METHOD AND SYSTEM FOR ENHANCING THE SECURITY OF ELECTRONIC TRANSACTIONS

1 . A method of securing communications between a sales terminal and a transaction control server, said method comprising

the construction, by the transaction control server, according to a first cryptographic algorithm, of a first encrypted message from at least one first data item;

the construction, by the sales terminal, according to the same said first cryptographic algorithm, of a second encrypted message from at least one second data item, assumed to be the same as said first data item;

said method characterized in that it further comprises

the construction, by said sales terminal, according to a second encryption algorithm, of a third encrypted message from at least one third data item, by using said second encrypted message as the encryption key;

the transmission, by said sales terminal, of said third encrypted message to said transaction control server;

the deciphering, by said transaction control server, according to said second encryption algorithm, of said third encrypted message, by using said first encrypted message as the decryption key;

the construction, by said transaction control server, according to a third encryption algorithm, of a fourth encrypted message based on the content of said third deciphered message, by using said first encrypted message as the encryption key;

the transmission, by said transaction control server, of said fourth encrypted message to said sales terminal;

the deciphering, by said sales terminal, according to said third encryption algorithm, of said fourth encrypted message, by using said second encrypted message as the decryption key.

2 . The method according to claim 1 , further comprising a step of authorizing or completing a transaction by said sales terminal, based on said fourth deciphered message.

3 . The method according to claim 1 , wherein said third data item includes a randomized string containing, at positions known to the sales terminal and the transaction control server, an item of information agreed to in advance between the sales terminal and the transaction control server.

4 . The method according to claim 1 , wherein the construction of said fourth encrypted message includes the encryption of a randomized string containing, at positions known to the sales terminal and the transaction control server, a transaction return code.

5 . The method according to claim 1 , wherein said return code is completed by control bytes during its construction.

6 . The method according to claim 1 , wherein said first data item and said second data item correspond to a user's secret code.

7 . The method according to claim 1 , wherein said first data item and said second data item comprise the same randomized string.

8 . A transaction control server configured for:

constructing, according to a first cryptographic algorithm, a first encrypted message from at least one first data item;

receiving a second encrypted message;

deciphering, according to a second encryption algorithm, said second encrypted message, by using said first encrypted message as the decryption key;

using said first encrypted message as the encryption key, in order to construct, according to a third encryption algorithm, a third encrypted message based on the content of said second deciphered message;

transmitting said third encrypted message.

9 . A sales terminal configured for

constructing, according to a first cryptographic algorithm, a first encrypted message from at least one first data item;

using said first encrypted message as the encryption key, in order to construct, according to a second encryption algorithm, a second encrypted message from at least one second data item;

transmitting said second encrypted message;

receiving a third encrypted message;

deciphering, according to a third encryption algorithm, said third encrypted message, by using said first encrypted message as the decryption key;

authorizing or completing a transaction based on said third deciphered message.

10 . A system for securing communications between a sales terminal and a transaction control server, said system comprising

a transaction control server configured for constructing, according to a first cryptographic algorithm, a first encrypted message from at least one first data item;

a sales terminal configured for constructing, according to the same said first cryptographic algorithm, a second encrypted message from at least one second data item, assumed to be the same as said first data item;

said system characterized in that it further comprises

the sales terminal configured for constructing, according to a second encryption algorithm, a third encrypted message from at least one third data item, by using said second encrypted message as the encryption key;

the sales terminal configured for transmitting said third encrypted message to said transaction control server;

the transaction control server configured for deciphering, according to said second encryption algorithm, said third encrypted message, by using said first encrypted message as the decryption key;

the transaction control server configured for constructing, according to a third encryption algorithm, a fourth encrypted message based on the content of said third encrypted message, by using said first encrypted message as the encryption key;

the transaction control server configured for transmitting said fourth encrypted message to said sales terminal;

the sales terminal configured for deciphering, according to said third encryption algorithm, said fourth encrypted message, by using said second encrypted message as the decryption key.

11 . The system according to claim 1 wherein the sales terminal is further configured to apply a step of authorization or of completion of transaction based on said fourth deciphered message.

12 . A computer program product implemented on a storage medium, capable of being run on a data processing unit and comprising instructions for the implementation of a method according to claim 1 .