# Crypto Multihash
[](https://travis-ci.org/mseri/crypto-multihash)
Multihash library implemented on top of [cryptonite](https://hackage.haskell.org/package/cryptonite) cryptographic library.
Multihash is a protocol for encoding the hash algorithm and digest length at the start of the digest, see the official [multihash github page](https://github.com/jbenet/multihash/).
This library is still experimental and the api is not guaranteed stable.
I will increment the version number appropriately in case of breaking changes.
For the moment the library implements all the expected hashing algorithms with the exception of shake-128 and shake-256. A Multihash can be encoded in hex (`Base16`), bitcoin base58 (`Base58`) and base64 (`Base64`).
The `Base32` encoding is not yet supported due to discrepancy between the encoding from `Data.ByteArray.Encoding` and the one appearing in the official multihash page.
# Usage
```{.haskell}
-- in ghci `:set -XOverloadedStrings`
{-# LANGUAGE OverloadedStrings #-}
import Crypto.Multihash
import Data.ByteString (ByteString)
main = do
let v = "test"::ByteString
let m = multihash SHA256 v
putStrLn $ "Base16: " ++ (encode' Base16 m)
-- You might need to specify the encoded string type
putStrLn $ "Base58: " ++ (encode' Base58 m :: String)
-- `encode` is the safe interface returning an `Either` type
putStrLn $ "Base64: " ++ show (encode Base64 m :: Either String String)
let h = encode' Base58 m :: ByteString
checkMultihash h v
-- Right True
-- There is also an unsafe version, as for encode
checkMultihash' "whatever" v
-- *** Exception: Unable to infer an encoding
checkMultihash' "Eiwhatever" v
-- *** Exception: base64: input: invalid length
checkMultihash' "EiCfhtCBiEx9ZZov6qDFWtAVo79PGysLgizRXWwVsPA1CA==" v
-- False
checkMultihash' h v
-- True
```
# Test
Some preliminary tests can be performed with `stack test`.
A simple example encoder is in `app/Main.hs`.
You can run it on files
```{.bash}
echo -n test | stack exec mh -- somefile someotherfile
```
or read data from the standard input
```{.bash}
echo -n test | stack exec mh -- -`
```
# Contribution
1. Fork repository
2. Do some changes
3. Create pull request
4. Wait for CI build and review
You can use stack to build the project: `stack build`
To run tests: `stack test`
# TODO
- ~~Improve documentation~~
- ~~Implement hash checker that takes some data and an encoded multihash and check that the multihash corresponds to the data (inferring automatically the appropriate hash function)~~
- ~~Evaluate if throwing an error in the encode function is the wanted behaviour and anyway implement a safe version returning an Either type~~
- Add testing for ~~the newly introduced checker and~~ for raised exceptions
- Add multihash checker into the cli example
- Implement `shake-128` and `shake-256` multihashes
- Implement `Base32` encoding waiting for https://github.com/jbenet/multihash/issues/31 to be resolved)