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. C++

#include <CkCrypt2.h>
#include <CkPrivateKey.h>
#include <CkPrng.h>
#include <CkEcc.h>
#include <CkAsn.h>
#include <CkXml.h>
#include <CkBinData.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.

    CkCrypt2 crypt;
    crypt.put_HashAlgorithm("SHA256");
    crypt.put_Charset("utf-8");
    crypt.put_EncodingMode("base64");

    //  Hash a string.
    const char *hash1 = crypt.hashStringENC("The quick brown fox jumps over the lazy dog");
    std::cout << "hash1 = " << hash1 << "\r\n";

    //  -----------------------------------------------------------
    //  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-----

    CkPrivateKey privKey;
    success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != true) {
        std::cout << privKey.lastErrorText() << "\r\n";
        return;
    }

    //  Sign the hash..
    CkPrng prng;
    CkEcc ecdsa;
    const char *ecdsaSigBase64 = ecdsa.signHashENC(hash1,"base64",privKey,prng);
    if (ecdsa.get_LastMethodSuccess() != true) {
        std::cout << ecdsa.lastErrorText() << "\r\n";
        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

    std::cout << "Base64 ECDSA signature = " << ecdsaSigBase64 << "\r\n";

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

    //  The R and X will be in hexidecimal in the XML.
    CkXml xml;
    xml.LoadXml(asn.asnToXml());
    std::cout << xml.getXml() << "\r\n";

    //  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.
    CkBinData bd;
    const char *r = xml.getChildContent("int[0]");
    const char *s = xml.getChildContent("int[1]");
    bd.AppendEncoded(r,"hex");
    bd.AppendEncoded(s,"hex");

    std::cout << "Number of bytes in bd: " << bd.get_NumBytes() << "\r\n";
    }