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41 results

ecc-ecdsa-sign.c

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  • ecc-ecdsa-sign.c 2.69 KiB
    /* ecc-ecdsa-sign.c
    
       Copyright (C) 2013, 2014 Niels Möller
    
       This file is part of GNU Nettle.
    
       GNU Nettle is free software: you can redistribute it and/or
       modify it under the terms of either:
    
         * the GNU Lesser General Public License as published by the Free
           Software Foundation; either version 3 of the License, or (at your
           option) any later version.
    
       or
    
         * 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.
    
       or both in parallel, as here.
    
       GNU Nettle 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 copies of the GNU General Public License and
       the GNU Lesser General Public License along with this program.  If
       not, see http://www.gnu.org/licenses/.
    */
    
    /* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
    
    #if HAVE_CONFIG_H
    # include "config.h"
    #endif
    
    #include <assert.h>
    #include <stdlib.h>
    
    #include "ecdsa.h"
    #include "ecc-internal.h"
    
    /* Low-level ECDSA signing */
    
    mp_size_t
    ecc_ecdsa_sign_itch (const struct ecc_curve *ecc)
    {
      /* Needs 3*ecc->p.size + scratch for ecc->mul_g. Currently same for
         ecc_mul_g and ecc_mul_g_eh. */
      return ECC_ECDSA_SIGN_ITCH (ecc->p.size);
    }
    
    /* NOTE: Caller should check if r or s is zero. */
    void
    ecc_ecdsa_sign (const struct ecc_curve *ecc,
    		const mp_limb_t *zp,
    		/* Random nonce, must be invertible mod ecc group
    		   order. */
    		const mp_limb_t *kp,
    		size_t length, const uint8_t *digest,
    		mp_limb_t *rp, mp_limb_t *sp,
    		mp_limb_t *scratch)
    {
    #define P	    scratch
    #define kinv	    scratch                /* Needs 5*ecc->p.size for computation */
    #define hp	    (scratch  + ecc->p.size) /* NOTE: ecc->p.size + 1 limbs! */
    #define tp	    (scratch + 2*ecc->p.size)
      /* Procedure, according to RFC 6090, "KT-I". q denotes the group
         order.
    
         1. k <-- uniformly random, 0 < k < q
    
         2. R <-- (r_x, r_y) = k g
    
         3. s1 <-- r_x mod q
    
         4. s2 <-- (h + z*s1)/k mod q.
      */
    
      ecc->mul_g (ecc, P, kp, P + 3*ecc->p.size);
      /* x coordinate only, modulo q */
      ecc->h_to_a (ecc, 2, rp, P, P + 3*ecc->p.size);
    
      /* Invert k, uses 4 * ecc->p.size including scratch */
      ecc->q.invert (&ecc->q, kinv, kp, tp); /* NOTE: Also clobbers hp */
      
      /* Process hash digest */
      ecc_hash (&ecc->q, hp, length, digest);
    
      ecc_modq_mul (ecc, tp, zp, rp);
      ecc_modq_add (ecc, hp, hp, tp);
      ecc_modq_mul (ecc, tp, hp, kinv);
    
      mpn_copyi (sp, tp, ecc->p.size);
    #undef P
    #undef hp
    #undef kinv
    #undef tp
    }