C

Create ECSDA Signature using Raw r and s Format (not ASN.1)

See more ECC Examples

Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

C

#include <C_CkStringBuilder.h>
#include <C_CkPrivateKey.h>
#include <C_CkPrng.h>
#include <C_CkEcc.h>
#include <C_CkPublicKey.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkStringBuilder sb;
    const char *hash;
    HCkPrivateKey privKey;
    HCkPrng prng;
    HCkEcc ecdsa;
    const char *ecdsaSigBase64;
    HCkPublicKey pubKey;
    int result;

    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.

    sb = CkStringBuilder_Create();
    CkStringBuilder_Append(sb,"The quick brown fox jumps over the lazy dog");
    hash = CkStringBuilder_getHash(sb,"sha256","base64","utf-8");

    // Load the ECDSA key to be used for signing.
    privKey = CkPrivateKey_Create();
    success = CkPrivateKey_LoadPemFile(privKey,"qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != TRUE) {
        printf("%s\n",CkPrivateKey_lastErrorText(privKey));
        CkStringBuilder_Dispose(sb);
        CkPrivateKey_Dispose(privKey);
        return;
    }

    prng = CkPrng_Create();
    ecdsa = CkEcc_Create();

    // Produce a signature that is not ASN.1, but is instead the concatenation
    // of the raw r and s signature parts.
    // This feature was added in Chilkat v9.5.0.97
    CkEcc_putAsnFormat(ecdsa,FALSE);

    ecdsaSigBase64 = CkEcc_signHashENC(ecdsa,hash,"base64",privKey,prng);
    if (CkEcc_getLastMethodSuccess(ecdsa) != TRUE) {
        printf("%s\n",CkEcc_lastErrorText(ecdsa));
        CkStringBuilder_Dispose(sb);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_Dispose(ecdsa);
        return;
    }

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

    // -----------------------------------------------------------
    // Now let's verify the signature using the public key.

    pubKey = CkPublicKey_Create();
    success = CkPublicKey_LoadFromFile(pubKey,"qa_data/ecc/secp256r1-pubkey.pem");
    if (success != TRUE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubKey));
        CkStringBuilder_Dispose(sb);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_Dispose(ecdsa);
        CkPublicKey_Dispose(pubKey);
        return;
    }

    // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    result = CkEcc_VerifyHashENC(ecdsa,hash,ecdsaSigBase64,"base64",pubKey);
    if (result == 1) {
        printf("Signature is valid.\n");
        CkStringBuilder_Dispose(sb);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_Dispose(ecdsa);
        CkPublicKey_Dispose(pubKey);
        return;
    }

    if (result == 0) {
        printf("Signature is invalid.\n");
        CkStringBuilder_Dispose(sb);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_Dispose(ecdsa);
        CkPublicKey_Dispose(pubKey);
        return;
    }

    if (result < 0) {
        printf("%s\n",CkEcc_lastErrorText(ecdsa));
        printf("The VerifyHashENC method call failed.\n");
        CkStringBuilder_Dispose(sb);
        CkPrivateKey_Dispose(privKey);
        CkPrng_Dispose(prng);
        CkEcc_Dispose(ecdsa);
        CkPublicKey_Dispose(pubKey);
        return;
    }



    CkStringBuilder_Dispose(sb);
    CkPrivateKey_Dispose(privKey);
    CkPrng_Dispose(prng);
    CkEcc_Dispose(ecdsa);
    CkPublicKey_Dispose(pubKey);

    }