(C) Duplicate openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

Demonstrates how to duplicate this OpenSSL command:

openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

1. Creates a SHA256 digest of the contents of the input file.
2. Verifies the SHA256 digest using the public key.

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#include <C_CkPublicKey.h>
#include <C_CkBinData.h>
#include <C_CkRsa.h>

void ChilkatSample(void)
    {
    HCkPublicKey pubKey;
    BOOL success;
    HCkBinData bdFileData;
    HCkBinData bdSig;
    HCkRsa rsa;

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

    pubKey = CkPublicKey_Create();

    // Load the public key from an PEM file:
    success = CkPublicKey_LoadFromFile(pubKey,"pubKey.pem");
    if (success != TRUE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubKey));
        CkPublicKey_Dispose(pubKey);
        return;
    }

    // Load the data of the original file that was signed.
    bdFileData = CkBinData_Create();
    success = CkBinData_LoadFile(bdFileData,"in.dat");

    // Load the signature.
    bdSig = CkBinData_Create();
    success = CkBinData_LoadFile(bdSig,"signature.sig");

    rsa = CkRsa_Create();

    // Import the public key into the RSA component:
    success = CkRsa_ImportPublicKeyObj(rsa,pubKey);
    if (success != TRUE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPublicKey_Dispose(pubKey);
        CkBinData_Dispose(bdFileData);
        CkBinData_Dispose(bdSig);
        CkRsa_Dispose(rsa);
        return;
    }

    // OpenSSL uses big-endian.
    CkRsa_putLittleEndian(rsa,FALSE);

    success = CkRsa_VerifyBd(rsa,bdFileData,"sha256",bdSig);
    if (success != TRUE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        printf("The signature was invalid.\n");
        CkPublicKey_Dispose(pubKey);
        CkBinData_Dispose(bdFileData);
        CkBinData_Dispose(bdSig);
        CkRsa_Dispose(rsa);
        return;
    }

    printf("The signature was verified.\n");


    CkPublicKey_Dispose(pubKey);
    CkBinData_Dispose(bdFileData);
    CkBinData_Dispose(bdSig);
    CkRsa_Dispose(rsa);

    }