Electronic transaction system

An electronic transaction system for electronically sending and receiving digital signatures concerning a transaction message M between a first terminal for a first transacting party and a second terminal for a second transacting party, comprising:

• A. in said first terminal:
• first means for generating a Hash total h'(M) of the transaction message M derived by compression-encoding said transaction message M and a Hash total h(M) different from said Hash total h'(M);
• second means for preparing a digital signature T(A) by encoding data including at least first data containing the Hash total h'(M) and a first certificate not containing the transaction message M by using a secret key of the first transacting party, based on a public key cryptograph system;
• third means coupled to the output of said second means for sending the prepared digital signature T(A) from said first terminal to said second terminal;
• B. in said second terminal:
• fourth means for preparing a digital signature S(B) by encoding data including at least second data containing the Hash total h(M) different from the Hash total h'(M) and a second certificate not containing the transaction message M by using a secret key of the second transacting party, based on said public key cryptograph system;
• fifth means coupled to the output of said fourth means for sending the digital signature S(B) from said second terminal to said first terminal;
• and
• C. in said first terminal:
• sixth means responsive to reception of the digital signature S(B) from said second terminal for encoding data including at least third data containing the Hash total h(M) and a first certificate not containing the transaction message M by using the secret key of the first transacting party, based on said public key cryptograph system to obtain a digital signature S(A) and for sending the digital signature S(A) from said first terminal to said second terminal.