crypto: add function getDiffieHellman()

Returns a well known, predefined RFC group.

doc/api/crypto.markdown

@@ -264,6 +264,36 @@ or `'base64'`. Defaults to `'binary'`.
 Sets the Diffie-Hellman private key. Key encoding can be `'binary'`, `'hex'`,
 or `'base64'`. Defaults to `'binary'`.
 
+### crypto.getDiffieHellman(group_name)
+
+Creates a predefined Diffie-Hellman key exchange object.
+The supported groups are: `'modp1'`, `'modp2'`, `'modp5'`
+(defined in [RFC 2412](http://www.rfc-editor.org/rfc/rfc2412.txt ))
+and `'modp14'`, `'modp15'`, `'modp16'`, `'modp17'`, `'modp18'`
+(defined in [RFC 3526](http://www.rfc-editor.org/rfc/rfc3526.txt )).
+The returned object mimics the interface of objects created by
+[crypto.createDiffieHellman()](#crypto.createDiffieHellman) above, but
+will not allow to change the keys (with
+[diffieHellman.setPublicKey()](#diffieHellman.setPublicKey) for example).
+The advantage of using this routine is that the parties don't have to
+generate nor exchange group modulus beforehand, saving both processor and
+communication time.
+
+Example (obtaining a shared secret):
+
+    var crypto = require('crypto');
+    var alice = crypto.getDiffieHellman('modp5');
+    var bob = crypto.getDiffieHellman('modp5');
+
+    alice.generateKeys();
+    bob.generateKeys();
+
+    var alice_secret = alice.computeSecret(bob.getPublicKey(), 'binary', 'hex');
+    var bob_secret = bob.computeSecret(alice.getPublicKey(), 'binary', 'hex');
+
+    /* alice_secret and bob_secret should be the same */
+    console.log(alice_secret == bob_secret);
+
 ### pbkdf2(password, salt, iterations, keylen, callback)
 
 Asynchronous PBKDF2 applies pseudorandom function HMAC-SHA1 to derive

lib/crypto.js

@@ -30,6 +30,7 @@ try {
   var Sign = binding.Sign;
   var Verify = binding.Verify;
   var DiffieHellman = binding.DiffieHellman;
+  var DiffieHellmanGroup = binding.DiffieHellmanGroup;
   var PBKDF2 = binding.PBKDF2;
   var randomBytes = binding.randomBytes;
   var pseudoRandomBytes = binding.pseudoRandomBytes;
@@ -173,6 +174,9 @@ exports.createDiffieHellman = function(size_or_key, enc) {
   }
 
 };
+exports.getDiffieHellman = function(group_name) {
+  return new DiffieHellmanGroup(group_name);
+};
 
 exports.pbkdf2 = PBKDF2;
 

src/node_crypto.cc

@@ -20,6 +20,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #include <node_crypto.h>
+#include <node_crypto_groups.h>
 #include <v8.h>
 
 #include <node.h>
@@ -3535,6 +3536,18 @@ class DiffieHellman : public ObjectWrap {
     NODE_SET_PROTOTYPE_METHOD(t, "setPrivateKey", SetPrivateKey);
 
     target->Set(String::NewSymbol("DiffieHellman"), t->GetFunction());
+
+    Local<FunctionTemplate> t2 = FunctionTemplate::New(DiffieHellmanGroup);
+    t2->InstanceTemplate()->SetInternalFieldCount(1);
+
+    NODE_SET_PROTOTYPE_METHOD(t2, "generateKeys", GenerateKeys);
+    NODE_SET_PROTOTYPE_METHOD(t2, "computeSecret", ComputeSecret);
+    NODE_SET_PROTOTYPE_METHOD(t2, "getPrime", GetPrime);
+    NODE_SET_PROTOTYPE_METHOD(t2, "getGenerator", GetGenerator);
+    NODE_SET_PROTOTYPE_METHOD(t2, "getPublicKey", GetPublicKey);
+    NODE_SET_PROTOTYPE_METHOD(t2, "getPrivateKey", GetPrivateKey);
+
+    target->Set(String::NewSymbol("DiffieHellmanGroup"), t2->GetFunction());
   }
 
   bool Init(int primeLength) {
@@ -3557,7 +3570,48 @@ class DiffieHellman : public ObjectWrap {
     return true;
   }
 
+  bool Init(unsigned char* p, int p_len, unsigned char* g, int g_len) {
+    dh = DH_new();
+    dh->p = BN_bin2bn(p, p_len, 0);
+    dh->g = BN_bin2bn(g, g_len, 0);
+    initialised_ = true;
+    return true;
+  }
+
  protected:
+  static Handle<Value> DiffieHellmanGroup(const Arguments& args) {
+    HandleScope scope;
+
+    DiffieHellman* diffieHellman = new DiffieHellman();
+
+    if (args.Length() != 1 || !args[0]->IsString()) {
+      return ThrowException(Exception::Error(
+          String::New("No group name given")));
+    }
+
+    String::Utf8Value group_name(args[0]->ToString());
+
+    modp_group* it = modp_groups;
+
+    while(it->name != NULL) {
+      if (!strcasecmp(*group_name, it->name))
+          break;
+      it++;
+    }
+
+    if (it->name != NULL) {
+      diffieHellman->Init(it->prime, it->prime_size,
+              it->gen, it->gen_size);
+    } else {
+      return ThrowException(Exception::Error(
+          String::New("Unknown group")));
+    }
+
+    diffieHellman->Wrap(args.This());
+
+    return args.This();
+  }
+
   static Handle<Value> New(const Arguments& args) {
     HandleScope scope;
 
@@ -4375,4 +4429,3 @@ void InitCrypto(Handle<Object> target) {
 }  // namespace node
 
 NODE_MODULE(node_crypto, node::crypto::InitCrypto)
-