Part I: 並行処理の基礎

概要

本章では、並行処理の基礎として逐次処理を学びます。

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パスワードクラッカーの実装

SHA-256 ハッシュ計算

{-# LANGUAGE OverloadedStrings #-}

module Ch02.PasswordCracker where

import Crypto.Hash.SHA256 (hash)
import Data.ByteString.Builder (byteStringHex, toLazyByteString)
import qualified Data.ByteString.Char8 as C8
import qualified Data.ByteString.Lazy as BL

-- | Compute SHA-256 hash of a password
getCryptoHash :: String -> String
getCryptoHash password =
    let hashBytes = hash (C8.pack password)
        hexBytes = toLazyByteString (byteStringHex hashBytes)
    in C8.unpack (BL.toStrict hexBytes)

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ブルートフォース探索

-- | Crack password by brute force (sequential)
crackPassword :: String -> String -> Int -> Maybe String
crackPassword _ _ 0 = Nothing
crackPassword cryptoHash alphabet len =
    crackRecursive cryptoHash alphabet "" len

crackRecursive :: String -> String -> String -> Int -> Maybe String
crackRecursive cryptoHash alphabet prefix 0 =
    if getCryptoHash prefix == cryptoHash
        then Just prefix
        else Nothing
crackRecursive cryptoHash alphabet prefix remaining =
    foldr tryChar Nothing alphabet
  where
    tryChar c acc =
        case crackRecursive cryptoHash alphabet (prefix ++ [c]) (remaining - 1) of
            Just result -> Just result
            Nothing -> acc

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使用例

main :: IO ()
main = do
    let alphabet = "ab"
    let targetHash = getCryptoHash "ab"

    case crackPassword targetHash alphabet 2 of
        Just password -> putStrLn $ "Found: " ++ password
        Nothing -> putStrLn "Not found"

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Haskell の特徴

概念	説明
Maybe a	値が存在しない可能性を表現
純粋関数	副作用なし、参照透過性
遅延評価	必要になるまで計算しない
foldr	右畳み込みによる短絡評価

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次のステップ

Part II では、スレッドを使った並行処理を学びます。