1 files changed, 149 insertions, 0 deletions
diff --git a/doc/examples/rsa_enc.cpp b/doc/examples/rsa_enc.cpp
new file mode 100644
index 000000000..49b62989c
--- /dev/null
+++ b/doc/examples/rsa_enc.cpp
@@ -0,0 +1,149 @@
+/*
+  Grab an RSA public key from the file given as an argument, grab a message
+  from another file, and encrypt the message.
+
+  Algorithms used:
+    RSA with EME1(SHA-1) padding to encrypt the master key
+    CAST-128 in CBC mode with PKCS#7 padding to encrypt the message.
+    HMAC with SHA-1 is used to authenticate the message
+
+  The keys+IV used are derived from the master key (the thing that's encrypted
+  with RSA) using KDF2(SHA-1). The 3 outputs of KDF2 are parameterized by P,
+  where P is "CAST", "IV" or "MAC", in order to make each key/IV unique.
+
+  The format is:
+     1) First line is the master key, encrypted with the recipients public key
+        using EME1(SHA-1), and then base64 encoded.
+     2) Second line is the first 96 bits (12 bytes) of the HMAC(SHA-1) of
+        the _plaintext_
+     3) Following lines are base64 encoded ciphertext (CAST-128 as described),
+        each broken after ~72 characters.
+
+Written by Jack Lloyd ([email protected]), June 3, 2002
+   Updated to use KDF2, September 8, 2002
+   Updated to read X.509 keys, October 21, 2002
+
+This file is in the public domain
+*/
+
+#include <iostream>
+#include <fstream>
+#include <string>
+#include <memory>
+
+#include <botan/botan.h>
+#include <botan/look_pk.h>
+#include <botan/rsa.h>
+using namespace Botan;
+
+std::string b64_encode(const SecureVector<byte>&);
+SymmetricKey derive_key(const std::string&, const SymmetricKey&, u32bit);
+
+int main(int argc, char* argv[])
+   {
+   if(argc != 3)
+      {
+      std::cout << "Usage: " << argv[0] << " keyfile messagefile" << std::endl;
+      return 1;
+      }
+
+   std::ifstream message(argv[2]);
+   if(!message)
+      {
+      std::cout << "Couldn't read the message file." << std::endl;
+      return 1;
+      }
+
+   std::string output_name(argv[2]);
+   output_name += ".enc";
+   std::ofstream ciphertext(output_name.c_str());
+   if(!ciphertext)
+      {
+      std::cout << "Couldn't write the ciphertext to " << output_name
+           << std::endl;
+      return 1;
+      }
+
+   try {
+
+      LibraryInitializer init;
+
+      std::auto_ptr<X509_PublicKey> key(X509::load_key(argv[1]));
+      RSA_PublicKey* rsakey = dynamic_cast<RSA_PublicKey*>(key.get());
+      if(!rsakey)
+         {
+         std::cout << "The loaded key is not a RSA key!\n";
+         return 1;
+         }
+
+      std::auto_ptr<PK_Encryptor> encryptor(get_pk_encryptor(*rsakey,
+                                                             "EME1(SHA-1)"));
+
+      /* Generate the master key (the other keys are derived from this)
+
+         Basically, make the key as large as can be encrypted by this key, up
+         to a limit of 256 bits. For 512 bit keys, the master key will be >160
+         bits. A >600 bit key will use the full 256 bit master key.
+
+         In theory, this is not enough, because we derive 16+16+8=40 bytes of
+         secrets (if you include the IV) using the master key, so they are not
+         statistically indepedent. Practically speaking I don't think this is
+         a problem.
+      */
+      SymmetricKey masterkey(std::min(32U, encryptor->maximum_input_size()));
+
+      SymmetricKey cast_key = derive_key("CAST", masterkey, 16);
+      SymmetricKey mac_key  = derive_key("MAC",  masterkey, 16);
+      SymmetricKey iv       = derive_key("IV",   masterkey, 8);
+
+      SecureVector<byte> encrypted_key =
+         encryptor->encrypt(masterkey.bits_of());
+
+      ciphertext << b64_encode(encrypted_key) << std::endl;
+
+      Pipe pipe(new Fork(
+                   new Chain(
+                      get_cipher("CAST-128/CBC/PKCS7", cast_key, iv,
+                                 ENCRYPTION),
+                      new Base64_Encoder(true) // true == do linebreaking
+                      ),
+                   new Chain(
+                      new MAC_Filter("HMAC(SHA-1)", mac_key, 12),
+                      new Base64_Encoder
+                      )
+                   )
+         );
+
+      pipe.start_msg();
+      message >> pipe;
+      pipe.end_msg();
+
+      /* Write the MAC as the second line. That way we can pull it off right
+         from the start, and feed the rest of the file right into a pipe on the
+         decrypting end.
+      */
+
+      ciphertext << pipe.read_all_as_string(1) << std::endl;
+      ciphertext << pipe.read_all_as_string(0);
+   }
+   catch(std::exception& e)
+      {
+      std::cout << "Exception: " << e.what() << std::endl;
+      }
+   return 0;
+   }
+
+std::string b64_encode(const SecureVector<byte>& in)
+   {
+   Pipe pipe(new Base64_Encoder);
+   pipe.process_msg(in);
+   return pipe.read_all_as_string();
+   }
+
+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);
+   }