(Swift 3,4,5...) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

func chilkatTest() {
    // 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"

    // Return the SHA-1 hash of a file.  The file may be any size.
    // The Chilkat Crypt component will stream the file when 
    // computing the hash, keeping the memory usage constant
    // and reasonable.
    // The 20-byte SHA-1 hash is returned as a hex-encoded string.
    var hashStr: String? = crypt.hashFileENC("hamlet.xml")

    let dsa = CkoDsa()!

    // Load a DSA private key from a PEM file.  Chilkat DSA
    // provides the ability to load and save DSA public and private
    // keys from encrypted or non-encrypted PEM or DER.
    // The LoadText method is for convenience only.  You may
    // use any means to load the contents of a PEM file into
    // a string.
    var pemPrivateKey: String?
    pemPrivateKey = dsa.loadText("dsa_priv.pem")
    var success: Bool = dsa.fromPem(pemPrivateKey)
    if success != true {
        print("\(dsa.lastErrorText!)")
        return
    }

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    success = dsa.verifyKey()
    if success != true {
        print("\(dsa.lastErrorText!)")
        return
    }

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

    // Now that the DSA object contains both the private key and hash,
    // it is ready to create the signature:
    success = dsa.signHash()
    if success != true {
        print("\(dsa.lastErrorText!)")
        return
    }

    // If SignHash is successful, the DSA object contains the
    // signature.  It may be accessed as a hex or base64 encoded
    // string.  (It is also possible to access directly in byte array form via
    // the "Signature" property.)
    var hexSig: String? = dsa.getEncodedSignature("hex")
    print("Signature:")
    print("\(hexSig!)")

    // -----------------------------------------------------------
    // Step 2: Verify the DSA Signature
    // -----------------------------------------------------------

    let dsa2 = CkoDsa()!

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

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

    // Load the signature:
    success = dsa2.setEncodedSignature("hex", encodedSig: hexSig)
    if success != true {
        print("\(dsa2.lastErrorText!)")
        return
    }

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


}