Update crypto code from Catacomb 2.3.0.1-45-g9c14.

[secnet] / f25519.h

/* -*-c-*-
 *
 * Arithmetic modulo 2^255 - 19
 *
 * (c) 2017 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of secnet.
 * See README for full list of copyright holders.
 *
 * secnet is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version d of the License, or
 * (at your option) any later version.
 *
 * secnet is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 3 along with secnet; if not, see
 * https://www.gnu.org/licenses/gpl.html.
 *
 * This file was originally part of Catacomb, but has been automatically
 * modified for incorporation into secnet: see `import-catacomb-crypto'
 * for details.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#ifndef CATACOMB_F25519_H
#define CATACOMB_F25519_H

#ifdef __cplusplus
  extern "C" {
#endif

/*----- Header files ------------------------------------------------------*/

#include "fake-mLib-bits.h"

#ifndef CATACOMB_QFARITH_H
#  include "qfarith.h"
#endif

/*----- Data structures ---------------------------------------------------*/

typedef union {
  int32 p26[10];
} f25519;

/*----- Functions provided ------------------------------------------------*/

/* --- @f25519_set@ --- *
 *
 * Arguments:   @f25519 *z@ = where to write the result
 *              @int a@ = a small-ish constant
 *
 * Returns:     ---
 *
 * Use:         Sets @z@ to equal @a@.
 */

extern void f25519_set(f25519 */*x*/, int /*a*/);

/* --- @f25519_load@ --- *
 *
 * Arguments:   @f25519 *z@ = where to store the result
 *              @const octet xv[32]@ = source to read
 *
 * Returns:     ---
 *
 * Use:         Reads an element of %$\gf{2^{255} - 19}$% in external
 *              representation from @xv@ and stores it in @z@.
 *
 *              External representation is little-endian base-256.  Elements
 *              have multiple encodings, which are not produced by correct
 *              software; use of noncanonical encodings is not an error, and
 *              toleration of them is considered a performance feature.
 *
 *              Some specifications, e.g., RFC7748, require the topmost bit
 *              (i.e., bit 7 of @wv[31]@) to be ignored.  Callers
 *              implementing such specifications should clear the bit
 *              explicitly.  (It's much easier for a caller who wants the bit
 *              to be ignored to clear it than for a caller who wants the bit
 *              to be significant to apply the necessary change by hand.)
 */

extern void f25519_load(f25519 */*z*/, const octet /*xv*/[32]);

/* --- @f25519_store@ --- *
 *
 * Arguments:   @octet zv[32]@ = where to write the result
 *              @const f25519 *x@ = the field element to write
 *
 * Returns:     ---
 *
 * Use:         Stores a field element in the given octet vector in external
 *              representation.  A canonical encoding is always stored, so,
 *              in particular, the top bit of @xv[31]@ is always left clear.
 */

extern void f25519_store(octet /*zv*/[32], const f25519 */*x*/);

/* --- @f25519_pick2@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@ or @y@)
 *              @const f25519 *x, *y@ = two operands
 *              @uint32 m@ = a mask
 *
 * Returns:     ---
 *
 * Use:         If @m@ is zero, set @z = y@; if @m@ is all-bits-set, then set
 *              @z = x@.  If @m@ has some other value, then scramble @z@ in
 *              an unhelpful way.
 */

extern void f25519_pick2(f25519 */*z*/, const f25519 */*x*/,
                         const f25519 */*y*/, uint32 /*m*/);

/* --- @f25519_pickn@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result
 *              @const f25519 *v@ = a table of entries
 *              @size_t n@ = the number of entries in @v@
 *              @size_t i@ = an index
 *
 * Returns:     ---
 *
 * Use:         If @0 <= i < n < 32@ then set @z = v[i]@.  If @n >= 32@ then
 *              do something unhelpful; otherwise, if @i >= n@ then set @z@
 *              to zero.
 */

extern void f25519_pickn(f25519 */*z*/, const f25519 */*v*/, size_t /*n*/,
                         size_t /*i*/);

