US Patent 6904527 Intellectual property protection in a programmable logic device

Individual IP vendors can directly license their IP modules to PLD users. Each PLD has a unique device identifier (UDI). If a user obtains a license to use an IP module on a particular PLD, then the IP vendor issues the user an authorization code (AC). The user supplies the AC to a license manager. The license manager decrypts the AC and checks that the UDI of the supplied AC matches the UDI of the PLD. If the two match, then the license manager encrypts a key, and sends the encrypted key to the PLD. The PLD uses a private key to decrypt the key. When the configuration bitstream for the design is later sent to the PLD, the license manager encrypts the IP module portion of the bitstream with the key. The PLD receives the bitstream and uses the decrypted key to decrypt the IP module portion.