Xojo Plugin

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. Xojo Plugin

Dim success As Boolean
success = False

// 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
crlfLineEnding = True
Dim i As Int32
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 Chilkat.PublicKey
success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
If (success = False) Then
    System.DebugLog(pubKey.LastErrorText)
    Return
End If

Dim rsa As New Chilkat.Rsa
success = rsa.UsePublicKey(pubKey)
If (success = False) Then
    System.DebugLog(rsa.LastErrorText)
    Return
End If

// 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 = False) Then
    System.DebugLog(rsa.LastErrorText)
    System.DebugLog("Signature invalid.")
Else
    System.DebugLog("Signature valid.")
End If