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

void ChilkatSample(void)
    {
    BOOL success;
    HCkCrypt2 crypt;
    const char *hash1;
    HCkPrivateKey privKey;
    HCkPrng prng;
    HCkEcc ecdsa;
    const char *ecdsaSigBase64;
    HCkAsn asn;
    HCkXml xml;
    HCkBinData bd;
    const char *r;
    const char *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 = CkCrypt2_Create();
    CkCrypt2_putHashAlgorithm(crypt,"SHA256");
    CkCrypt2_putCharset(crypt,"utf-8");
    CkCrypt2_putEncodingMode(crypt,"base64");

    // Hash a string.
    hash1 = CkCrypt2_hashStringENC(crypt,"The quick brown fox jumps over the lazy dog");
    printf("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 = CkPrivateKey_Create();
    success = CkPrivateKey_LoadPemFile(privKey,"qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != TRUE) {
        printf("%s\n",CkPrivateKey_lastErrorText(privKey));
        CkCrypt2_Dispose(crypt);
        CkPrivateKey_Dispose(privKey);
        return;
    }

    // Sign the hash..
    prng = CkPrng_Create();
    ecdsa = CkEcc_Create();
    ecdsaSigBase64 = CkEcc_signHashENC(ecdsa,hash1,"base64",privKey,prng);
    if (CkEcc_getLastMethodSuccess(ecdsa) != TRUE) {
        printf("%s\n",CkEcc_lastErrorText(ecdsa));
        CkCrypt2_Dispose(crypt);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_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

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

    // If the raw R and S values are needed, here's how to get them:
    asn = CkAsn_Create();
    success = CkAsn_LoadEncoded(asn,ecdsaSigBase64,"base64");
    if (success == FALSE) {
        printf("%s\n",CkAsn_lastErrorText(asn));
        CkCrypt2_Dispose(crypt);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_Dispose(ecdsa);
        CkAsn_Dispose(asn);
        return;
    }

    // The R and X will be in hexidecimal in the XML.
    xml = CkXml_Create();
    CkXml_LoadXml(xml,CkAsn_asnToXml(asn));
    printf("%s\n",CkXml_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 = CkBinData_Create();
    r = CkXml_getChildContent(xml,"int[0]");
    s = CkXml_getChildContent(xml,"int[1]");
    CkBinData_AppendEncoded(bd,r,"hex");
    CkBinData_AppendEncoded(bd,s,"hex");

    printf("Number of bytes in bd: %d\n",CkBinData_getNumBytes(bd));


    CkCrypt2_Dispose(crypt);
    CkPrivateKey_Dispose(privKey);
    CkPrng_Dispose(prng);
    CkEcc_Dispose(ecdsa);
    CkAsn_Dispose(asn);
    CkXml_Dispose(xml);
    CkBinData_Dispose(bd);

    }