GB1391441A - Enciphering and deciphering systems for teleprinter signals - Google Patents

Abstract

1391441 Data transmission; ciphering SIEMENS AG 20 Aug 1963 [21 Aug 1962] 32818/63 Heading H4P In a system for enciphering and deciphering teleprinter signals in which unciphered characters are enciphered by mixing with a cipher character, when the first of two particular characters which it is not desired to transmit, e.g. 32 (00000 in the International Five Element Alphabet No. 2), occurs as an enciphered character at the transmitting station, before it is transmitted, a first specific character, e.g. the "line shift" character ZL (01000), not employed as an unciphered character is substituted for the first particula character and mixed with the cipher character to form a substitute enciphered character; and when the second of the two particular characters, e.g. the "who are you?" character D (10010) occurs as an enciphered character at the transmitting station, before it is transmitted, a second specific character, e.g. 32 (00000), not employed as an unciphered character is substituted for the second particular character and mixed with the cipher character to form a substitute enciphered character. One example of the above is illustrated in the following table: Great significance should not be attached to the enciphered signal being identical to the original plain-language signal. Using electronic means three mixing operations finishing consecutively in close succession and can be completed during the time of transmission of the start element of the enciphered signal. To permit transmission of any desired information without employing the two specific characters in the plain-language signals, a single teleprinter signal must be employed to represent two concurrent functions. By combining the functions of "carriage return" and "line shift" under the character normally used for the "carriage return" function, the "line shift" character ZL (01000) can be made available. In order to prevent the occurence of an undesirably large line spacing, a unit may be provided in the receiving teleprinter station which effects "line shift" only on reception of the first of these successively arriving characters, suppressing this function on immediately following occasions. Alternatively, it is possible with each appearance of the "carriage return"/"line shift" combination to effect "line shift" by half a normal step; thus, after the said character has been received twice, the normal line spacing is obtained. It it is desired to avoid a third mixing process, then one possibility is to use "signal identification". Since the two special cases are characterized by the simultaneous occurrence of either D (plain-language signal) and Bu (cipher signal) or of J (plain-language signal and H (cipher signal), a special circuit can be used to immediately produce the enciphered signal ZL or J. In this case, the second mixing process is also rendered unnecessary. If this signal identification is limited to the appropriate signals at the second mixing stage, then only the third mixing process is omitted.