(C) ECDSA Sign and Verify

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

Chilkat C/C++ Library Downloads
MS Visual C/C++ Linux/CentOS C/C++ Alpine Linux C/C++ MAC OS X C/C++	armhf/aarch64 C/C++ C++ Builder iOS C/C++ Android C/C++	Solaris C/C++ MinGW C/C++

#include <C_CkPrivateKey.h>
#include <C_CkBinData.h>
#include <C_CkCrypt2.h>
#include <C_CkEcc.h>
#include <C_CkPrng.h>
#include <C_CkAsn.h>
#include <C_CkXml.h>
#include <C_CkPublicKey.h>

void ChilkatSample(void)
    {
    HCkPrivateKey privKey;
    BOOL success;
    HCkBinData bd;
    HCkCrypt2 crypt;
    const char *hashStr;
    HCkEcc ecdsa;
    HCkPrng prng;
    const char *sig;
    HCkAsn asn;
    HCkXml xml;
    const char *r;
    const char *s;
    HCkPublicKey pubKey;
    HCkEcc ecc2;
    int result;
    HCkXml xml2;
    HCkAsn asn2;
    const char *encodedSig;

    // 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 = CkPrivateKey_Create();
    success = CkPrivateKey_LoadEncryptedPemFile(privKey,"qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret");
    if (success == FALSE) {
        printf("%s\n",CkPrivateKey_lastErrorText(privKey));
        CkPrivateKey_Dispose(privKey);
        return;
    }

    // Sign the SHA256 hash of some data.
    bd = CkBinData_Create();
    success = CkBinData_LoadFile(bd,"qa_data/hamlet.xml");
    if (success == FALSE) {
        printf("Failed to load file to be hashed.\n");
        CkPrivateKey_Dispose(privKey);
        CkBinData_Dispose(bd);
        return;
    }

    crypt = CkCrypt2_Create();
    CkCrypt2_putHashAlgorithm(crypt,"sha256");
    CkCrypt2_putEncodingMode(crypt,"base64");
    hashStr = CkCrypt2_hashBdENC(crypt,bd);

    ecdsa = CkEcc_Create();
    prng = CkPrng_Create();
    // Returns ASN.1 signature as a base64 string.
    sig = CkEcc_signHashENC(ecdsa,hashStr,"base64",privKey,prng);
    printf("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 = CkAsn_Create();
    CkAsn_LoadEncoded(asn,sig,"base64");
    xml = CkXml_Create();
    CkXml_LoadXml(xml,CkAsn_asnToXml(asn));

    printf("%s\n",CkXml_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 = CkXml_getChildContentByIndex(xml,0);
    s = CkXml_getChildContentByIndex(xml,1);

    printf("r = %s\n",r);
    printf("s = %s\n",s);

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

    // Get the corresponding public key.
    pubKey = CkPublicKey_Create();
    success = CkPublicKey_LoadFromFile(pubKey,"qa_data/ecc/secp256r1-pub.pem");
    if (success == FALSE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubKey));
        CkPrivateKey_Dispose(privKey);
        CkBinData_Dispose(bd);
        CkCrypt2_Dispose(crypt);
        CkEcc_Dispose(ecdsa);
        CkPrng_Dispose(prng);
        CkAsn_Dispose(asn);
        CkXml_Dispose(xml);
        CkPublicKey_Dispose(pubKey);
        return;
    }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    ecc2 = CkEcc_Create();
    result = CkEcc_VerifyHashENC(ecc2,hashStr,sig,"base64",pubKey);
    if (result != 1) {
        printf("%s\n",CkEcc_lastErrorText(ecc2));
        CkPrivateKey_Dispose(privKey);
        CkBinData_Dispose(bd);
        CkCrypt2_Dispose(crypt);
        CkEcc_Dispose(ecdsa);
        CkPrng_Dispose(prng);
        CkAsn_Dispose(asn);
        CkXml_Dispose(xml);
        CkPublicKey_Dispose(pubKey);
        CkEcc_Dispose(ecc2);
        return;
    }

    printf("Verified!\n");

    // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
    xml2 = CkXml_Create();
    CkXml_putTag(xml2,"sequence");
    CkXml_NewChild2(xml2,"int",r);
    CkXml_NewChild2(xml2,"int",s);

    asn2 = CkAsn_Create();
    CkAsn_LoadAsnXml(asn2,CkXml_getXml(xml2));
    encodedSig = CkAsn_getEncodedDer(asn2,"base64");
    printf("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...


    CkPrivateKey_Dispose(privKey);
    CkBinData_Dispose(bd);
    CkCrypt2_Dispose(crypt);
    CkEcc_Dispose(ecdsa);
    CkPrng_Dispose(prng);
    CkAsn_Dispose(asn);
    CkXml_Dispose(xml);
    CkPublicKey_Dispose(pubKey);
    CkEcc_Dispose(ecc2);
    CkXml_Dispose(xml2);
    CkAsn_Dispose(asn2);

    }