Method for identifying subscribers and for generating and verifying electronic signatures in a data exchange system

In a method for mutual identification of subscribers in a data exchange system working with processor chip cards and using identification data coded into the cards by a card-issuing center including subscriber-related public keys and stored in the respective chip cards along with private keys which have a logical relationship to the public keys, whereby random number-dependent check data are exchanged between the subscribers, comprising the steps of:

• transmitting from a chip card the coded identification data together with a signature of the center to a subscriber entering into an information exchange with the chip card;
• at the subscriber checking the correctness of the coded identification data with reference to known information including a public list or reference to the signature of the center;
• forming in the chip card a x value proceeding from a random, discrete logarithm r.epsilon.(1, . . . , p-1), where p is a declared prime number modulus, and according to the rule
• x:=2.sup.r (mod p):
• transmitting the x value to the subscriber;
• transmitting from the subscriber a random bit sequence
• e=(e.sub.l,l. . . ,e.sub.t,k).epsilon.{0,1}.sup.kt
• to the chip card;
• multiplying the stored, private key s.sub.j representing a discrete logarithm with a binary number formed from the bits of the random bit sequence e transmitted from the subscriber to the chip card and adding the random number r allocated to the previously-transmitted x value to calculate, at the chip card, a number y according to the rule ##EQU15## transmitting the number y to the subscriber;
• at the subscriber, calculating a number x with reference to the number y according to the rule ##EQU16## checking the identity of the chip card user by comparing the calculated number x and the x value previously communicated to the subscriber.