(VB.NET) Verify the RSA Signature of a SHA256 Hash

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Demonstrates how to verify an RSA signature of a SHA256 hash.

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' 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.

Dim pubKey As New Chilkat.PublicKey
Dim success As Boolean = pubKey.LoadFromFile("rsaPubKey.pem")
If (success = False) Then
    Debug.WriteLine(pubKey.LastErrorText)
    Exit Sub
End If


Dim rsa As New Chilkat.Rsa

' Get the public key.
success = rsa.ImportPublicKeyObj(pubKey)
If (success = False) Then
    Debug.WriteLine(rsa.LastErrorText)
    Exit Sub
End If


' Get the 32-byte SHA256 hash.
Dim bdHash As New Chilkat.BinData
success = bdHash.LoadFile("myHash.sha256")
If (success = False) Then
    Debug.WriteLine("Failed to load SHA256 hash.")
    Exit Sub
End If


' Get the RSA signature to be validated.
Dim bdSig As New Chilkat.BinData
success = bdSig.LoadFile("mySig.sig")
If (success = False) Then
    Debug.WriteLine("Failed to load RSA signature.")
    Exit Sub
End If


' Verify the signature against the SHA256 hash.
Dim enc As String = "base64"
rsa.EncodingMode = enc
success = rsa.VerifyHashENC(bdHash.GetEncoded(enc),"sha256",bdSig.GetEncoded(enc))
If (success = False) Then
    Debug.WriteLine(rsa.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Signature validated.")