VB.NET

ECDSA Sign and Verify

See more ECC Examples

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

Dim success As Boolean = False

' 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
success = 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...