C++

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

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

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

void ChilkatSample(void)
    {
    bool 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.

    CkPublicKey pubKey;
    success = pubKey.LoadFromFile("rsaPubKey.pem");
    if (success == false) {
        std::cout << pubKey.lastErrorText() << "\r\n";
        return;
    }

    CkRsa rsa;

    // Get the public key.
    success = rsa.UsePublicKey(pubKey);
    if (success == false) {
        std::cout << rsa.lastErrorText() << "\r\n";
        return;
    }

    // Get the 32-byte SHA256 hash.
    CkBinData bdHash;
    success = bdHash.LoadFile("myHash.sha256");
    if (success == false) {
        std::cout << "Failed to load SHA256 hash." << "\r\n";
        return;
    }

    // Get the RSA signature to be validated.
    CkBinData bdSig;
    success = bdSig.LoadFile("mySig.sig");
    if (success == false) {
        std::cout << "Failed to load RSA signature." << "\r\n";
        return;
    }

    // Verify the signature against the SHA256 hash.
    const char *enc = "base64";
    rsa.put_EncodingMode(enc);
    success = rsa.VerifyHashENC(bdHash.getEncoded(enc),"sha256",bdSig.getEncoded(enc));
    if (success == false) {
        std::cout << rsa.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Signature validated." << "\r\n";
    }