Unicode C++

ECDSA Sign Data and Get Raw R and S Values

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Demonstrates getting the raw R and S value of an ECDSA signature. Unicode C++

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

void ChilkatSample(void)
    {
    bool success = false;

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

    //  To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    //  is signed.

    CkCrypt2W crypt;
    crypt.put_HashAlgorithm(L"SHA256");
    crypt.put_Charset(L"utf-8");
    crypt.put_EncodingMode(L"base64");

    //  Hash a string.
    const wchar_t *hash1 = crypt.hashStringENC(L"The quick brown fox jumps over the lazy dog");
    wprintf(L"hash1 = %s\n",hash1);

    //  -----------------------------------------------------------
    //  An ECDSA private key is used for signing.  The public key is for signature verification.
    //  Load our ECC private key.
    //  Our private key file contains this:

    //  	// -----BEGIN PRIVATE KEY-----
    //  	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
    //  	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
    //  	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
    //  	-----END PRIVATE KEY-----

    CkPrivateKeyW privKey;
    success = privKey.LoadPemFile(L"qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != true) {
        wprintf(L"%s\n",privKey.lastErrorText());
        return;
    }

    //  Sign the hash..
    CkPrngW prng;
    CkEccW ecdsa;
    const wchar_t *ecdsaSigBase64 = ecdsa.signHashENC(hash1,L"base64",privKey,prng);
    if (ecdsa.get_LastMethodSuccess() != true) {
        wprintf(L"%s\n",ecdsa.lastErrorText());
        return;
    }

    //  The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
    //  For example:
    //  SEQUENCE (2 elem)
    //    INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
    //    INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

    wprintf(L"Base64 ECDSA signature = %s\n",ecdsaSigBase64);

    //  If the raw R and S values are needed, here's how to get them:
    CkAsnW asn;
    success = asn.LoadEncoded(ecdsaSigBase64,L"base64");
    if (success == false) {
        wprintf(L"%s\n",asn.lastErrorText());
        return;
    }

    //  The R and X will be in hexidecimal in the XML.
    CkXmlW xml;
    xml.LoadXml(asn.asnToXml());
    wprintf(L"%s\n",xml.getXml());

    //  The XML looks like this:
    //  <sequence>
    //  <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
    //  <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
    //  </sequence>

    //  Copy raw R and S hex values into a Chilkat BinData object.
    CkBinDataW bd;
    const wchar_t *r = xml.getChildContent(L"int[0]");
    const wchar_t *s = xml.getChildContent(L"int[1]");
    bd.AppendEncoded(r,L"hex");
    bd.AppendEncoded(s,L"hex");

    wprintf(L"Number of bytes in bd: %d\n",bd.get_NumBytes());
    }