(Swift 2) 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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func chilkatTest() {
    // 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.

    let sb = CkoStringBuilder()
    sb.Append("The quick brown fox jumps over the lazy dog")
    var hash: String? = sb.GetHash("sha256", encoding: "base64", charset: "utf-8")

    // Load the ECDSA key to be used for signing.
    let privKey = CkoPrivateKey()
    var success: Bool = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
    if success != true {
        print("\(privKey.LastErrorText)")
        return
    }

    let prng = CkoPrng()
    let ecdsa = CkoEcc()

    // 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.AsnFormat = false

    var ecdsaSigBase64: String? = ecdsa.SignHashENC(hash, encoding: "base64", privkey: privKey, prng: prng)
    if ecdsa.LastMethodSuccess != true {
        print("\(ecdsa.LastErrorText)")
        return
    }

    print("ECDSA signature = \(ecdsaSigBase64!)")

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

    let pubKey = CkoPublicKey()
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
    if success != true {
        print("\(pubKey.LastErrorText)")
        return
    }

    // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    var result: Int = ecdsa.VerifyHashENC(hash, encodedSig: ecdsaSigBase64, encoding: "base64", pubkey: pubKey).intValue
    if result == 1 {
        print("Signature is valid.")
        return
    }

    if result == 0 {
        print("Signature is invalid.")
        return
    }

    if result < 0 {
        print("\(ecdsa.LastErrorText)")
        print("The VerifyHashENC method call failed.")
        return
    }


}