(Unicode C) DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature.

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

void ChilkatSample(void)
    {
    HCkCrypt2W crypt;
    const wchar_t *hashStr;
    HCkDsaW dsa;
    const wchar_t *pemPrivateKey;
    BOOL success;
    const wchar_t *asnSig;
    HCkAsnW asn;
    HCkXmlW xml;
    const wchar_t *r;
    const wchar_t *s;
    HCkDsaW dsa2;
    const wchar_t *pemPublicKey;

    // 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");

    hashStr = CkCrypt2W_hashFileENC(crypt,L"qa_data/hamlet.xml");
    wprintf(L"hash to sign: %s\n",hashStr);

    dsa = CkDsaW_Create();

    pemPrivateKey = CkDsaW_loadText(dsa,L"qa_data/dsa/dsaPrivKey2.pem");
    success = CkDsaW_FromPem(dsa,pemPrivateKey);
    if (success == FALSE) {
        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 == FALSE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        return;
    }

    // Sign the hash.
    success = CkDsaW_SignHash(dsa);
    if (success == FALSE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        return;
    }

    // Get the ASN.1 signature.
    asnSig = CkDsaW_getEncodedSignature(dsa,L"base64");
    wprintf(L"Signature: %s\n",asnSig);

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    asn = CkAsnW_Create();
    success = CkAsnW_LoadEncoded(asn,asnSig,L"base64");
    if (success == FALSE) {
        wprintf(L"%s\n",CkAsnW_lastErrorText(asn));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkAsnW_Dispose(asn);
        return;
    }

    // Get the ASN.1 as XML.
    xml = CkXmlW_Create();
    success = CkXmlW_LoadXml(xml,CkAsnW_asnToXml(asn));
    wprintf(L"Signature as XML: \n");
    wprintf(L"%s\n",CkXmlW_getXml(xml));

    // Sample XML shown here.
    // The r and s values are the two hex strings in the XML.

    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
    //     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
    // </sequence>

    // Pretend we're starting with r,s
    r = L"2C187F3AB6E47A66497B86CE97BB39E2133810F5";
    s = L"588E53D3F7B69636B48FD7175E99A3961BD7D775";

    // Build the XML that will be converted to ASN.1
    CkXmlW_Clear(xml);
    CkXmlW_putTag(xml,L"sequence");
    CkXmlW_NewChild2(xml,L"int",r);
    CkXmlW_NewChild2(xml,L"int",s);

    // Convert the XML to ASN.1
    success = CkAsnW_LoadAsnXml(asn,CkXmlW_getXml(xml));

    // Emit the signature as DER encoded ASN.1 (base64)
    asnSig = CkAsnW_getEncodedDer(asn,L"base64");

    // --------------------------------------------------------------------
    // Verify the signature using the asnSig we built from the r,s values
    // --------------------------------------------------------------------

    dsa2 = CkDsaW_Create();

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

    pemPublicKey = CkDsaW_loadText(dsa2,L"qa_data/dsa/dsaPubKey2.pem");
    success = CkDsaW_FromPublicPem(dsa2,pemPublicKey);
    if (success == FALSE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa2));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkAsnW_Dispose(asn);
        CkXmlW_Dispose(xml);
        CkDsaW_Dispose(dsa2);
        return;
    }

    // Load the hash to be verified.
    success = CkDsaW_SetEncodedHash(dsa2,L"hex",hashStr);
    if (success == FALSE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa2));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkAsnW_Dispose(asn);
        CkXmlW_Dispose(xml);
        CkDsaW_Dispose(dsa2);
        return;
    }

    // Load the ASN.1 signature:
    success = CkDsaW_SetEncodedSignature(dsa2,L"base64",asnSig);
    if (success == FALSE) {
        wprintf(L"%s\n",CkDsaW_lastErrorText(dsa2));
        CkCrypt2W_Dispose(crypt);
        CkDsaW_Dispose(dsa);
        CkAsnW_Dispose(asn);
        CkXmlW_Dispose(xml);
        CkDsaW_Dispose(dsa2);
        return;
    }

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



    CkCrypt2W_Dispose(crypt);
    CkDsaW_Dispose(dsa);
    CkAsnW_Dispose(asn);
    CkXmlW_Dispose(xml);
    CkDsaW_Dispose(dsa2);

    }