The Technical Details

For more information also see Tony Sale's dedicated web site - www.codesandciphers.org.uk

Encoding Modes

SZ42 serial encoding, tri-tone

SZ42 traffic will be transmitted first using the original serial encoding scheme - The International Telegraph Alphabet No.2 (or ITA No.2 for short). ITA No. 2 is a five bit scheme allowing encoding of 32 different characters. To accommodate all the letters of the alphabet and numerals, two of the 32 combinations [letters] and [figures] are used to select alternate character sets.

	Bit
Letters	1	2	3	4	5	Figures
A	M	M	S	S	S	-
B	M	S	S	M	M	?
C	S	M	M	M	S	:
D	M	S	S	M	S	WHO ARE YOU
E	M	S	S	S	S	3
F	M	S	M	M	S	%
G	S	M	S	M	M	@
H	S	S	M	S	M	£
I	S	M	M	S	S	8
J	M	M	S	M	S	BELL
K	M	M	M	M	S	(
L	S	M	S	S	M	)
M	S	S	M	M	M	.
N	S	S	M	M	S	,
O	S	S	S	M	M	0
P	S	M	M	S	M	9
Q	M	M	M	S	M	1
R	S	M	S	M	S	4
S	M	S	M	S	S	'
T	S	S	S	S	M	5
U	M	M	M	S	S	7
V	S	M	M	M	M	=
W	M	M	S	S	M	2
X	M	M	S	S	M	/
Y	M	S	M	S	M	6
Z	M	S	S	S	M	+
Carriage Return	S	S	S	M	S	CARRIAGE RETURN
Line Feed	S	M	S	S	S	LINE FEED
Letters	M	M	M	M	M	LETTERS
Figures	M	M	S	M	M	FIGURES
Space	S	S	M	S	S	SPACE
All Space	S	S	S	S	S	ALL SPACE

 

Letter mappings in the original International Telegraph Alphabet No.2

ITA No. 2 is transmitted as Marks and Spaces. Marks are a "1" (a punched hole on paper tape), Spaces are "0" (NO punched hole on paper tape). Each five-bit word is bracketed by a start bit (space) and a stop bit (mark).

RTTY
Since many Radio Amateurs and Short Wave Listeners will not have the necessary equipment to receive and decode the original SZ42 signals, we shall also transmit the messages in radio teletype (RTTY) mode. We expect there to be a delay of 24 hours between the original format transmissions and the RTTY transmissions. Radio teletype (RTTY) as used in amateur radio generally runs at a baud rate of 45.45 (and sometimes 50) with a Frequency shift of 170Hz. We expect to transmit the ciphertext using audio frequency shift keying (AFSK) with standard frequencies of 2125Hz for mark and 2295Hz for space.

Transmission Modes

HF SSB
We anticipate that the ciphertexts will be transmitted using single sideband suppressed carrier modulation and frequency shift keyed audio tone. This mode is referred to under the Telecommunication Convention as J2B.

Internet Publication
To encourage worldwide participation in the breaking of the cipher traffic we also plan to publish the ciphertexts on the web. The definitive location for this will be on www.ccht.co.uk. We plan to publish the ciphertexts after a 48 hour delay from the original transmissions (although we expect there to be plenty of unofficial posts prior to that time).

Transmission Format

Ciphertext transmissions will be of the same basic format with a preamble to indicate which challenge is being transmitted. The transmission format will comprise three main sections:

 

Preamble [RTTY Shift 170 Hz, Mark 2125 Hz, Space 2295 Hz]

DE DL0HNF RYRYRYRYRYRYRYRYRYRYRYRYRY DL0HNF

DE DL0HNF RYRYRYRYRYRYRYRYRYRYRYRYRY DL0HNF

THIS IS DL0HNF CELEBRATING THE CIPHER EVENT:

A COLOSSAL CHALLENGE - RECREATING THE PAST -

THE COMPLETION OF THE COLOSSUS MARK 2 REBUILD

AT BLETCHLEY PARK AND RECREATING CRYPTOGRAPHIC

HISTORY. FULL DETAILS AT WWW.TNMOC.ORG/CIPHER1.HTM

THIS IS DL0HNF CELEBRATING THE CIPHER EVENT:

A COLOSSAL CHALLENGE - RECREATING THE PAST -

THE COMPLETION OF THE COLOSSUS MARK 2 REBUILD

AT BLETCHLEY PARK AND RECREATING CRYPTOGRAPHIC

HISTORY. FULL DETAILS AT WWW.TNMOC.ORG/CIPHER1.HTM

TRANSMISSION FOLLOWS IN 3-TONE

ENCODED MARK AND SPACE AS THREE SIMULTANEOUSLY

TRANSMITTED TONES:

MARK: 900Hz, 1620Hz, 2340Hz

SPACE: 540Hz, 1260Hz, 1980Hz

AT 50 BAUD

FIRST TRANSMITTING PLAIN-TEXT FOR CALIBRATION

FOLLOWED BY SCRAMBLED TEXT 1

NOW SWITCHING TO THE HISTORICAL SZ42 TRANSMISSION

MODE PSE QRX

Body [SZ42 Tri-Tone, Shift 360Hz]

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

ABCDE FGHIJ KLMNO PQRST UVWXY Z0123 45678 9XXXX

DE DL0HNF RYRYRYRYRYRYRYRYRYRYRYRYRY DL0HNF

NOW TRANSMITTING SZ42 CIPHERTEXT

PSE QRX

(Stream of ciphertext transmitted here)

 

DE DL0HNF RYRYRYRYRYRYRYRYRYRYRYRYRY DL0HNF

GB2BP DE DL0HNF

NOW SWITCHING TO NORMAL MODE

PSE QRX

Close [RTTY Shift 170 Hz, Mark 2125 Hz, Space 2295 Hz]

DE DL0HNF RYRYRYRYRYRYRYRYRYRYRYRYRY DL0HNF

DE DL0HNF RYRYRYRYRYRYRYRYRYRYRYRYRY DL0HNF

GB2BP DE DL0HNF TRANSMISSION COMPLETE

 

Transmission Length

Each ciphertext transmission will total approximately 6000 characters and will take in the order of 15 minutes to transmit.