1 files changed, 173 insertions, 0 deletions
diff --git a/doc/examples/decrypt.cpp b/doc/examples/decrypt.cpp
new file mode 100644
index 000000000..ea510c5e9
--- /dev/null
+++ b/doc/examples/decrypt.cpp
@@ -0,0 +1,173 @@
+/*
+* (C) 2009 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+/*
+Decrypt files encrypted with the 'encrypt' example application.
+
+I'm being lazy and writing the output to stdout rather than stripping
+off the ".enc" suffix and writing it there. So all diagnostics go to
+stderr so there is no confusion.
+*/
+
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <cstring>
+#include <memory>
+
+#include <botan/botan.h>
+
+#if defined(BOTAN_HAS_COMPRESSOR_ZLIB)
+  #include <botan/zlib.h>
+#endif
+
+using namespace Botan;
+
+SecureVector<byte> b64_decode(const std::string&);
+
+int main(int argc, char* argv[])
+   {
+   if(argc < 2)
+      {
+      std::cout << "Usage: " << argv[0] << " [-p passphrase] file\n"
+                << "   -p : Use this passphrase to decrypt\n";
+      return 1;
+      }
+
+   Botan::LibraryInitializer init;
+
+   std::string filename, passphrase;
+
+   for(int j = 1; argv[j] != 0; j++)
+      {
+      if(std::strcmp(argv[j], "-p") == 0)
+         {
+         if(argv[j+1])
+            {
+            passphrase = argv[j+1];
+            j++;
+            }
+         else
+            {
+            std::cout << "No argument for -p option" << std::endl;
+            return 1;
+            }
+         }
+      else
+         {
+         if(filename != "")
+            {
+            std::cout << "You can only specify one file at a time\n";
+            return 1;
+            }
+         filename = argv[j];
+         }
+      }
+
+   if(passphrase == "")
+      {
+      std::cout << "You have to specify a passphrase!" << std::endl;
+      return 1;
+      }
+
+   std::ifstream in(filename.c_str());
+   if(!in)
+      {
+      std::cout << "ERROR: couldn't open " << filename << std::endl;
+      return 1;
+      }
+
+   std::string algo;
+
+   try {
+      std::string header, salt_str, mac_str;
+      std::getline(in, header);
+      std::getline(in, algo);
+      std::getline(in, salt_str);
+      std::getline(in, mac_str);
+
+      if(header != "-------- ENCRYPTED FILE --------")
+         {
+         std::cout << "ERROR: File is missing the usual header" << std::endl;
+         return 1;
+         }
+
+      const BlockCipher* cipher_proto = global_state().algorithm_factory().prototype_block_cipher(algo);
+
+      if(!cipher_proto)
+         {
+         std::cout << "Don't know about the block cipher \"" << algo << "\"\n";
+         return 1;
+         }
+
+      const u32bit key_len = cipher_proto->maximum_keylength();
+      const u32bit iv_len = cipher_proto->block_size();
+
+      std::auto_ptr<PBKDF> pbkdf(get_pbkdf("PBKDF2(SHA-1)"));
+
+      const u32bit PBKDF2_ITERATIONS = 8192;
+
+      SecureVector<byte> salt = b64_decode(salt_str);
+
+      SymmetricKey bc_key = pbkdf->derive_key(key_len, "BLK" + passphrase,
+                                              &salt[0], salt.size(),
+                                              PBKDF2_ITERATIONS);
+
+      InitializationVector iv = pbkdf->derive_key(iv_len, "IVL" + passphrase,
+                                                  &salt[0], salt.size(),
+                                                  PBKDF2_ITERATIONS);
+
+      SymmetricKey mac_key = pbkdf->derive_key(16, "MAC" + passphrase,
+                                               &salt[0], salt.size(),
+                                               PBKDF2_ITERATIONS);
+
+      Pipe pipe(new Base64_Decoder,
+                get_cipher(algo + "/CBC", bc_key, iv, DECRYPTION),
+#ifdef BOTAN_HAS_COMPRESSOR_ZLIB
+                new Zlib_Decompression,
+#endif
+                new Fork(
+                   0,
+                   new Chain(new MAC_Filter("HMAC(SHA-1)", mac_key),
+                             new Base64_Encoder)
+                   )
+         );
+
+      pipe.start_msg();
+      in >> 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";
+
+      std::cout << pipe.read_all_as_string(0);
+   }
+   catch(Algorithm_Not_Found)
+      {
+      std::cout << "Don't know about the block cipher \"" << algo << "\"\n";
+      return 1;
+      }
+   catch(Decoding_Error)
+      {
+      std::cout << "Bad passphrase or corrupt file\n";
+      return 1;
+      }
+   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();
+   }