labo2-fsharp/CryptoFile/API.fs

   1 namespace CryptoFile
   2 open System.IO
   3
   4 type internal Metadata (d: (string * string) list) =
   5     new (stream : Stream) =
   6         let reader = new BinaryReader (stream)
   7         let length = reader.ReadByte () |> int
   8         new Metadata ([for i in 1..length -> reader.ReadString (), reader.ReadString ()])
   9
  10     // May raise 'KeyNotFoundException'.
  11     member this.get (key: string) : string =
  12         List.pick (function
  13                     | (k, v) when k = key -> Some (v)
  14                     | _ -> None) d
  15
  16     member this.WriteTo (stream : Stream) =
  17         let writer = new BinaryWriter (stream)
  18         writer.Write (byte d.Length)
  19         List.iter (fun (key : string, value : string) -> writer.Write key; writer.Write value) d
  20
  21 module API =
  22     module internal Metadata =
  23         let filename = "filename"
  24         let creationTimeKey = "file-creation-time"
  25
  26     let generatKeysPair : Key * Key = Crypto.generateRSAKeysPair
  27
  28     // Encrypt a given file
  29     let encryptFile (inputFilePath : string) (outputFilePath : string) (signaturePrivKey: Key) (cryptPubKey : Key)  =
  30         let keyAES, keyMAC, iv = Crypto.rand 32, Crypto.rand 32, Crypto.rand 16
  31         let fileInfo = new FileInfo (inputFilePath)
  32         use inputStream = new FileStream (inputFilePath, FileMode.Open, FileAccess.Read)
  33         use outputStream = new FileStream (outputFilePath, FileMode.Create, FileAccess.Write)
  34         let writer = new BinaryWriter (outputStream)
  35
  36         writer.Seek (32 + 256, SeekOrigin.Current) |> ignore // Skips mac and signature. They will be written later.
  37
  38         Crypto.encryptRSA cryptPubKey (Array.append keyAES <| Array.append keyMAC iv) |> writer.Write
  39
  40         let (hmacStream, hmac) = Crypto.HMACStream keyMAC outputStream
  41         use cryptoStream = Crypto.encryptAES keyAES iv hmacStream
  42         let cryptoWriter = new BinaryWriter (cryptoStream)
  43
  44         // Write the file metadata.
  45         let metaData = new Metadata ([Metadata.filename, fileInfo.Name
  46                                       Metadata.creationTimeKey, fileInfo.CreationTimeUtc.Ticks.ToString ()])
  47         metaData.WriteTo cryptoStream
  48
  49         // Write the content of the file.
  50         inputStream.CopyTo cryptoStream
  51         cryptoStream.FlushFinalBlock ()
  52
  53         // Write the HMAC at the begining of the file.
  54         outputStream.Position <- 0L
  55         writer.Write hmac.Hash
  56
  57         // Write the signature.
  58         Crypto.signRSA signaturePrivKey hmac.Hash |> writer.Write
  59         ()
  60
  61     let decryptFile (sourceFilePath : string) (targetDirPath : string) (signaturePubKey: Key) (decryptPrivKey : Key) =
  62         use inputStream = new FileStream (sourceFilePath, FileMode.Open, FileAccess.Read)
  63         use reader = new BinaryReader (inputStream)
  64         let mac = reader.ReadBytes 32
  65         let signature = reader.ReadBytes 256
  66         let keys = reader.ReadBytes 256 |> Crypto.decryptRSA decryptPrivKey
  67         let keyAES = keys.[0..31]
  68         let keyMAC = keys.[32..63]
  69         let iv = keys.[64..79]
  70
  71         // Integrity validation.
  72         let mac' = Crypto.ComputeHMAC keyMAC inputStream
  73         if mac' <> mac then
  74             raise IntegrityError
  75
  76         // Authentication validation.
  77         if not <| Crypto.verifySignRSA signaturePubKey mac' signature then
  78             raise SignatureMismatch
  79
  80         // Decrypt metadata.
  81         inputStream.Position <- 32L + 256L + 256L
  82         use cryptoStream = Crypto.decryptAES keyAES iv inputStream
  83         let metadata = new Metadata (cryptoStream)
  84
  85         // Create the file and write.
  86         let filename = metadata.get Metadata.filename
  87         use outputStream = new FileStream (Path.Combine (targetDirPath, filename), FileMode.Create, FileAccess.Write)
  88         cryptoStream.CopyTo outputStream
  89         ()