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arcfour.h

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  • Forked from Nettle / nettle
    Source project has a limited visibility.
    arcfour.c 1.91 KiB
    /* arcfour.c
     *
     * The arcfour/rc4 stream cipher.
     */
    
    /* nettle, low-level cryptographics library
     *
     * Copyright (C) 2001 Niels Mller
     *  
     * The nettle library 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.
     * 
     * The nettle library 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 the nettle library; see the file COPYING.LIB.  If not, write to
     * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
     * MA 02111-1307, USA.
     */
    
    #if HAVE_CONFIG_H
    # include "config.h"
    #endif
    
    #include <assert.h>
    
    #include "arcfour.h"
    
    #define SWAP(a,b) do { int _t = a; a = b; b = _t; } while(0)
    
    void
    arcfour_set_key(struct arcfour_ctx *ctx,
    		unsigned length, const uint8_t *key)
    {
      unsigned i, j, k;
      
      assert(length >= ARCFOUR_MIN_KEY_SIZE);
      assert(length <= ARCFOUR_MAX_KEY_SIZE);
    
      /* Initialize context */
      for (i = 0; i<256; i++)
        ctx->S[i] = i;
    
      for (i = j = k = 0; i<256; i++)
        {
          j += ctx->S[i] + key[k]; j &= 0xff;
          SWAP(ctx->S[i], ctx->S[j]);
          /* Repeat key as needed */
          k = (k + 1) % length;
        }
      ctx->i = ctx->j = 0;
    }
    
    void
    arcfour_stream(struct arcfour_ctx *ctx,
    	       unsigned length, uint8_t *dst)
    {
      register uint8_t i, j;
      register int si, sj;
    
      i = ctx->i; j = ctx->j;
      while(length--)
        {
          i++; i &= 0xff;
          si = ctx->S[i];
          j += si; j &= 0xff;
          sj = ctx->S[i] = ctx->S[j];
          ctx->S[j] = si;
          *dst++ = ctx->S[ (si + sj) & 0xff ];
        }
      ctx->i = i; ctx->j = j;
    }