1 files changed, 129 insertions, 0 deletions
diff --git a/doc/examples/rsa_dec.cpp b/doc/examples/rsa_dec.cpp
new file mode 100644
index 000000000..81592328c
--- /dev/null
+++ b/doc/examples/rsa_dec.cpp
@@ -0,0 +1,129 @@
+/*
+* (C) 2002-2010 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+/*
+Decrypt an encrypted RSA private key. Then use that key to decrypt a
+message. This program can decrypt messages generated by rsa_enc, and uses the
+same key format as that generated by rsa_kgen.
+*/
+
+#include <iostream>
+#include <fstream>
+#include <string>
+#include <memory>
+
+#include <botan/botan.h>
+#include <botan/pubkey.h>
+#include <botan/rsa.h>
+using namespace Botan;
+
+SecureVector<byte> b64_decode(const std::string&);
+SymmetricKey derive_key(const std::string&, const SymmetricKey&, u32bit);
+
+const std::string SUFFIX = ".enc";
+
+int main(int argc, char* argv[])
+   {
+   if(argc != 4)
+      {
+      std::cout << "Usage: " << argv[0] << " keyfile messagefile passphrase"
+                << std::endl;
+      return 1;
+      }
+
+   Botan::LibraryInitializer init;
+
+   try
+      {
+      AutoSeeded_RNG rng;
+
+      std::auto_ptr<PKCS8_PrivateKey> key(
+         PKCS8::load_key(argv[1], rng, argv[3]));
+
+      RSA_PrivateKey* rsakey = dynamic_cast<RSA_PrivateKey*>(key.get());
+      if(!rsakey)
+         {
+         std::cout << "The loaded key is not a RSA key!\n";
+         return 1;
+         }
+
+      std::ifstream message(argv[2]);
+      if(!message)
+         {
+         std::cout << "Couldn't read the message file." << std::endl;
+         return 1;
+         }
+
+      std::string outfile(argv[2]);
+      outfile = outfile.replace(outfile.find(SUFFIX), SUFFIX.length(), "");
+
+      std::ofstream plaintext(outfile.c_str(), std::ios::binary);
+      if(!plaintext)
+         {
+         std::cout << "Couldn't write the plaintext to "
+                   << outfile << std::endl;
+         return 1;
+         }
+
+      std::string enc_masterkey_str;
+      std::getline(message, enc_masterkey_str);
+      std::string mac_str;
+      std::getline(message, mac_str);
+
+      SecureVector<byte> enc_masterkey = b64_decode(enc_masterkey_str);
+
+      PK_Decryptor_EME decryptor(*rsakey, "EME1(SHA-1)");
+
+      SecureVector<byte> masterkey = decryptor.decrypt(enc_masterkey);
+
+      SymmetricKey cast_key   = derive_key("CAST", masterkey, 16);
+      InitializationVector iv = derive_key("IV",   masterkey, 8);
+      SymmetricKey mac_key    = derive_key("MAC",  masterkey, 16);
+
+      Pipe pipe(new Base64_Decoder,
+                get_cipher("CAST-128/CBC/PKCS7", cast_key, iv, DECRYPTION),
+                new Fork(
+                   0,
+                   new Chain(
+                      new MAC_Filter("HMAC(SHA-1)", mac_key, 12),
+                      new Base64_Encoder
+                      )
+                   )
+         );
+
+      pipe.start_msg();
+      message >> pipe;
+      pipe.end_msg();
+
+      std::string our_mac = pipe.read_all_as_string(1);
+
+      if(our_mac != mac_str)
+         std::cout << "WARNING: MAC in message failed to verify\n";
+
+      plaintext << pipe.read_all_as_string(0);
+   }
+   catch(std::exception& e)
+      {
+      std::cout << "Exception caught: " << e.what() << std::endl;
+      return 1;
+      }
+   return 0;
+   }
+
+SecureVector<byte> b64_decode(const std::string& in)
+   {
+   Pipe pipe(new Base64_Decoder);
+   pipe.process_msg(in);
+   return pipe.read_all();
+   }
+
+SymmetricKey derive_key(const std::string& param,
+                        const SymmetricKey& masterkey,
+                        u32bit outputlength)
+   {
+   std::auto_ptr<KDF> kdf(get_kdf("KDF2(SHA-1)"));
+   return kdf->derive_key(outputlength, masterkey.bits_of(), param);
+   }