(Go) 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.

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

    crypt := chilkat.NewCrypt2()

    crypt.SetEncodingMode("hex")
    crypt.SetHashAlgorithm("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.
    hashStr := crypt.HashFileENC("hamlet.xml")

    dsa := chilkat.NewDsa()

    // 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 = new(string)
    pemPrivateKey = dsa.LoadText("dsa_priv.pem")
    success := dsa.FromPem(*pemPrivateKey)
    if success != true {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        return
    }

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    success = dsa.VerifyKey()
    if success != true {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        return
    }

    // Load the hash to be signed into the DSA object:
    success = dsa.SetEncodedHash("hex",*hashStr)
    if success != true {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        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 {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        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.)
    hexSig := dsa.GetEncodedSignature("hex")
    fmt.Println("Signature:")
    fmt.Println(*hexSig)

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

    dsa2 := chilkat.NewDsa()

    // Load the DSA public key to be used for verification:
    var pemPublicKey *string = new(string)
    pemPublicKey = dsa2.LoadText("dsa_pub.pem")
    success = dsa2.FromPublicPem(*pemPublicKey)
    if success != true {
        fmt.Println(dsa2.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        dsa2.DisposeDsa()
        return
    }

    // Load the hash to be verified against the signature.
    success = dsa2.SetEncodedHash("hex",*hashStr)
    if success != true {
        fmt.Println(dsa2.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        dsa2.DisposeDsa()
        return
    }

    // Load the signature:
    success = dsa2.SetEncodedSignature("hex",*hexSig)
    if success != true {
        fmt.Println(dsa2.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        dsa2.DisposeDsa()
        return
    }

    // Verify:
    success = dsa2.Verify()
    if success != true {
        fmt.Println(dsa2.LastErrorText())
    }
    else {
        fmt.Println("DSA Signature Verified!")
    }


    crypt.DisposeCrypt2()
    dsa.DisposeDsa()
    dsa2.DisposeDsa()