/* * Elliptic curves over GF(p) * * Copyright (C) 2012, Brainspark B.V. * * This file is part of PolarSSL (http://www.polarssl.org) * Lead Maintainer: Paul Bakker * * All rights reserved. * * This program 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 2 of the License, or * (at your option) any later version. * * This program 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 along * with this program; if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */ /* * References: * * SEC1 http://www.secg.org/index.php?action=secg,docs_secg * GECC = Guide to Elliptic Curve Cryptography - Hankerson, Menezes, Vanstone * FIPS 186-3 http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf */ #include "polarssl/config.h" #if defined(POLARSSL_ECP_C) #include "polarssl/ecp.h" #include #include #if defined(POLARSSL_SELF_TEST) /* * Counts of point addition and doubling operations. * Used to test resistance of point multiplication to SPA/timing attacks. */ unsigned long add_count, dbl_count; #endif /* * Initialize (the components of) a point */ void ecp_point_init( ecp_point *pt ) { if( pt == NULL ) return; mpi_init( &pt->X ); mpi_init( &pt->Y ); mpi_init( &pt->Z ); } /* * Initialize (the components of) a group */ void ecp_group_init( ecp_group *grp ) { if( grp == NULL ) return; mpi_init( &grp->P ); mpi_init( &grp->B ); ecp_point_init( &grp->G ); mpi_init( &grp->N ); grp->pbits = 0; grp->nbits = 0; grp->modp = NULL; } /* * Unallocate (the components of) a point */ void ecp_point_free( ecp_point *pt ) { if( pt == NULL ) return; mpi_free( &( pt->X ) ); mpi_free( &( pt->Y ) ); mpi_free( &( pt->Z ) ); } /* * Unallocate (the components of) a group */ void ecp_group_free( ecp_group *grp ) { if( grp == NULL ) return; mpi_free( &grp->P ); mpi_free( &grp->B ); ecp_point_free( &grp->G ); mpi_free( &grp->N ); } /* * Set point to zero */ int ecp_set_zero( ecp_point *pt ) { int ret; MPI_CHK( mpi_lset( &pt->X , 1 ) ); MPI_CHK( mpi_lset( &pt->Y , 1 ) ); MPI_CHK( mpi_lset( &pt->Z , 0 ) ); cleanup: return( ret ); } /* * Copy the contents of Q into P */ int ecp_copy( ecp_point *P, const ecp_point *Q ) { int ret; MPI_CHK( mpi_copy( &P->X, &Q->X ) ); MPI_CHK( mpi_copy( &P->Y, &Q->Y ) ); MPI_CHK( mpi_copy( &P->Z, &Q->Z ) ); cleanup: return( ret ); } /* * Import a non-zero point from ASCII strings */ int ecp_point_read_string( ecp_point *P, int radix, const char *x, const char *y ) { int ret; MPI_CHK( mpi_read_string( &P->X, radix, x ) ); MPI_CHK( mpi_read_string( &P->Y, radix, y ) ); MPI_CHK( mpi_lset( &P->Z, 1 ) ); cleanup: return( ret ); } /* * Import an ECP group from ASCII strings */ int ecp_group_read_string( ecp_group *grp, int radix, const char *p, const char *b, const char *gx, const char *gy, const char *n) { int ret; MPI_CHK( mpi_read_string( &grp->P, radix, p ) ); MPI_CHK( mpi_read_string( &grp->B, radix, b ) ); MPI_CHK( ecp_point_read_string( &grp->G, radix, gx, gy ) ); MPI_CHK( mpi_read_string( &grp->N, radix, n ) ); grp->pbits = mpi_msb( &grp->P ); grp->nbits = mpi_msb( &grp->N ); cleanup: return( ret ); } /* * Wrapper around fast quasi-modp functions, with fall-back to mpi_mod_mpi. * See the documentation of struct ecp_group. */ static int ecp_modp( mpi *N, const ecp_group *grp ) { int ret; if( grp->modp == NULL ) return( mpi_mod_mpi( N, N, &grp->P ) ); if( mpi_cmp_int( N, 0 ) < 0 || mpi_msb( N ) > 2 * grp->pbits ) return( POLARSSL_ERR_ECP_GENERIC ); MPI_CHK( grp->modp( N ) ); while( mpi_cmp_int( N, 0 ) < 0 ) MPI_CHK( mpi_add_mpi( N, N, &grp->P ) ); while( mpi_cmp_mpi( N, &grp->P ) >= 0 ) MPI_CHK( mpi_sub_mpi( N, N, &grp->P ) ); cleanup: return( ret ); } /* * 192 bits in terms of t_uint */ #define P192_SIZE_INT ( 192 / CHAR_BIT / sizeof( t_uint ) ) /* * Table to get S1, S2, S3 of FIPS 186-3 D.2.1: * -1 means let this chunk be 0 * a positive value i means A_i. */ #define P192_CHUNKS 3 #define P192_CHUNK_CHAR ( 64 / CHAR_BIT ) #define P192_CHUNK_INT ( P192_CHUNK_CHAR / sizeof( t_uint ) ) const signed char p192_tbl[][P192_CHUNKS] = { { -1, 3, 3 }, /* S1 */ { 4, 4, -1 }, /* S2 */ { 5, 5, 5 }, /* S3 */ }; /* * Fast quasi-reduction modulo p192 (FIPS 186-3 D.2.1) */ static int ecp_mod_p192( mpi *N ) { int ret; unsigned char i, j, offset; signed char chunk; mpi tmp, acc; t_uint tmp_p[P192_SIZE_INT], acc_p[P192_SIZE_INT + 1]; tmp.s = 1; tmp.n = sizeof( tmp_p ) / sizeof( tmp_p[0] ); tmp.p = tmp_p; acc.s = 1; acc.n = sizeof( acc_p ) / sizeof( acc_p[0] ); acc.p = acc_p; MPI_CHK( mpi_grow( N, P192_SIZE_INT * 2 ) ); /* * acc = T */ memset( acc_p, 0, sizeof( acc_p ) ); memcpy( acc_p, N->p, P192_CHUNK_CHAR * P192_CHUNKS ); for( i = 0; i < sizeof( p192_tbl ) / sizeof( p192_tbl[0] ); i++) { /* * tmp = S_i */ memset( tmp_p, 0, sizeof( tmp_p ) ); for( j = 0, offset = P192_CHUNKS - 1; j < P192_CHUNKS; j++, offset-- ) { chunk = p192_tbl[i][j]; if( chunk >= 0 ) memcpy( tmp_p + offset * P192_CHUNK_INT, N->p + chunk * P192_CHUNK_INT, P192_CHUNK_CHAR ); } /* * acc += tmp */ MPI_CHK( mpi_add_abs( &acc, &acc, &tmp ) ); } MPI_CHK( mpi_copy( N, &acc ) ); cleanup: return( ret ); } /* * Size of p521 in terms of t_uint */ #define P521_SIZE_INT ( 521 / CHAR_BIT / sizeof( t_uint ) + 1 ) /* * Bits to keep in the most significant t_uint */ #if defined(POLARSS_HAVE_INT8) #define P521_MASK 0x01 #else #define P521_MASK 0x01FF #endif /* * Fast quasi-reduction modulo p521 (FIPS 186-3 D.2.5) */ static int ecp_mod_p521( mpi *N ) { int ret; t_uint Mp[P521_SIZE_INT]; mpi M; if( N->n < P521_SIZE_INT ) return( 0 ); memset( Mp, 0, P521_SIZE_INT * sizeof( t_uint ) ); memcpy( Mp, N->p, P521_SIZE_INT * sizeof( t_uint ) ); Mp[P521_SIZE_INT - 1] &= P521_MASK; M.s = 1; M.n = P521_SIZE_INT; M.p = Mp; MPI_CHK( mpi_shift_r( N, 521 ) ); MPI_CHK( mpi_add_abs( N, N, &M ) ); cleanup: return( ret ); } /* * Domain parameters for secp192r1 */ #define SECP192R1_P \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFFFFFFFFFFFF" #define SECP192R1_B \ "64210519E59C80E70FA7E9AB72243049FEB8DEECC146B9B1" #define SECP192R1_GX \ "188DA80EB03090F67CBF20EB43A18800F4FF0AFD82FF1012" #define SECP192R1_GY \ "07192B95FFC8DA78631011ED6B24CDD573F977A11E794811" #define SECP192R1_N \ "FFFFFFFFFFFFFFFFFFFFFFFF99DEF836146BC9B1B4D22831" /* * Domain parameters for secp224r1 */ #define SECP224R1_P \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF000000000000000000000001" #define SECP224R1_B \ "B4050A850C04B3ABF54132565044B0B7D7BFD8BA270B39432355FFB4" #define SECP224R1_GX \ "B70E0CBD6BB4BF7F321390B94A03C1D356C21122343280D6115C1D21" #define SECP224R1_GY \ "BD376388B5F723FB4C22DFE6CD4375A05A07476444D5819985007E34" #define SECP224R1_N \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFF16A2E0B8F03E13DD29455C5C2A3D" /* * Domain parameters for secp256r1 */ #define SECP256R1_P \ "FFFFFFFF00000001000000000000000000000000FFFFFFFFFFFFFFFFFFFFFFFF" #define SECP256R1_B \ "5AC635D8AA3A93E7B3EBBD55769886BC651D06B0CC53B0F63BCE3C3E27D2604B" #define SECP256R1_GX \ "6B17D1F2E12C4247F8BCE6E563A440F277037D812DEB33A0F4A13945D898C296" #define SECP256R1_GY \ "4FE342E2FE1A7F9B8EE7EB4A7C0F9E162BCE33576B315ECECBB6406837BF51F5" #define SECP256R1_N \ "FFFFFFFF00000000FFFFFFFFFFFFFFFFBCE6FAADA7179E84F3B9CAC2FC632551" /* * Domain parameters for secp384r1 */ #define SECP384R1_P \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \ "FFFFFFFFFFFFFFFEFFFFFFFF0000000000000000FFFFFFFF" #define SECP384R1_B \ "B3312FA7E23EE7E4988E056BE3F82D19181D9C6EFE814112" \ "0314088F5013875AC656398D8A2ED19D2A85C8EDD3EC2AEF" #define SECP384R1_GX \ "AA87CA22BE8B05378EB1C71EF320AD746E1D3B628BA79B98" \ "59F741E082542A385502F25DBF55296C3A545E3872760AB7" #define SECP384R1_GY \ "3617DE4A96262C6F5D9E98BF9292DC29F8F41DBD289A147C" \ "E9DA3113B5F0B8C00A60B1CE1D7E819D7A431D7C90EA0E5F" #define SECP384R1_N \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \ "C7634D81F4372DDF581A0DB248B0A77AECEC196ACCC52973" /* * Domain parameters for secp521r1 */ #define SECP521R1_P \ "000001FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \ "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" #define SECP521R1_B \ "00000051953EB9618E1C9A1F929A21A0B68540EEA2DA725B" \ "99B315F3B8B489918EF109E156193951EC7E937B1652C0BD" \ "3BB1BF073573DF883D2C34F1EF451FD46B503F00" #define SECP521R1_GX \ "000000C6858E06B70404E9CD9E3ECB662395B4429C648139" \ "053FB521F828AF606B4D3DBAA14B5E77EFE75928FE1DC127" \ "A2FFA8DE3348B3C1856A429BF97E7E31C2E5BD66" #define SECP521R1_GY \ "0000011839296A789A3BC0045C8A5FB42C7D1BD998F54449" \ "579B446817AFBD17273E662C97EE72995EF42640C550B901" \ "3FAD0761353C7086A272C24088BE94769FD16650" #define SECP521R1_N \ "000001FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \ "FFFFFFFFFFFFFFFFFFFFFFFA51868783BF2F966B7FCC0148" \ "F709A5D03BB5C9B8899C47AEBB6FB71E91386409" /* * Set a group using well-known domain parameters */ int ecp_use_known_dp( ecp_group *grp, size_t index ) { switch( index ) { case POLARSSL_ECP_DP_SECP192R1: grp->modp = ecp_mod_p192; return( ecp_group_read_string( grp, 16, SECP192R1_P, SECP192R1_B, SECP192R1_GX, SECP192R1_GY, SECP192R1_N ) ); case POLARSSL_ECP_DP_SECP224R1: return( ecp_group_read_string( grp, 16, SECP224R1_P, SECP224R1_B, SECP224R1_GX, SECP224R1_GY, SECP224R1_N ) ); case POLARSSL_ECP_DP_SECP256R1: return( ecp_group_read_string( grp, 16, SECP256R1_P, SECP256R1_B, SECP256R1_GX, SECP256R1_GY, SECP256R1_N ) ); case POLARSSL_ECP_DP_SECP384R1: return( ecp_group_read_string( grp, 16, SECP384R1_P, SECP384R1_B, SECP384R1_GX, SECP384R1_GY, SECP384R1_N ) ); case POLARSSL_ECP_DP_SECP521R1: grp->modp = ecp_mod_p521; return( ecp_group_read_string( grp, 16, SECP521R1_P, SECP521R1_B, SECP521R1_GX, SECP521R1_GY, SECP521R1_N ) ); } return( POLARSSL_ERR_ECP_GENERIC ); } /* * Fast mod-p functions expect their argument to be in the 0..p^2 range. * * In order to guarantee that, we need to ensure that operands of * mpi_mul_mpi are in the 0..p range. So, after each operation we will * bring the result back to this range. * * The following macros are shortcuts for doing that. */ /* * Reduce a mpi mod p in-place, general case, to use after mpi_mul_mpi */ #define MOD_MUL( N ) MPI_CHK( ecp_modp( &N, grp ) ) /* * Reduce a mpi mod p in-place, to use after mpi_sub_mpi */ #define MOD_SUB( N ) \ while( mpi_cmp_int( &N, 0 ) < 0 ) \ MPI_CHK( mpi_add_mpi( &N, &N, &grp->P ) ) /* * Reduce a mpi mod p in-place, to use after mpi_add_mpi and mpi_mul_int */ #define MOD_ADD( N ) \ while( mpi_cmp_mpi( &N, &grp->P ) >= 0 ) \ MPI_CHK( mpi_sub_mpi( &N, &N, &grp->P ) ) /* * Check that a point is valid as a public key (SEC1 3.2.3.1) */ int ecp_check_pubkey( const ecp_group *grp, const ecp_point *pt ) { int ret; mpi YY, RHS; if( mpi_cmp_int( &pt->Z, 0 ) == 0 ) return( POLARSSL_ERR_ECP_GENERIC ); /* * pt coordinates must be normalized for our checks */ if( mpi_cmp_int( &pt->Z, 1 ) != 0 ) return( POLARSSL_ERR_ECP_GENERIC ); if( mpi_cmp_int( &pt->X, 0 ) < 0 || mpi_cmp_int( &pt->Y, 0 ) < 0 || mpi_cmp_mpi( &pt->X, &grp->P ) >= 0 || mpi_cmp_mpi( &pt->Y, &grp->P ) >= 0 ) return( POLARSSL_ERR_ECP_GENERIC ); mpi_init( &YY ); mpi_init( &RHS ); /* * YY = Y^2 * RHS = X (X^2 - 3) + B = X^3 - 3X + B */ MPI_CHK( mpi_mul_mpi( &YY, &pt->Y, &pt->Y ) ); MOD_MUL( YY ); MPI_CHK( mpi_mul_mpi( &RHS, &pt->X, &pt->X ) ); MOD_MUL( RHS ); MPI_CHK( mpi_sub_int( &RHS, &RHS, 3 ) ); MOD_SUB( RHS ); MPI_CHK( mpi_mul_mpi( &RHS, &RHS, &pt->X ) ); MOD_MUL( RHS ); MPI_CHK( mpi_add_mpi( &RHS, &RHS, &grp->B ) ); MOD_ADD( RHS ); if( mpi_cmp_mpi( &YY, &RHS ) != 0 ) ret = POLARSSL_ERR_ECP_GENERIC; cleanup: mpi_free( &YY ); mpi_free( &RHS ); return( ret ); } /* * Normalize jacobian coordinates so that Z == 0 || Z == 1 (GECC 3.2.1) */ static int ecp_normalize( const ecp_group *grp, ecp_point *pt ) { int ret; mpi Zi, ZZi; if( mpi_cmp_int( &pt->Z, 0 ) == 0 ) return( 0 ); mpi_init( &Zi ); mpi_init( &ZZi ); /* * X = X / Z^2 mod p */ MPI_CHK( mpi_inv_mod( &Zi, &pt->Z, &grp->P ) ); MPI_CHK( mpi_mul_mpi( &ZZi, &Zi, &Zi ) ); MOD_MUL( ZZi ); MPI_CHK( mpi_mul_mpi( &pt->X, &pt->X, &ZZi ) ); MOD_MUL( pt->X ); /* * Y = Y / Z^3 mod p */ MPI_CHK( mpi_mul_mpi( &pt->Y, &pt->Y, &ZZi ) ); MOD_MUL( pt->Y ); MPI_CHK( mpi_mul_mpi( &pt->Y, &pt->Y, &Zi ) ); MOD_MUL( pt->Y ); /* * Z = 1 */ MPI_CHK( mpi_lset( &pt->Z, 1 ) ); cleanup: mpi_free( &Zi ); mpi_free( &ZZi ); return( ret ); } /* * Normalize jacobian coordinates of an array of points, * using Montgomery's trick to perform only one inversion mod P. * (See for example Cohen's "A Course in Computational Algebraic Number * Theory", Algorithm 10.3.4.) * * Warning: fails if one of the points is zero! * This should never happen, see choice of w in ecp_mul(). */ static int ecp_normalize_many( const ecp_group *grp, ecp_point T[], size_t t_len ) { int ret; size_t i; mpi *c, u, Zi, ZZi; if( t_len < 2 ) return( ecp_normalize( grp, T ) ); if( ( c = (mpi *) malloc( t_len * sizeof( mpi ) ) ) == NULL ) return( POLARSSL_ERR_ECP_GENERIC ); mpi_init( &u ); mpi_init( &Zi ); mpi_init( &ZZi ); for( i = 0; i < t_len; i++ ) mpi_init( &c[i] ); /* * c[i] = Z_0 * ... * Z_i */ MPI_CHK( mpi_copy( &c[0], &T[0].Z ) ); for( i = 1; i < t_len; i++ ) { MPI_CHK( mpi_mul_mpi( &c[i], &c[i-1], &T[i].Z ) ); MOD_MUL( c[i] ); } /* * u = 1 / (Z_0 * ... * Z_n) mod P */ MPI_CHK( mpi_inv_mod( &u, &c[t_len-1], &grp->P ) ); for( i = t_len - 1; ; i-- ) { /* * Zi = 1 / Z_i mod p * u = 1 / (Z_0 * ... * Z_i) mod P */ if( i == 0 ) { MPI_CHK( mpi_copy( &Zi, &u ) ); } else { MPI_CHK( mpi_mul_mpi( &Zi, &u, &c[i-1] ) ); MOD_MUL( Zi ); MPI_CHK( mpi_mul_mpi( &u, &u, &T[i].Z ) ); MOD_MUL( u ); } /* * proceed as in normalize() */ MPI_CHK( mpi_mul_mpi( &ZZi, &Zi, &Zi ) ); MOD_MUL( ZZi ); MPI_CHK( mpi_mul_mpi( &T[i].X, &T[i].X, &ZZi ) ); MOD_MUL( T[i].X ); MPI_CHK( mpi_mul_mpi( &T[i].Y, &T[i].Y, &ZZi ) ); MOD_MUL( T[i].Y ); MPI_CHK( mpi_mul_mpi( &T[i].Y, &T[i].Y, &Zi ) ); MOD_MUL( T[i].Y ); MPI_CHK( mpi_lset( &T[i].Z, 1 ) ); if( i == 0 ) break; } cleanup: mpi_free( &u ); mpi_free( &Zi ); mpi_free( &ZZi ); for( i = 0; i < t_len; i++ ) mpi_free( &c[i] ); free( c ); return( ret ); } /* * Point doubling R = 2 P, Jacobian coordinates (GECC 3.21) */ static int ecp_double_jac( const ecp_group *grp, ecp_point *R, const ecp_point *P ) { int ret; mpi T1, T2, T3, X, Y, Z; #if defined(POLARSSL_SELF_TEST) dbl_count++; #endif if( mpi_cmp_int( &P->Z, 0 ) == 0 ) return( ecp_set_zero( R ) ); mpi_init( &T1 ); mpi_init( &T2 ); mpi_init( &T3 ); mpi_init( &X ); mpi_init( &Y ); mpi_init( &Z ); MPI_CHK( mpi_mul_mpi( &T1, &P->Z, &P->Z ) ); MOD_MUL( T1 ); MPI_CHK( mpi_sub_mpi( &T2, &P->X, &T1 ) ); MOD_SUB( T2 ); MPI_CHK( mpi_add_mpi( &T1, &P->X, &T1 ) ); MOD_ADD( T1 ); MPI_CHK( mpi_mul_mpi( &T2, &T2, &T1 ) ); MOD_MUL( T2 ); MPI_CHK( mpi_mul_int( &T2, &T2, 3 ) ); MOD_ADD( T2 ); MPI_CHK( mpi_mul_int( &Y, &P->Y, 2 ) ); MOD_ADD( Y ); MPI_CHK( mpi_mul_mpi( &Z, &Y, &P->Z ) ); MOD_MUL( Z ); MPI_CHK( mpi_mul_mpi( &Y, &Y, &Y ) ); MOD_MUL( Y ); MPI_CHK( mpi_mul_mpi( &T3, &Y, &P->X ) ); MOD_MUL( T3 ); MPI_CHK( mpi_mul_mpi( &Y, &Y, &Y ) ); MOD_MUL( Y ); /* * For Y = Y / 2 mod p, we must make sure that Y is even before * using right-shift. No need to reduce mod p afterwards. */ if( mpi_get_bit( &Y, 0 ) == 1 ) MPI_CHK( mpi_add_mpi( &Y, &Y, &grp->P ) ); MPI_CHK( mpi_shift_r( &Y, 1 ) ); MPI_CHK( mpi_mul_mpi( &X, &T2, &T2 ) ); MOD_MUL( X ); MPI_CHK( mpi_mul_int( &T1, &T3, 2 ) ); MOD_ADD( T1 ); MPI_CHK( mpi_sub_mpi( &X, &X, &T1 ) ); MOD_SUB( X ); MPI_CHK( mpi_sub_mpi( &T1, &T3, &X ) ); MOD_SUB( T1 ); MPI_CHK( mpi_mul_mpi( &T1, &T1, &T2 ) ); MOD_MUL( T1 ); MPI_CHK( mpi_sub_mpi( &Y, &T1, &Y ) ); MOD_SUB( Y ); MPI_CHK( mpi_copy( &R->X, &X ) ); MPI_CHK( mpi_copy( &R->Y, &Y ) ); MPI_CHK( mpi_copy( &R->Z, &Z ) ); cleanup: mpi_free( &T1 ); mpi_free( &T2 ); mpi_free( &T3 ); mpi_free( &X ); mpi_free( &Y ); mpi_free( &Z ); return( ret ); } /* * Addition or subtraction: R = P + Q or R = P + Q, * mixed affine-Jacobian coordinates (GECC 3.22) * * The coordinates of Q must be normalized (= affine), * but those of P don't need to. R is not normalized. * * If sign >= 0, perform addition, otherwise perform subtraction, * taking advantage of the fact that, for Q != 0, we have * -Q = (Q.X, -Q.Y, Q.Z) */ static int