(Unicode C++) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

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#include <CkCrypt2W.h>
#include <CkDsaW.h>

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

    CkCrypt2W crypt;

    crypt.put_EncodingMode(L"hex");
    crypt.put_HashAlgorithm(L"sha-1");

    // Return the SHA-1 hash of a file.  The file may be any size.
    // The Chilkat Crypt component will stream the file when 
    // computing the hash, keeping the memory usage constant
    // and reasonable.
    // The 20-byte SHA-1 hash is returned as a hex-encoded string.
    const wchar_t *hashStr = crypt.hashFileENC(L"hamlet.xml");

    CkDsaW dsa;

    // Load a DSA private key from a PEM file.  Chilkat DSA
    // provides the ability to load and save DSA public and private
    // keys from encrypted or non-encrypted PEM or DER.
    // The LoadText method is for convenience only.  You may
    // use any means to load the contents of a PEM file into
    // a string.
    const wchar_t *pemPrivateKey = 0;
    pemPrivateKey = dsa.loadText(L"dsa_priv.pem");
    bool success = dsa.FromPem(pemPrivateKey);
    if (success != true) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    success = dsa.VerifyKey();
    if (success != true) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // Load the hash to be signed into the DSA object:
    success = dsa.SetEncodedHash(L"hex",hashStr);
    if (success != true) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // Now that the DSA object contains both the private key and hash,
    // it is ready to create the signature:
    success = dsa.SignHash();
    if (success != true) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // If SignHash is successful, the DSA object contains the
    // signature.  It may be accessed as a hex or base64 encoded
    // string.  (It is also possible to access directly in byte array form via
    // the "Signature" property.)
    const wchar_t *hexSig = dsa.getEncodedSignature(L"hex");
    wprintf(L"Signature:\n");
    wprintf(L"%s\n",hexSig);

    // -----------------------------------------------------------
    // Step 2: Verify the DSA Signature
    // -----------------------------------------------------------

    CkDsaW dsa2;

    // Load the DSA public key to be used for verification:
    const wchar_t *pemPublicKey = 0;
    pemPublicKey = dsa2.loadText(L"dsa_pub.pem");
    success = dsa2.FromPublicPem(pemPublicKey);
    if (success != true) {
        wprintf(L"%s\n",dsa2.lastErrorText());
        return;
    }

    // Load the hash to be verified against the signature.
    success = dsa2.SetEncodedHash(L"hex",hashStr);
    if (success != true) {
        wprintf(L"%s\n",dsa2.lastErrorText());
        return;
    }

    // Load the signature:
    success = dsa2.SetEncodedSignature(L"hex",hexSig);
    if (success != true) {
        wprintf(L"%s\n",dsa2.lastErrorText());
        return;
    }

    // Verify:
    success = dsa2.Verify();
    if (success != true) {
        wprintf(L"%s\n",dsa2.lastErrorText());
    }
    else {
        wprintf(L"DSA Signature Verified!\n");
    }
    }