Method and system for secure position determination

A navigation system for determining a position relative to an object, the system comprising:

• a transmission transducer to transmit at least one challenge message;
• a reception transducer to receive at least one response message, wherein the response message includes, a direction of said transmission transducer, a time of transmission of said at least one response message, and a time of receipt of said at least one challenge message;
• and a microprocessor configured to determine whether said response message is received from a direction within a predetermined angular bound;
• the microprocessor configured to accept the response message if it is within the bound;
• the microprocessor cryptographically verifying the response message and accepting it if it is cryptographically valid;
• the microprocessor configured to determine a time difference between the challenge message transmission and the response message receipt and accepting the response message if it is within a predetermined time frame;
• the microprocessor configured to reject the response message if it is not within the angular bound or not within the predetermined time frame or cryptographically invalid;
• and the microprocessor configured to provide the object position with improved security and accuracy,
• and the microprocessor further configured to transmit cryptographically authenticated information about the object's position after completing determination of the object's position.

A non-transitory computer readable program embodied in an article of manufacture, comprising computer readable program instructions for determining a position relative to an object, said program comprising:

• program instructions for causing a computer to determine whether encoded information is cryptographically derived from at least one challenge message and whether authentication information was sent by said object;
• program instructions for causing said computer to determine a time differential between a time of transmission of said at least one challenge message and a time of receipt of at least one response message;
• program instructions for causing said computer to determine an adjusted time measurement by subtracting a processing delay time from said time differential;
• program instructions for causing said computer to determine a maximum distance to said object based at least in part on one or more of said adjusted time measurement, a speed of propagation of said at least one challenge message and a speed of propagation of said at least one response message;
• program instructions for causing a computer to determine at least one of a direction of transmission of said at least one challenge message and a direction of receipt of said at least one response message;
• program instructions for causing a computer to determine whether said response message is received from a direction within a predetermined angular bound and to accept the response message if it is within the bound and
• program instructions for causing a computer to determine the position relative to said object based at least in part on said maximum distance to said object and at least one of said direction of transmission of said at least one challenge message and said direction of receipt of said at least one response message,
• and further comprising program instructions for transmitting cryptographically authenticated information about the object's position after completing determination of the object's position.