(Xojo Plugin) DSA R,S Signature Values

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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.

Chilkat Xojo Plugin Download Xojo Plugin for Windows, Linux, Mac OS X, and ARM, ARM64

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

Dim crypt As New Chilkat.Crypt2

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

Dim hashStr As String
hashStr = crypt.HashFileENC("qa_data/hamlet.xml")
System.DebugLog("hash to sign: " + hashStr)

Dim dsa As New Chilkat.Dsa

Dim pemPrivateKey As String
pemPrivateKey = dsa.LoadText("qa_data/dsa/dsaPrivKey2.pem")
Dim success As Boolean
success = dsa.FromPem(pemPrivateKey)
If (success = False) Then
    System.DebugLog(dsa.LastErrorText)
    Return
End If

// Load the hash to be signed into the DSA object:
success = dsa.SetEncodedHash("hex",hashStr)
If (success = False) Then
    System.DebugLog(dsa.LastErrorText)
    Return
End If

// Sign the hash.
success = dsa.SignHash()
If (success = False) Then
    System.DebugLog(dsa.LastErrorText)
    Return
End If

// Get the ASN.1 signature.
Dim asnSig As String
asnSig = dsa.GetEncodedSignature("base64")
System.DebugLog("Signature: " + asnSig)

// Examine the details of the ASN.1 signature.
// We want to get the r,s values as hex strings..
Dim asn As New Chilkat.Asn
success = asn.LoadEncoded(asnSig,"base64")
If (success = False) Then
    System.DebugLog(asn.LastErrorText)
    Return
End If

// Get the ASN.1 as XML.
Dim xml As New Chilkat.Xml
success = xml.LoadXml(asn.AsnToXml())
System.DebugLog("Signature as XML: ")
System.DebugLog(xml.GetXml())

// 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
Dim r As String
r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
Dim s As String
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
// --------------------------------------------------------------------

Dim dsa2 As New Chilkat.Dsa

// Load the DSA public key to be used for verification:
Dim pemPublicKey As String
pemPublicKey = dsa2.LoadText("qa_data/dsa/dsaPubKey2.pem")
success = dsa2.FromPublicPem(pemPublicKey)
If (success = False) Then
    System.DebugLog(dsa2.LastErrorText)
    Return
End If

// Load the hash to be verified.
success = dsa2.SetEncodedHash("hex",hashStr)
If (success = False) Then
    System.DebugLog(dsa2.LastErrorText)
    Return
End If

// Load the ASN.1 signature:
success = dsa2.SetEncodedSignature("base64",asnSig)
If (success = False) Then
    System.DebugLog(dsa2.LastErrorText)
    Return
End If

// Verify:
success = dsa2.Verify()
If (success = False) Then
    System.DebugLog(dsa2.LastErrorText)
Else
    System.DebugLog("DSA Signature Verified!")
End If