An example of using PEM encoded RSA private keys with CAPI

main.c

/*
* An example of using PEM encoded RSA private keys with CAPI
*    - Modified on March 29th 2014 to show how to use PEM encoded RSA public key
*
* Copyright (c) 2012 Mounir IDRASSI <mounir.idrassi@idrix.fr>. All rights reserved.
*
* This program is distributed in the hope that it will be useful, 
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
* or FITNESS FOR A PARTICULAR PURPOSE.
* 
*/

#ifndef _WIN32_WINNT         
#define _WIN32_WINNT 0x0501
#endif

#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>

const char* szPemPrivKey = 
    "-----BEGIN RSA PRIVATE KEY-----"
    "MIICXAIBAAKBgQCf6YAJOSBYPve1jpYDzq+w++8YVoATI/YCi/RKZaQk+l2ZfoUQ"
    "g0qrYrfkzeoOa/qd5VLjTTvHEgwXnlDXMfo+vSgxosUxDOZXMTBqJGOViv5K2QBv"
    "k8A1wi4k8tuo/7OWya29HvcfavUk3YXaV2YFe8V6ssaZjNcVWmDdjqNkXwIDAQAB"
    "AoGALrd+ijNAOcebglT3ioE1XpUbUpbir7TPyAqvAZUUESF7er41jY9tnwgmBRgL"
    "Cs+M1dgLERCdKBkjozrDDzswifFQmq6PrmYrBkFFqCoLJwepSYdWnK1gbZ/d43rR"
    "2sXzSGZngscx0CxO7KZ7xUkwENGd3+lKXV7J6/vgzJ4XnkECQQDTP6zWKT7YDckk"
    "We04hbhHyBuNOW068NgUUvoZdBewerR74MJx6nz28Tp+DeNvc0EveiQxsEnbV8u+"
    "NRkX5y0xAkEAwcnEAGBn5kJd6SpU0ALA9XEpUv7tHTAGQYgCRbfTT59hhOq6I22A"
    "ivjOCNG9c6E7EB2kcPVGuCpYUhy7XBIGjwJAK5lavKCqncDKoLwGn8HJdNcyCIWv"
    "q5iFoDw37gTt1ricg2yx9PzmabkDz3xiUmBBNeFJkw/FToXiQRGIakyGIQJAJIem"
    "PPPvYgZssYFbT4LVYO8d/Rk1FWVyKHQ9CWtnmADRXz7oK7l+m7PfEuaGsf9YpOcR"
    "koGJ/TluQLxNzUNQnQJBAImwr/yYFenIx3HQ6UX/fCt6qpGDv0VfOLyR64MNeegx"
    "o7DhNxHbFkIGzk4lKhMKcHKDrawZbdJtS9ie2geSwVQ="
    "-----END RSA PRIVATE KEY-----";

const char* szPemPubKey = 
	"-----BEGIN RSA PUBLIC KEY-----"
	"MIGJAoGBAJ/pgAk5IFg+97WOlgPOr7D77xhWgBMj9gKL9EplpCT6XZl+hRCDSqti"
	"t+TN6g5r+p3lUuNNO8cSDBeeUNcx+j69KDGixTEM5lcxMGokY5WK/krZAG+TwDXC"
	"LiTy26j/s5bJrb0e9x9q9STdhdpXZgV7xXqyxpmM1xVaYN2Oo2RfAgMBAAE="
	"-----END RSA PUBLIC KEY-----";

const char* szDataToSign = "Data to be signed by the private key";

int main(int argc, char* argv[])
{  
    DWORD dwBufferLen = 0, cbKeyBlob = 0, cbSignature = 0,i;
    LPBYTE pbBuffer = NULL, pbKeyBlob = NULL, pbSignature = NULL;
    HCRYPTPROV hProv = NULL;
    HCRYPTKEY hKey = NULL;
    HCRYPTHASH hHash = NULL;

    if (!CryptStringToBinaryA(szPemPrivKey, 0, CRYPT_STRING_BASE64HEADER, NULL, &dwBufferLen, NULL, NULL))
    {
        printf("Failed to convert BASE64 private key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    pbBuffer = (LPBYTE) LocalAlloc(0, dwBufferLen);
    if (!CryptStringToBinaryA(szPemPrivKey, 0, CRYPT_STRING_BASE64HEADER, pbBuffer, &dwBufferLen, NULL, NULL))
    {
        printf("Failed to convert BASE64 private key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    if (!CryptDecodeObjectEx(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, PKCS_RSA_PRIVATE_KEY, pbBuffer, dwBufferLen, 0, NULL, NULL, &cbKeyBlob))
    {
        printf("Failed to parse private key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }       