ecp_add_mixed( const ecp_group *grp, ecp_point *R, const ecp_point *P, const ecp_point *Q, signed char sign ) { int ret; mpi T1, T2, T3, T4, X, Y, Z; #if defined(POLARSSL_SELF_TEST) add_count++; #endif /* * Trivial cases: P == 0 or Q == 0 * (Check Q first, so that we know Q != 0 when we compute -Q.) */ if( mpi_cmp_int( &Q->Z, 0 ) == 0 ) return( ecp_copy( R, P ) ); if( mpi_cmp_int( &P->Z, 0 ) == 0 ) { ret = ecp_copy( R, Q ); /* * -R.Y mod P = P - R.Y unless R.Y == 0 */ if( ret == 0 && sign < 0) if( mpi_cmp_int( &R->Y, 0 ) != 0 ) ret = mpi_sub_mpi( &R->Y, &grp->P, &R->Y ); return( ret ); } /* * Make sure Q coordinates are normalized */ if( mpi_cmp_int( &Q->Z, 1 ) != 0 ) return( POLARSSL_ERR_ECP_GENERIC ); mpi_init( &T1 ); mpi_init( &T2 ); mpi_init( &T3 ); mpi_init( &T4 ); mpi_init( &X ); mpi_init( &Y ); mpi_init( &Z ); MPI_CHK( mpi_mul_mpi( &T1, &P->Z, &P->Z ) ); MOD_MUL( T1 ); MPI_CHK( mpi_mul_mpi( &T2, &T1, &P->Z ) ); MOD_MUL( T2 ); MPI_CHK( mpi_mul_mpi( &T1, &T1, &Q->X ) ); MOD_MUL( T1 ); MPI_CHK( mpi_mul_mpi( &T2, &T2, &Q->Y ) ); MOD_MUL( T2 ); /* * For subtraction, -Q.Y should have been used instead of Q.Y, * so we replace T2 by -T2, which is P - T2 mod P */ if( sign < 0 ) { MPI_CHK( mpi_sub_mpi( &T2, &grp->P, &T2 ) ); MOD_SUB( T2 ); } MPI_CHK( mpi_sub_mpi( &T1, &T1, &P->X ) ); MOD_SUB( T1 ); MPI_CHK( mpi_sub_mpi( &T2, &T2, &P->Y ) ); MOD_SUB( T2 ); if( mpi_cmp_int( &T1, 0 ) == 0 ) { if( mpi_cmp_int( &T2, 0 ) == 0 ) { ret = ecp_double_jac( grp, R, P ); goto cleanup; } else { ret = ecp_set_zero( R ); goto cleanup; } } MPI_CHK( mpi_mul_mpi( &Z, &P->Z, &T1 ) ); MOD_MUL( Z ); MPI_CHK( mpi_mul_mpi( &T3, &T1, &T1 ) ); MOD_MUL( T3 ); MPI_CHK( mpi_mul_mpi( &T4, &T3, &T1 ) ); MOD_MUL( T4 ); MPI_CHK( mpi_mul_mpi( &T3, &T3, &P->X ) ); MOD_MUL( T3 ); MPI_CHK( mpi_mul_int( &T1, &T3, 2 ) ); MOD_ADD( T1 ); MPI_CHK( mpi_mul_mpi( &X, &T2, &T2 ) ); MOD_MUL( X ); MPI_CHK( mpi_sub_mpi( &X, &X, &T1 ) ); MOD_SUB( X ); MPI_CHK( mpi_sub_mpi( &X, &X, &T4 ) ); MOD_SUB( X ); MPI_CHK( mpi_sub_mpi( &T3, &T3, &X ) ); MOD_SUB( T3 ); MPI_CHK( mpi_mul_mpi( &T3, &T3, &T2 ) ); MOD_MUL( T3 ); MPI_CHK( mpi_mul_mpi( &T4, &T4, &P->Y ) ); MOD_MUL( T4 ); MPI_CHK( mpi_sub_mpi( &Y, &T3, &T4 ) ); MOD_SUB( Y ); MPI_CHK( mpi_copy( &R->X, &X ) ); MPI_CHK( mpi_copy( &R->Y, &Y ) ); MPI_CHK( mpi_copy( &R->Z, &Z ) ); cleanup: mpi_free( &T1 ); mpi_free( &T2 ); mpi_free( &T3 ); mpi_free( &T4 ); mpi_free( &X ); mpi_free( &Y ); mpi_free( &Z ); return( ret ); } /* * Addition: R = P + Q, result's coordinates normalized */ int ecp_add( const ecp_group *grp, ecp_point *R, const ecp_point *P, const ecp_point *Q ) { int ret; MPI_CHK( ecp_add_mixed( grp, R, P, Q , 1 ) ); MPI_CHK( ecp_normalize( grp, R ) ); cleanup: return( ret ); } /* * Subtraction: R = P - Q, result's coordinates normalized */ int ecp_sub( const ecp_group *grp, ecp_point *R, const ecp_point *P, const ecp_point *Q ) { int ret; MPI_CHK( ecp_add_mixed( grp, R, P, Q, -1 ) ); MPI_CHK( ecp_normalize( grp, R ) ); cleanup: return( ret ); } /* * Compute a modified width-w non-adjacent form (NAF) of a number, * with a fixed pattern for resistance to SPA/timing attacks, * see . * (The resulting multiplication algorithm can also been seen as a * modification of 2^w-ary multiplication, with signed coefficients, * all of them odd.) * * Input: * m must be an odd positive mpi less than w * k bits long * x must be an array of k elements * w must be less than a certain maximum (currently 8) * * The result is a sequence x[0], ..., x[k-1] with x[i] in the range * - 2^(width - 1) .. 