cms_algo.cpp

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/*
* CMS Algorithm Specific Code
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
 
#include <botan/cms_enc.h>
#include <botan/der_enc.h>
#include <botan/sha160.h>
#include <botan/cbc.h>
#include <botan/filters.h>
#include <botan/libstate.h>
 
#if defined(BOTAN_HAS_RC2)
  #include <botan/rc2.h>
#endif
 
namespace Botan {
 
namespace {
 
/*
* Wrap a key as specified in RFC 3217
*/
SecureVector<byte> do_rfc3217_wrap(RandomNumberGenerator& rng,
                                   const std::string& cipher_name,
                                   const SymmetricKey& kek,
                                   const SecureVector<byte>& input)
   {
   class Flip_Bytes : public Filter
      {
      public:
         std::string name() const { return "Fip_Bytes"; }
 
         void write(const byte data[], size_t length)
            {
            buf += std::make_pair(data, length);
            }
         void end_msg()
            {
            for(size_t j = 0; j != buf.size(); j++)
               send(buf[buf.size()-j-1]);
            buf.clear();
            }
 
         Flip_Bytes(const SecureVector<byte>& prefix) : buf(prefix) {}
      private:
         SecureVector<byte> buf;
      };
 
   Algorithm_Factory& af = global_state().algorithm_factory();
 
   const BlockCipher* cipher = af.prototype_block_cipher(cipher_name);
 
   if(!cipher || cipher->block_size() != 8)
      throw Encoding_Error("do_rfc3217_wrap: Bad cipher: " + cipher_name);
 
   Pipe icv(new Hash_Filter(new SHA_160, 8));
   icv.process_msg(input);
 
   InitializationVector iv(rng, 8);
   InitializationVector fixed("4ADDA22C79E82105");
 
   Pipe pipe(new CBC_Encryption(cipher->clone(), new Null_Padding, kek, iv),
             new Flip_Bytes(iv.bits_of()),
             new CBC_Encryption(cipher->clone(), new Null_Padding, kek, iv));
 
   pipe.start_msg();
   pipe.write(input);
   pipe.write(icv.read_all());
   pipe.end_msg();
   return pipe.read_all();
   }
 
}
 
/*
* Wrap a CEK with a KEK
*/
SecureVector<byte> CMS_Encoder::wrap_key(RandomNumberGenerator& rng,
                                         const std::string& cipher,
                                         const SymmetricKey& cek,
                                         const SymmetricKey& kek)
   {
#if defined(BOTAN_HAS_DES)
   if(cipher == "TripleDES")
      {
      SymmetricKey cek_parity = cek;
      cek_parity.set_odd_parity();
      return do_rfc3217_wrap(rng, cipher, kek, cek_parity.bits_of());
      }
#endif
 
#if defined(BOTAN_HAS_RC2) || defined(BOTAN_HAS_CAST)
   if(cipher == "RC2" || cipher == "CAST-128")
      {
      if(kek.length() != 16)
         throw Encoding_Error("CMS: 128-bit KEKs must be used with " + cipher);
 
      SecureVector<byte> lcekpad;
      lcekpad.push_back(static_cast<byte>(cek.length()));
      lcekpad += cek.bits_of();
      while(lcekpad.size() % 8)
         lcekpad.push_back(rng.next_byte());
      return do_rfc3217_wrap(rng, cipher, kek, lcekpad);
      }
#endif
 
   throw Invalid_Argument("CMS_Encoder::wrap: Unknown cipher " + cipher);
   }
 
/*
* Encode the parameters for an encryption algo
*/
SecureVector<byte> CMS_Encoder::encode_params(const std::string& cipher,
                                              const SymmetricKey& key,
                                              const InitializationVector& iv)
   {
   DER_Encoder encoder;
 
#if defined(BOTAN_HAS_RC2)
   if(cipher == "RC2")
      {
      encoder.start_cons(SEQUENCE).
         encode(static_cast<size_t>(RC2::EKB_code(8*key.length()))).
         encode(iv.bits_of(), OCTET_STRING).
      end_cons();
      return encoder.get_contents();
      }
#endif
 
   if(cipher == "CAST-128")
      {
      encoder.start_cons(SEQUENCE).
         encode(iv.bits_of(), OCTET_STRING).
         encode(8*key.length()).
      end_cons();
      }
   else
      encoder.encode(iv.bits_of(), OCTET_STRING);
 
   return encoder.get_contents();
   }
 
/*
* Generate a CEK or KEK for the cipher
*/
SymmetricKey CMS_Encoder::setup_key(RandomNumberGenerator& rng,
                                    const std::string& cipher)
   {
   size_t keysize = 0;
 
   if(cipher == "TripleDES") keysize = 24;
   if(cipher == "RC2")       keysize = 16;
   if(cipher == "CAST-128")  keysize = 16;
 
   if(keysize == 0)
      throw Invalid_Argument("CMS: Cannot encrypt with cipher " + cipher);
 
   SymmetricKey key(rng, keysize);
   if(cipher == "DES" || cipher == "TripleDES")
      key.set_odd_parity();
   return key;
   }
 
}