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/*
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.
Written by Jack Lloyd (lloyd@randombit.net), June 3-5, 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> // for get_kdf
#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;
}
try
{
std::auto_ptr<RandomNumberGenerator> rng(
RandomNumberGenerator::make_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());
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);
std::auto_ptr<PK_Decryptor> decryptor(get_pk_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);
}
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