Method and apparatus for verifying secure document timestamping

1. A method comprising:

receiving a timestamp from a caller via a telephone connection;

receiving a device identifier from the caller, in which the device identifier identifies a device;

determining a cryptographic key based on the device identifier;

determining a representation of a time based on the timestamp and the cryptographic key;

providing the representation of the time to the caller;

determining an account; and

charging a fee to the account.

2. The method of claim 1 , in which the timestamp is optically detectable on a physical document.

3. The method of claim 1 , in which receiving the timestamp comprises:

receiving the timestamp at a central controller.

4. The method of claim 1 , further comprising:

receiving a telephone call from the caller.

5. The method of claim 1 , in which receiving the timestamp comprises:

receiving a sequence of DTMF signals; and

determining the timestamp based on the DTMF signals.

6. The method of claim 5 , in which the sequence is entered by the caller at a keypad.

7. The method of claim 1 , in which receiving the timestamp comprises:

receiving a sequence of signals via an interactive response unit (IRU).

8. The method of claim 1 , in which receiving the timestamp comprises:

receiving the timestamp via a toll-based telephone line.

9. The method of claim 8 , in which the toll-based telephone line is associated with a 900 number.

10. The method of claim 1 , in which the timestamp comprises a sequence of alphanumeric characters.

11. The method of claim 1 , in which determining the account comprises:

receiving an account identifier that identifies the account.

12. The method of claim 1 , in which the timestamp comprises an account identifier that identifies the account.

13. The method of claim 1 , in which the account is associated with the caller.

14. The method of claim 1 , in which the account is associated with a third party.

15. The method of claim 1 , in which determining the account comprises:

determining the account based on the device identifier.

16. The method of claim 1 , in which the account is a prepaid account.

17. The method of claim 1 , in which charging the fee comprises:

debiting the account based on the fee.

18. The method of claim 1 , in which determining the representation of the time comprises:

performing a cryptographic operation on the timestamp.

19. The method of claim 1 , in which determining the representation of the time comprises:

decrypting the timestamp based on the cryptographic key.

20. The method of claim 1 , in which providing the representation of the time comprises:

transmitting the representation of the time to the caller.

21. The method of claim 1 , in which providing the representation of the time comprises:

displaying the representation of the time to the caller.

22. The method of claim 1 , in which determining the cryptographic key comprises:

selecting a database record based on the device identifier, in which the database record comprises the device identifier.

23. A method comprising:

receiving a sequence of DTMF signals from a caller via a telephone connection;

determining a timestamp based on the DTMF signals;

receiving a device identifier from the caller, in which the device identifier identifies a device;

determining a cryptographic key based on the device identifier;

determining a representation of a time based on the timestamp and the cryptographic key;

providing the representation of the time to the caller;

determining an account; and

charging a fee to the account.

24. A method comprising:

receiving a timestamp from a timestamp recipient via an Internet connection;

receiving a device identifier via the Internet connection, in which the device identifier identifies a device;

determining a cryptographic key based on the device identifier;

determining a representation of a time based on the timestamp and the cryptographic key;

providing the representation of the time to the timestamp recipient via the Internet connection;

determining an account; and

charging a fee to the account.