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openssl_dh_compute_key

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

openssl_dh_compute_key — ローカルのDH秘密鍵とリモート側のDH公開鍵を使い、共有シークレットを計算する

説明

openssl_dh_compute_key(string $public_key, OpenSSLAsymmetricKey $private_key): string|false

openssl_dh_compute_key() 関数が返す共有シークレットは、リモート側と秘密の通信をするための暗号鍵としてよく使われます。これはディフィー・ヘルマン鍵共有として知られています。

注意: ECDH は、PHP 8.1.0 以降、かつ OpenSSL 3.0.0 以降でのみサポートされています。

パラメータ

public_key: リモート側の DH 公開鍵
private_key: ローカル側の DH 秘密鍵。これは、リモート側と共有している公開鍵に対応します。

戻り値

成功した場合、共有シークレットを返します。失敗した場合に false を返します.

変更履歴

バージョン	説明
8.0.0	`private_key` は、 OpenSSLAsymmetricKey クラスのインスタンスを受け入れるようになりました。これより前のバージョンでは、 `OpenSSL key` 型のリソースを受け入れていました。

例

例1 共有シークレットを計算する

まず DH 公開鍵/秘密鍵キーペアをローカルで生成します。そしてリモート側でも同じことをします。 openssl コマンドラインユーティリティを使う必要があります。

# generate private/public key keypair
openssl dhparam -out dhparam.pem 2048
openssl genpkey -paramfile dhparam.pem -out privatekey.pem

# extract public key only
openssl pkey -in privatekey.pem -pubout -out publickey.pem

次に、あなたの公開鍵をリモート側に送ります。あなたが送る公開鍵をリモート側で調べるために、 openssl pkey コマンドを使ってください。

openssl pkey -pubin -in remotepublickey.pem -text -noout

上の例の出力は、たとえば以下のようになります。

PKCS#3 DH Public-Key: (2048 bit)
    public-key:
        67:e5:e5:fa:e0:7b:0f:96:2c:dc:96:44:5f:50:02:
        9e:8d:c2:6c:04:68:b0:d1:1d:75:66:fc:63:f5:e3:
        42:30:b8:96:c1:45:cc:08:60:b4:21:3b:dd:ee:66:
        88:db:77:d9:1e:11:89:d4:5c:f2:7a:f2:f1:fe:1c:
        77:9d:6f:13:b8:b2:56:00:ef:cb:3b:60:79:74:02:
        98:f5:f9:8e:3e:b5:62:08:de:ca:8c:c3:40:4a:80:
        79:d5:43:06:17:a8:19:56:af:cc:95:5e:e2:32:2d:
        d2:14:7b:76:5a:9a:f1:3c:76:76:35:cc:7b:c1:a5:
        f4:39:e5:b6:ca:71:3f:7c:3f:97:e5:ab:86:c1:cd:
        0e:e6:ee:04:c9:e6:2d:80:7e:59:c0:49:eb:b6:64:
        4f:a8:f9:bb:a3:87:b3:3d:76:01:9e:2b:16:94:a4:
        37:30:fb:35:e2:63:be:23:90:b9:ef:3f:46:46:04:
        94:8f:60:79:7a:51:55:d6:1a:1d:f5:d9:7f:4a:3e:
        aa:ac:b0:d0:82:cc:c2:e0:94:e0:54:c1:17:83:0b:
        74:08:4d:5a:79:ae:ff:7f:1c:04:ab:23:39:4a:ae:
        87:83:55:43:ab:7a:7c:04:9d:20:80:bb:af:5f:16:
        a3:e3:20:b9:21:47:8c:f8:7f:a8:60:80:9e:61:77:
        36
 [...abbreviated...]

この公開鍵を openssl_dh_compute_key() のパラメーターとして渡し、共有シークレットを計算します

<?php
$remote_public_key = '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';

$local_priv_key = openssl_pkey_get_private('file://privatekey.pem');

$shared_secret = openssl_dh_compute_key(hex2bin($remote_public_key), $local_priv_key);
echo bin2hex($shared_secret)."\n";
?>

例2 DH public/private キーペアをPHPで生成する

まず、DH prime を生成します。

openssl dhparam -out dhparam.pem 2048
openssl dh -in dhparam.pem -noout  -text

上の例の出力は、たとえば以下のようになります。

    PKCS#3 DH Parameters: (2048 bit)
        prime:
            00:a3:25:1e:73:3f:44:b9:2b:ee:f4:9d:9f:37:6a:
            4b:fd:1d:bd:f4:af:da:c8:10:77:59:41:c6:5f:73:
            d2:88:29:39:cd:1c:5f:c3:9f:0f:22:d2:9c:20:c1:
            e4:c0:18:03:b8:b6:d8:da:ad:3b:39:a6:da:8e:fe:
            12:30:e9:03:5d:22:ba:ef:18:d2:7b:69:f9:5b:cb:
            78:c6:0c:8c:6b:f2:49:92:c2:49:e0:45:77:72:b3:
            55:36:30:f2:40:17:89:18:50:03:fa:2d:54:7a:7f:
            34:4c:73:32:b6:88:14:51:14:be:80:57:95:e6:a3:
            f6:51:ff:17:47:4f:15:d6:0e:6c:47:53:72:2c:2a:
            4c:21:cb:7d:f3:49:97:c9:47:5e:40:33:7b:99:52:
            7e:7a:f3:52:27:80:de:1b:26:6b:40:bb:14:11:0b:
            fb:e6:d8:2f:cf:a0:06:2f:96:b9:1c:0b:b4:cb:d3:
            a6:62:9c:48:67:f6:81:f2:c6:ff:45:03:0a:9d:67:
            9d:ce:27:d9:6b:48:5d:ca:fb:c2:5d:84:9b:8b:cb:
            40:c7:a4:0c:8a:6e:f4:ab:ba:b6:10:c3:b8:25:4d:
            cf:60:96:f4:db:e8:00:1c:58:47:7a:fb:51:86:d1:
            22:d7:4e:94:31:7a:d5:da:3d:53:de:da:bb:64:8d:
            62:6b
        generator: 2 (0x2)

