Unicode C++

ECDSA Sign and Verify

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Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify. Unicode C++

#include <CkPrivateKeyW.h>
#include <CkBinDataW.h>
#include <CkCrypt2W.h>
#include <CkEccW.h>
#include <CkPrngW.h>
#include <CkAsnW.h>
#include <CkXmlW.h>
#include <CkPublicKeyW.h>

void ChilkatSample(void)
    {
    bool success = false;

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

    // First load an ECDSA private key to be used for signing.
    CkPrivateKeyW privKey;
    success = privKey.LoadEncryptedPemFile(L"qa_data/ecc/secp256r1-key-pkcs8-secret.pem",L"secret");
    if (success == false) {
        wprintf(L"%s\n",privKey.lastErrorText());
        return;
    }

    // Sign the SHA256 hash of some data.
    CkBinDataW bd;
    success = bd.LoadFile(L"qa_data/hamlet.xml");
    if (success == false) {
        wprintf(L"Failed to load file to be hashed.\n");
        return;
    }

    CkCrypt2W crypt;
    crypt.put_HashAlgorithm(L"sha256");
    crypt.put_EncodingMode(L"base64");
    const wchar_t *hashStr = crypt.hashBdENC(bd);

    CkEccW ecdsa;
    CkPrngW prng;
    // Returns ASN.1 signature as a base64 string.
    const wchar_t *sig = ecdsa.signHashENC(hashStr,L"base64",privKey,prng);
    wprintf(L"sig = %s\n",sig);

    // The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
    // SEQUENCE (2 elem)
    //   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
    //   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

    // If you wish, you can get the r and s components of the signature like this:
    CkAsnW asn;
    asn.LoadEncoded(sig,L"base64");
    CkXmlW xml;
    xml.LoadXml(asn.asnToXml());

    wprintf(L"%s\n",xml.getXml());

    // We now have this:
    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
    //     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
    // </sequence>

    // Get the "r" and "s" as hex strings
    const wchar_t *r = xml.getChildContentByIndex(0);
    const wchar_t *s = xml.getChildContentByIndex(1);

    wprintf(L"r = %s\n",r);
    wprintf(L"s = %s\n",s);

    // --------------------------------------------------------------------
    // Now verify against the hash of the original data.

    // Get the corresponding public key.
    CkPublicKeyW pubKey;
    success = pubKey.LoadFromFile(L"qa_data/ecc/secp256r1-pub.pem");
    if (success == false) {
        wprintf(L"%s\n",pubKey.lastErrorText());
        return;
    }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    CkEccW ecc2;
    int result = ecc2.VerifyHashENC(hashStr,sig,L"base64",pubKey);
    if (result != 1) {
        wprintf(L"%s\n",ecc2.lastErrorText());
        return;
    }

    wprintf(L"Verified!\n");

    // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
    CkXmlW xml2;
    xml2.put_Tag(L"sequence");
    xml2.NewChild2(L"int",r);
    xml2.NewChild2(L"int",s);

    CkAsnW asn2;
    asn2.LoadAsnXml(xml2.getXml());
    const wchar_t *encodedSig = asn2.getEncodedDer(L"base64");
    wprintf(L"encoded DSS signature: %s\n",encodedSig);

    // You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
    // You will see the ASN.1 such as this:

    // SEQUENCE (2 elem)
    //   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
    //   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...
    }