(Visual Basic 6.0) 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 ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

' 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 ChilkatStringBuilder
Dim crlfLineEnding As Long
crlfLineEnding = 1
Dim i As Long
For i = 0 To 10
    success = sb.AppendLine("This is a test.",crlfLineEnding)
Next

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

' Get the public key to be used for signature verification.
Dim pubKey As New PublicKey
Dim success As Long
success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
If (success = 0) Then
    Debug.Print pubKey.LastErrorText
    Exit Sub
End If

Dim rsa As New ChilkatRsa
success = 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
signedString = sb.GetAsString()
success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig)

If (success = 0) Then
    Debug.Print rsa.LastErrorText
    Debug.Print "Signature invalid."
Else
    Debug.Print "Signature valid."
End If