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         Metadata ([for _ 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 MetadataKeys =
  28         let filename = "filename"
  29         let modificationTime = "file-modification-time"
  30
  31     let internal (@@) a1 a2 = Array.append a1 a2
  32
  33     let test = 256 / 8
  34     let hmacSize = 256 / 8 // [byte].
  35     let signatureSize = Crypto.rsaKeySize / 8 // [byte].
  36     let keysSize = Crypto.rsaKeySize / 8 // [byte].
  37
  38     let generatKeysPair () : Key * Key = Crypto.generateRSAKeysPair ()
  39
  40     /// Format of the container:
  41     ///  <mac><signature><encrypted keys><cyphertext>
  42     /// Where the sizes of the three first parts are given by 'hmacSize', 'signatureSize' and 'keysSize'.
  43     let encryptFile (inputFilePath : string) (outputFilePath : string) (signaturePrivKey: Key) (cryptPubKey : Key)  =
  44         let keyAES, keyMAC, iv = Crypto.rand 16, Crypto.rand 32, Crypto.rand 16
  45         let fileInfo = FileInfo (inputFilePath)
  46         use inputStream = fileInfo.OpenRead ()
  47         use outputStream = new FileStream (outputFilePath, FileMode.Create, FileAccess.Write)
  48         use writer = new BinaryWriter (outputStream)
  49
  50         outputStream.Position <- (int64 <| hmacSize + signatureSize) // Skips mac and signature. They will be written later.
  51
  52         Crypto.encryptRSA cryptPubKey (keyAES @@ keyMAC @@ iv) |> writer.Write
  53
  54         // Plaintext -> cryptoStream -> hmacStream -> cyphertext.
  55         let hmacStream, hmac = Crypto.HMACStream keyMAC outputStream
  56         use cryptoStream = Crypto.encryptAES keyAES iv hmacStream
  57         use cryptoWriter = new BinaryWriter (cryptoStream)
  58
  59         // Write the file metadata.
  60         let metaData = Metadata ([MetadataKeys.filename, fileInfo.Name
  61                                   MetadataKeys.modificationTime, fileInfo.LastWriteTimeUtc.Ticks.ToString ()])
  62         metaData.WriteTo cryptoStream
  63
  64         // Write the content of the file.
  65         inputStream.CopyTo cryptoStream
  66         cryptoStream.FlushFinalBlock ()
  67
  68         // Write the HMAC at the begining of the file.
  69         outputStream.Position <- 0L
  70         writer.Write hmac.Hash
  71
  72         // Write the signature.
  73         Crypto.signRSA signaturePrivKey hmac.Hash |> writer.Write
  74
  75     /// May raise one of the following error:
  76     ///  * IntegrityError
  77     ///  * SignatureMismatch
  78     ///  * UnableToDecryptAESKeys
  79     let decryptFile (sourceFilePath : string) (targetDirPath : string) (signaturePubKey: Key) (decryptPrivKey : Key) =
  80         use inputStream = new FileStream (sourceFilePath, FileMode.Open, FileAccess.Read)
  81         use reader = new BinaryReader (inputStream)
  82         let mac = reader.ReadBytes hmacSize
  83         let signature = reader.ReadBytes signatureSize
  84         let keys =
  85             try reader.ReadBytes keysSize |> Crypto.decryptRSA decryptPrivKey
  86             with
  87                 | :? Security.Cryptography.CryptographicException -> raise UnableToDecryptKeys
  88         let keyAES = keys.[0 .. 15]
  89         let keyMAC = keys.[16 .. 47]
  90         let iv = keys.[48 .. 63]
  91
  92         // Integrity validation.
  93         let mac' = Crypto.ComputeHMAC keyMAC inputStream
  94         if mac' <> mac then
  95             raise IntegrityError
  96
  97         // Authentication validation.
  98         if not <| Crypto.verifySignRSA signaturePubKey mac' signature then
  99             raise SignatureMismatch
 100
 101         // Decrypt metadata.
 102         inputStream.Position <- (int64 <| hmacSize + signatureSize + keysSize)
 103         use cryptoStream = Crypto.decryptAES keyAES iv inputStream
 104         let metadata = Metadata cryptoStream
 105
 106         // Create the file and write its content and metadata.
 107         let filePath = Path.Combine (targetDirPath, metadata.get MetadataKeys.filename)
 108         let modificationTime = DateTime (metadata.get MetadataKeys.modificationTime |> int64)
 109         let fileInfo = FileInfo filePath
 110         using (fileInfo.Create ()) cryptoStream.CopyTo // We have to close the result file before updating the modification time.
 111         fileInfo.LastWriteTimeUtc <- modificationTime
 112