/* --- @f25519_condswap@ --- *
 *
 * Arguments:   @f25519 *x, *y@ = two operands
 *              @uint32 m@ = a mask
 *
 * Returns:     ---
 *
 * Use:         If @m@ is zero, do nothing; if @m@ is all-bits-set, then
 *              exchange @x@ and @y@.  If @m@ has some other value, then
 *              scramble @x@ and @y@ in an unhelpful way.
 */

extern void f25519_condswap(f25519 */*x*/, f25519 */*y*/, uint32 /*m*/);

/* --- @f25519_add@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@ or @y@)
 *              @const f25519 *x, *y@ = two operands
 *
 * Returns:     ---
 *
 * Use:         Set @z@ to the sum %$x + y$%.
 */

extern void f25519_add(f25519 */*z*/,
                       const f25519 */*x*/, const f25519 */*y*/);

/* --- @f25519_sub@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@ or @y@)
 *              @const f25519 *x, *y@ = two operands
 *
 * Returns:     ---
 *
 * Use:         Set @z@ to the difference %$x - y$%.
 */

extern void f25519_sub(f25519 */*z*/,
                       const f25519 */*x*/, const f25519 */*y*/);

/* --- @f25519_neg@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@)
 *              @const f25519 *x@ = an operand
 *
 * Returns:     ---
 *
 * Use:         Set @z = -x@.
 */

extern void f25519_neg(f25519 */*z*/, const f25519 */*x*/);

/* --- @f25519_condneg@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@)
 *              @const f25519 *x@ = an operand
 *              @uint32 m@ = a mask
 *
 * Returns:     ---
 *
 * Use:         If @m@ is zero, set @z = x@; if @m@ is all-bits-set, then set
 *              @z = -x@.  If @m@ has some other value then scramble @z@ in
 *              an unhelpful way.
 */

extern void f25519_condneg(f25519 */*z*/, const f25519 */*x*/, uint32 /*m*/);

/* --- @f25519_mulconst@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@)
 *              @const f25519 *x@ = an operand
 *              @long a@ = a small-ish constant; %$|a| < 2^{20}$%.
 *
 * Returns:     ---
 *
 * Use:         Set @z@ to the product %$a x$%.
 */

extern void f25519_mulconst(f25519 */*z*/, const f25519 */*x*/, long /*a*/);

/* --- @f25519_mul@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@ or @y@)
 *              @const f25519 *x, *y@ = two operands
 *
 * Returns:     ---
 *
 * Use:         Set @z@ to the product %$x y$%.
 */

extern void f25519_mul(f25519 */*z*/,
                       const f25519 */*x*/, const f25519 */*y*/);

/* --- @f25519_sqr@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@ or @y@)
 *              @const f25519 *x@ = an operand
 *
 * Returns:     ---
 *
 * Use:         Set @z@ to the square %$x^2$%.
 */

extern void f25519_sqr(f25519 */*z*/, const f25519 */*x*/);

/* --- @f25519_inv@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@)
 *              @const f25519 *x@ = an operand
 *
 * Returns:     ---
 *
 * Use:         Stores in @z@ the multiplicative inverse %$x^{-1}$%.  If
 *              %$x = 0$% then @z@ is set to zero.  This is considered a
 *              feature.
 */

extern void f25519_inv(f25519 */*z*/, const f25519 */*x*/);

/* --- @f25519_quosqrt@ --- *
 *
 * Arguments:   @f25519 *z@ = where to put the result (may alias @x@ or @y@)
 *              @const f25519 *x, *y@ = two operands
 *
 * Returns:     Zero if successful, @-1@ if %$x/y$% is not a square.
 *
 * Use:         Stores in @z@ the one of the square roots %$\pm\sqrt{x/y}$%.
 *              If %$x = y = 0% then the result is zero; if %$y = 0$% but %$x
 *              \ne 0$% then the operation fails.  If you wanted a specific
 *              square root then you'll have to pick it yourself.
 */

extern int f25519_quosqrt(f25519 */*z*/,
                          const f25519 */*x*/, const f25519 */*y*/);

/*----- That's all, folks -------------------------------------------------*/

#ifdef __cplusplus
  }
#endif

#endif