diff options
Diffstat (limited to 'grub-core/lib/libgcrypt/mpi/mpi-mod.c')
| -rw-r--r-- | grub-core/lib/libgcrypt/mpi/mpi-mod.c | 184 |
1 files changed, 184 insertions, 0 deletions
diff --git a/grub-core/lib/libgcrypt/mpi/mpi-mod.c b/grub-core/lib/libgcrypt/mpi/mpi-mod.c new file mode 100644 index 0000000..7ebfe6d --- /dev/null +++ b/grub-core/lib/libgcrypt/mpi/mpi-mod.c @@ -0,0 +1,184 @@ +/* mpi-mod.c - Modular reduction + Copyright (C) 1998, 1999, 2001, 2002, 2003, + 2007 Free Software Foundation, Inc. + + This file is part of Libgcrypt. + + Libgcrypt is free software; you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of + the License, or (at your option) any later version. + + Libgcrypt 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 Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser 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. */ + + +#include <config.h> +#include <stdio.h> +#include <stdlib.h> + +#include "mpi-internal.h" +#include "longlong.h" +#include "g10lib.h" + + +/* Context used with Barrett reduction. */ +struct barrett_ctx_s +{ + gcry_mpi_t m; /* The modulus - may not be modified. */ + int m_copied; /* If true, M needs to be released. */ + int k; + gcry_mpi_t y; + gcry_mpi_t r1; /* Helper MPI. */ + gcry_mpi_t r2; /* Helper MPI. */ + gcry_mpi_t r3; /* Helper MPI allocated on demand. */ +}; + + + +void +_gcry_mpi_mod (gcry_mpi_t rem, gcry_mpi_t dividend, gcry_mpi_t divisor) +{ + _gcry_mpi_fdiv_r (rem, dividend, divisor); + rem->sign = 0; +} + + +/* This function returns a new context for Barrett based operations on + the modulus M. This context needs to be released using + _gcry_mpi_barrett_free. If COPY is true M will be transferred to + the context and the user may change M. If COPY is false, M may not + be changed until gcry_mpi_barrett_free has been called. */ +mpi_barrett_t +_gcry_mpi_barrett_init (gcry_mpi_t m, int copy) +{ + mpi_barrett_t ctx; + gcry_mpi_t tmp; + + mpi_normalize (m); + ctx = gcry_xcalloc (1, sizeof *ctx); + + if (copy) + { + ctx->m = mpi_copy (m); + ctx->m_copied = 1; + } + else + ctx->m = m; + + ctx->k = mpi_get_nlimbs (m); + tmp = mpi_alloc (ctx->k + 1); + + /* Barrett precalculation: y = floor(b^(2k) / m). */ + mpi_set_ui (tmp, 1); + mpi_lshift_limbs (tmp, 2 * ctx->k); + mpi_fdiv_q (tmp, tmp, m); + + ctx->y = tmp; + ctx->r1 = mpi_alloc ( 2 * ctx->k + 1 ); + ctx->r2 = mpi_alloc ( 2 * ctx->k + 1 ); + + return ctx; +} + +void +_gcry_mpi_barrett_free (mpi_barrett_t ctx) +{ + if (ctx) + { + mpi_free (ctx->y); + mpi_free (ctx->r1); + mpi_free (ctx->r2); + if (ctx->r3) + mpi_free (ctx->r3); + if (ctx->m_copied) + mpi_free (ctx->m); + gcry_free (ctx); + } +} + + +/* R = X mod M + + Using Barrett reduction. Before using this function + _gcry_mpi_barrett_init must have been called to do the + precalculations. CTX is the context created by this precalculation + and also conveys M. If the Barret reduction could no be done a + starightforward reduction method is used. + + We assume that these conditions are met: + Input: x =(x_2k-1 ...x_0)_b + m =(m_k-1 ....m_0)_b with m_k-1 != 0 + Output: r = x mod m + */ +void +_gcry_mpi_mod_barrett (gcry_mpi_t r, gcry_mpi_t x, mpi_barrett_t ctx) +{ + gcry_mpi_t m = ctx->m; + int k = ctx->k; + gcry_mpi_t y = ctx->y; + gcry_mpi_t r1 = ctx->r1; + gcry_mpi_t r2 = ctx->r2; + + mpi_normalize (x); + if (mpi_get_nlimbs (x) > 2*k ) + { + mpi_mod (r, x, m); + return; + } + + /* 1. q1 = floor( x / b^k-1) + * q2 = q1 * y + * q3 = floor( q2 / b^k+1 ) + * Actually, we don't need qx, we can work direct on r2 + */ + mpi_set ( r2, x ); + mpi_rshift_limbs ( r2, k-1 ); + mpi_mul ( r2, r2, y ); + mpi_rshift_limbs ( r2, k+1 ); + + /* 2. r1 = x mod b^k+1 + * r2 = q3 * m mod b^k+1 + * r = r1 - r2 + * 3. if r < 0 then r = r + b^k+1 + */ + mpi_set ( r1, x ); + if ( r1->nlimbs > k+1 ) /* Quick modulo operation. */ + r1->nlimbs = k+1; + mpi_mul ( r2, r2, m ); + if ( r2->nlimbs > k+1 ) /* Quick modulo operation. */ + r2->nlimbs = k+1; + mpi_sub ( r, r1, r2 ); + + if ( mpi_is_neg( r ) ) + { + if (!ctx->r3) + { + ctx->r3 = mpi_alloc ( k + 2 ); + mpi_set_ui (ctx->r3, 1); + mpi_lshift_limbs (ctx->r3, k + 1 ); + } + mpi_add ( r, r, ctx->r3 ); + } + + /* 4. while r >= m do r = r - m */ + while ( mpi_cmp( r, m ) >= 0 ) + mpi_sub ( r, r, m ); + +} + + +void +_gcry_mpi_mul_barrett (gcry_mpi_t w, gcry_mpi_t u, gcry_mpi_t v, + mpi_barrett_t ctx) +{ + gcry_mpi_mul (w, u, v); + mpi_mod_barrett (w, w, ctx); +} |