Visual Basic 6.0

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. Visual Basic 6.0

Dim success As Long
success = 0

' 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 PrivateKey
success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
If (success = 0) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
End If

' Sign the SHA256 hash of some data.
Dim bd As New ChilkatBinData
success = bd.LoadFile("qa_data/hamlet.xml")
If (success = 0) Then
    Debug.Print "Failed to load file to be hashed."
    Exit Sub
End If

Dim crypt As New ChilkatCrypt2
crypt.HashAlgorithm = "sha256"
crypt.EncodingMode = "base64"
Dim hashStr As String
hashStr = crypt.HashBdENC(bd)

Dim ecdsa As New ChilkatEcc
Dim prng As New ChilkatPrng
' Returns ASN.1 signature as a base64 string.
Dim sig As String
sig = ecdsa.SignHashENC(hashStr,"base64",privKey,prng)
Debug.Print "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 ChilkatAsn
success = asn.LoadEncoded(sig,"base64")
Dim xml As New ChilkatXml
success = xml.LoadXml(asn.AsnToXml())

Debug.Print 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
r = xml.GetChildContentByIndex(0)
Dim s As String
s = xml.GetChildContentByIndex(1)

Debug.Print "r = " & r
Debug.Print "s = " & s

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

' Get the corresponding public key.
Dim pubKey As New PublicKey
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
If (success = 0) Then
    Debug.Print 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 ChilkatEcc
Dim result As Long
result = ecc2.VerifyHashENC(hashStr,sig,"base64",pubKey)
If (result <> 1) Then
    Debug.Print ecc2.LastErrorText
    Exit Sub
End If

Debug.Print "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 ChilkatXml
xml2.Tag = "sequence"
xml2.NewChild2 "int",r
xml2.NewChild2 "int",s

Dim asn2 As New ChilkatAsn
success = asn2.LoadAsnXml(xml2.GetXml())
Dim encodedSig As String
encodedSig = asn2.GetEncodedDer("base64")
Debug.Print "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...