IEEE P1735 is a draft standard that defines methods of encryption of IP cores. Both VHDL and Verilog files can be encrypted, while syntax is a bit different for those file types. Although still a draft, it is widely supported by various vendors including Xilinx, Mentor Graphics, Aldec, Synopsys and others. Unfortunately, at this time no public documentation on this standard is available.
The most frustrating thing aboud encrypting IP cores is that a piece of software (say, modelsim) sooner or later decrypts it. Decryption is done at source level, i.e. it is possible to recover full source code of encryped module (provided you have an extracted private key from the software you're using). Usually software vendors do not care much about hiding their private keys. The decryption is done in two stages. First, using the private key, a session key is decrypted using RSA decryption procedure. Second, data block is decoded using this session key and AES-128-CBC decryption procedure.
First, set up PYTHONPATH to point to P1735Parser.py location and PATH -- to decrypt.py (or simply run decrypt.py from local directory).
Example usage:
decrypt.py -keyname ALDEC08_001 -key keys/ALDEC08_001.pem -in encrypted_file.vhdp -out decrypted_file.vhdIt will decrypt file encrypted_file.vhdp and place it to decrypted_file.vhd using private key keys/ALDEC08_001.pem named ALDEC08_001.