PHP implements Diffie–Hellman key exchange (Diffie–Hellman) algorithm

How does PHP implement the Diffie–Hellman key exchange (Diffie–Hellman) algorithm? This article mainly introduces the principle of Diffie-Hellman key exchange (Diffie-Hellman) algorithm and PHP implementation examples. I hope to be helpful.

Diffie-Hellman is an algorithm that allows both parties to establish a secret key on an insecure public channel. Both parties can later use this secret key for encryption (such as RC4) content.
The principle of Diffie–Hellman algorithm is very simple:

The above principle is easy to prove through mathematical principles(g^ b%p)^a%p = (g^a%p)^b%p, so they get the same key.
Except for a, b and the final public key, which are secret, the others can be transmitted on the public channel. In actual applications, p is very large (more than 300 bits), and g usually takes 2 or 5. Then it is almost impossible to calculate a from p, g and g^a%p (discrete math problem).

Many languages ​​have implemented this algorithm, take Crypt_DiffieHellman in the PHP package as an example:

<?php
include &#39;DiffieHellman.php&#39;;
 
/*
 *   Alice: prime = 563
 *       generator = 5
 *       private key = 9
 *   Bob:  prime = 563
 *       generator = 5
 *       private key = 14
 */
 
$p = 563;
$g = 5;
$alice = new Crypt_DiffieHellman($p, $g, 9);
$alice_pubKey = $alice->generateKeys()->getPublicKey();
 
$bob = new Crypt_DiffieHellman($p, $g, 14);
$bob_pubKey = $bob->generateKeys()->getPublicKey();
 
$alice_computeKey = $alice->computeSecretKey($bob_pubKey)->getSharedSecretKey();
$bob_computeKey = $bob->computeSecretKey($alice_pubKey)->getSharedSecretKey();
 
echo "{$alice_pubKey}-{$bob_pubKey}-{$alice_computeKey}-{$bob_computeKey}"; //78-534-117-117

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