The real KL-43 shipped with the classified SAVILLE algorithm. This emulator lets you pick a substitute. Both stations must select the same backend, key, and update level to round-trip a message.

For fun and historical re-creation only. None of these backends is appropriate for protecting real information. Even the AES option has no message authentication — a tampered ciphertext decrypts to modified plaintext without warning, just like on the real KL-43. Do not use this software to protect anything that matters.

Tune the FSK demodulator's acquisition gate. Lower thresholds make the receiver pick up quieter or noisier signals, at the cost of more false triggers from room noise. Changes apply live — you do not need to stop the mic. Defaults are tuned for over-the-air coupling between phone speaker and laptop mic.

Random 32-letter key (30 body letters + 2-letter checksum). Use it at the Key Change prompt.

Not a real secure key. This emulator uses toy and educational ciphers — generated keys are for playing with the KL-43 experience, not for protecting anything that matters.