int AsymmCipher::decrypt(const byte* cipher, int cipherlen, byte* out, int numbytes)
{
Integer m;
if (!decodeintarray(&m, 1, cipher, cipherlen))
{
return 0;
}
rsadecrypt(key, &m);
unsigned l = key[AsymmCipher::PRIV_P].ByteCount() + key[AsymmCipher::PRIV_Q].ByteCount() - 2;
if (m.ByteCount() > l)
{
l = m.ByteCount();
}
l -= numbytes;
while (numbytes--)
{
out[numbytes] = m.GetByte(l++);
}
return 1;
}
int AsymmCipher::decrypt(const byte* c, int cl, byte* out, int numbytes)
{
Integer m;
if (!decodeintarray(&m,1,c,cl)) return 0;
rsadecrypt(key,&m);
unsigned l = key[AsymmCipher::PRIV_D].ByteCount()-2;
if (m.ByteCount() > l) l = m.ByteCount();
l -= numbytes;
while (numbytes--) out[numbytes] = m.GetByte(l++);
return 1;
}
extern "C" int rsa_pss_sign(const char *key_file, const unsigned char *msg,
int len, unsigned char *sig_buf, unsigned char *modulus_buf)
{
try {
AutoSeededRandomPool rng;
FileSource file(key_file, true);
RSA::PrivateKey key;
ByteQueue bq;
// Load the key
file.TransferTo(bq);
bq.MessageEnd();
key.BERDecodePrivateKey(bq, false, bq.MaxRetrievable());
// Write the modulus
Integer mod = key.GetModulus();
// error check
if (mod.ByteCount() != RCM_RSA_MODULUS_SIZE)
throw std::length_error("incorrect rsa key modulus length");
for (int i = 0; i < mod.ByteCount(); i++)
modulus_buf[i] = mod.GetByte(i);
// Sign the message
RSASS<PSS, SHA256>::Signer signer(key);
size_t length = signer.MaxSignatureLength();
SecByteBlock signature(length);
length = signer.SignMessage(rng, msg, len, signature);
// Copy in reverse order
for (int i = 0; i < length; i++)
sig_buf[length - i - 1] = signature[i];
}
catch(const CryptoPP::Exception& e) {
cerr << e.what() << endl;
return 1;
}
catch(std::length_error& le) {
cerr << "Error: " << le.what() << endl;
return 1;
}
return 0;
}
