| 摘要 |
Method and arrangement for transmission of digital information, where the encryption and decryption is done by means of a so-called external key in the form of a bit sequence of random characters, which is transmitted after the transmission of the encrypted information. According to the invention, there are current switch elements S1, S2, S3, S1r, S2r, by means of which a time reference pattern from a time reference signal generator SG is repeatedly transmitted from the transmitter T to the receiver R and a new external key is transmitted in conjunction with each such time reference pattern, which is identified by means of said pattern. Preferably, a sequence p1-p16 of the transmitted bit stream is selected as new external key for a subsequent time interval B2 and this selected external key can be transmitted several times multiplexed into the bit stream. The selected and transmitted external keys are entered into the encryption generator KG both at the transmitter end and the receiver end at a time t01, t12 dictated by said reference time pattern. Thus, the same external key will only be used for a brief time, namely, the time required for selection and transmission of a new external key with corresponding identification time reference pattern, which makes illicit decryption difficult. If the transmission is disrupted so that the synchronisation is lost, the system will automatically resynchronise itself by transmission of the next time reference pattern and corresponding new external key after the disturbance. The invention can be used in voice encryption equipment. <IMAGE> |
