bruteforce-double-sha1.rb

require "openssl"

def enumerate(n, set, target)
    set.repeated_permutation(n) do |arr|
        if OpenSSL::Digest.digest("sha1", OpenSSL::Digest.digest("sha1", arr.join)) == target
            return arr
        end
    end
    return nil
end

target = [207, 145, 125, 199, 75, 210, 227, 4, 202, 157, 34, 133, 79, 100, 133, 38, 187, 182, 131, 134].pack("c*")
set = ("a".."z").map(&:to_s)
p enumerate(5, set, target)