Public Key Cryptography

Prerequisites: Completion of Symmetric Encryption Fundamentals; Python 3.10+ with cryptography installed.

Verified against the pyca/cryptography documentation, NIST SP 800-57 Part 1 Revision 5 (key-strength equivalence table), and NIST SP 800-131A Revision 2, July 2026. Key-size guidance here reflects NIST's current position: RSA-2048 provides roughly 112 bits of security and remains acceptable for now, but NIST's own schedule only treats 112-bit strength as sufficient through 2030 — new systems should target RSA-3072 (128-bit strength) or, preferably, an elliptic-curve alternative like X25519/Ed25519, which reach 128-bit security at a fraction of the key size. This project defaults to those stronger choices rather than the RSA-2048 examples still common in older tutorials.

Symmetric encryption has a bootstrapping problem: both parties need the same key before they can talk securely, but how do you get that key to them securely in the first place without already having a secure channel? Public key (asymmetric) cryptography breaks that circularity — each party has a mathematically linked key pair, one half published openly (the public key) and one half kept secret (the private key), where data encrypted with the public key can only be decrypted with the matching private key.

Two families dominate real-world use today: RSA, based on the difficulty of factoring large numbers, and elliptic curve cryptography (ECC), based on the difficulty of the discrete logarithm problem on an elliptic curve. Both remain secure against classical computers at appropriate key sizes; this project uses both so you can see the size and performance difference directly, not just read about it.