S Meaden S Meaden - 10 months ago 80
C++ Question

Can Microsoft Cryptographic API allow creation of ECDSA keys from a stream of bytes?

So I am pondering which cryptographic C++ library to use (I already figured out how to do equivalent in C#) for the verification of a licence file signed hash.

Reading the Microsoft documentation for CNG it seems that it is not possible to generate an ECDSA key in code from a stream of bytes despite this being possible for a RSA key (I think, not 100% sure).

Because I wanted in code byte stream generation, I looked at crypto++ and I managed to get the test suite compiled but cryptolib.lib is an outsize 90 megabytes and I am facing a slew of link errors simply trying to do something basic. So I am less keen in crypto++ now.

So I want to turn back to using something shipped by Microsoft in its desktop Windows OS but I am back to my original problem of no in code bytestream generated keys.

Can an expert confirm that this really isn't possible? Also, can they suggest alternative, I am happy to fall back to RSA with a long (2048?) key.

The following code compiles and runs for me. It can be found at the MSDN article -
Signing Data with CNG
. I was wondering if it could be adapted. Does this code (a) create an ECDSA key on the fly (b) sign a hash (c) save key to a certificate store (d) retrieve the key and verify signed hash. If so then I guess it's demo code. What I would need is an example of a hard coded ECDSA key not one created on the fly.

// CngECDSA.cpp : Defines the entry point for the console application.
// Based on https://msdn.microsoft.com/en-us/library/windows/desktop/aa376304(v=vs.85).aspx

#include "stdafx.h"

#include <Windows.h>
#include <stdint.h>
#include <Bcrypt.h>
#include <ncrypt.h>

#pragma comment(lib, "bcrypt")
#pragma comment(lib, "ncrypt")


#define NT_SUCCESS(Status) (((NTSTATUS)(Status)) >= 0)
#define STATUS_UNSUCCESSFUL ((NTSTATUS)0xC0000001L)

static const BYTE rgbMsg[] =
{
0x04, 0x87, 0xec, 0x66, 0xa8, 0xbf, 0x17, 0xa6,
0xe3, 0x62, 0x6f, 0x1a, 0x55, 0xe2, 0xaf, 0x5e,
0xbc, 0x54, 0xa4, 0xdc, 0x68, 0x19, 0x3e, 0x94,
};

BYTE value[] =
{ 0x02,0x00,0x00,0x00 };

void __cdecl wmain(
int argc,
__in_ecount(argc) LPWSTR *wargv)
{
NCRYPT_PROV_HANDLE hProv = NULL;
NCRYPT_KEY_HANDLE hKey = NULL;
BCRYPT_KEY_HANDLE hTmpKey = NULL;
SECURITY_STATUS secStatus = ERROR_SUCCESS;
BCRYPT_ALG_HANDLE hHashAlg = NULL,
hSignAlg = NULL;
BCRYPT_HASH_HANDLE hHash = NULL;
NTSTATUS status = STATUS_UNSUCCESSFUL;
DWORD cbData = 0,
cbHash = 0,
cbBlob = 0,
cbSignature = 0,
cbHashObject = 0;
PBYTE pbHashObject = NULL;
PBYTE pbHash = NULL,
pbBlob = NULL,
pbSignature = NULL;

UNREFERENCED_PARAMETER(argc);
UNREFERENCED_PARAMETER(wargv);

//open an algorithm handle
if (!NT_SUCCESS(status = BCryptOpenAlgorithmProvider(
&hHashAlg,
BCRYPT_SHA1_ALGORITHM,
NULL,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptOpenAlgorithmProvider\n", status);
goto Cleanup;
}

if (!NT_SUCCESS(status = BCryptOpenAlgorithmProvider(
&hSignAlg,
BCRYPT_ECDSA_P256_ALGORITHM,
NULL,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptOpenAlgorithmProvider\n", status);
goto Cleanup;
}

//calculate the size of the buffer to hold the hash object
if (!NT_SUCCESS(status = BCryptGetProperty(
hHashAlg,
BCRYPT_OBJECT_LENGTH,
(PBYTE)&cbHashObject,
sizeof(DWORD),
&cbData,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptGetProperty\n", status);
goto Cleanup;
}

