Padding Is invalid - rijndael encryption method - vb.net

Question

I've been trying to encrypt the connection string so I don't write it anywhere.
Using ChatGPT I came across the Rijndael method.
Module:
Imports System.Security.Cryptography
Imports System.Text
Module DB
' Encrypt the connection string
Public Function EncryptConnectionString(connectionString As String, key As Byte(), iv As Byte()) As String
' Create a new Rijndael instance
Dim rijndael As New RijndaelManaged()
rijndael.Padding = PaddingMode.PKCS7
rijndael.Key = key
rijndael.IV = iv
' Convert the connection string to a byte array
Dim data As Byte() = Encoding.UTF8.GetBytes(connectionString)
' Encrypt the data using the Rijndael instance
Dim encryptedData As Byte() = rijndael.CreateEncryptor().TransformFinalBlock(data, 0, data.Length)
' Concatenate the key, the initialization vector, and the encrypted data
Dim encryptedConnectionString As Byte() = New Byte(rijndael.Key.Length + rijndael.IV.Length + encryptedData.Length - 1) {}
Array.Copy(rijndael.Key, encryptedConnectionString, rijndael.Key.Length)
Array.Copy(rijndael.IV, 0, encryptedConnectionString, rijndael.Key.Length, rijndael.IV.Length)
Array.Copy(encryptedData, 0, encryptedConnectionString, rijndael.Key.Length + rijndael.IV.Length, encryptedData.Length)
' Convert the encrypted connection string to a base64 string
Return Convert.ToBase64String(encryptedConnectionString)
End Function
' Decrypt the connection string
Public Function DecryptConnectionString(encryptedConnectionString As String, key As Byte(), iv As Byte()) As String
' Convert the encrypted connection string from a base64 string
Dim encryptedConnectionBytes As Byte() = Convert.FromBase64String(encryptedConnectionString)
' Extract the key and initialization vector from the encrypted connection string
Dim decryptedKey As Byte() = New Byte(key.Length - 1) {}
Dim decryptedIV As Byte() = New Byte(iv.Length - 1) {}
Array.Copy(encryptedConnectionBytes, decryptedKey, key.Length)
Array.Copy(encryptedConnectionBytes, key.Length, decryptedIV, 0, iv.Length)
'Create a New Rijndael instance
Dim rijndael As New RijndaelManaged()
rijndael.Padding = PaddingMode.PKCS7
rijndael.Key = decryptedKey
rijndael.IV = decryptedIV
' Extract the encrypted data from the encrypted connection string
Dim encryptedData As Byte() = New Byte(encryptedConnectionBytes.Length - key.Length - iv.Length - 1) {}
Array.Copy(encryptedConnectionBytes, key.Length + iv.Length, encryptedData, 0, encryptedData.Length)
' Decrypt the data using the Rijndael instance
Dim decryptedData As Byte() = rijndael.CreateDecryptor().TransformFinalBlock(encryptedData, 0, encryptedData.Length)
' Convert the decrypted data to a string and return it
Return Encoding.UTF8.GetString(decryptedData)
End Function
End Module`
Form to test:
Imports System.Security.Cryptography
Imports System.Text
Public Class Form1
Private Sub BtnEncrypt_Click(sender As Object, e As EventArgs) Handles btnEncrypt.Click
' Generate a new key and initialization vector
Dim key As Byte() = New Byte(31) {}
Dim iv As Byte() = New Byte(15) {}
Using rng As New RNGCryptoServiceProvider()
rng.GetBytes(key)
rng.GetBytes(iv)
End Using
' Encrypt the connection string
Dim connectionString As String = "Server=" & txtIP.Text & ";Database=" & txtDatabase.Text & ";User ID=" & txtUsername.Text & ";Password=" & txtPassword.Text & ";port=" & txtPort.Text & ";"
Dim rijndael As New RijndaelManaged()
rijndael.Padding = PaddingMode.PKCS7
rijndael.Key = key
rijndael.IV = iv
Dim data As Byte() = Encoding.UTF8.GetBytes(connectionString)
Dim encryptedData As Byte() = rijndael.CreateEncryptor().TransformFinalBlock(data, 0, data.Length)
Dim encryptedConnectionString As String = Convert.ToBase64String(encryptedData)
'Save the encrypted connection string And the key And IV to the settings
My.Settings.EncryptedConnectionString = encryptedConnectionString
My.Settings.Key = Convert.ToBase64String(key)
My.Settings.IV = Convert.ToBase64String(iv)
My.Settings.Save()
txtconnectionstring.Text = encryptedConnectionString
txtKey.Text = Convert.ToBase64String(key)
txtIV.Text = Convert.ToBase64String(iv)
End Sub
Private Sub btnDecrypt_Click(sender As Object, e As EventArgs) Handles btnDecrypt.Click
' Retrieve the encrypted connection string, key, and IV from your settings or configuration
Dim encryptedConnectionString As String = My.Settings.EncryptedConnectionString
Dim key As Byte() = Convert.FromBase64String(txtKey.Text)
Dim iv As Byte() = Convert.FromBase64String(txtIV.Text)
' Decrypt the connection string using the key and IV
Dim connectionString As String = DecryptConnectionString(encryptedConnectionString, key, iv)
txtconnectionstring.Clear()
txtconnectionstring.Text = connectionString
End Sub
End Class
So Encryption is working good but decrypt is giving me hell. Error is: Padding is invalid and cannot be removed.
System.Security.Cryptography.CryptographicException
HResult=0x80131430
Message=Padding is invalid and cannot be removed.
Source=mscorlib
StackTrace:
at System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, Int32 outputOffset, PaddingMode paddingMode, Boolean fLast)
at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount)
For a little bit more context because i've read that the IV or KEY neeed to be the same. I saved those keys manual on the settings or i've saved it on the text box. I've always got the same error while decrypting.
If anyone could help,
Fábio
Tried to encrypt my connection string and save it to the settings of the app. Now I was trying to decrypt it so it could be used to connection to the mysql server.