(Classic ASP) ECDSA Sign and Verify

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

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

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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.
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.PrivateKey")
set privKey = Server.CreateObject("Chilkat.PrivateKey")
success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( privKey.LastErrorText) & "</pre>"
    Response.End
End If

' Sign the SHA256 hash of some data.
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.BinData")
set bd = Server.CreateObject("Chilkat.BinData")
success = bd.LoadFile("qa_data/hamlet.xml")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Failed to load file to be hashed.") & "</pre>"
    Response.End
End If

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Crypt2")
set crypt = Server.CreateObject("Chilkat.Crypt2")
crypt.HashAlgorithm = "sha256"
crypt.EncodingMode = "base64"
hashStr = crypt.HashBdENC(bd)

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Ecc")
set ecdsa = Server.CreateObject("Chilkat.Ecc")
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Prng")
set prng = Server.CreateObject("Chilkat.Prng")
' Returns ASN.1 signature as a base64 string.
sig = ecdsa.SignHashENC(hashStr,"base64",privKey,prng)
Response.Write "<pre>" & Server.HTMLEncode( "sig = " & sig) & "</pre>"

' 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:
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Asn")
set asn = Server.CreateObject("Chilkat.Asn")
success = asn.LoadEncoded(sig,"base64")
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Xml")
set xml = Server.CreateObject("Chilkat.Xml")
success = xml.LoadXml(asn.AsnToXml())

Response.Write "<pre>" & Server.HTMLEncode( xml.GetXml()) & "</pre>"

' 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
r = xml.GetChildContentByIndex(0)
s = xml.GetChildContentByIndex(1)

Response.Write "<pre>" & Server.HTMLEncode( "r = " & r) & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( "s = " & s) & "</pre>"

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

' Get the corresponding public key.
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.PublicKey")
set pubKey = Server.CreateObject("Chilkat.PublicKey")
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( pubKey.LastErrorText) & "</pre>"
    Response.End
End If

' We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Ecc")
set ecc2 = Server.CreateObject("Chilkat.Ecc")
result = ecc2.VerifyHashENC(hashStr,sig,"base64",pubKey)
If (result <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( ecc2.LastErrorText) & "</pre>"
    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "Verified!") & "</pre>"

' Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Xml")
set xml2 = Server.CreateObject("Chilkat.Xml")
xml2.Tag = "sequence"
xml2.NewChild2 "int",r
xml2.NewChild2 "int",s

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Asn")
set asn2 = Server.CreateObject("Chilkat.Asn")
success = asn2.LoadAsnXml(xml2.GetXml())
encodedSig = asn2.GetEncodedDer("base64")
Response.Write "<pre>" & Server.HTMLEncode( "encoded DSS signature: " & encodedSig) & "</pre>"

' 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...

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