2^(width - 1) - 1 such that * m = (2 * x[0] + 1) + 2^width * (2 * x[1] + 1) + ... * + 2^((k-1) * width) * (2 * x[k-1] + 1) * * Compared to "Algorithm SPA-resistant Width-w NAF with Odd Scalar" * p. 335 of the cited reference, here we return only u, not d_w since * it is known that the other d_w[j] will be 0. Moreover, the returned * string doesn't actually store u_i but x_i = u_i / 2 since it is known * that u_i is odd. Also, since we always select a positive value for d * mod 2^w, we don't need to check the sign of u[i-1] when the reference * does. Finally, there is an off-by-one error in the reference: the * last index should be k-1, not k. */ static int ecp_w_naf_fixed( signed char x[], size_t k, unsigned char w, const mpi *m ) { int ret; unsigned int i, u, mask, carry; mpi M; mpi_init( &M ); MPI_CHK( mpi_copy( &M, m ) ); mask = ( 1 << w ) - 1; carry = 1 << ( w - 1 ); for( i = 0; i < k; i++ ) { u = M.p[0] & mask; if( ( u & 1 ) == 0 && i > 0 ) x[i - 1] -= carry; x[i] = u >> 1; mpi_shift_r( &M, w ); } /* * We should have consumed all the bits now */ if( mpi_cmp_int( &M, 0 ) != 0 ) ret = POLARSSL_ERR_ECP_GENERIC; cleanup: mpi_free( &M ); return( ret ); } /* * Precompute odd multiples of P up to (2 * t_len - 1) P. * The table is filled with T[i] = (2 * i + 1) P. */ static int ecp_precompute( const ecp_group *grp, ecp_point T[], size_t t_len, const ecp_point *P ) { int ret; size_t i; ecp_point PP; ecp_point_init( &PP ); MPI_CHK( ecp_add( grp, &PP, P, P ) ); MPI_CHK( ecp_copy( &T[0], P ) ); for( i = 1; i < t_len; i++ ) MPI_CHK( ecp_add_mixed( grp, &T[i], &T[i-1], &PP, +1 ) ); /* * T[0] = P already has normalized coordinates */ MPI_CHK( ecp_normalize_many( grp, T + 1, t_len - 1 ) ); cleanup: ecp_point_free( &PP ); return( ret ); } /* * Maximum length of the precomputed table */ #define MAX_PRE_LEN ( 1 << (POLARSSL_ECP_WINDOW_SIZE - 1) ) /* * Maximum length of the NAF: ceil( grp->nbits + 1 ) / w * (that is: grp->nbits / w + 1) * Allow p_bits + 1 bits in case M = grp->N + 1 is one bit longer than N. */ #define MAX_NAF_LEN ( POLARSSL_ECP_MAX_N_BITS / 2 + 1 ) /* * Integer multiplication: R = m * P * * Based on fixed-pattern width-w NAF, see comments of ecp_w_naf_fixed() * and . * * This function executes a fixed number of operations for * random m in the range 0 .. 2^nbits - 1. */ int ecp_mul( const ecp_group *grp, ecp_point *R, const mpi *m, const ecp_point *P ) { int ret; unsigned char w, m_is_odd; size_t pre_len, naf_len, i, j; signed char naf[ MAX_NAF_LEN ]; ecp_point Q, T[ MAX_PRE_LEN ]; mpi M; if( mpi_cmp_int( m, 0 ) < 0 || mpi_msb( m ) > grp->nbits ) return( POLARSSL_ERR_ECP_GENERIC ); w = grp->nbits >= 521 ? 6 : grp->nbits >= 224 ? 