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DSA Signature Create and Verify

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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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Local $bSuccess = False

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

$oCrypt = ObjCreate("Chilkat.Crypt2")

$oCrypt.EncodingMode = "hex"
$oCrypt.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.
Local $sHashStr = $oCrypt.HashFileENC("hamlet.xml")

$oDsa = ObjCreate("Chilkat.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.
Local $sPemPrivateKey
$sPemPrivateKey = $oDsa.LoadText("dsa_priv.pem")
$bSuccess = $oDsa.FromPem($sPemPrivateKey)
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa.LastErrorText & @CRLF)
    Exit
EndIf

;  You may optionally verify the key to ensure that it is a valid
;  DSA key.
$bSuccess = $oDsa.VerifyKey()
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa.LastErrorText & @CRLF)
    Exit
EndIf

;  Load the hash to be signed into the DSA object:
$bSuccess = $oDsa.SetEncodedHash("hex",$sHashStr)
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa.LastErrorText & @CRLF)
    Exit
EndIf

;  Now that the DSA object contains both the private key and hash,
;  it is ready to create the signature:
$bSuccess = $oDsa.SignHash()
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa.LastErrorText & @CRLF)
    Exit
EndIf

;  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.)
Local $sHexSig = $oDsa.GetEncodedSignature("hex")
ConsoleWrite("Signature:" & @CRLF)
ConsoleWrite($sHexSig & @CRLF)

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

$oDsa2 = ObjCreate("Chilkat.Dsa")

;  Load the DSA public key to be used for verification:
Local $sPemPublicKey
$sPemPublicKey = $oDsa2.LoadText("dsa_pub.pem")
$bSuccess = $oDsa2.FromPublicPem($sPemPublicKey)
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa2.LastErrorText & @CRLF)
    Exit
EndIf

;  Load the hash to be verified against the signature.
$bSuccess = $oDsa2.SetEncodedHash("hex",$sHashStr)
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa2.LastErrorText & @CRLF)
    Exit
EndIf

;  Load the signature:
$bSuccess = $oDsa2.SetEncodedSignature("hex",$sHexSig)
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa2.LastErrorText & @CRLF)
    Exit
EndIf

;  Verify:
$bSuccess = $oDsa2.Verify()
If ($bSuccess <> True) Then
    ConsoleWrite($oDsa2.LastErrorText & @CRLF)
Else
    ConsoleWrite("DSA Signature Verified!" & @CRLF)
EndIf