//allocate the hash object on the heap
pbHashObject = (PBYTE)HeapAlloc(GetProcessHeap(), 0, cbHashObject);
if (NULL == pbHashObject)
{
wprintf(L"**** memory allocation failed\n");
goto Cleanup;
}

//calculate the length of the hash
if (!NT_SUCCESS(status = BCryptGetProperty(
hHashAlg,
BCRYPT_HASH_LENGTH,
(PBYTE)&cbHash,
sizeof(DWORD),
&cbData,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptGetProperty\n", status);
goto Cleanup;
}

//allocate the hash buffer on the heap
pbHash = (PBYTE)HeapAlloc(GetProcessHeap(), 0, cbHash);
if (NULL == pbHash)
{
wprintf(L"**** memory allocation failed\n");
goto Cleanup;
}

//create a hash
if (!NT_SUCCESS(status = BCryptCreateHash(
hHashAlg,
&hHash,
pbHashObject,
cbHashObject,
NULL,
0,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptCreateHash\n", status);
goto Cleanup;
}


//hash some data
if (!NT_SUCCESS(status = BCryptHashData(
hHash,
(PBYTE)rgbMsg,
sizeof(rgbMsg),
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptHashData\n", status);
goto Cleanup;
}

//close the hash
if (!NT_SUCCESS(status = BCryptFinishHash(
hHash,
pbHash,
cbHash,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptFinishHash\n", status);
goto Cleanup;
}

//open handle to KSP
if (FAILED(secStatus = NCryptOpenStorageProvider(
&hProv,
MS_KEY_STORAGE_PROVIDER,
0)))
{
wprintf(L"**** Error 0x%x returned by NCryptOpenStorageProvider\n", secStatus);
goto Cleanup;
}

//create a persisted key
if (FAILED(secStatus = NCryptCreatePersistedKey(
hProv,
&hKey,
NCRYPT_ECDSA_P256_ALGORITHM,
L"my ecc key",
0,
0)))
{
wprintf(L"**** Error 0x%x returned by NCryptCreatePersistedKey\n", secStatus);
goto Cleanup;
}

//create key on disk
if (FAILED(secStatus = NCryptFinalizeKey(hKey, 0)))
{
wprintf(L"**** Error 0x%x returned by NCryptFinalizeKey\n", secStatus);
goto Cleanup;
}

//sign the hash
if (FAILED(secStatus = NCryptSignHash(
hKey,
NULL,
pbHash,
cbHash,
NULL,
0,
&cbSignature,
0)))
{
wprintf(L"**** Error 0x%x returned by NCryptSignHash\n", secStatus);
goto Cleanup;
}


//allocate the signature buffer
pbSignature = (PBYTE)HeapAlloc(GetProcessHeap(), 0, cbSignature);
if (NULL == pbSignature)
{
wprintf(L"**** memory allocation failed\n");
goto Cleanup;
}

if (FAILED(secStatus = NCryptSignHash(
hKey,
NULL,
pbHash,
cbHash,
pbSignature,
cbSignature,
&cbSignature,
0)))
{
wprintf(L"**** Error 0x%x returned by NCryptSignHash\n", secStatus);
goto Cleanup;
}

if (FAILED(secStatus = NCryptExportKey(
hKey,
NULL,
BCRYPT_ECCPUBLIC_BLOB,
NULL,
NULL,
0,
&cbBlob,
0)))
{
wprintf(L"**** Error 0x%x returned by NCryptExportKey\n", secStatus);
goto Cleanup;
}

pbBlob = (PBYTE)HeapAlloc(GetProcessHeap(), 0, cbBlob);
if (NULL == pbBlob)
{
wprintf(L"**** memory allocation failed\n");
goto Cleanup;
}

if (FAILED(secStatus = NCryptExportKey(
hKey,
NULL,
BCRYPT_ECCPUBLIC_BLOB,
NULL,
pbBlob,
cbBlob,
&cbBlob,
0)))
{
wprintf(L"**** Error 0x%x returned by NCryptExportKey\n", secStatus);
goto Cleanup;
}