5 : 4; /* * Make sure w is within the limits. * The last test ensures that none of the precomputed points is zero, * which wouldn't be handled correctly by ecp_normalize_many(). * It is only useful for small curves, as used in the test suite. */ if( w > POLARSSL_ECP_WINDOW_SIZE ) w = POLARSSL_ECP_WINDOW_SIZE; if( w < 2 || w >= grp->nbits ) w = 2; pre_len = 1 << ( w - 1 ); naf_len = grp->nbits / w + 1; mpi_init( &M ); ecp_point_init( &Q ); for( i = 0; i < pre_len; i++ ) ecp_point_init( &T[i] ); m_is_odd = ( mpi_get_bit( m, 0 ) == 1 ); /* * Make sure M is odd: * later we'll get m * P by subtracting * P or 2 * P to M * P. */ MPI_CHK( mpi_copy( &M, m ) ); MPI_CHK( mpi_add_int( &M, &M, 1 + m_is_odd ) ); /* * Compute the fixed-pattern NAF and precompute odd multiples */ MPI_CHK( ecp_w_naf_fixed( naf, naf_len, w, &M ) ); MPI_CHK( ecp_precompute( grp, T, pre_len, P ) ); /* * Compute M * P, using a variant of left-to-right 2^w-ary multiplication: * at each step we add (2 * naf[i] + 1) P, then multiply by 2^w. * * If naf[i] >= 0, we have (2 * naf[i] + 1) P == T[ naf[i] ] * Otherwise, (2 * naf[i] + 1) P == - ( 2 * ( - naf[i] - 1 ) + 1) P * == T[ - naf[i] - 1 ] */ MPI_CHK( ecp_set_zero( &Q ) ); i = naf_len - 1; while( 1 ) { if( naf[i] < 0 ) { MPI_CHK( ecp_add_mixed( grp, &Q, &Q, &T[ - naf[i] - 1 ], -1 ) ); } else { MPI_CHK( ecp_add_mixed( grp, &Q, &Q, &T[ naf[i] ], +1 ) ); } if( i == 0 ) break; i--; for( j = 0; j < w; j++ ) { MPI_CHK( ecp_double_jac( grp, &Q, &Q ) ); } } /* * Now get m * P from M * P. * Since we don't need T[] any more, we can recycle it: * we already have T[0] = P, now set T[1] = 2 * P. */ MPI_CHK( ecp_add( grp, &T[1], P, P ) ); MPI_CHK( ecp_sub( grp, R, &Q, &T[m_is_odd] ) ); cleanup: mpi_free( &M ); ecp_point_free( &Q ); for( i = 0; i < pre_len; i++ ) ecp_point_free( &T[i] ); return( ret ); } #if defined(POLARSSL_SELF_TEST) /* * Checkup routine */ int ecp_self_test( int verbose ) { int ret; size_t i; ecp_group grp; ecp_point R; mpi m; unsigned long add_c_prev, dbl_c_prev; char *exponents[] = { "000000000000000000000000000000000000000000000000", /* zero */ "000000000000000000000000000000000000000000000001", /* one */ "FFFFFFFFFFFFFFFFFFFFFFFF99DEF836146BC9B1B4D22831", /* N */ "5EA6F389A38B8BC81E767753B15AA5569E1782E30ABE7D25", /* random */ "400000000000000000000000000000000000000000000000", "7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", "555555555555555555555555555555555555555555555555", }; ecp_group_init( &grp ); ecp_point_init( &R ); mpi_init( &m ); MPI_CHK( ecp_use_known_dp( &grp, POLARSSL_ECP_DP_SECP192R1 ) ); if( verbose != 0 ) printf( " ECP test #1 (SPA resistance): " ); add_count = 0; dbl_count = 0; MPI_CHK( mpi_read_string( &m, 16, exponents[0] ) ); MPI_CHK( ecp_mul( &grp, &R, &m, &grp.G ) ); for( i = 1; i < sizeof( exponents ) / sizeof( exponents[0] ); i++ ) { add_c_prev = add_count; dbl_c_prev = dbl_count; add_count = 0; dbl_count = 0; MPI_CHK( mpi_read_string( &m, 16, exponents[i] ) ); MPI_CHK( ecp_mul( &grp, &R, &m, &grp.G ) ); if( add_count != add_c_prev || dbl_count != dbl_c_prev ) { if( verbose != 0 ) printf( "failed (%zu)\n", i ); ret = 1; goto cleanup; } } if( verbose != 0 ) printf( "passed\n" ); cleanup: if( ret < 0 && verbose != 0 ) printf( "Unexpected error, return code = %08X\n", ret ); ecp_group_free( &grp ); ecp_point_free( &R ); mpi_free( &m ); if( verbose != 0 ) printf( "\n" ); return( ret ); } #endif #endif