PIN Encryption & Decryption with RSA in Node.js

Table of Contents Why PIN encryption matters Core terms defined How RSA works Anatomy of a key pair The OpenSSLUtil class, line by line The full encrypt → transmit → decrypt flow Working with keys in the terminal Common pitfalls & security notes Conclusion 1. Why PIN encryption matters Every time a user taps their 4-digit PIN into a mobile banking app or payment terminal, those four digits travel from device to server. If they travel as plain text — say, {"pin": "1234"} — anyone who can intercept the HTTP request, peek at server logs, or read a database dump will see that PIN immediately. That is a catastrophic failure mode. The solution is asymmetric encryption. The server holds a private key that it never shares. The client has a copy of the corresponding public key. The client encrypts the PIN before it leaves the device, and only the server — with its private key — can decrypt it. No intermediary, no log, no network sniffer can read the PIN in transit. The code snippet in this arti