if (!NT_SUCCESS(status = BCryptImportKeyPair(
hSignAlg,
NULL,
BCRYPT_ECCPUBLIC_BLOB,
&hTmpKey,
pbBlob,
cbBlob,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptImportKeyPair\n", status);
goto Cleanup;
}

if (!NT_SUCCESS(status = BCryptVerifySignature(
hTmpKey,
NULL,
pbHash,
cbHash,
pbSignature,
cbSignature,
0)))
{
wprintf(L"**** Error 0x%x returned by BCryptVerifySignature\n", status);
goto Cleanup;
}

wprintf(L"Success!\n");

Cleanup:

if (hHashAlg)
{
BCryptCloseAlgorithmProvider(hHashAlg, 0);
}

if (hSignAlg)
{
BCryptCloseAlgorithmProvider(hSignAlg, 0);
}

if (hHash)
{
BCryptDestroyHash(hHash);
}

if (pbHashObject)
{
HeapFree(GetProcessHeap(), 0, pbHashObject);
}

if (pbHash)
{
HeapFree(GetProcessHeap(), 0, pbHash);
}

if (pbSignature)
{
HeapFree(GetProcessHeap(), 0, pbSignature);
}

if (pbBlob)
{
HeapFree(GetProcessHeap(), 0, pbBlob);
}

if (hTmpKey)
{
BCryptDestroyKey(hTmpKey);
}

if (hKey)
{
NCryptDeleteKey(hKey, 0);
}

if (hProv)
{
NCryptFreeObject(hProv);
}
}


Just to be clear, I aiming at 384 bit and for compatibility with OpenSsl and C# curvename is NIST recommended curve
secp384r1 – {1.3.132.0.34}
And I will be using SHA256 hash twice (just like BitCoin).

Answer Source

Does this code (a) create an ECDSA key on the fly (b) sign a hash (c) save key to a certificate store (d) retrieve the key and verify signed hash. If so then I guess it's demo code.

A) Yes.

B) Yes.

C) Yes. It saves the key as a persisted object named "my ec key". But since it never asked for it by name again, nullptr/NULL could have been passed to make it be an ephemeral key. (And it saved it to the "key store", not a "certificate store".

D) Yes to verify, no to retrieve.


Getting your publicKey data (this is the output of openssl ec -in eckey.pem -pubout -outform der | xxd -g1 translated into the C array) and signature (in the IEEE P1363 format) is an exercise left to the reader.

static const BYTE data[] =
{
    '1', '2', '3', '4',
};

static const BYTE publicKey[] =
{
    0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86,
    0x48, 0xce, 0x3d, 0x02, 0x01, 0x06, 0x08, 0x2a,
    0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03,
    0x42, 0x00, 0x04, 0x23, 0x63, 0xdd, 0x13, 0x1d,
    0xa6, 0x5e, 0x89, 0x9a, 0x2e, 0x63, 0xe9, 0xe0,
    0x5e, 0x50, 0xc8, 0x30, 0xd4, 0x99, 0x46, 0x62,
    0xff, 0xe8, 0x83, 0xdb, 0x2b, 0x9a, 0x76, 0x7d,
    0xcc, 0xab, 0xa2, 0xf0, 0x70, 0x81, 0xb5, 0x71,
    0x1b, 0xe1, 0xde, 0xe9, 0x0d, 0xfc, 0x8d, 0xe1,
    0x79, 0x70, 0xc2, 0xd9, 0x37, 0xa1, 0x6c, 0xd3,
    0x45, 0x81, 0xf5, 0x2b, 0x8d, 0x59, 0xc9, 0xe9,
    0x53, 0x2d, 0x13,
};

static const BYTE signature[] =
{
    // r
    0xc6, 0x4c, 0x14, 0x55, 0xfe, 0xc0, 0x2f, 0xe7,
    0x4a, 0x25, 0x87, 0xe7, 0x0c, 0x10, 0x4e, 0x73,
    0xf0, 0x28, 0x86, 0x18, 0x28, 0xae, 0xef, 0x4f,
    0xe5, 0xa0, 0xcc, 0x7a, 0xa8, 0xe4, 0x1f, 0xbf,

