S~~D: A61 QA9 

\J.6.1.i.J 6. .._. 1(24 

USCIB: 29. 2/10 

20 September 1954 

BESREi 

MEMORANDUM FOR THE MEMBERS OF USCIB: 

Subject: Disclosure of Details of ROCKEX to the French. 

1. The enclosure is forwa~ded for consideration by vote sheet 

at the request of the Director, National Security Agency. It is 

requested that vote sheet replies be retumed to this office by 

1200, 28 September 1954. 

2. The enclosure has been distributed to members of USCSB for 

inf orrna.tion. 

EpcJ_osure 

Memo from Director, NSA 

to Members of USCIB, 

dtd 13 Sep 19 54 

USCIB: 29. 2/10 
. - . 

13 SEP 1954 

SE0Rfl'i' 

MEMORJ\NDUM FOR THE MEMBERS OF USCIB 

SUBJECT: Disclosure of Details of ROCKEX to the French 

l. The use of national one-time systems for the encryption of 

NATO TOP SECRET, NATO SECRET, and all COSMIC messages is forbidden 

without specific Standing Group authorization. This has i'orced the 

U. K. Foreign Office to use a NATO approved cipher ma.chine at installations where use oi' the U. K. cipher machine ROCiillX would have been 

more convenient and secur·e. The Fo't'eign Office is therefore anxious 

tha.t the U. K. obtain Standing Group approval for the use of ROCKEX 

for all classifications. To obtain such approval, i'ull details of 

the equipment must be disclosed to the French. The Director, GCHQ, 

has approved such disclosure and similar approval by U. S. authorities has been requested by the British Cryptographic Liaison Of-.f'icer 

in Washington. 

2. ROCK.EX is a one-time tape device for use with appropriate 

teletypewriter equipment. The one-time tapes used are composed o!' 

five-letter groups with appropriate line feed and carriage returns 

inserted at fixed intervals. Six-level tape is used. This tape 

meets the minimum tape standards promulgated by the Standing Group. 

Other details of the equipment and tape are as follows: 

a. The ROCKEX mixer·is designed so that cipher outpu:t; consists of 26 letters. This is arranged by a feature which causes key 

letters to be transmitted directly whenever plain text plus key wou.ld 

yield a functions character as the cipher result. The plain-text 

character involved is added to successive letters of key until a 

literal cipher result is produced. In decipherment, the "by-passed" 

key letters are recognized since they decipher as BLKS. BLKS are 

not used in the plain-text input. 

b. Tapes are divided into 49-group segments with each 50th 

group composing a segment indicator. Each tape contains approximately 

263 letters. . 

c. The ma.chine has radiation characteristics similar to 

SIGTOT. 

d. Some ma.chines are provided with tape-slitters to prevent 

reuse of key tapes. 

e. Tape reels are equipped with special bosses which prevent 

the use of DECIPHER tapes f'or encipherment. 

SECRET 
• 

3. Releo.se of the equipment itself for use by NA'l'O nations 

other than the u. K. is not contemplated at the present time since 

there is no surplus of' ROCKEX ID'l".!hincs. 'l'he baste cr;y:ptoprinciple 

used "in ROCKJ!X is the same as that used in already approved NATO 

one-time tape systems. 

11. I can perceive no objection to disclosure of' i'ull details 

of ROCKEX to the F'renc~'l .for the purpose indicated and, in the absence 

of objection on the part of any other memberJ I will inform the 

Brttish of USCIB concurrence. 

• 

Lieutenant cner 1, 

Director 

SEC:RET 

•