Unicode C

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. Unicode C

#include <C_CkPublicKeyW.h>
#include <C_CkRsaW.h>
#include <C_CkBinDataW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkPublicKeyW pubKey;
    HCkRsaW rsa;
    HCkBinDataW bdHash;
    HCkBinDataW bdSig;
    const wchar_t *enc;

    success = FALSE;

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Let's say you have a file containing the 32-bytes of a SHA256 hash,
    // and a file that is an RSA signature of those 32 bytes.
    // Here's how you verify using the RSA public key found in a PEM.

    pubKey = CkPublicKeyW_Create();
    success = CkPublicKeyW_LoadFromFile(pubKey,L"rsaPubKey.pem");
    if (success == FALSE) {
        wprintf(L"%s\n",CkPublicKeyW_lastErrorText(pubKey));
        CkPublicKeyW_Dispose(pubKey);
        return;
    }

    rsa = CkRsaW_Create();

    // Get the public key.
    success = CkRsaW_UsePublicKey(rsa,pubKey);
    if (success == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        CkPublicKeyW_Dispose(pubKey);
        CkRsaW_Dispose(rsa);
        return;
    }

    // Get the 32-byte SHA256 hash.
    bdHash = CkBinDataW_Create();
    success = CkBinDataW_LoadFile(bdHash,L"myHash.sha256");
    if (success == FALSE) {
        wprintf(L"Failed to load SHA256 hash.\n");
        CkPublicKeyW_Dispose(pubKey);
        CkRsaW_Dispose(rsa);
        CkBinDataW_Dispose(bdHash);
        return;
    }

    // Get the RSA signature to be validated.
    bdSig = CkBinDataW_Create();
    success = CkBinDataW_LoadFile(bdSig,L"mySig.sig");
    if (success == FALSE) {
        wprintf(L"Failed to load RSA signature.\n");
        CkPublicKeyW_Dispose(pubKey);
        CkRsaW_Dispose(rsa);
        CkBinDataW_Dispose(bdHash);
        CkBinDataW_Dispose(bdSig);
        return;
    }

    // Verify the signature against the SHA256 hash.
    enc = L"base64";
    CkRsaW_putEncodingMode(rsa,enc);
    success = CkRsaW_VerifyHashENC(rsa,CkBinDataW_getEncoded(bdHash,enc),L"sha256",CkBinDataW_getEncoded(bdSig,enc));
    if (success == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        CkPublicKeyW_Dispose(pubKey);
        CkRsaW_Dispose(rsa);
        CkBinDataW_Dispose(bdHash);
        CkBinDataW_Dispose(bdSig);
        return;
    }

    wprintf(L"Signature validated.\n");


    CkPublicKeyW_Dispose(pubKey);
    CkRsaW_Dispose(rsa);
    CkBinDataW_Dispose(bdHash);
    CkBinDataW_Dispose(bdSig);

    }