    // s
    0x35, 0x9f, 0x23, 0xfd, 0xc3, 0xd6, 0x33, 0xfb,
    0x52, 0x47, 0x9b, 0xef, 0x2b, 0x2a, 0x48, 0xa8,
    0x6f, 0x37, 0x04, 0xd0, 0x8c, 0xc3, 0x49, 0x04,
    0x21, 0x53, 0xb8, 0x3c, 0x9d, 0x8c, 0x6c, 0xf5,
};

#define NT_SUCCESS(Status)          (((NTSTATUS)(Status)) >= 0)

int main()
{
    NTSTATUS status = NTE_BAD_DATA;
    int exitCode = ERROR_INVALID_FUNCTION;
    BCRYPT_KEY_HANDLE importedPublicKey = nullptr;
    PCERT_PUBLIC_KEY_INFO subjectPublicKeyInfo = (PCERT_PUBLIC_KEY_INFO)LocalAlloc(0, 2048);
    BCRYPT_ALG_HANDLE sha256 = nullptr;
    BCRYPT_HASH_HANDLE hHash = nullptr;
    BYTE dataHash[256 >> 3];

    DWORD structSize = 2048;
    if (!CryptDecodeObject(
        X509_ASN_ENCODING,
        X509_PUBLIC_KEY_INFO,
        publicKey,
        sizeof(publicKey),
        0,
        subjectPublicKeyInfo,
        &structSize))
    {
        wprintf(L"**** Error 0x%x returned by CryptDecodeObject\n", GetLastError());
        goto Cleanup;
    }

    if (!CryptImportPublicKeyInfoEx2(
        X509_ASN_ENCODING,
        subjectPublicKeyInfo,
        0,
        nullptr,
        &importedPublicKey))
    {
        wprintf(L"**** Error 0x%x returned by CryptImportPublicKeyInfoEx2\n", GetLastError());
        goto Cleanup;
    }

    if (!NT_SUCCESS(status = BCryptOpenAlgorithmProvider(&sha256, BCRYPT_SHA256_ALGORITHM, nullptr, 0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptOpenAlgorithmProvider\n", status);
        goto Cleanup;
    }

    if (!NT_SUCCESS(status = BCryptCreateHash(sha256, &hHash, nullptr, 0, nullptr, 0, 0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptCreateHash\n", status);
        goto Cleanup;
    }

    if (!NT_SUCCESS(status = BCryptHashData(hHash, (PUCHAR)data, sizeof(data), 0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptHashData\n", status);
        goto Cleanup;
    }

    if (!NT_SUCCESS(status = BCryptFinishHash(hHash, (PUCHAR)dataHash, sizeof(dataHash), 0)))
    {
        wprintf(L"**** Error 0x%x returned by BCryptFinishHash\n", status);
        goto Cleanup;
    }

    status = BCryptVerifySignature(
        importedPublicKey,
        nullptr,
        (PUCHAR)dataHash,
        sizeof(dataHash),
        (PUCHAR)signature,
        sizeof(signature),
        0);

    switch (status)
    {
        case STATUS_SUCCESS:
            wprintf(L"Signature verified successfully\n");
            exitCode = ERROR_SUCCESS;
            break;
        case STATUS_INVALID_SIGNATURE:
            wprintf(L"Signature did not verify\n");
            exitCode = ERROR_INVALID_DATA;
            break;
        default:
            wprintf(L"**** Error 0x%x returned by BCryptVerifySignature\n", status);
            goto Cleanup;
    }



Cleanup:
    if (hHash != nullptr)
        BCryptDestroyHash(hHash);

    if (sha256 != nullptr)
        BCryptCloseAlgorithmProvider(sha256, 0);

    if (importedPublicKey != nullptr)
        BCryptDestroyKey(importedPublicKey);

    LocalFree(subjectPublicKeyInfo);

    return exitCode;
}
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