I'm trying to sign some bytes in C# thanks to the class RSACryptoServiceProvider and to verify it in C++ with the Crypto++ library. Despite all my attempts, the validation fail although I'm sure of my key and signature.
In C# I sign as follow :
var message = "hello";
var bytes = System.Text.Encoding.UTF8.GetBytes(message);
byte[] signedHash;
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
// Import the key information.
rsa.ImportParameters(privateKey);
// Sign the data, using SHA256 as the hashing algorithm
signedHash = rsa.SignData(bytes, CryptoConfig.MapNameToOID("SHA256"));
}
My keys are generated as follow :
CspParameters parameters = new CspParameters();
parameters.KeyNumber = (int)KeyNumber.Signature;
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(1024, parameters))
{
privateKeyInfo = rsa.ExportParameters(true);
publicKeyInfo = rsa.ExportParameters(false);
}
In C++, I create the public key and try to verify it as follow :
RSA::PublicKey publicKey;
byte signature[128];
signature[0]= 150;
//....fill up to 127 , corresponds to "signedHash" variable from c# code
signature[127]= 89;
string simplemessage = "hello";
string modulus = "0Z8GUI/rxlXanCCjkiP+c9HyvdlOibst2YD5XmZk4F86aLr7LbLtI7FMnr6rcQZa6RXkAykb5MIbasmkOmkLzSjhdTThnaZyuKBOBoybYB5mDecF2VMXfUIryEBFn4i6y58qhy0BnDnIhucdNXX0px10HL3uYzR2KBTC0lSFFmE=";
string exponent = "AQAB";
char modulusCharred[1024];
strncpy_s(modulusCharred, base64ToHex(modulus).c_str(), sizeof(modulusCharred));
modulusCharred[sizeof(modulusCharred) - 1] = 0;
char exponentCharred[1024];
strncpy_s(exponentCharred, base64ToHex(exponent).c_str(), sizeof(exponentCharred));
exponentCharred[sizeof(exponentCharred) - 1] = 0;
Integer n(modulusCharred);
Integer e(exponentCharred);
publicKey.Initialize(n, e);
AutoSeededRandomPool rnd;
if(!publicKey.Validate(rnd, 3))
throw runtime_error("Rsa public key validation failed"); // no error is thrown
RSASS<PSS, SHA256>::Verifier verifier(publicKey);
bool result = verifier.VerifyMessage((const byte*)simplemessage.c_str(),simplemessage.length(), signature,128);
if(true == result) {
cout << "Signature on message verified" << endl;
} else {
cout << "Message verification failed" << endl; // always fail...
}
Modulus and exponent are copy/past from the xml obtained in c# using rsa.ToXmlString(false). The function base64toHex is given by (found on another SO post):
std::string base64ToHex(std::string base64String)
{
std::string decodedString, finalString;
CryptoPP::StringSource river(base64String, true,
new CryptoPP::Base64Decoder(new CryptoPP::StringSink(decodedString)));
CryptoPP::StringSource stream(decodedString, true,
new CryptoPP::HexEncoder(new CryptoPP::StringSink(finalString)));
finalString.erase(std::remove(finalString.begin(), finalString.end(), '\n'), finalString.end());
return finalString;
}
I do not want to use any external files, only bytes (or string) variable. Also I'm not sure of the way I define my verifier : RSASS<PSS, SHA256>::Verifier.
Could you help me with this ?
This answer is for both crypto++ and the windows API.
After a lot of trials/errors I finally succeed, the problem came from the way I built the crypto++ rsa keys ( Integer type : modulus and exponent).
I have created a new function GetIntegerFromBase64String that convert directly the modulus and exponent we obtain from the xml output of rsa.ToXmlString to the Integer type to initialize key in cryptopp.
Full crypto++ Example :
string signature_64str = "G+PQaArLByTNYF5c5BZo2X3Guf1AplyJyik6NXCJmXnZ7CD5AC/OKq+Iswcv8GboUVsMTvl8G+lCa9Od0DfytnDui7kA/c1qtH7BZzF55yA5Yf9DGOfD1RHOl3OkRvpK/mF+Sf8nJwgxsg51C3pk/oBFjA450q2zq8HfFG2KJcs=";
string modulus_64str = "0Z8GUI/rxlXanCCjkiP+c9HyvdlOibst2YD5XmZk4F86aLr7LbLtI7FMnr6rcQZa6RXkAykb5MIbasmkOmkLzSjhdTThnaZyuKBOBoybYB5mDecF2VMXfUIryEBFn4i6y58qhy0BnDnIhucdNXX0px10HL3uYzR2KBTC0lSFFmE=";
string exponent_64str = "AQAB";
Integer mod_integer = GetIntegerFromBase64String(modulus_64str);
Integer pub_integer = GetIntegerFromBase64String(exponent_64str);
InvertibleRSAFunction param;
param.SetModulus(mod_integer);
param.SetPublicExponent(pub_integer);
RSA::PublicKey pubkey(param);
string decoded_sig = DecodeBase64String(signature_64str);
if(!pubkey.Validate(rnd, 3))
cout << "Rsa public key validation failed" << endl;
else
cout << " key validation success"<< endl;
RSASS<PKCS1v15, SHA512>::Verifier verif(pubkey);
bool res = verif.VerifyMessage( reinterpret_cast<const byte*>(message.c_str()), message.length(), reinterpret_cast<const byte*>(decoded_sig.c_str()), decoded_sig.length() );
if( res ) {
cout << "Signature on message verified " << endl;
} else {
cout << "Message verification failed " << endl;
}
with :
string DecodeBase64String(string encoded )
{
string decoded;
Base64Decoder decoder;
decoder.Attach( new StringSink( decoded ) );
decoder.Put( (byte*)encoded.data(), encoded.size() );
decoder.MessageEnd();
return decoded;
}
Integer GetIntegerFromBase64String(string encoded)
{
string decoded = DecodeBase64String(encoded);
Integer integer( (byte*)decoded.c_str(),decoded.length());
return integer;
}
Additionaly, I have reproduced the verification with the windows API, for this case I do not use the xml key but directly the blob key (encoded in 64 bit) that I obtain from rsa.ExportCspBlob(false)
Full windows api example :
In c# I got the CspBlob as follow :
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.ImportParameters(privateKey);
var cspBlob = rsa.ExportCspBlob(false);
var cspBlobBase_64str = Convert.ToBase64String(cspBlob);// <---- HERE
Then in c++, I load the blob and verify the signature as follow :
#include <windows.h>
...
