Unicode C

DSA Signature Create and Verify

See more DSA Examples

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.

Unicode C

#include <C_CkCrypt2W.h>
#include <C_CkDsaW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkCrypt2W crypt;
    const wchar_t *hashStr;
    HCkDsaW dsa;
    const wchar_t *pemPrivateKey;
    const wchar_t *hexSig;
    HCkDsaW dsa2;
    const wchar_t *pemPublicKey;

    success = FALSE;

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

    crypt = CkCrypt2W_Create();

    CkCrypt2W_putEncodingMode(crypt,L"hex");
    CkCrypt2W_putHashAlgorithm(crypt,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.
    hashStr = CkCrypt2W_hashFileENC(crypt,L"hamlet.xml");

    dsa = CkDsaW_Create();

    //  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.

    pemPrivateKey = CkDsaW_loadText(dsa,L"dsa_priv.pem");
    success = CkDsaW_FromPem(dsa,pemPrivateKey);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        return;
    }

    //  You may optionally verify the key to ensure that it is a valid
    //  DSA key.
    success = CkDsaW_VerifyKey(dsa);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        return;
    }

    //  Load the hash to be signed into the DSA object:
    success = CkDsaW_SetEncodedHash(dsa,L"hex",hashStr);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        return;
    }

    //  Now that the DSA object contains both the private key and hash,
    //  it is ready to create the signature:
    success = CkDsaW_SignHash(dsa);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        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.)
    hexSig = CkDsaW_getEncodedSignature(dsa,L"hex");
    wprintf(L"Signature:\n");
    wprintf(L"%s\n",hexSig);

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

    dsa2 = CkDsaW_Create();

    //  Load the DSA public key to be used for verification:

    pemPublicKey = CkDsaW_loadText(dsa2,L"dsa_pub.pem");
    success = CkDsaW_FromPublicPem(dsa2,pemPublicKey);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa2));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkDsaW_Dispose(dsa2);
        return;
    }

    //  Load the hash to be verified against the signature.
    success = CkDsaW_SetEncodedHash(dsa2,L"hex",hashStr);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa2));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkDsaW_Dispose(dsa2);
        return;
    }

    //  Load the signature:
    success = CkDsaW_SetEncodedSignature(dsa2,L"hex",hexSig);
    if (success != TRUE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa2));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkDsaW_Dispose(dsa2);
        return;
    }

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



    CkCrypt2W_Dispose(crypt);
    CkDsaW_Dispose(dsa);
    CkDsaW_Dispose(dsa2);

    }