Imports System

Imports System.Collections.Generic

Imports System.Security.Cryptography

Imports System.Linq

​

Public Module Module1

    Public Sub Main()

        Dim existingPassword = Authentication.EncryptPlainText("Password123456789")

​

        Do

            Console.Write("Password: ")

            Dim incomingPassword = Console.ReadLine()

            Dim authenticated = Authentication.Authenticate(incomingPassword, existingPassword)

            If (authenticated) Then

                Console.WriteLine("Authenticated!")

            Else

                Console.WriteLine("Invalid login.")

            End If

            Console.WriteLine()

        Loop

    End Sub

End Module

​

Public Class Authentication

​

    Private Shared ReadOnly _byteLength As Integer = 32

    Private Shared ReadOnly _rcfIterations As Integer = 100000

​

    Public Shared Function Authenticate(plaintext As String, encryptedText As Byte()) As Boolean

        Dim authenticated = True

        Dim salt(_byteLength - 1) As Byte

        If (encryptedText.Length > _byteLength) Then

            For index = 0 To _byteLength - 1

                salt(index) = encryptedText(index)

            Next

        Else

            For index = 0 To _byteLength - 1

                salt(index) = [Byte].MinValue

            Next

            authenticated = False

        End If

        Dim hash = Authentication.GenerateHash(plaintext, salt)

        If (encryptedText.Length - _byteLength = hash.Length) Then

            For index = 0 To hash.Length - 1

                If (authenticated) Then

                    authenticated = hash(index) = encryptedText(_byteLength + index)

                Else

                    authenticated = [Byte].MinValue = [Byte].MaxValue

                End If

            Next

        Else

            For index = 0 To hash.Length - 1

                authenticated = [Byte].MinValue = [Byte].MaxValue

            Next

        End If

        Return authenticated

    End Function

​

    Public Shared Function CombineSaltAndHash(salt As Byte(), hash As Byte()) As IEnumerable(Of Byte)

        If (_byteLength < 1) Then

            Throw New Exception($"{NameOf(_byteLength)} cannot be less than 1")

        End If

        If (salt.Length <> _byteLength) Then

            Throw New ArgumentOutOfRangeException(NameOf(salt), "The incoming salt is invalid")

        End If

        If (hash.Length <> _byteLength) Then

            Throw New ArgumentOutOfRangeException(NameOf(hash), "The incoming hash is invalid")

        End If

​

        Return salt.Concat(hash).ToArray()

    End Function

​

    Public Shared Function EncryptPlainText(plaintext As String) As IEnumerable(Of Byte)

        Dim salt = Authentication.GenerateSalt()

        Dim hash = Authentication.GenerateHash(plaintext, salt)

        Dim combinedHash = Authentication.CombineSaltAndHash(salt, hash)

        Return combinedHash

    End Function

​

    Public Shared Function GenerateHash(plaintext As String, salt As Byte()) As Byte()

        If (_byteLength < 1) Then

            Throw New Exception($"{NameOf(_byteLength)} cannot be less than 1")

        End If

        If (_rcfIterations < 1) Then

            Throw New Exception($"{NameOf(_rcfIterations)} cannot be less than 1")

        End If

        If (String.IsNullOrWhiteSpace(plaintext)) Then

            Throw New ArgumentNullException(NameOf(plaintext))

        End If

        If (salt.Length <> _byteLength) Then

            Throw New ArgumentOutOfRangeException(NameOf(salt), "The incoming salt is invalid")

        End If

​

        Dim hash() As Byte = {}

        Using rcf = New Rfc2898DeriveBytes(plaintext, salt, _rcfIterations)

            hash = rcf.GetBytes(_byteLength)

        End Using

​

        Return hash

    End Function

​

    Public Shared Function GenerateSalt() As Byte()

        If (_byteLength < 1) Then

            Throw New Exception($"{NameOf(_byteLength)} cannot be less than 1")

        End If

​

        Dim salt(_byteLength - 1) As Byte

        Using provider = RandomNumberGenerator.Create()

            provider.GetBytes(salt)

        End Using

        Return salt

    End Function

​

End Class

​