SSH2: Add support for curve25519-sha256@libssh.org.txt via libsodium-php.

composer.json

@@ -55,6 +55,7 @@
         "squizlabs/php_codesniffer": "~2.0"
     },
     "suggest": {
+        "ext-libsodium": "SSH2/SFTP can make use of some algorithms provided by the libsodium-php extension.",
         "ext-mcrypt": "Install the Mcrypt extension in order to speed up a wide variety of cryptographic operations.",
         "ext-gmp": "Install the GMP (GNU Multiple Precision) extension in order to speed up arbitrary precision integer arithmetic operations."
     },

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "hash": "a8adabfa04c250bbec41c87f79a59b31",
+    "hash": "b24ab20be15b6312e532ee2ffa18d5fa",
     "packages": [],
     "packages-dev": [
         {

phpseclib/Net/SSH2.php

@@ -953,7 +953,10 @@ class SSH2
                   31 => 'NET_SSH2_MSG_KEXDH_GEX_GROUP',
                   32 => 'NET_SSH2_MSG_KEXDH_GEX_INIT',
                   33 => 'NET_SSH2_MSG_KEXDH_GEX_REPLY',
-                  34 => 'NET_SSH2_MSG_KEXDH_GEX_REQUEST')
+                  34 => 'NET_SSH2_MSG_KEXDH_GEX_REQUEST'),
+            // RFC 5656 - Elliptic Curves (for curve25519-sha256@libssh.org)
+            array(30 => 'NET_SSH2_MSG_KEX_ECDH_INIT',
+                  31 => 'NET_SSH2_MSG_KEX_ECDH_REPLY')
         );
 
         if (is_resource($host)) {
@@ -1110,9 +1113,13 @@ class SSH2
      */
     function _generate_identifier()
     {
-        $identifier = 'SSH-2.0-phpseclib_0.3';
+        $identifier = 'SSH-2.0-phpseclib_2.0';
 
         $ext = array();
+        if (extension_loaded('libsodium')) {
+            $ext[] = 'libsodium';
+        }
+
         if (extension_loaded('openssl')) {
             $ext[] = 'openssl';
         } elseif (extension_loaded('mcrypt')) {
@@ -1141,11 +1148,24 @@ class SSH2
     function _key_exchange($kexinit_payload_server)
     {
         static $kex_algorithms = array(
+            // Elliptic Curve Diffie-Hellman Key Agreement (ECDH) using
+            // Curve25519. See doc/curve25519-sha256@libssh.org.txt in the
+            // libssh repository for more information.
+            'curve25519-sha256@libssh.org',
+
+            // Diffie-Hellman Key Agreement (DH) using integer modulo prime
+            // groups.
             'diffie-hellman-group1-sha1', // REQUIRED
             'diffie-hellman-group14-sha1', // REQUIRED
             'diffie-hellman-group-exchange-sha1', // RFC 4419
             'diffie-hellman-group-exchange-sha256', // RFC 4419
         );
+        if (!class_exists('\Sodium')) {
+            $kex_algorithms = array_diff(
+                $kex_algorithms,
+                array('curve25519-sha256@libssh.org')
+            );
+        }
 
         static $server_host_key_algorithms = array(
             'ssh-rsa', // RECOMMENDED  sign   Raw RSA Key
@@ -1359,14 +1379,23 @@ class SSH2
             return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
         }
 
-        $keyLength = $decryptKeyLength > $encryptKeyLength ? $decryptKeyLength : $encryptKeyLength;
-
         // through diffie-hellman key exchange a symmetric key is obtained
         $kex_algorithm = $this->_array_intersect_first($kex_algorithms, $this->kex_algorithms);
         if ($kex_algorithm === false) {
             user_error('No compatible key exchange algorithms found');
             return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
         }
+
+        // Only relevant in diffie-hellman-group-exchange-sha{1,256}, otherwise empty.
+        $exchange_hash_rfc4419 = '';
+
+        if ($kex_algorithm === 'curve25519-sha256@libssh.org') {
+            $x = Random::string(32);
+            $eBytes = \Sodium::crypto_box_publickey_from_secretkey($x);
+            $clientKexInitMessage = NET_SSH2_MSG_KEX_ECDH_INIT;
+            $serverKexReplyMessage = NET_SSH2_MSG_KEX_ECDH_REPLY;
+            $kexHash = new Hash('sha256');
+        } else {
             if (strpos($kex_algorithm, 'diffie-hellman-group-exchange') === 0) {
                 $dh_group_sizes_packed = pack(
                     'NNN',
@@ -1439,7 +1468,6 @@ class SSH2
                 // the generator field element is 2 (decimal) and the hash function is sha1.
                 $g = new BigInteger(2);
                 $prime = new BigInteger($prime, 16);
-            $exchange_hash_rfc4419 = '';
                 $clientKexInitMessage = NET_SSH2_MSG_KEXDH_INIT;
                 $serverKexReplyMessage = NET_SSH2_MSG_KEXDH_REPLY;
             }
@@ -1460,7 +1488,7 @@ class SSH2
 
             -- http://tools.ietf.org/html/rfc4419#section-6.2 */
             $one = new BigInteger(1);
-        $keyLength = min($keyLength, $kexHash->getLength());
+            $keyLength = min($kexHash->getLength(), max($encryptKeyLength, $decryptKeyLength));
             $max = $one->bitwise_leftShift(16 * $keyLength); // 2 * 8 * $keyLength
             $max = $max->subtract($one);
 
@@ -1468,6 +1496,7 @@ class SSH2
             $e = $g->modPow($x, $prime);
 
             $eBytes = $e->toBytes(true);
+        }
         $data = pack('CNa*', $clientKexInitMessage, strlen($eBytes), $eBytes);
 
         if (!$this->_send_binary_packet($data)) {
@@ -1495,7 +1524,6 @@ class SSH2
 
         $temp = unpack('Nlength', $this->_string_shift($response, 4));
         $fBytes = $this->_string_shift($response, $temp['length']);
-        $f = new BigInteger($fBytes, -256);
 
         $temp = unpack('Nlength', $this->_string_shift($response, 4));
         $this->signature = $this->_string_shift($response, $temp['length']);
@@ -1503,7 +1531,17 @@ class SSH2
         $temp = unpack('Nlength', $this->_string_shift($this->signature, 4));
         $this->signature_format = $this->_string_shift($this->signature, $temp['length']);
 
+        if ($kex_algorithm === 'curve25519-sha256@libssh.org') {
+            if (strlen($fBytes) !== 32) {
+                user_error('Received curve25519 public key of invalid length.');
+                return false;
+            }
+            $key = new BigInteger(\Sodium::crypto_scalarmult($x, $fBytes), 256);
+            \Sodium::sodium_memzero($x);
+        } else {
+            $f = new BigInteger($fBytes, -256);
             $key = $f->modPow($x, $prime);
+        }
         $keyBytes = $key->toBytes(true);
 
         $this->exchange_hash = pack(

tests/Unit/Net/SSH2Test.php

@@ -39,7 +39,11 @@ class Unit_Net_SSH2Test extends PhpseclibTestCase
     public function testGenerateIdentifier()
     {
         $identifier = $this->createSSHMock()->_generate_identifier();
-        $this->assertStringStartsWith('SSH-2.0-phpseclib_0.3', $identifier);
+        $this->assertStringStartsWith('SSH-2.0-phpseclib_2.0', $identifier);
+
+        if (extension_loaded('libsodium')) {
+            $this->assertContains('libsodium', $identifier);
+        }
 
         if (extension_loaded('openssl')) {
             $this->assertContains('openssl', $identifier);