prac/cell.hpp

#ifndef __CELL_HPP__
#define __CELL_HPP__

#include "mpcio.hpp"
#include "options.hpp"

// This file demonstrates how to implement custom ORAM wide cell types.
// Such types can be structures of arbitrary numbers of RegAS and RegXS
// fields.  The example here imagines a cell of a binary search tree,
// where you would want the key to be additively shared (so that you can
// easily do comparisons), the pointers field to be XOR shared (so that
// you can easily do bit operations to pack two pointers and maybe some
// tree balancing information into one field) and the value doesn't
// really matter, but XOR shared is usually slightly more efficient.

struct Cell {
    RegAS key;
    RegXS pointers;
    RegXS value;

// Field-access macros so we can write A[i].CELL_KEY instead of
// A[i].field(&Cell::key)

#define CELL_KEY field(&Cell::key)
#define CELL_POINTERS field(&Cell::pointers)
#define CELL_VALUE field(&Cell::value)

    // For debugging and checking answers
    void dump() const {
        printf("[%016lx %016lx %016lx]", key.share(), pointers.share(),
            value.share());
    }

    // You'll need to be able to create a random element, and do the
    // operations +=, +, -=, - (binary and unary).  Note that for
    // XOR-shared fields, + and - are both really XOR.

    inline void randomize() {
        key.randomize();
        pointers.randomize();
        value.randomize();
    }

    inline Cell &operator+=(const Cell &rhs) {
        this->key += rhs.key;
        this->pointers += rhs.pointers;
        this->value += rhs.value;
        return *this;
    }

    inline Cell operator+(const Cell &rhs) const {
        Cell res = *this;
        res += rhs;
        return res;
    }

    inline Cell &operator-=(const Cell &rhs) {
        this->key -= rhs.key;
        this->pointers -= rhs.pointers;
        this->value -= rhs.value;
        return *this;
    }

    inline Cell operator-(const Cell &rhs) const {
        Cell res = *this;
        res -= rhs;
        return res;
    }

    inline Cell operator-() const {
        Cell res;
        res.key = -this->key;
        res.pointers = -this->pointers;
        res.value = -this->value;
        return res;
    }

    // Multiply each field by the local share of the corresponding field
    // in the argument
    inline Cell mulshare(const Cell &rhs) const {
        Cell res = *this;
        res.key.mulshareeq(rhs.key);
        res.pointers.mulshareeq(rhs.pointers);
        res.value.mulshareeq(rhs.value);
        return res;
    }

    // You need a method to turn a leaf node of a DPF into a share of a
    // unit element of your type.  Typically set each RegAS to
    // dpf.unit_as(leaf) and each RegXS or RegBS to dpf.unit_bs(leaf).
    // Note that RegXS will extend a RegBS of 1 to the all-1s word, not
    // the word with value 1.  This is used for ORAM reads, where the
    // same DPF is used for all the fields.
    template <nbits_t WIDTH>
    inline void unit(const RDPF<WIDTH> &dpf,
        typename RDPF<WIDTH>::LeafNode leaf) {
        key = dpf.unit_as(leaf);
        pointers = dpf.unit_bs(leaf);
        value = dpf.unit_bs(leaf);
    }

    // Perform an update on each of the fields, using field-specific
    // MemRefs constructed from the Shape shape and the index idx
    template <typename Sh, typename U>
    inline static void update(Sh &shape, yield_t &shyield, U idx,
            const Cell &M) {
        run_coroutines(shyield,
            [&shape, &idx, &M] (yield_t &yield) {
                Sh Sh_coro = shape.context(yield);
                Sh_coro[idx].CELL_KEY += M.key;
            },
            [&shape, &idx, &M] (yield_t &yield) {
                Sh Sh_coro = shape.context(yield);
                Sh_coro[idx].CELL_POINTERS += M.pointers;
            },
            [&shape, &idx, &M] (yield_t &yield) {
                Sh Sh_coro = shape.context(yield);
                Sh_coro[idx].CELL_VALUE += M.value;
            });
    }
};

// I/O operations (for sending over the network)

template <typename T>
T& operator>>(T& is, Cell &x)
{
    is >> x.key >> x.pointers >> x.value;
    return is;
}

template <typename T>
T& operator<<(T& os, const Cell &x)
{
    os << x.key << x.pointers << x.value;
    return os;
}

// This macro will define I/O on tuples of two or three of the cell type
DEFAULT_TUPLE_IO(Cell)

void cell(MPCIO &mpcio,
    const PRACOptions &opts, char **args);

#endif