Crypto Multihash

Multihash library implemented on top of 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.

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

-- in ghci `:set -XOverloadedStrings`
{-# LANGUAGE OverloadedStrings #-}

-- `:m +Crypto.Multihash`
import Crypto.Multihash
import Data.ByteString (ByteString)

main = do
    let v = "test"::ByteString
    let m = multihash SHA256 v

    -- If using the Weak module
    -- let m' = weakMultihash "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
    -- You can check that a multihash corresponds to some data `v`
    -- but you need to wrap the data in the newtype `Payload`
    checkPayload h (Payload v)
    -- Right True

    -- Or if you have a Multihash to compare you can use it
    check h m
    -- Right True

    -- There is also an unsafe version, as for encode
    -- note that sometimes you will need to specify the string types
    checkPayload' ("whatever"::String) (Payload v)
    -- *** Exception: Unable to infer an encoding
    checkPayload' ("Eiwhatever"::ByteString) (Payload v)
    -- *** Exception: base64: input: invalid length
    check' ("EiCfhtCBiEx9ZZov6qDFWtAVo79PGysLgizRXWwVsPA1CA=="::ByteString) m
    -- False

    checkPayload' h (Payload v)
    -- True
    check' h m
    -- True

The of import Crypto.Multihash.Weak is almost identical, but it additionally introduces the function toWeakMultihash that tries to import a string as a WeakMultihashDigest.

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

echo -n test | stack exec mh -- somefile someotherfile

or read data from the standard input

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

• Use the hash length in checkPayload to treat correctly truncated hashes (see https://github.com/jbenet/multihash/issues/1#issuecomment-91783612)
• Improve documentation
• Improve testing for for raised exceptions
• Implement shake-128 and shake-256 multihashes
• Implement Base32 encoding waiting for https://github.com/jbenet/multihash/issues/31 to be resolved)