i2pd/libi2pd/Siphash.h

/**
   This code is licensed under the MCGSI Public License
   Copyright 2018 Jeff Becker

   Kovri go write your own code

 */
#ifndef SIPHASH_H
#define SIPHASH_H

#include <cstdint>

namespace i2p
{
namespace crypto 
{
    namespace siphash
    {
        constexpr int crounds = 2;
        constexpr int drounds = 4;

        uint64_t rotl(const uint64_t & x, int b)
        {
            uint64_t ret = x << b;
            ret |= x >> (64 - b);
            return ret;
        }

        void u32to8le(const uint32_t & v, uint8_t * p)
        {
            p[0] = (uint8_t) v;
            p[1] = (uint8_t) (v >> 8);
            p[2] = (uint8_t) (v >> 16);
            p[3] = (uint8_t) (v >> 24);
        }

        void u64to8le(const uint64_t & v, uint8_t * p)
        {
            p[0] = v & 0xff;
            p[1] = (v >> 8)  & 0xff;
            p[2] = (v >> 16) & 0xff;
            p[3] = (v >> 24) & 0xff;
            p[4] = (v >> 32) & 0xff;
            p[5] = (v >> 40) & 0xff;
            p[6] = (v >> 48) & 0xff;
            p[7] = (v >> 56) & 0xff;
        }

        uint64_t u8to64le(const uint8_t * p)
        {
            uint64_t i = 0;
            int idx = 0;
            while(idx < 8)
            {
                i |= ((uint64_t) p[idx]) << (idx * 8);
                ++idx;
            }
            return i;
        }
        
        void round(uint64_t & _v0, uint64_t & _v1, uint64_t & _v2, uint64_t & _v3)
        {
            _v0 += _v1; 
            _v1 = rotl(_v1, 13); 
            _v1 ^= _v0;  
            _v0 = rotl(_v0, 32); 
            _v2 += _v3;  
            _v3 = rotl(_v3, 16);  
            _v3 ^= _v2;         
            _v0 += _v3;                                                              
            _v3 = rotl(_v3, 21);                                                     
            _v3 ^= _v0;                                                              
            _v2 += _v1;                                                              
            _v1 = rotl(_v1, 17);                                                     
            _v1 ^= _v2;                                                              
            _v2 = rotl(_v2, 32); 
        }
    }
   
    /** hashsz must be 8 or 16 */
    template<std::size_t hashsz>
    void Siphash(uint8_t * h, const uint8_t * buf, std::size_t bufsz, const uint8_t * key)
    {
        uint64_t v0 = 0x736f6d6570736575ULL;
        uint64_t v1 = 0x646f72616e646f6dULL;
        uint64_t v2 = 0x6c7967656e657261ULL;
        uint64_t v3 = 0x7465646279746573ULL;
        const uint64_t k0 = siphash::u8to64le(key);
        const uint64_t k1 = siphash::u8to64le(key + 8);
        uint64_t msg;
        int i;
        const uint8_t * end = buf + bufsz - (bufsz % sizeof(uint64_t));
        auto left = bufsz & 7;
        uint64_t b = ((uint64_t)bufsz) << 56;
        v3 ^= k1;
        v2 ^= k0;
        v1 ^= k1;
        v0 ^= k0;

        if(hashsz == 16) v1 ^= 0xee;

        while(buf != end)
        {
            msg = siphash::u8to64le(buf);
            v3 ^= msg;
            for(i = 0; i < siphash::crounds; ++i)
                siphash::round(v0, v1, v2, v3);
            
            v0 ^= msg;
            buf += 8;
        }

        while(left)
        {
            --left;
            b |= ((uint64_t)(buf[left])) << (left  * 8);
        }

        v3 ^= b;

        for(i = 0; i < siphash::crounds; ++i)
            siphash::round(v0, v1, v2, v3);

        v0 ^= b;


        if(hashsz == 16)
            v2 ^= 0xee;
        else
            v2 ^= 0xff;

        for(i = 0; i  < siphash::drounds; ++i)
            siphash::round(v0, v1, v2, v3);

        b = v0 ^ v1 ^ v2 ^ v3;

        siphash::u64to8le(b, h);

        if(hashsz == 8) return;

        v1 ^= 0xdd;

        for (i = 0; i < siphash::drounds; ++i)
            siphash::round(v0, v1, v2, v3);

        b = v0 ^ v1 ^ v2 ^ v3;
        siphash::u64to8le(b, h + 8);
    }
}
}

#endif