(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_CkCrypt2.h>
#include <C_CkDsa.h>
#include <C_CkAsn.h>
#include <C_CkXml.h>

void ChilkatSample(void)
    {
    HCkCrypt2 crypt;
    const char *hashStr;
    HCkDsa dsa;
    const char *pemPrivateKey;
    BOOL success;
    const char *asnSig;
    HCkAsn asn;
    HCkXml xml;
    const char *r;
    const char *s;
    HCkDsa dsa2;
    const char *pemPublicKey;

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

    crypt = CkCrypt2_Create();

    CkCrypt2_putEncodingMode(crypt,"hex");
    CkCrypt2_putHashAlgorithm(crypt,"sha-1");

    hashStr = CkCrypt2_hashFileENC(crypt,"qa_data/hamlet.xml");
    printf("hash to sign: %s\n",hashStr);

    dsa = CkDsa_Create();

    pemPrivateKey = CkDsa_loadText(dsa,"qa_data/dsa/dsaPrivKey2.pem");
    success = CkDsa_FromPem(dsa,pemPrivateKey);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        return;
    }

    // Load the hash to be signed into the DSA object:
    success = CkDsa_SetEncodedHash(dsa,"hex",hashStr);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        return;
    }

    // Sign the hash.
    success = CkDsa_SignHash(dsa);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        return;
    }

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

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    asn = CkAsn_Create();
    success = CkAsn_LoadEncoded(asn,asnSig,"base64");
    if (success == FALSE) {
        printf("%s\n",CkAsn_lastErrorText(asn));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        CkAsn_Dispose(asn);
        return;
    }

    // Get the ASN.1 as XML.
    xml = CkXml_Create();
    success = CkXml_LoadXml(xml,CkAsn_asnToXml(asn));
    printf("Signature as XML: \n");
    printf("%s\n",CkXml_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 = "2C187F3AB6E47A66497B86CE97BB39E2133810F5";
    s = "588E53D3F7B69636B48FD7175E99A3961BD7D775";

    // Build the XML that will be converted to ASN.1
    CkXml_Clear(xml);
    CkXml_putTag(xml,"sequence");
    CkXml_NewChild2(xml,"int",r);
    CkXml_NewChild2(xml,"int",s);

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

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

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

    dsa2 = CkDsa_Create();

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

    pemPublicKey = CkDsa_loadText(dsa2,"qa_data/dsa/dsaPubKey2.pem");
    success = CkDsa_FromPublicPem(dsa2,pemPublicKey);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa2));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        CkAsn_Dispose(asn);
        CkXml_Dispose(xml);
        CkDsa_Dispose(dsa2);
        return;
    }

    // Load the hash to be verified.
    success = CkDsa_SetEncodedHash(dsa2,"hex",hashStr);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa2));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        CkAsn_Dispose(asn);
        CkXml_Dispose(xml);
        CkDsa_Dispose(dsa2);
        return;
    }

    // Load the ASN.1 signature:
    success = CkDsa_SetEncodedSignature(dsa2,"base64",asnSig);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa2));
        CkCrypt2_Dispose(crypt);
        CkDsa_Dispose(dsa);
        CkAsn_Dispose(asn);
        CkXml_Dispose(xml);
        CkDsa_Dispose(dsa2);
        return;
    }

    // Verify:
    success = CkDsa_Verify(dsa2);
    if (success == FALSE) {
        printf("%s\n",CkDsa_lastErrorText(dsa2));
    }
    else {
        printf("DSA Signature Verified!\n");
    }



    CkCrypt2_Dispose(crypt);
    CkDsa_Dispose(dsa);
    CkAsn_Dispose(asn);
    CkXml_Dispose(xml);
    CkDsa_Dispose(dsa2);

    }