(PowerBuilder) 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 ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

integer li_rc
oleobject loo_Crypt
string ls_HashStr
oleobject loo_Dsa
string ls_PemPrivateKey
integer li_Success
string ls_HexSig
oleobject loo_Dsa2
string ls_PemPublicKey

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

loo_Crypt = create oleobject
li_rc = loo_Crypt.ConnectToNewObject("Chilkat_9_5_0.Crypt2")
if li_rc < 0 then
    destroy loo_Crypt
    MessageBox("Error","Connecting to COM object failed")
    return
end if

loo_Crypt.EncodingMode = "hex"
loo_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.
ls_HashStr = loo_Crypt.HashFileENC("hamlet.xml")

loo_Dsa = create oleobject
li_rc = loo_Dsa.ConnectToNewObject("Chilkat_9_5_0.Dsa")

// 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.

ls_PemPrivateKey = loo_Dsa.LoadText("dsa_priv.pem")
li_Success = loo_Dsa.FromPem(ls_PemPrivateKey)
if li_Success <> 1 then
    Write-Debug loo_Dsa.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    return
end if

// You may optionally verify the key to ensure that it is a valid
// DSA key.
li_Success = loo_Dsa.VerifyKey()
if li_Success <> 1 then
    Write-Debug loo_Dsa.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    return
end if

// Load the hash to be signed into the DSA object:
li_Success = loo_Dsa.SetEncodedHash("hex",ls_HashStr)
if li_Success <> 1 then
    Write-Debug loo_Dsa.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    return
end if

// Now that the DSA object contains both the private key and hash,
// it is ready to create the signature:
li_Success = loo_Dsa.SignHash()
if li_Success <> 1 then
    Write-Debug loo_Dsa.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    return
end if

// 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.)
ls_HexSig = loo_Dsa.GetEncodedSignature("hex")
Write-Debug "Signature:"
Write-Debug ls_HexSig

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

loo_Dsa2 = create oleobject
li_rc = loo_Dsa2.ConnectToNewObject("Chilkat_9_5_0.Dsa")

// Load the DSA public key to be used for verification:

ls_PemPublicKey = loo_Dsa2.LoadText("dsa_pub.pem")
li_Success = loo_Dsa2.FromPublicPem(ls_PemPublicKey)
if li_Success <> 1 then
    Write-Debug loo_Dsa2.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    destroy loo_Dsa2
    return
end if

// Load the hash to be verified against the signature.
li_Success = loo_Dsa2.SetEncodedHash("hex",ls_HashStr)
if li_Success <> 1 then
    Write-Debug loo_Dsa2.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    destroy loo_Dsa2
    return
end if

// Load the signature:
li_Success = loo_Dsa2.SetEncodedSignature("hex",ls_HexSig)
if li_Success <> 1 then
    Write-Debug loo_Dsa2.LastErrorText
    destroy loo_Crypt
    destroy loo_Dsa
    destroy loo_Dsa2
    return
end if

// Verify:
li_Success = loo_Dsa2.Verify()
if li_Success <> 1 then
    Write-Debug loo_Dsa2.LastErrorText
else
    Write-Debug "DSA Signature Verified!"
end if



destroy loo_Crypt
destroy loo_Dsa
destroy loo_Dsa2