prime と generator の値を 'p' と 'g' として openssl_pkey_new() 関数に渡します。

<?php
$configargs = array();
$configargs['p'] = hex2bin('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');
$configargs['g'] = hex2bin('02');
$private_key = openssl_pkey_new(array('dh' => $configargs));
openssl_pkey_export_to_file($private_key,'privatekey.pem',$passphrase='y0urp@s5phr@se');

$details = openssl_pkey_get_details($private_key);
$local_pub_key = $details['dh']['pub_key'];
echo bin2hex($local_pub_key)."\n";//you can send your public key to the remote party

$details = openssl_pkey_get_details(openssl_pkey_get_public("file://remotepublickey.pem"));
$remote_public_key = $details['dh']['pub_key'];
$shared_secret = openssl_dh_compute_key($remote_public_key, $private_key);
echo bin2hex($shared_secret)."\n";
?>

参考

openssl_pkey_new() - 新規に秘密鍵を生成する
openssl_pkey_get_details() - キーの詳細の配列を返す
openssl_pkey_get_private() - 秘密鍵を取得する
openssl_pkey_get_public() - 証明書から公開鍵を抽出し、使用できるようにする

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User Contributed Notes 4 notes

down

k.s.swaminathan at live dot com ¶

2 years ago


// Purpose: Provide a working example of Diffie-Hellman, entirely in php.

// This function generates a configuration for Diffie-Hellman keypair
// We start with an empty config and have openssl_pkey_new create 
// a prime and a generator. This is a time consuming step. 

function get_DH_params ($keylength=2048, $digest_alg="sha512")
{
    $pkey = openssl_pkey_new(["digest_alg" => $digest_alg,
                        "private_key_bits" => $keylength,
                        "private_key_type" => OPENSSL_KEYTYPE_DH]);
    $details = openssl_pkey_get_details($pkey);
    return [
            "digest_alg" => $digest_alg,
            "private_key_bits" => $keylength,
            "dh" => array('p' => $details['dh']['p'], 'g' => $details['dh']['g']),
            "private_key_type" => OPENSSL_KEYTYPE_DH,
        ];
}

// Now Alice and Bob can create their respective keypairs
function get_DH_keyPair ($DH_params) 
{
    $pkey = openssl_pkey_new($DH_params);           
    $privkey = openssl_pkey_get_private($pkey);
    $pubkey = openssl_pkey_get_details($pkey)['dh']['pub_key'];
    return (object) compact('pubkey','privkey');
}

// Now Alice and Bob can create a mutual secret
function get_DH_mutualsecret($peers_public, $my_private)
{
    return bin2hex(openssl_dh_compute_key($peers_public, $my_private));
}

// Usage
>>> $dh_params = get_DH_params();
=> [
     "digest_alg" => "sha512",
     "private_key_bits" => 2048,
     "dh" => [
       "p" => b"ó»¸'#ð\x18\x04Û_Ä\tõyÁZàx\x15\x14\x11ƒ┬l=Ü┤H\0",
       "g" => "\x02",
     ],
     "private_key_type" => 2,
   ]

// Alice & Bob generate their keys from the same dh_params.
// Binary values truncated.

>>> $alice = get_DH_keypair($dh_params);
=> {#3773
     +"pubkey": b"""EØüÔSðÔîË╚ùà5ÜLÜ$┘▄±ü6]",
     +"privkey": OpenSSLAsymmetricKey {#3771},
   }

>>> $bob = get_DH_keypair($dh_params);
=> {#3774
     +"pubkey": b"'ua¥ªo\ê\x11║OM©\vó╣ßÜWöíþ³e÷:\t9Ô\rB┌\x13",
     +"privkey": OpenSSLAsymmetricKey {#3765},
   }

>>> $alice_secret = get_DH_mutualsecret($bob->pubkey, $alice->privkey);
=> "5fbf9df2f13da103f106.  ....."

>>> $bob_secret = get_DH_mutualsecret($alice->pubkey, $bob->privkey);
=> "5fbf9df2f13da103f106.  ....."

>>> $bob_secret == $alice_secret;
=> true

// Now Alice and Bob have a shared secret which they can use as a symmetric key. The key will be 2048 bits long (same as the DH key length parameter). They can hash it to get a shorter key if they want. 

// A third person, Charlie, can also create a key pair like Alice and Bob. 
// And Charlie and Alice can create their own Alice and Bob did.
// And Charlie and Bob can create their own (separate) secret. 
//

down

vangelier at hotmail dot com ¶

3 years 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

down

vangelier at hotmail dot com ¶

3 years 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.

down

-1

vangelier at hotmail dot com ¶

3 years ago


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!

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