Method and a system for validating identifiers

A method of validating an identifier, the method comprising the steps of:

• receiving an identifier;
• determining one or more validation codes corresponding to respective one or more counter values for a counter;
• comparing the identifier with at least one of the one or more validation codes;
• and
• if the identifier matches any one of the one or more validation codes, validating the identifier.

A system for validating an identifier, the system comprising:

• an input for receiving an identifier;
• a memory for storing:
• data representing the identifier;
• and
• data representing one or more validation codes corresponding to respective one or more counter values;
• and
• a processor configured to:
• determine the one or more validation codes;
• compare the received identifier with at least one of the one or more determined validation codes;
• and
• if the received identifier matches any one of the one or more determined validation codes, validate the received identifier.

A method of validating an identifier during an electronic transaction between an unauthenticated party device and an authenticating party system in response to receiving an unexpected identifier at the authenticating party system, including:

• incrementing a counter from a current count value in each of a plurality of successive iterations up to a predetermined number of iterations;
• for each of the successive iterations:
• determining a validation code corresponding with the incremented counter value;
• comparing the received identifier with the validation code associated with the incremented counter value;
• and
• in the event that the identifier matches the validation code associated with the incremented counter value, validating the identifier and storing the incremented counter value as the current count value.

A method of validating an identifier during an electronic transaction between an unauthenticated party and an authenticating party, including:

• an authenticating party system receiving the identifier for validation;
• determining, by the authenticating party system, a first validation code associated with a current value of a counter;
• comparing the received identifier with the first validation code;
• responsive to the comparison, and in the event that the identifier does not match the first validation code, the authenticating party system comparing the identifier with one or more further validation codes, each further validation code associated with a respective other value for the counter from within a validation window of counter values;
• and
• validating the identifier if the identifier matches one of the further validation codes.