Abstract: The device (12) comprises nine encryption stages (61.1, 61.2, 69), the first eight of which are constructed identically. It further comprises a key subblock generation unit (63), an input unit (21), and an output unit (79). It serves for the block-by-block encryption of a plaintext (X) proceeding from a message source (11) into a ciphertext (Y) to be delivered on a transmission line (13), wherein a secret key block (Z) is inputted beforehand via a secure channel 17. The encryption is effected in a step-by-step and parallel manner for four subblocks (X.sub.1 -X.sub.4 ; W.sub.11 -W.sub.14 ; W.sub.21 -W.sub.24 ; W.sub.81 -W.sub.84 ; Y.sub.1 -Y.sub.4). Every encryption stage (61.1, 61.2, 69) comprises four first inputs (25-28; 35-38), six and four second inputs (29, 30, 32, 33, 49, 52; 129, 130, 132, 133), respectively, and four outputs (75-78). A total of fifty-two key subblocks (Z.sub.1 -Z.sub.52) which are formed from the key block (Z) are connected to the second inputs.

Abstract: In a multiple access method for the simultaneous exchange of several data streams ({B.sub.1,m }, {B.sub.2,m }, {B.sub.3,m }) among several participants of a transmission system, various data streams ({B.sub.1,m }, {B.sub.2,m }, {B.sub.3,m }) with the same spread sequence (s[.]) are expanded to a corresponding DSSS signal ({B.sub.1,m s[.]}, {B.sub.2,m s[.]}, {B.sub.3,m s[.]}. During transmission, the various DSSS signals ({B.sub.1,m s[.]}, {B.sub.2,m s[.]}, {B.sub.3,m s[.]}) are heterodyned to a single incoming signal. For detecting the various data streams in a receiver, the incoming signal is filtered in a filter that is inverse with respect to the joint spread sequence (s[.]). In order to permit reliable detection, heterodyning takes place in each case so that the spread sequence intervals pertaining to different data streams are chronologically shifted with respect to one another by a given minimum value (delta.sub.-- T).

Abstract: A converter or running-key for generator producing pseudo-random sequences under the supervision of a secret or confidential key or code is substantially formed by a combination device containing a memory circuit and a feedback circuit. Periodic digital sequences are summed in an adder circuit, and the thus obtained composite digital sequence is separated in a divider circuit. A part of this composite digital sequence is used as a digital feedback sequence which is fed to an input of the same adder circuit through the feedback circuit comprising an auxiliary digital memory device or storage and an auxiliary logic circuit. In this manner, the desired memory and feedback is achieved which results in more complicated or complex pseudo-random sequences. In an advantageous exemplary embodiment, a substitution block is inserted as the auxiliary digital memory device or storage. This substitution block can be implemented by a commercially available read-and-write memory (RAM).

Abstract: Elements of the finite field GF(2.sup.m) are represented by a vector of m binary digits in such a way that multiplication can be performed by using the same logic function to compute each binary component of the product of two elements, squaring can be performed by logic circuitry that rotates the vector representing the element to be squared, and addition can be performed by logic circuitry that forms the modulo-two sum of the corresponding components of the two vectors representing the elements to be summed.

Abstract: A private message of m bits is conveyed from its sender to its receiver by transmission of a public message of m bits, transmission of a public reply of m bits, and another transmission of a public message of m bits such that only the intended receiver can easily recover the private message from the three public messages. This private message now available to both the sender and intended receiver also allows all subsequent private messages between these two points to require only one public message for each private message while maintaining the property that only the intended receiver of each message can easily recover the private message for each public message.

Abstract: In an apparatus and a method for recognizing the start of a noise-corrupted received telegram signal, and wherein the telegram signal consists of an information-containing sequence of bits ahead of the telegram signal, thereafter transmitting an intermediate sequence of bits following the preliminary sequence, but still ahead of the telegram signal, wherein the preliminary and the intermediate sequences are correlated with different parts of the preliminary and of the intermediate sequence in a pre-arranged manner, and detecting the pre-arranged manner so as to positively signal termination of the intermediate sequence; recognition of the start of the telegram signal is thereby ensured.