c.
Federal Standard 1026: Telecommunications: InteroperabAity and Security
Requirements for Use of the Data Encryption Standard
in the Physical Layer of Data Communications. (Copies of this standard are
available from the General Services Administration
Specification Unit (WFSIS), Room 6039, 7th and D Streets S.W., Washington, D.C.
20407).
d.
Federal Standard 1027: Telecommunications: General Security Requirements
for Equipment Using the Data Encryption Standard.
(Copies of this standard are available from the General Services Administration
Specification Unit (WFSIS), Room 6039, 7th and D
Streets S.W., Washington, D.C. 20407).
e.
Federal Standard 1062: Telecommunications: Group 3 Facsimile Apparatus
for Document Transmission. (Copies of this standard
are available from the General Services Administration Specification Unit
(WFSIS), Room 6039, 7th and D Streets S.W., Washington,
D.C. 20407).
f.
Federal Standard 1063: Telecommunications: Procedures for Document
Facsimile Transmission. (Copies of this standard are
available from the General Services Administration Specification Unit (WFSIS),
Room 6039, 7th and D Streets S.W., Washington, D.C.
20407).
g.
National Communications Security Glossary (Controlled Distribution).
Copies of this glossary may be requested from the National
Communications Security Committee (NCSC) Secretariat, Room C-2A40, Operations
Building 3, National Security Agency, Fort
George G. Meade, MD 20755.
3.
Requirements
3.1Overview. CCITT (i.e. International Telegraph and Telephone Consultative
Committee) Group 3 digital facsimile, transmitted at
2.4, 4.8, 7.2, or 9.6 kbits/s, is encrypted using the Data Encryption Standard
(DES) algorithm in the same manner as is described for
encrypting synchronous data in Federal Standard 1 026. Only Group 3 facsimile
documents and optional 2.4 kbit/s binary-coded signals
are encrypted. Group 3 facsimile is described in Federal Standard 1062. Binary-
coded signals are described in Federal Standard 1063.
3.2
Mode of Operation. The 1-bit Cipher Feedback mode of operation shall be
used. (Ref. Federal Information Processing Standards
Publication 81).
3.3
Transmission. Upon Clear to Send indication (e.g., CCITT Interchange
Circuit 106, Ready for Sending, ON) from a primary (i.e.,
CCITT V.27 ter or V.29) modem, the modem input (e.g., CCITT Interchange Circuit
103, Transmitted Data) is typically in a MARK
(ail ONES) state. A 48-bit Initializing Vector (IV) is sent at this point in
time, preceded by a single ZERO bit (SPACE) to delimit the
IV. The first bit transferred of the 48-bit IV is placed in bit position 17 of
the DES device input block (Ref. Federal Information
Processing Standards Publication 81). After transmission of the IV, all bits
passing through the primary modem are first encrypted.
Encryption continues until Clear to Send indication is turned off.
3.4
Reception. Upon Receiver Ready indication (e.g., CCITT Interchange Circuit
1 09, Data Channel Received Line Signal Detector,