B4X

DSA R,S Signature Values

See more DSA Examples

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. B4X

Dim success As Boolean = False

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

Dim crypt As ChilkatCrypt2
crypt.Initialize("crypt")

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

Dim hashStr As String = crypt.HashFileENC("qa_data/hamlet.xml")
Log("hash to sign: " & hashStr)

Dim dsa As ChilkatDsa
dsa.Initialize

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


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


'  Sign the hash.
success = dsa.SignHash
If success = False Then
    Log(dsa.LastErrorText)
    Return
End If


'  Get the ASN.1 signature.
Dim asnSig As String = dsa.GetEncodedSignature("base64")
Log("Signature: " & asnSig)

'  Examine the details of the ASN.1 signature.
'  We want to get the r,s values as hex strings..
Dim asn As ChilkatAsn
asn.Initialize
success = asn.LoadEncoded(asnSig, "base64")
If success = False Then
    Log(asn.LastErrorText)
    Return
End If


'  Get the ASN.1 as XML.
Dim xml As ChilkatXml
xml.Initialize
success = xml.LoadXml(asn.AsnToXml)
Log("Signature as XML: ")
Log(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 = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
Dim s As String = "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 ChilkatDsa
dsa2.Initialize

'  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
    Log(dsa2.LastErrorText)
    Return
End If


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


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


'  Verify:
success = dsa2.Verify
If success = False Then
    Log(dsa2.LastErrorText)
Else
    Log("DSA Signature Verified!")
End If