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