(C) Verify the RSA Signature of a SHA256 Hash

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

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

void ChilkatSample(void)
    {
    HCkPublicKey pubKey;
    BOOL success;
    HCkRsa rsa;
    HCkBinData bdHash;
    HCkBinData bdSig;
    const char *enc;

    // 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 = CkPublicKey_Create();
    success = CkPublicKey_LoadFromFile(pubKey,"rsaPubKey.pem");
    if (success == FALSE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubKey));
        CkPublicKey_Dispose(pubKey);
        return;
    }

    rsa = CkRsa_Create();

    // Get the public key.
    success = CkRsa_ImportPublicKeyObj(rsa,pubKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa);
        return;
    }

    // Get the 32-byte SHA256 hash.
    bdHash = CkBinData_Create();
    success = CkBinData_LoadFile(bdHash,"myHash.sha256");
    if (success == FALSE) {
        printf("Failed to load SHA256 hash.\n");
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa);
        CkBinData_Dispose(bdHash);
        return;
    }

    // Get the RSA signature to be validated.
    bdSig = CkBinData_Create();
    success = CkBinData_LoadFile(bdSig,"mySig.sig");
    if (success == FALSE) {
        printf("Failed to load RSA signature.\n");
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa);
        CkBinData_Dispose(bdHash);
        CkBinData_Dispose(bdSig);
        return;
    }

    // Verify the signature against the SHA256 hash.
    enc = "base64";
    CkRsa_putEncodingMode(rsa,enc);
    success = CkRsa_VerifyHashENC(rsa,CkBinData_getEncoded(bdHash,enc),"sha256",CkBinData_getEncoded(bdSig,enc));
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa);
        CkBinData_Dispose(bdHash);
        CkBinData_Dispose(bdSig);
        return;
    }

    printf("Signature validated.\n");


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

    }