Re: [boost] Need to use SHA1 implementation in boost

Subject: Re: [boost] Need to use SHA1 implementation in boost
From: Lee Clagett (forum_at_[hidden])
Date: 2016-04-19 19:01:29

On Mon, 18 Apr 2016 07:03:03 -0400
Vinnie Falco <vinnie.falco_at_[hidden]> wrote:
> On Mon, Apr 18, 2016 at 6:55 AM, Thijs van den Berg <thijs_at_[hidden]>
> wrote:
> > Maybe it's a good idea to release you version using the std::hash
> > (or boost:hash) interface, although a separte library of common
> > predefined hash function would be a more natural place for it?  
> 
> We've got a proposal winding its way through the C++ standard process
> which provides a new interface to computing hashes on objects suitable
> for use with unordered containers:
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3980.html
> 
> The problem is that while these interfaces are great for the purposes
> of generating 32-bit or 64-bit digests for hash tables, they are
> deficient for cryptographic purposes (i.e. producing a message
> authentication code). For example, regular std::hash doesn't deal with
> endiannes. But computing a cryptographic digest must yield the same
> results on all platforms, and therefore cares about endianness.

The hash function could return a machine independent value like
`std::array<std::uint8_t, sha1_length>`. From the document listed above:

    template <class HashAlgorithm>
    struct uhash
    {
        using result_type = typename HashAlgorithm::result_type;

        template <class T>
        result_type
        operator()(T const& t) const noexcept
        {
            HashAlgorithm h;
            using std::hash_append;
            hash_append(h, t);
            return static_cast<result_type>(h);
        }
    };

Lee