Does this seem like a solid encryption method? - vb.net

Question

I found this code on a forum:
Public Shared Sub Encryptor(wme As String, password As String)
            Try
                Dim key As Byte() = New Byte(31) {}
                Encoding.Default.GetBytes(password).CopyTo(key, 0)
                Dim aes As New RijndaelManaged() With
            {
                .Mode = CipherMode.CBC,
                .KeySize = 256,
                .BlockSize = 256,
                .Padding = PaddingMode.Zeros
            }
                Dim buffer As Byte() = File.ReadAllBytes(wme)
                Using matrizStream As New MemoryStream
                    Using cStream As New CryptoStream(matrizStream, aes.CreateEncryptor(key, key), CryptoStreamMode.Write)
                        cStream.Write(buffer, 0, buffer.Length)
                        Dim appendBuffer As Byte() = matrizStream.ToArray()
                        Dim finalBuffer As Byte() = New Byte(appendBuffer.Length - 1) {}
                        appendBuffer.CopyTo(finalBuffer, 0)
                        File.WriteAllBytes(wme, finalBuffer)
                    End Using
                End Using
                File.Move(wme, wme)
            Catch
            End Try
        End Sub
wme is the file path. Password is the password for the encryption. I was woundering if this was a strong encryption method or its some bad encryption method.

Answer 1

Rijndael with a BlockSize of 256-bits is not AES, AES only supports a block size if 128-bits. Not 31 bytes, there would be some unknown padding applied.
For AES use: .BlockSize = 128.
You need to supply an Initialization Vector (IV). The IV will also be the same as the block size, 128-bits (16-bytes), make it exactly that size. Use a random IV and prefix the encrypted data with it so it will be available for decryption.
Also AES supports three key sizes, 128, 192 and 256 bits, make the keys exactly the correct size.
Further, null padding is a bad idea and does not support binary data, instead the usual padding is PKCS#7 (sometimes specified as PKCS#5).