SpiceCrypt is a Python library that decrypts LTspice encrypted model files, supporting both text-based (.CIR/.SUB) and binary formats. The tool automatically detects file formats and uses modified DES and XOR stream ciphers to decrypt protected SPICE models. Engineers can now use third-party models in open-source simulators like NGSpice and Xyce.

Installation is straightforward via uv package manager, with both command-line and Python API interfaces available. The library handles the complex decryption process, including integrity verification through CRC checksums. Text-based files contain hex-encoded ciphertext with comment headers, while binary files use a two-layer XOR cipher with a specific 20-byte signature.

This reverse engineering effort addresses a significant limitation in the SPICE modeling ecosystem. Many vendors distribute models exclusively as LTspice-encrypted files, restricting their use to proprietary software. SpiceCrypt restores interoperability by allowing engineers to use lawfully obtained models across different simulation platforms, which is legally permitted under U.S. and EU interoperability provisions.