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openssl_dh_compute_keyComputes shared secret for public value of remote DH public key and local DH key Description
stringfalse openssl_dh_compute_key(string
$public_key , #[\SensitiveParameter]OpenSSLAsymmetricKey $private_key )The shared secret returned by openssl_dh_compute_key is often used as an encryption key to secretly communicate with a remote party. This is known as the Diffie-Hellman key exchange. Caution
It is important to use the same DH parameters for remote and local key pairs; otherwise, the generated secret between the two parties will not match.
Parameters
Return Values
Returns shared secret on success or Changelog
Examples
Example #1 Compute a shared secret First generate a public/private DH keypair locally, and have
the remote party do the same. We need to use the # 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
Next, send your public key to the remote party. Use the openssl pkey -pubin -in remotepublickey.pem -text -noout The above example will output something similar to: 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...] Use this public key as a parameter to openssl_dh_compute_key in order to compute the shared secret.
Example #2 Generate a DH public/private keypair in php First, generate the DH prime number openssl dhparam -out dhparam.pem 2048 openssl dh -in dhparam.pem -noout -text The above example will output something similar to: 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 and generator values ares passed as p and g into openssl_pkey_new
See Also
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