Diffie-Hellman Key Exchange Simulator

Diffie-Hellman (1976) was the breakthrough that made public-key cryptography possible: two people who have never met can agree on a shared secret while an eavesdropper watches every message. This simulator lets you set the public prime and generator, choose Alice's and Bob's private exponents, and see each public value and the resulting shared secret computed with exact BigInt arithmetic.

The math is g^a mod p and g^b mod p exchanged in the open; each side raises the other's public value to its own private exponent, both landing on g^(ab) mod p. Small demo parameters are used so the numbers are readable — real deployments use 2048-bit or larger primes, or elliptic-curve variants.

Like everything on encrypt.tools, this runs entirely in your browser — nothing you enter is transmitted or stored.