Classic ASP
DSA R,S Signature Values

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.
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Classic ASP
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<%
success = 0

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

set crypt = Server.CreateObject("Chilkat.Crypt2")

crypt.EncodingMode = "hex"
crypt.HashAlgorithm = "sha-1"

hashStr = crypt.HashFileENC("qa_data/hamlet.xml")
Response.Write "<pre>" & Server.HTMLEncode( "hash to sign: " & hashStr) & "</pre>"

set dsa = Server.CreateObject("Chilkat.Dsa")

pemPrivateKey = dsa.LoadText("qa_data/dsa/dsaPrivKey2.pem")
success = dsa.FromPem(pemPrivateKey)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa.LastErrorText) & "</pre>"
    Response.End
End If

' Load the hash to be signed into the DSA object:
success = dsa.SetEncodedHash("hex",hashStr)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa.LastErrorText) & "</pre>"
    Response.End
End If

' Sign the hash.
success = dsa.SignHash()
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa.LastErrorText) & "</pre>"
    Response.End
End If

' Get the ASN.1 signature.
asnSig = dsa.GetEncodedSignature("base64")
Response.Write "<pre>" & Server.HTMLEncode( "Signature: " & asnSig) & "</pre>"

' Examine the details of the ASN.1 signature.
' We want to get the r,s values as hex strings..
set asn = Server.CreateObject("Chilkat.Asn")
success = asn.LoadEncoded(asnSig,"base64")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( asn.LastErrorText) & "</pre>"
    Response.End
End If

' Get the ASN.1 as XML.
set xml = Server.CreateObject("Chilkat.Xml")
success = xml.LoadXml(asn.AsnToXml())
Response.Write "<pre>" & Server.HTMLEncode( "Signature as XML: ") & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( xml.GetXml()) & "</pre>"

' 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
r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
s = "588E53D3F7B69636B48FD7175E99A3961BD7D775"

' Build the XML that will be converted to ASN.1
xml.Clear 
xml.Tag = "sequence"
xml.NewChild2 "int",r
xml.NewChild2 "int",s

' Convert the XML to ASN.1
success = asn.LoadAsnXml(xml.GetXml())

' Emit the signature as DER encoded ASN.1 (base64)
asnSig = asn.GetEncodedDer("base64")

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

set dsa2 = Server.CreateObject("Chilkat.Dsa")

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

pemPublicKey = dsa2.LoadText("qa_data/dsa/dsaPubKey2.pem")
success = dsa2.FromPublicPem(pemPublicKey)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa2.LastErrorText) & "</pre>"
    Response.End
End If

' Load the hash to be verified.
success = dsa2.SetEncodedHash("hex",hashStr)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa2.LastErrorText) & "</pre>"
    Response.End
End If

' Load the ASN.1 signature:
success = dsa2.SetEncodedSignature("base64",asnSig)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa2.LastErrorText) & "</pre>"
    Response.End
End If

' Verify:
success = dsa2.Verify()
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( dsa2.LastErrorText) & "</pre>"
Else
    Response.Write "<pre>" & Server.HTMLEncode( "DSA Signature Verified!") & "</pre>"
End If


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