Classic ASP
Verify the RSA Signature of a SHA256 Hash

Demonstrates how to verify an RSA signature of a SHA256 hash.
Chilkat Classic ASP Downloads

Classic ASP
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<%
success = 0

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

' Let's say you have a file containing the 32-bytes of a SHA256 hash,
' and a file that is an RSA signature of those 32 bytes.
' Here's how you verify using the RSA public key found in a PEM.

set pubKey = Server.CreateObject("Chilkat.PublicKey")
success = pubKey.LoadFromFile("rsaPubKey.pem")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( pubKey.LastErrorText) & "</pre>"
    Response.End
End If

set rsa = Server.CreateObject("Chilkat.Rsa")

' Get the public key.
success = rsa.UsePublicKey(pubKey)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( rsa.LastErrorText) & "</pre>"
    Response.End
End If

' Get the 32-byte SHA256 hash.
set bdHash = Server.CreateObject("Chilkat.BinData")
success = bdHash.LoadFile("myHash.sha256")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Failed to load SHA256 hash.") & "</pre>"
    Response.End
End If

' Get the RSA signature to be validated.
set bdSig = Server.CreateObject("Chilkat.BinData")
success = bdSig.LoadFile("mySig.sig")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Failed to load RSA signature.") & "</pre>"
    Response.End
End If

' Verify the signature against the SHA256 hash.
enc = "base64"
rsa.EncodingMode = enc
success = rsa.VerifyHashENC(bdHash.GetEncoded(enc),"sha256",bdSig.GetEncoded(enc))
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( rsa.LastErrorText) & "</pre>"
    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "Signature validated.") & "</pre>"

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