Update DH example for PK changes

1 files changed, 29 insertions, 14 deletions

diff --git a/doc/examples/dh.cpp b/doc/examples/dh.cpp
index 4c6961234..23d6c3952 100644
--- a/doc/examples/dh.cpp
+++ b/doc/examples/dh.cpp
@@ -1,12 +1,12 @@
 /*
-* (C) 2009 Jack Lloyd
+* (C) 2009-2010 Jack Lloyd
 *
 * Distributed under the terms of the Botan license
 */
 
 #include <botan/botan.h>
 #include <botan/dh.h>
-#include <botan/rng.h>
+#include <botan/pubkey.h>
 using namespace Botan;
 
 #include <iostream>
@@ -15,25 +15,40 @@ using namespace Botan;
 int main()
    {
    Botan::LibraryInitializer init;
-   
+
    try
       {
       AutoSeeded_RNG rng;
 
+      // Alice and Bob agree on a DH domain to use
+      DL_Group shared_domain("modp/ietf/1024");
+
       // Alice creates a DH key and sends (the public part) to Bob
-      DH_PrivateKey private_a(rng, DL_Group("modp/ietf/1024"));
-      DH_PublicKey public_a = private_a; // Bob gets this
+      DH_PrivateKey private_a(rng, shared_domain);
+
+      // Alice sends to Bob her public key:
+      MemoryVector<byte> public_a = private_a.public_value();
 
       // Bob creates a key with a matching group
-      DH_PrivateKey private_b(rng, public_a.get_domain());
+      DH_PrivateKey private_b(rng, shared_domain);
+
+      // Bob sends his public key to Alice
+      MemoryVector<byte> public_b = private_b.public_value();
+
+      PK_Key_Agreement ka1(private_a, get_kdf("KDF2(SHA-1)"));
+      PK_Key_Agreement ka2(private_b, get_kdf("KDF2(SHA-1)"));
 
-      // Bob sends the key back to Alice
-      DH_PublicKey public_b = private_b; // Alice gets this
+      /*
+      * Preferably, include some salt or parameter that binds this key
+      * generation to the current session (for instance a session
+      * identifier, if guaranteed unique, would be a good choice).  Or
+      * anything else that both sides can agree on that will never
+      * repeat.
+      */
+      const std::string ka_salt = "alice and bob agree on a key";
 
-      // Both of them create a key using their private key and the other's
-      // public key
-      SymmetricKey alice_key = private_a.derive_key(public_b);
-      SymmetricKey bob_key = private_b.derive_key(public_a);
+      SymmetricKey alice_key = ka1.derive_key(32, public_b, ka_salt);
+      SymmetricKey bob_key = ka2.derive_key(32, public_a, ka_salt);
 
       if(alice_key == bob_key)
          {
@@ -42,12 +57,12 @@ int main()
          }
       else
          {
-         std::cout << "The two keys didn't match!\n";
+         std::cout << "The two keys didn't match! Hmmm...\n";
          std::cout << "Alice's key was: " << alice_key.as_string() << "\n";
          std::cout << "Bob's key was: " << bob_key.as_string() << "\n";
          }
 
-      // Now Alice and Bob hash the key and use it for something
+      // Now use the shared key for encryption or MACing or whatever
    }
    catch(std::exception& e)
       {