(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 <CkPublicKey.h>
#include <CkBinData.h>
#include <CkRsa.h>

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

    CkPublicKey pubKey;

    // Load the public key from an PEM file:
    bool success = pubKey.LoadFromFile("pubKey.pem");
    if (success != true) {
        std::cout << pubKey.lastErrorText() << "\r\n";
        return;
    }

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

    // Load the signature.
    CkBinData bdSig;
    success = bdSig.LoadFile("signature.sig");

    CkRsa rsa;

    // Import the public key into the RSA component:
    success = rsa.ImportPublicKeyObj(pubKey);
    if (success != true) {
        std::cout << rsa.lastErrorText() << "\r\n";
        return;
    }

    // OpenSSL uses big-endian.
    rsa.put_LittleEndian(false);

    success = rsa.VerifyBd(bdFileData,"sha256",bdSig);
    if (success != true) {
        std::cout << rsa.lastErrorText() << "\r\n";
        std::cout << "The signature was invalid." << "\r\n";
        return;
    }

    std::cout << "The signature was verified." << "\r\n";
    }