(Classic ASP) Create ECSDA Signature using Raw r and s Format (not ASN.1)

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Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

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

' To create an ECDSA signature, the data first needs to be hashed.  Then the hash
' is signed.

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.StringBuilder")
set sb = Server.CreateObject("Chilkat.StringBuilder")
success = sb.Append("The quick brown fox jumps over the lazy dog")
hash = sb.GetHash("sha256","base64","utf-8")

' Load the ECDSA 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.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If (success <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( privKey.LastErrorText) & "</pre>"
    Response.End
End If

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Prng")
set prng = Server.CreateObject("Chilkat.Prng")
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Ecc")
set ecdsa = Server.CreateObject("Chilkat.Ecc")

' Produce a signature that is not ASN.1, but is instead the concatenation
' of the raw r and s signature parts.
' This feature was added in Chilkat v9.5.0.97
ecdsa.AsnFormat = 0

ecdsaSigBase64 = ecdsa.SignHashENC(hash,"base64",privKey,prng)
If (ecdsa.LastMethodSuccess <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( ecdsa.LastErrorText) & "</pre>"
    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "ECDSA signature = " & ecdsaSigBase64) & "</pre>"

' -----------------------------------------------------------
' Now let's verify the signature using the 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-pubkey.pem")
If (success <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( pubKey.LastErrorText) & "</pre>"
    Response.End
End If

' Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
result = ecdsa.VerifyHashENC(hash,ecdsaSigBase64,"base64",pubKey)
If (result = 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Signature is valid.") & "</pre>"
    Response.End
End If

If (result = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Signature is invalid.") & "</pre>"
    Response.End
End If

If (result < 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( ecdsa.LastErrorText) & "</pre>"
    Response.Write "<pre>" & Server.HTMLEncode( "The VerifyHashENC method call failed.") & "</pre>"
    Response.End
End If


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