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 <C_CkPrivateKeyW.h>
#include <C_CkBinDataW.h>
#include <C_CkCrypt2W.h>
#include <C_CkEccW.h>
#include <C_CkPrngW.h>
#include <C_CkAsnW.h>
#include <C_CkXmlW.h>
#include <C_CkPublicKeyW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkPrivateKeyW privKey;
    HCkBinDataW bd;
    HCkCrypt2W crypt;
    const wchar_t *hashStr;
    HCkEccW ecdsa;
    HCkPrngW prng;
    const wchar_t *sig;
    HCkAsnW asn;
    HCkXmlW xml;
    const wchar_t *r;
    const wchar_t *s;
    HCkPublicKeyW pubKey;
    HCkEccW ecc2;
    int result;
    HCkXmlW xml2;
    HCkAsnW asn2;
    const wchar_t *encodedSig;

    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.
    privKey = CkPrivateKeyW_Create();
    success = CkPrivateKeyW_LoadEncryptedPemFile(privKey,L"qa_data/ecc/secp256r1-key-pkcs8-secret.pem",L"secret");
    if (success == FALSE) {
        wprintf(L"%s\n",CkPrivateKeyW_lastErrorText(privKey));
        CkPrivateKeyW_Dispose(privKey);
        return;
    }

    // Sign the SHA256 hash of some data.
    bd = CkBinDataW_Create();
    success = CkBinDataW_LoadFile(bd,L"qa_data/hamlet.xml");
    if (success == FALSE) {
        wprintf(L"Failed to load file to be hashed.\n");
        CkPrivateKeyW_Dispose(privKey);
        CkBinDataW_Dispose(bd);
        return;
    }

    crypt = CkCrypt2W_Create();
    CkCrypt2W_putHashAlgorithm(crypt,L"sha256");
    CkCrypt2W_putEncodingMode(crypt,L"base64");
    hashStr = CkCrypt2W_hashBdENC(crypt,bd);

    ecdsa = CkEccW_Create();
    prng = CkPrngW_Create();
    // Returns ASN.1 signature as a base64 string.
    sig = CkEccW_signHashENC(ecdsa,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:
    asn = CkAsnW_Create();
    CkAsnW_LoadEncoded(asn,sig,L"base64");
    xml = CkXmlW_Create();
    CkXmlW_LoadXml(xml,CkAsnW_asnToXml(asn));

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

    // 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
    r = CkXmlW_getChildContentByIndex(xml,0);
    s = CkXmlW_getChildContentByIndex(xml,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.
    pubKey = CkPublicKeyW_Create();
    success = CkPublicKeyW_LoadFromFile(pubKey,L"qa_data/ecc/secp256r1-pub.pem");
    if (success == FALSE) {
        wprintf(L"%s\n",CkPublicKeyW_lastErrorText(pubKey));
        CkPrivateKeyW_Dispose(privKey);
        CkBinDataW_Dispose(bd);
        CkCrypt2W_Dispose(crypt);
        CkEccW_Dispose(ecdsa);
        CkPrngW_Dispose(prng);
        CkAsnW_Dispose(asn);
        CkXmlW_Dispose(xml);
        CkPublicKeyW_Dispose(pubKey);
        return;
    }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    ecc2 = CkEccW_Create();
    result = CkEccW_VerifyHashENC(ecc2,hashStr,sig,L"base64",pubKey);
    if (result != 1) {
        wprintf(L"%s\n",CkEccW_lastErrorText(ecc2));
        CkPrivateKeyW_Dispose(privKey);
        CkBinDataW_Dispose(bd);
        CkCrypt2W_Dispose(crypt);
        CkEccW_Dispose(ecdsa);
        CkPrngW_Dispose(prng);
        CkAsnW_Dispose(asn);
        CkXmlW_Dispose(xml);
        CkPublicKeyW_Dispose(pubKey);
        CkEccW_Dispose(ecc2);
        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:
    xml2 = CkXmlW_Create();
    CkXmlW_putTag(xml2,L"sequence");
    CkXmlW_NewChild2(xml2,L"int",r);
    CkXmlW_NewChild2(xml2,L"int",s);

    asn2 = CkAsnW_Create();
    CkAsnW_LoadAsnXml(asn2,CkXmlW_getXml(xml2));
    encodedSig = CkAsnW_getEncodedDer(asn2,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...


    CkPrivateKeyW_Dispose(privKey);
    CkBinDataW_Dispose(bd);
    CkCrypt2W_Dispose(crypt);
    CkEccW_Dispose(ecdsa);
    CkPrngW_Dispose(prng);
    CkAsnW_Dispose(asn);
    CkXmlW_Dispose(xml);
    CkPublicKeyW_Dispose(pubKey);
    CkEccW_Dispose(ecc2);
    CkXmlW_Dispose(xml2);
    CkAsnW_Dispose(asn2);

    }