jj: Database version 0.0.3

Filesystem/Encryption.vb

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+Imports System.IO
+Imports System.Security.Cryptography
+
+''' <summary>
+''' https://stackoverflow.com/questions/10168240/encrypting-decrypting-a-string-in-c-sharp
+''' </summary>
+Friend Class Encryption
+    ' This constant is used to determine the keysize of the encryption algorithm in bits.
+    ' We divide this by 8 within the code below to get the equivalent number of bytes.
+    Private Const Keysize As Integer = 256
+    ' This constant determines the number of iterations for the password bytes generation function.
+    Private Const DerivationIterations As Integer = 1000
+    Private ReadOnly password As String
+
+    Public Sub New(password As String)
+        If IsNothing(password) Then
+            Throw New ArgumentNullException("password")
+        End If
+
+        Me.password = password
+    End Sub
+
+    Public Async Function EncryptAsync(plainTextBytes As Byte()) As Task(Of Byte())
+        Return Await Task.Run(Function() As Byte()
+                                  Return Encrypt(plainTextBytes)
+                              End Function)
+    End Function
+
+    Public Function Encrypt(plainTextBytes As Byte()) As Byte()
+        ' Salt and IV is randomly generated each time, but is preprended to encrypted cipher text
+        ' so that the same Salt and IV values can be used when decrypting.  
+        Dim saltStringBytes = Generate256BitsOfRandomEntropy()
+        Dim ivStringBytes = Generate256BitsOfRandomEntropy()
+        Using password = New Rfc2898DeriveBytes(Me.password, saltStringBytes, DerivationIterations)
+            Dim keyBytes = password.GetBytes(Keysize / 8)
+            Using symmetricKey = New RijndaelManaged()
+                symmetricKey.BlockSize = 256
+                symmetricKey.Mode = CipherMode.CBC
+                symmetricKey.Padding = PaddingMode.PKCS7
+                Using encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes)
+                    Using memoryStream = New MemoryStream()
+                        Using cryptoStream = New CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write)
+                            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length)
+                            cryptoStream.FlushFinalBlock()
+                            ' Create the final bytes as a concatenation of the random salt bytes, the random iv bytes and the cipher bytes.
+                            Dim cipherTextBytes = saltStringBytes
+                            cipherTextBytes = cipherTextBytes.Concat(ivStringBytes).ToArray()
+                            cipherTextBytes = cipherTextBytes.Concat(memoryStream.ToArray()).ToArray()
+                            memoryStream.Close()
+                            cryptoStream.Close()
+                            Return cipherTextBytes
+                        End Using
+                    End Using
+                End Using
+            End Using
+        End Using
+    End Function
+
+    Public Async Function DecryptAsync(cipherTextBytesWithSaltAndIv As Byte()) As Task(Of Byte())
+        Return Await Task.Run(Function() As Byte()
+                                  Return Decrypt(cipherTextBytesWithSaltAndIv)
+                              End Function)
+    End Function
+
+    Public Function Decrypt(cipherTextBytesWithSaltAndIv As Byte()) As Byte()
+        ' Get the complete stream of bytes that represent:
+        ' [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]
+        ' Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes.
+        Dim saltStringBytes = cipherTextBytesWithSaltAndIv.Take(Keysize / 8).ToArray()
+        ' Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.
+        Dim ivStringBytes = cipherTextBytesWithSaltAndIv.Skip(Keysize / 8).Take(Keysize / 8).ToArray()
+        ' Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.
+        Dim cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip((Keysize / 8) * 2).Take(cipherTextBytesWithSaltAndIv.Length - ((Keysize / 8) * 2)).ToArray()
+
+        Using password = New Rfc2898DeriveBytes(Me.password, saltStringBytes, DerivationIterations)
+            Dim keyBytes = password.GetBytes(Keysize / 8)
+            Using symmetricKey = New RijndaelManaged()
+                symmetricKey.BlockSize = 256
+                symmetricKey.Mode = CipherMode.CBC
+                symmetricKey.Padding = PaddingMode.PKCS7
+                Using decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes)
+                    Using memoryStream = New MemoryStream(cipherTextBytes)
+                        Using cryptoStream = New CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read)
+                            Dim plainTextBytes = New Byte(cipherTextBytes.Length - 1) {}
+                            Dim decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length)
+                            memoryStream.Close()
+                            cryptoStream.Close()
+                            Return plainTextBytes
+                        End Using
+                    End Using
+                End Using
+            End Using
+        End Using
+    End Function
+
+    Private Shared Function Generate256BitsOfRandomEntropy() As Byte()
+        Dim randomBytes = New Byte(31) {}
+        ' 32 Bytes will give us 256 bits.
+        Using rngCsp = New RNGCryptoServiceProvider()
+            ' Fill the array with cryptographically secure random bytes.
+            rngCsp.GetBytes(randomBytes)
+        End Using
+        Return randomBytes
+    End Function
+End Class