(VB.NET) ECDSA Sign and Verify

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify.

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

' First load an ECDSA private key to be used for signing.
Dim privKey As New Chilkat.PrivateKey
Dim success As Boolean = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
If (success = False) Then
    Debug.WriteLine(privKey.LastErrorText)
    Exit Sub
End If


' Sign the SHA256 hash of some data.
Dim bd As New Chilkat.BinData
success = bd.LoadFile("qa_data/hamlet.xml")
If (success = False) Then
    Debug.WriteLine("Failed to load file to be hashed.")
    Exit Sub
End If


Dim crypt As New Chilkat.Crypt2
crypt.HashAlgorithm = "sha256"
crypt.EncodingMode = "base64"
Dim hashStr As String = crypt.HashBdENC(bd)

Dim ecdsa As New Chilkat.Ecc
Dim prng As New Chilkat.Prng
' Returns ASN.1 signature as a base64 string.
Dim sig As String = ecdsa.SignHashENC(hashStr,"base64",privKey,prng)
Debug.WriteLine("sig = " & sig)

' The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
' SEQUENCE (2 elem)
'   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
'   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

' If you wish, you can get the r and s components of the signature like this:
Dim asn As New Chilkat.Asn
asn.LoadEncoded(sig,"base64")
Dim xml As New Chilkat.Xml
xml.LoadXml(asn.AsnToXml())

Debug.WriteLine(xml.GetXml())

' We now have this:
' <?xml version="1.0" encoding="utf-8"?>
' <sequence>
'     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
'     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
' </sequence>

' Get the "r" and "s" as hex strings
Dim r As String = xml.GetChildContentByIndex(0)
Dim s As String = xml.GetChildContentByIndex(1)

Debug.WriteLine("r = " & r)
Debug.WriteLine("s = " & s)

' --------------------------------------------------------------------
' Now verify against the hash of the original data.

' Get the corresponding public key.
Dim pubKey As New Chilkat.PublicKey
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
If (success = False) Then
    Debug.WriteLine(pubKey.LastErrorText)
    Exit Sub
End If


' We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
Dim ecc2 As New Chilkat.Ecc
Dim result As Integer = ecc2.VerifyHashENC(hashStr,sig,"base64",pubKey)
If (result <> 1) Then
    Debug.WriteLine(ecc2.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Verified!")

' Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
Dim xml2 As New Chilkat.Xml
xml2.Tag = "sequence"
xml2.NewChild2("int",r)
xml2.NewChild2("int",s)

Dim asn2 As New Chilkat.Asn
asn2.LoadAsnXml(xml2.GetXml())
Dim encodedSig As String = asn2.GetEncodedDer("base64")
Debug.WriteLine("encoded DSS signature: " & encodedSig)

' You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
' You will see the ASN.1 such as this:

' SEQUENCE (2 elem)
'   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
'   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...