string ErrorMessage;
string signature_64str = "G+PQaArLByTNYF5c5BZo2X3Guf1AplyJyik6NXCJmXnZ7CD5AC/OKq+Iswcv8GboUVsMTvl8G+lCa9Od0DfytnDui7kA/c1qtH7BZzF55yA5Yf9DGOfD1RHOl3OkRvpK/mF+Sf8nJwgxsg51C3pk/oBFjA450q2zq8HfFG2KJcs=";
string public_key_blob_64_bit_encoded = "BgIAAACkAABSU0ExAAQAAAEAAQBhFoVU0sIUKHY0Y+69HHQdp/R1NR3nhsg5nAEthyqfy7qIn0VAyCtCfRdT2QXnDWYeYJuMBk6guHKmneE0deEozQtpOqTJahvC5BspA+QV6VoGcau+nkyxI+2yLfu6aDpf4GRmXvmA2S27iU7ZvfLRc/4jkqMgnNpVxuuPUAaf0Q==";
string message = "hello";
if( RSA_VerifySignature(message, signature_64str, public_key_blob_64_bit_encoded, ErrorMessage))
{
cout << "OK : Signature on message verified " << endl;
}
else
{
cout << "Message verification failed, Error : " << ErrorMessage << endl;
}
with :
bool RSA_VerifySignature(string message, string signature_64BitEncoded, string publickeyBlob_64BitEncoded, string &ErrorMessage)
{
const size_t LENGHT_SIGNATURE = 128; // 128 bytes == 1024 RSA Key bits
const size_t LENGHT_BLOB_PUBLIC_KEY = 148; // 148 bytes
bool isSigOk = false;
HCRYPTHASH hash;
byte decoded_Blob[LENGHT_BLOB_PUBLIC_KEY] ;
size_t size_pubkey = Base64Decode(publickeyBlob_64BitEncoded, decoded_Blob, LENGHT_BLOB_PUBLIC_KEY);
byte decoded_signature[LENGHT_SIGNATURE] ;
size_t size_signature =Base64Decode(signature_64BitEncoded, decoded_signature, LENGHT_SIGNATURE);
//reverse bytes
byte reverse_decoded_signature[LENGHT_SIGNATURE];
for(int i=0;i<sizeof(reverse_decoded_signature);i++)
reverse_decoded_signature[i] = decoded_signature[LENGHT_SIGNATURE-i-1];
HCRYPTPROV cryptProvider;
// Get a handle to the PROV_RSA_AES (for CALG_SHA_512).
if (!CryptAcquireContext(&cryptProvider, 0, 0, PROV_RSA_AES, CRYPT_VERIFYCONTEXT)){
ErrorMessage = "Failure to acquire context";
goto Exit;
}
HCRYPTKEY publicKeyc;
// convert the blob to the public key
if(!CryptImportKey(cryptProvider, decoded_Blob, LENGHT_BLOB_PUBLIC_KEY, 0, 0, &publicKeyc)){
ErrorMessage = "Failure to import key";
goto Exit;
}
// create the hash object
if(!CryptCreateHash(cryptProvider, CALG_SHA_512 , 0, 0, &hash)){
ErrorMessage = "Failure to creat Hash" ;
goto Exit;
}
//hash the message
if(!CryptHashData(hash, (byte*) message.c_str(), message.length(), 0)){
ErrorMessage = "Failure to Hash Data" ;
goto Exit;
}
isSigOk = CryptVerifySignature(hash, reverse_decoded_signature, sizeof(reverse_decoded_signature), publicKeyc, nullptr, 0);
if(!isSigOk) ErrorMessage = "Invalid Signature" ;
Exit:
// After processing, hHash and cryptProvider must be released.
if(hash)
CryptDestroyHash(hash);
if(cryptProvider)
CryptReleaseContext(cryptProvider,0);
return isSigOk;
}
where Base64Decode comes from this SO answer.
ps: note that I have switched to SHA512 in this answer .