I'm trying to use RSA keys generated by openssl in Crypto++ encryption
and decryption routines. I realise that openssl outputs the keys in PEM
format and Crypto++ uses DER format.
I thought PEM format "consists of the DER format base64 encoded with
additional header and footer lines.", Openssl manual
(http://www.openssl.org/docs/apps/rsa.html), so I thought that if I just
got rid of the header and footer lines I'd have a DER Base64 encoded
file that I could feed into the Crypto++ routines as the keys.
When I try this and try encoding data, using the public key, it appears
to produce an encoded message, ie it all completes successfully. But
when I try and decode the message, private key, I get a "BER decode
error" exception.
The routines I have work fine so long as the keys are generated with the
crypto++ functions.
If anyone out there can offer advice or point me in the right direction
it would be much appreciated.
The openssl command lines I'm using are:
openssl genrsa -out privkey.asc 2048
openssl rsa -in privkey.asc -pubout -out pubkey.asc
I seperated my code into 3 programs to help with debugging. The crypto
programs that comprise my tests are (stolen right out of the test
program :-):
Key generation:
---------------
void GenerateRSAKey(unsigned int keyLength,
const char *privFilename,
const char *pubFilename,
const char *seed)
{
RandomPool randPool;
randPool.Put((byte *)seed, strlen(seed));
RSAES_OAEP_SHA_Decryptor priv(randPool, keyLength);
Base64Encoder privFile(new FileSink(privFilename));
priv.DEREncode(privFile);
privFile.MessageEnd();
RSAES_OAEP_SHA_Encryptor pub(priv);
Base64Encoder pubFile(new FileSink(pubFilename));
pub.DEREncode(pubFile);
pubFile.MessageEnd();
}
int main(int argc, char** argv)
{
GenerateRSAKey( 2048, "privkey.asc", "pubkey.asc", "A random string
or 345%");
}
Encrypt the message:
--------------------
string RSAEncryptString(const char *pubFilename,
const char *seed,
const char *message)
{
FileSource pubFile(pubFilename, true, new Base64Decoder);
RSAES_OAEP_SHA_Encryptor pub(pubFile);
RandomPool randPool;
randPool.Put((byte *)seed, strlen(seed));
string result;
StringSource(message, true, new PK_EncryptorFilter(randPool, pub,
new HexEncoder(new StringSink(result))));
Base64Encoder(new StringSink(result))));
return result;
}
int main(int argc, char** argv)
{
string encStr;
FILE *op;
try {
encStr = RSAEncryptString("pubkey.asc", "dribbleSeed23", "A few
good men, 175 to be exact\n");
op = fopen("rsaMsg.txt", "w");
fprintf(op, "%s\n", encStr.c_str());
fclose(op);
}
catch (std::exception const& e)
{
// This clause will also catch CryptoPP::Exception as well as
// all derived exception classes
cout << "std::exception caught:" << endl
<< e.what() << endl;
}
}
Decrypt the message:
--------------------
string RSADecryptString(const char *privFilename,
const char *ciphertext)
{
FileSource privFile(privFilename, true, new Base64Decoder);
RSAES_OAEP_SHA_Decryptor priv(privFile);
RandomPool randomPool;
string result;
StringSource(ciphertext,
true,
StringSink(result))));
new HexDecoder(new PK_DecryptorFilter(randomPool, priv,
new StringSink(result))));
return result;
}
int main(int argc, char** argv)
{
string decrStr;
FILE *ip;
char ipStr[3000];
ip = fopen("rsaMsg.txt", "r");
fgets(ipStr, 3000, ip);
// get rid of the \n at the end of the line
ipStr[strlen(ipStr) - 1] = '\0';
try {
decrStr = RSADecryptString("privkey.asc", ipStr);
printf("%s\n", decrStr.c_str());
fclose(ip);
}
catch (std::exception const& e)
{
// This clause will also catch CryptoPP::Exception as well as
// all derived exception classes, except for SpecificException
// which has already been caught above.
cout << "std::exception caught:" << endl
<< e.what() << endl;
}
}
