| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and a system for a cancellation server that maintains a database of cryptographic puzzle identifiers. SOLUTION: A cryptographic puzzle is formed of a unique identifier and a time stamp, and attached to an email message together with an answer to the puzzle. A recipient confirms that the answer is correct and that the time stamp is current, and further refers to a cancellation server for the puzzle identifier. When the identifier does not exist in the database, the recipient finds that the message received is legitimate. When the identifier already exists in the database, the message received is automatically erased from the recipient's computer. COPYRIGHT: (C)2006,JPO&NCIPI
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