labo2-fsharp/CryptoFile/API.fs

   1 namespace CryptoFile
   2
   3 open System
   4 open System.IO
   5
   6 // To read and write metadata.
   7 type internal Metadata (d: (string * string) list) =
   8     // Read metadata from a stream.
   9     new (stream : Stream) =
  10         let reader = new BinaryReader (stream)
  11         let length = reader.ReadByte () |> int
  12         new Metadata ([for i in 1..length -> reader.ReadString (), reader.ReadString ()])
  13
  14     // Write metadata to a stream.
  15     member this.WriteTo (stream : Stream) =
  16         let writer = new BinaryWriter (stream)
  17         writer.Write (byte d.Length)
  18         List.iter (fun (key : string, value : string) -> writer.Write key; writer.Write value) d
  19
  20     // May raise 'KeyNotFoundException'.
  21     member this.get (key: string) : string =
  22         List.pick (function
  23                     | (k, v) when k = key -> Some (v)
  24                     | _ -> None) d
  25
  26 module API =
  27     module internal Metadata =
  28         let filenameKey = "filename"
  29         let modificationTimeKey = "file-modification-time"
  30
  31     let generatKeysPair : Key * Key = Crypto.generateRSAKeysPair
  32
  33     let encryptFile (inputFilePath : string) (outputFilePath : string) (signaturePrivKey: Key) (cryptPubKey : Key)  =
  34         let keyAES, keyMAC, iv = Crypto.rand 32, Crypto.rand 32, Crypto.rand 16
  35         let fileInfo = new FileInfo (inputFilePath)
  36         use inputStream = new FileStream (inputFilePath, FileMode.Open, FileAccess.Read)
  37         use outputStream = new FileStream (outputFilePath, FileMode.Create, FileAccess.Write)
  38         let writer = new BinaryWriter (outputStream)
  39
  40         writer.Seek (32 + 256, SeekOrigin.Current) |> ignore // Skips mac and signature. They will be written later.
  41
  42         Crypto.encryptRSA cryptPubKey (Array.append keyAES <| Array.append keyMAC iv) |> writer.Write
  43
  44         // Plaintext -> cryptoStream -> hmacStream -> cyphertext.
  45         let hmacStream, hmac = Crypto.HMACStream keyMAC outputStream
  46         use cryptoStream = Crypto.encryptAES keyAES iv hmacStream
  47         let cryptoWriter = new BinaryWriter (cryptoStream)
  48
  49         // Write the file metadata.
  50         let metaData = new Metadata ([Metadata.filenameKey, fileInfo.Name
  51                                       Metadata.modificationTimeKey, fileInfo.LastWriteTimeUtc.Ticks.ToString ()])
  52         metaData.WriteTo cryptoStream
  53
  54         // Write the content of the file.
  55         inputStream.CopyTo cryptoStream
  56         cryptoStream.FlushFinalBlock ()
  57
  58         // Write the HMAC at the begining of the file.
  59         outputStream.Position <- 0L
  60         writer.Write hmac.Hash
  61
  62         // Write the signature.
  63         Crypto.signRSA signaturePrivKey hmac.Hash |> writer.Write
  64
  65     let decryptFile (sourceFilePath : string) (targetDirPath : string) (signaturePubKey: Key) (decryptPrivKey : Key) =
  66         use inputStream = new FileStream (sourceFilePath, FileMode.Open, FileAccess.Read)
  67         use reader = new BinaryReader (inputStream)
  68         let mac = reader.ReadBytes 32
  69         let signature = reader.ReadBytes 256
  70         let keys =
  71             try reader.ReadBytes 256 |> Crypto.decryptRSA decryptPrivKey
  72             with
  73                 | :? Security.Cryptography.CryptographicException -> raise UnableToDecryptAESKeys
  74         let keyAES = keys.[0..31]
  75         let keyMAC = keys.[32..63]
  76         let iv = keys.[64..79]
  77
  78         // Integrity validation.
  79         let mac' = Crypto.ComputeHMAC keyMAC inputStream
  80         if mac' <> mac then
  81             raise IntegrityError
  82
  83         // Authentication validation.
  84         if not <| Crypto.verifySignRSA signaturePubKey mac' signature then
  85             raise SignatureMismatch
  86
  87         // Decrypt metadata.
  88         inputStream.Position <- 32L + 256L + 256L
  89         use cryptoStream = Crypto.decryptAES keyAES iv inputStream
  90         let metadata = new Metadata (cryptoStream)
  91
  92         // Create the file and write its content and metadata.
  93         let filePath = Path.Combine (targetDirPath, metadata.get Metadata.filenameKey)
  94         let modificationTime = new DateTime (metadata.get Metadata.modificationTimeKey |> int64)
  95         let fileInfo = new FileInfo (filePath)
  96         using (fileInfo.Create ()) <| fun outputStream -> cryptoStream.CopyTo outputStream
  97         fileInfo.LastWriteTimeUtc <- modificationTime
  98