整数到IV类型的转换

Question

I am using AES256 from this library and types from this library. here ctrCombine function takes IV (Initialisation Vector) in IV cipher type.

Instead of generating random IV from makeIV function, I want to generate it from some Integers that I already have.

1. Is it possible to convert any Integer to 'IV cipher' type?

2. If it is possible how can I do it?

Answer 1

makeIV doesn't generate a random IV as you implied. It is exactly the function you want. Just serialize your integer to a bytestring of sufficient length then call makeIV on that bytestring:

makeIV $ runPut (putWord64be (fromIntegral i) >>putWord64be (fromIntegral (i `shiftR` 64)))

where the put operations are from the cereal package. You could use binary instead of cereal but then you'd have to make sure you get a strict bytestring.

EDIT: A more complete example:

import Data.Binary.Put
import Crypto.Cipher.Types
import Crypto.Cipher.AES (AES256)
import Data.ByteArray (unpack)
import qualified Data.ByteString.Lazy as LBS
import Data.Bits (shiftR)

example :: Integer -> IV AES256
example i =
  maybe (error "foo") id $
  -- ^^ makeIV returns a `Maybe` (Nothing for IVs of incorrect size
  makeIV $ LBS.toStrict $
  --      ^^ makeIV requires strict bytestrings
     runPut (putWord64be (fromIntegral i) >>
             putWord64be (fromIntegral (i `shiftR` 64)))
  -- ^^ Construct your IV bytestring however you'd like

main = do print $ unpack (example 0)
          print $ unpack (example 1)
          print $ unpack (example (2^63))
          print $ unpack (example (2^65))
          print $ unpack (example (2^112))
          print $ unpack (example (2^120))

Notice that this DOES NOT use crypto-cipher-types since that is sort of parallel to and separate from cryptonite. You should use the IV type from cryptonite instead (see Cryptonite's Crypto.Cipher.Types modules).