| 摘要 |
<p>Data are transmitted in ciphered form from a sending unit (DEE1) over a line switching junction (KN) to a receiving unit (DEE2) via sending (ST1) and receiving (ST2) trunks. At least the address data are deciphered before they reach the switching junction (KN) where the path to the receiving station is to be set up. This is done by providing a data gating switch in the cipher units (SG11,SG32) as well as in the decipher units (SH22,SG42) responsive to start or finish codes in data groups of the message stream. By means of the data switch the address and routing signals are first ciphered on application of a first instruction code (preamble), whereas the message data are ciphered in a different way by application of a second instruction code which, moreover, is phased into the data stream itself between the address signal group and the message signal group within the cipher unit (SG11) by storing and delaying the latter by at least the number of bits contained in the second instruction code. The address data are recovered in a unit (SG22) but reciphered in another unit (SG32).</p> |
