Patent Document ID: 9979697
Application ID: 15559787
Patent Flag: 1

Claim One:
1. A packet filtering apparatus comprising: a memory to store a rule set containing a rule in which a condition and an action are associated with each other, and a Zero-Suppressed Binary Decision Diagram (ZDD) that represents a logical expression in which the condition of the rule is described using a logical variable; and a processing circuitry to analyze a packet received from a network and extract collation information being a character string to be collated, collate the collation information extracted with the ZDD, execute the action associated with the condition that the collation information matches, and permit or deny communication of the packet, wherein the processing circuitry, in collation of the collation information with the ZDD, overwrites a value of the logical variable for which collation has been completed with 0, and determines whether or not a value of the logical expression including the logical variable overwritten with 0 is 0 when collation on the entire ZDD has been completed.