CRACKING CODES WITH PYTHON An Introduction to Building and Break...

If you could travel back to the early 1990s with this book, the contents of Chapter 23 that implement part of the RSA cipher would be illegal to export out of the United States. Because messages encrypted with RSA are impossible to hack, the export of encryption software like RSA was deemed a matter of national security and required State Department approval. In fact, strong cryptography was regulated at the same level as tanks, missiles, and flamethrowers.