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

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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.

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    // 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 := chilkat.NewStringBuilder()
    sb.Append("The quick brown fox jumps over the lazy dog")
    hash := sb.GetHash("sha256","base64","utf-8")

    // Load the ECDSA key to be used for signing.
    privKey := chilkat.NewPrivateKey()
    success := privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
    if success != true {
        fmt.Println(privKey.LastErrorText())
        sb.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        return
    }

    prng := chilkat.NewPrng()
    ecdsa := chilkat.NewEcc()

    // 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
    ecdsa.SetAsnFormat(false)

    ecdsaSigBase64 := ecdsa.SignHashENC(*hash,"base64",privKey,prng)
    if ecdsa.LastMethodSuccess() != true {
        fmt.Println(ecdsa.LastErrorText())
        sb.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        prng.DisposePrng()
        ecdsa.DisposeEcc()
        return
    }

    fmt.Println("ECDSA signature = ", *ecdsaSigBase64)

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

    pubKey := chilkat.NewPublicKey()
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
    if success != true {
        fmt.Println(pubKey.LastErrorText())
        sb.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        prng.DisposePrng()
        ecdsa.DisposeEcc()
        pubKey.DisposePublicKey()
        return
    }

    // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    result := ecdsa.VerifyHashENC(*hash,*ecdsaSigBase64,"base64",pubKey)
    if result == 1 {
        fmt.Println("Signature is valid.")
        sb.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        prng.DisposePrng()
        ecdsa.DisposeEcc()
        pubKey.DisposePublicKey()
        return
    }

    if result == 0 {
        fmt.Println("Signature is invalid.")
        sb.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        prng.DisposePrng()
        ecdsa.DisposeEcc()
        pubKey.DisposePublicKey()
        return
    }

    if result < 0 {
        fmt.Println(ecdsa.LastErrorText())
        fmt.Println("The VerifyHashENC method call failed.")
        sb.DisposeStringBuilder()
        privKey.DisposePrivateKey()
        prng.DisposePrng()
        ecdsa.DisposeEcc()
        pubKey.DisposePublicKey()
        return
    }


    sb.DisposeStringBuilder()
    privKey.DisposePrivateKey()
    prng.DisposePrng()
    ecdsa.DisposeEcc()
    pubKey.DisposePublicKey()