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

void ChilkatSample(void)
    {
    BOOL success;
    HCkCrypt2W crypt;
    const wchar_t *hash1;
    HCkPrivateKeyW privKey;
    HCkPrngW prng;
    HCkEccW ecdsa;
    const wchar_t *ecdsaSigBase64;
    HCkAsnW asn;
    HCkXmlW xml;
    HCkBinDataW bd;
    const wchar_t *r;
    const wchar_t *s;

    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.

    crypt = CkCrypt2W_Create();
    CkCrypt2W_putHashAlgorithm(crypt,L"SHA256");
    CkCrypt2W_putCharset(crypt,L"utf-8");
    CkCrypt2W_putEncodingMode(crypt,L"base64");

    // Hash a string.
    hash1 = CkCrypt2W_hashStringENC(crypt,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-----

    privKey = CkPrivateKeyW_Create();
    success = CkPrivateKeyW_LoadPemFile(privKey,L"qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != TRUE) {
        wprintf(L"%s\n",CkPrivateKeyW_lastErrorText(privKey));
        CkCrypt2W_Dispose(crypt);
        CkPrivateKeyW_Dispose(privKey);
        return;
    }

    // Sign the hash..
    prng = CkPrngW_Create();
    ecdsa = CkEccW_Create();
    ecdsaSigBase64 = CkEccW_signHashENC(ecdsa,hash1,L"base64",privKey,prng);
    if (CkEccW_getLastMethodSuccess(ecdsa) != TRUE) {
        wprintf(L"%s\n",CkEccW_lastErrorText(ecdsa));
        CkCrypt2W_Dispose(crypt);
        CkPrivateKeyW_Dispose(privKey);
        CkPrngW_Dispose(prng);
        CkEccW_Dispose(ecdsa);
        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:
    asn = CkAsnW_Create();
    success = CkAsnW_LoadEncoded(asn,ecdsaSigBase64,L"base64");
    if (success == FALSE) {
        wprintf(L"%s\n",CkAsnW_lastErrorText(asn));
        CkCrypt2W_Dispose(crypt);
        CkPrivateKeyW_Dispose(privKey);
        CkPrngW_Dispose(prng);
        CkEccW_Dispose(ecdsa);
        CkAsnW_Dispose(asn);
        return;
    }

    // The R and X will be in hexidecimal in the XML.
    xml = CkXmlW_Create();
    CkXmlW_LoadXml(xml,CkAsnW_asnToXml(asn));
    wprintf(L"%s\n",CkXmlW_getXml(xml));

    // 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.
    bd = CkBinDataW_Create();
    r = CkXmlW_getChildContent(xml,L"int[0]");
    s = CkXmlW_getChildContent(xml,L"int[1]");
    CkBinDataW_AppendEncoded(bd,r,L"hex");
    CkBinDataW_AppendEncoded(bd,s,L"hex");

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


    CkCrypt2W_Dispose(crypt);
    CkPrivateKeyW_Dispose(privKey);
    CkPrngW_Dispose(prng);
    CkEccW_Dispose(ecdsa);
    CkAsnW_Dispose(asn);
    CkXmlW_Dispose(xml);
    CkBinDataW_Dispose(bd);

    }