After some challenges I decided to write a C++ and PHP code samples.
As it can be very tricky to get a grib on how the Diffie and Hellman algoritm work. The code samples are cross compatible.
Gist with PHP code and C++ code:
https://gist.github.com/digitalhuman/2a2b85d61672e4bf83596d41351723ba
Enjoy!
openssl_dh_compute_key
(PHP 5 >= 5.3.11, PHP 7)
openssl_dh_compute_key — Computes shared secret for public value of remote DH key and local DH key
설명
string openssl_dh_compute_key
( string
$pub_key
, resource $dh_key
)Warning
이 함수는 현재 문서화 되어있지 않습니다; 인수 목록만을 제공합니다.
인수
-
pub_key -
Public key
-
dh_key -
DH key
반환값
Returns computed key on success실패 시 FALSE를 반환합니다.
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User Contributed Notes 3 notes
vangelier at hotmail dot com ¶
1 year ago
vangelier at hotmail dot com ¶
1 year ago
A working example. After some study and reading I finally get how this method is working.
You need to follow the below 4 steps;
1. You create a public key which is known to 1:n parties.
2. Each party creates their own keypair.
2a. Each party shared their public key with the members.
3. Each user can re-create the shared secret by using his Private Key and the Public Key of the other parties.
4. Compare the secrets as a handshake
/* 1. Create the first, global known public key. */
/**
* Get DH public/private keys
* @return array
*/
public static function get_keypair()
{
$keys = [];
$config = [
"digest_alg" => "sha512",
"private_key_bits" => 2048,
"private_key_type" => OPENSSL_KEYTYPE_DH,
];
// Create the private and public key
$res = openssl_pkey_new($config);
$pubKey = openssl_pkey_get_details($res);
$keys["public"] = $pubKey["key"];
openssl_pkey_export($res, $privKey);
$keys["private"] = $privKey;
return $keys;
}
Now you share the Public Key with every member of the party.
/* 2. Each user creates a new Key Pair with the P,G from the global public key info */
$key = openssl_get_publickey(base64_decode($publicKey));
$info = openssl_pkey_get_details($key);
$params = $info["dh"];
Now you have the P,G from the public key. Use it;
/**
* Create keypair from Prime and Generator for KeyExchange
* @param $prime
* @param $generator
*/
public static function create_keypair_from_pg($prime, $generator)
{
$config = [
"digest_alg" => "sha512",
"private_key_bits" => 2048,
"dh" => [
"p" => $prime,
"g" => $generator
],
"private_key_type" => OPENSSL_KEYTYPE_DH,
];
return openssl_pkey_new($config);
}
/* 3. Create a shared secret with your Private Key, and User 1:n's Public Key */
$privateKey = openssl_get_publickey(base64_decode($privateKeyData));
$secret1 = openssl_dh_compute_key($user1PublicKey, $privateKey);
if($secret !== false) {
return bin2hex($secret);
}else{
print_r(openssl_error_string());
}
$secret2 = openssl_dh_compute_key($user2PublicKey, $privateKey);
if($secret !== false) {
return bin2hex($secret);
}else{
print_r(openssl_error_string());
}
/* 4. Compare the secrets as a handshake method */
if(strcmp($secret1, $secret2) === 0) {
return true;
}
return false;
Good luck, enjoy!. Keep me posted about improvements and updates. vangelier AT hotmail DOT com
vangelier at hotmail dot com ¶
1 year ago
Is it possible for someone to post a working example? I have written many test and examples, and I just can't seem to get 2 secrets that are alike with this method.
I am following this; https://sandilands.info/sgordon/diffie-hellman-secret-key-exchange-with-openssl
With the console, it works great. With openssl_dh_compute_key it does not work.
