel II chip inside the Falcon II handheld radio. Photograph copyright Bryan Fields (W9CR) [2]

  1. Type 1 refers to NSA endorsed classified or controlled cryptographic items (CCI) that are approved for the transmission of Classified or Sensitive US Government Information (TOP SECRET, or TS). The fact that no export licence is required for Citadel, means that it is a Type 4 device.  More

  1. Description of the Citadel II encryption algorithm
    Customizable Cryptographic Architecture for Government and Military Communications Applications. Michael Kurdziel, Robert Clements & Gary Dennis, Harris Corporation.
    First published by IEEE, MILCOM, January 2004. 1
  1. Copy obtained from ResearchGate website [1].

Products that use Citadel II
  • RF-5800V-HH
    Falcon II VHF handheld radio
  • RF-7800T-HH
  1. Kurdziel et al., Customizable Cryptographic Architecture...
    Military Communications Conference, 2004. MILCOM 2004. IEEE Volume 1.

  2. Bryan Fields (W9CR), Harris Falcon
    Updated 3 December 2019.
Further information
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Crypto Museum. Created: Saturday 09 November 2019. Last changed: Sunday, 22 January 2023 - 21:15 CET.
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