Swift

DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature. Swift

func chilkatTest() {
    var success: Bool = false

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    let crypt = CkoCrypt2()!

    crypt.encodingMode = "hex"
    crypt.hashAlgorithm = "sha-1"

    var hashStr: String? = crypt.hashFileENC(path: "qa_data/hamlet.xml")
    print("hash to sign: \(hashStr!)")

    let dsa = CkoDsa()!

    var pemPrivateKey: String?
    pemPrivateKey = dsa.loadText(path: "qa_data/dsa/dsaPrivKey2.pem")
    success = dsa.fromPem(pemData: pemPrivateKey)
    if success == false {
        print("\(dsa.lastErrorText!)")
        return
    }

    // Load the hash to be signed into the DSA object:
    success = dsa.setEncodedHash(encoding: "hex", encodedHash: hashStr)
    if success == false {
        print("\(dsa.lastErrorText!)")
        return
    }

    // Sign the hash.
    success = dsa.signHash()
    if success == false {
        print("\(dsa.lastErrorText!)")
        return
    }

    // Get the ASN.1 signature.
    var asnSig: String? = dsa.getEncodedSignature(encoding: "base64")
    print("Signature: \(asnSig!)")

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    let asn = CkoAsn()!
    success = asn.loadEncoded(asnContent: asnSig, encoding: "base64")
    if success == false {
        print("\(asn.lastErrorText!)")
        return
    }

    // Get the ASN.1 as XML.
    let xml = CkoXml()!
    success = xml.load(xmlData: asn.asnToXml())
    print("Signature as XML: ")
    print("\(xml.getXml()!)")

    // Sample XML shown here.
    // The r and s values are the two hex strings in the XML.

    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
    //     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
    // </sequence>

    // Pretend we're starting with r,s
    var r: String? = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
    var s: String? = "588E53D3F7B69636B48FD7175E99A3961BD7D775"

    // Build the XML that will be converted to ASN.1
    xml.clear()
    xml.tag = "sequence"
    xml.newChild2(tagPath: "int", content: r)
    xml.newChild2(tagPath: "int", content: s)

    // Convert the XML to ASN.1
    success = asn.loadXml(xmlStr: xml.getXml())

    // Emit the signature as DER encoded ASN.1 (base64)
    asnSig = asn.getEncodedDer(encoding: "base64")

    // --------------------------------------------------------------------
    // Verify the signature using the asnSig we built from the r,s values
    // --------------------------------------------------------------------

    let dsa2 = CkoDsa()!

    // Load the DSA public key to be used for verification:
    var pemPublicKey: String?
    pemPublicKey = dsa2.loadText(path: "qa_data/dsa/dsaPubKey2.pem")
    success = dsa2.fromPublicPem(pemData: pemPublicKey)
    if success == false {
        print("\(dsa2.lastErrorText!)")
        return
    }

    // Load the hash to be verified.
    success = dsa2.setEncodedHash(encoding: "hex", encodedHash: hashStr)
    if success == false {
        print("\(dsa2.lastErrorText!)")
        return
    }

    // Load the ASN.1 signature:
    success = dsa2.setEncodedSignature(encoding: "base64", encodedSig: asnSig)
    if success == false {
        print("\(dsa2.lastErrorText!)")
        return
    }

    // Verify:
    success = dsa2.verify()
    if success == false {
        print("\(dsa2.lastErrorText!)")
    }
    else {
        print("DSA Signature Verified!")
    }


}