    pbKeyBlob = (LPBYTE) LocalAlloc(0, cbKeyBlob);
    if (!CryptDecodeObjectEx(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, PKCS_RSA_PRIVATE_KEY, pbBuffer, dwBufferLen, 0, NULL, pbKeyBlob, &cbKeyBlob))
    {
        printf("Failed to parse private key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    // Create a temporary and volatile CSP context in order to import
    // the key and use for signing
    if (!CryptAcquireContext(&hProv, NULL, MS_ENHANCED_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
    {
        printf("CryptAcquireContext failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    if (!CryptImportKey(hProv, pbKeyBlob, cbKeyBlob, NULL, 0, &hKey))
    {
        printf("CryptImportKey for private key failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    // Hash the data
    if (!CryptCreateHash(hProv, CALG_SHA1, NULL, 0, &hHash))
    {
        printf("CryptCreateHash failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    if (!CryptHashData(hHash, (LPCBYTE) szDataToSign, strlen(szDataToSign), 0))
    {
        printf("CryptHashData failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    // Sign the hash using our imported key
    if (!CryptSignHash(hHash, AT_KEYEXCHANGE, NULL, 0, NULL, &cbSignature))
    {
        printf("CryptSignHash failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    pbSignature = (LPBYTE) LocalAlloc(0, cbSignature);
    if (!CryptSignHash(hHash, AT_KEYEXCHANGE, NULL, 0, pbSignature, &cbSignature))
    {
        printf("CryptSignHash failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    printf("Signature = ");
    for (i = 0; i < cbSignature; i++)
    {
        printf("%.2X", pbSignature[i]);
    }
    printf("\n\n");

	/***************************************************
	 * Import the public key and verify the signature
	 ***************************************************/

    if (!CryptStringToBinaryA(szPemPubKey, 0, CRYPT_STRING_BASE64HEADER, NULL, &dwBufferLen, NULL, NULL))
    {
        printf("Failed to convert BASE64 public key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

	LocalFree(pbBuffer);
    pbBuffer = (LPBYTE) LocalAlloc(0, dwBufferLen);
    if (!CryptStringToBinaryA(szPemPubKey, 0, CRYPT_STRING_BASE64HEADER, pbBuffer, &dwBufferLen, NULL, NULL))
    {
        printf("Failed to convert BASE64 public key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    if (!CryptDecodeObjectEx(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, RSA_CSP_PUBLICKEYBLOB, pbBuffer, dwBufferLen, 0, NULL, NULL, &cbKeyBlob))
    {
        printf("Failed to parse public key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }   

	LocalFree(pbKeyBlob);
    pbKeyBlob = (LPBYTE) LocalAlloc(0, cbKeyBlob);
    if (!CryptDecodeObjectEx(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, RSA_CSP_PUBLICKEYBLOB, pbBuffer, dwBufferLen, 0, NULL, pbKeyBlob, &cbKeyBlob))
    {
        printf("Failed to parse public key. Error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    CryptDestroyHash(hHash);
    CryptDestroyKey(hKey);
    CryptReleaseContext(hProv, 0);

    if (!CryptAcquireContext(&hProv, NULL, MS_ENHANCED_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
    {
        printf("CryptAcquireContext failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    if (!CryptImportKey(hProv, pbKeyBlob, cbKeyBlob, NULL, 0, &hKey))
    {
        printf("CryptImportKey for public key failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    // Hash the data
    if (!CryptCreateHash(hProv, CALG_SHA1, NULL, 0, &hHash))
    {
        printf("CryptCreateHash failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    if (!CryptHashData(hHash, (LPCBYTE) szDataToSign, strlen(szDataToSign), 0))
    {
        printf("CryptHashData failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }

    // Sign the hash using our imported key
	if (!CryptVerifySignature(hHash, pbSignature, cbSignature, hKey, NULL, 0))
    {
        printf("Signature verification failed with error 0x%.8X\n", GetLastError());
        goto main_exit;
    }
	
	printf("Signature verified successfully!\n\n");

main_exit:
    if (pbBuffer) LocalFree(pbBuffer);
    if (pbKeyBlob) LocalFree(pbKeyBlob);
    if (pbSignature) LocalFree(pbSignature);
    if (hHash) CryptDestroyHash(hHash);
    if (hKey) CryptDestroyKey(hKey);
    if (hProv) CryptReleaseContext(hProv, 0);

    return 0;
}