(VB.NET) Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed.

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

' Create the same string we previously signed in this example: 
' RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

Dim sb As New Chilkat.StringBuilder
Dim crlfLineEnding As Boolean = True
Dim i As Integer
For i = 0 To 10
    sb.AppendLine("This is a test.",crlfLineEnding)
Next


Dim base64_rsa_sig As String = "gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ=="


' Get the public key to be used for signature verification.
Dim pubKey As New Chilkat.PublicKey
Dim success As Boolean = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
If (success = False) Then
    Debug.WriteLine(pubKey.LastErrorText)
    Exit Sub
End If


Dim rsa As New Chilkat.Rsa
rsa.ImportPublicKeyObj(pubKey)

' Verify the string against the signature.
' We signed the utf-8 byte representation of the string, so we must indicate
' to also validate against the utf-8 byte representation.
rsa.Charset = "utf-8"
rsa.EncodingMode = "base64"
Dim signedString As String = sb.GetAsString()
success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig)

If (success = False) Then
    Debug.WriteLine(rsa.LastErrorText)
    Debug.WriteLine("Signature invalid.")
Else
    Debug.WriteLine("Signature valid.")
End If