src/secp256k1/src/scalar.h

   1 /**********************************************************************
   2  * Copyright (c) 2014 Pieter Wuille                                   *
   3  * Distributed under the MIT software license, see the accompanying   *
   4  * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
   5  **********************************************************************/
   6
   7 #ifndef _SECP256K1_SCALAR_
   8 #define _SECP256K1_SCALAR_
   9
  10 #include "num.h"
  11
  12 #if defined HAVE_CONFIG_H
  13 #include "libsecp256k1-config.h"
  14 #endif
  15
  16 #if defined(EXHAUSTIVE_TEST_ORDER)
  17 #include "scalar_low.h"
  18 #elif defined(USE_SCALAR_4X64)
  19 #include "scalar_4x64.h"
  20 #elif defined(USE_SCALAR_8X32)
  21 #include "scalar_8x32.h"
  22 #else
  23 #error "Please select scalar implementation"
  24 #endif
  25
  26 /** Clear a scalar to prevent the leak of sensitive data. */
  27 static void secp256k1_scalar_clear(secp256k1_scalar *r);
  28
  29 /** Access bits from a scalar. All requested bits must belong to the same 32-bit limb. */
  30 static unsigned int secp256k1_scalar_get_bits(const secp256k1_scalar *a, unsigned int offset, unsigned int count);
  31
  32 /** Access bits from a scalar. Not constant time. */
  33 static unsigned int secp256k1_scalar_get_bits_var(const secp256k1_scalar *a, unsigned int offset, unsigned int count);
  34
  35 /** Set a scalar from a big endian byte array. */
  36 static void secp256k1_scalar_set_b32(secp256k1_scalar *r, const unsigned char *bin, int *overflow);
  37
  38 /** Set a scalar to an unsigned integer. */
  39 static void secp256k1_scalar_set_int(secp256k1_scalar *r, unsigned int v);
  40
  41 /** Convert a scalar to a byte array. */
  42 static void secp256k1_scalar_get_b32(unsigned char *bin, const secp256k1_scalar* a);
  43
  44 /** Add two scalars together (modulo the group order). Returns whether it overflowed. */
  45 static int secp256k1_scalar_add(secp256k1_scalar *r, const secp256k1_scalar *a, const secp256k1_scalar *b);
  46
  47 /** Conditionally add a power of two to a scalar. The result is not allowed to overflow. */
  48 static void secp256k1_scalar_cadd_bit(secp256k1_scalar *r, unsigned int bit, int flag);
  49
  50 /** Multiply two scalars (modulo the group order). */
  51 static void secp256k1_scalar_mul(secp256k1_scalar *r, const secp256k1_scalar *a, const secp256k1_scalar *b);
  52
  53 /** Shift a scalar right by some amount strictly between 0 and 16, returning
  54  *  the low bits that were shifted off */
  55 static int secp256k1_scalar_shr_int(secp256k1_scalar *r, int n);
  56
  57 /** Compute the square of a scalar (modulo the group order). */
  58 static void secp256k1_scalar_sqr(secp256k1_scalar *r, const secp256k1_scalar *a);
  59
  60 /** Compute the inverse of a scalar (modulo the group order). */
  61 static void secp256k1_scalar_inverse(secp256k1_scalar *r, const secp256k1_scalar *a);
  62
  63 /** Compute the inverse of a scalar (modulo the group order), without constant-time guarantee. */
  64 static void secp256k1_scalar_inverse_var(secp256k1_scalar *r, const secp256k1_scalar *a);
  65
  66 /** Compute the complement of a scalar (modulo the group order). */
  67 static void secp256k1_scalar_negate(secp256k1_scalar *r, const secp256k1_scalar *a);
  68
  69 /** Check whether a scalar equals zero. */
  70 static int secp256k1_scalar_is_zero(const secp256k1_scalar *a);
  71
  72 /** Check whether a scalar equals one. */
  73 static int secp256k1_scalar_is_one(const secp256k1_scalar *a);
  74
  75 /** Check whether a scalar, considered as an nonnegative integer, is even. */
  76 static int secp256k1_scalar_is_even(const secp256k1_scalar *a);
  77
  78 /** Check whether a scalar is higher than the group order divided by 2. */
  79 static int secp256k1_scalar_is_high(const secp256k1_scalar *a);
  80
  81 /** Conditionally negate a number, in constant time.
  82  * Returns -1 if the number was negated, 1 otherwise */
  83 static int secp256k1_scalar_cond_negate(secp256k1_scalar *a, int flag);
  84
  85 #ifndef USE_NUM_NONE
  86 /** Convert a scalar to a number. */
  87 static void secp256k1_scalar_get_num(secp256k1_num *r, const secp256k1_scalar *a);
  88
  89 /** Get the order of the group as a number. */
  90 static void secp256k1_scalar_order_get_num(secp256k1_num *r);
  91 #endif
  92
  93 /** Compare two scalars. */
  94 static int secp256k1_scalar_eq(const secp256k1_scalar *a, const secp256k1_scalar *b);
  95
  96 #ifdef USE_ENDOMORPHISM
  97 /** Find r1 and r2 such that r1+r2*2^128 = a. */
  98 static void secp256k1_scalar_split_128(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *a);
  99 /** Find r1 and r2 such that r1+r2*lambda = a, and r1 and r2 are maximum 128 bits long (see secp256k1_gej_mul_lambda). */
 100 static void secp256k1_scalar_split_lambda(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *a);
 101 #endif
 102
 103 /** Multiply a and b (without taking the modulus!), divide by 2**shift, and round to the nearest integer. Shift must be at least 256. */
 104 static void secp256k1_scalar_mul_shift_var(secp256k1_scalar *r, const secp256k1_scalar *a, const secp256k1_scalar *b, unsigned int shift);
 105
 106 #endif