Method for checking the integrity of data, system and mobile terminal

A system for checking the integrity of a first message transmitted between a sender in a transmitting end and a recipient in a receiving end, in which the system comprises means for calculating an authentication value for the first message and means for generating a random string, characterized in that in the transmitting end the system comprises

• means for forming a check code by combining the authentication value and the random string,
• means for transferring the first message from the sender to the recipient through the first channel, and
• means for transferring said check code from said sender to said recipient through the second secure channel,
• and in the receiving end the system comprises
• means for separating said authentication value and said random string from said check code,
• means for generating an authentication check from the received message and from either said random string or said authentication value, and
• means for comparing said authentication check with either said authentication value or said random string not used in the generation of said authentication check for checking the integrity of said received message compared to the first message.

A mobile terminal for checking the integrity of a message received, into which mobile terminal a first message is sent, characterized in that the mobile terminal comprises

• means for receiving a message,
• input means for inputting a check code of the first message received through a secure channel into said mobile terminal,
• means for separating an authentication value and a random string from said check code of said first message,
• means for generating an authentication check from said received message and from either said authentication value or said random string, and
• means for comparing said authentication check with either said authentication value or said random string not used in the generation of said authentication check for checking the integrity of said received message compared to the first message.