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Linux/crypto/arc4.c

  1 /*
  2  * Cryptographic API
  3  *
  4  * ARC4 Cipher Algorithm
  5  *
  6  * Jon Oberheide <jon@oberheide.org>
  7  *
  8  * This program is free software; you can redistribute it and/or modify
  9  * it under the terms of the GNU General Public License as published by
 10  * the Free Software Foundation; either version 2 of the License, or
 11  * (at your option) any later version.
 12  *
 13  */
 14 
 15 #include <linux/module.h>
 16 #include <linux/init.h>
 17 #include <linux/crypto.h>
 18 #include <crypto/algapi.h>
 19 
 20 #define ARC4_MIN_KEY_SIZE       1
 21 #define ARC4_MAX_KEY_SIZE       256
 22 #define ARC4_BLOCK_SIZE         1
 23 
 24 struct arc4_ctx {
 25         u32 S[256];
 26         u32 x, y;
 27 };
 28 
 29 static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
 30                         unsigned int key_len)
 31 {
 32         struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
 33         int i, j = 0, k = 0;
 34 
 35         ctx->x = 1;
 36         ctx->y = 0;
 37 
 38         for (i = 0; i < 256; i++)
 39                 ctx->S[i] = i;
 40 
 41         for (i = 0; i < 256; i++) {
 42                 u32 a = ctx->S[i];
 43                 j = (j + in_key[k] + a) & 0xff;
 44                 ctx->S[i] = ctx->S[j];
 45                 ctx->S[j] = a;
 46                 if (++k >= key_len)
 47                         k = 0;
 48         }
 49 
 50         return 0;
 51 }
 52 
 53 static void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in,
 54                        unsigned int len)
 55 {
 56         u32 *const S = ctx->S;
 57         u32 x, y, a, b;
 58         u32 ty, ta, tb;
 59 
 60         if (len == 0)
 61                 return;
 62 
 63         x = ctx->x;
 64         y = ctx->y;
 65 
 66         a = S[x];
 67         y = (y + a) & 0xff;
 68         b = S[y];
 69 
 70         do {
 71                 S[y] = a;
 72                 a = (a + b) & 0xff;
 73                 S[x] = b;
 74                 x = (x + 1) & 0xff;
 75                 ta = S[x];
 76                 ty = (y + ta) & 0xff;
 77                 tb = S[ty];
 78                 *out++ = *in++ ^ S[a];
 79                 if (--len == 0)
 80                         break;
 81                 y = ty;
 82                 a = ta;
 83                 b = tb;
 84         } while (true);
 85 
 86         ctx->x = x;
 87         ctx->y = y;
 88 }
 89 
 90 static void arc4_crypt_one(struct crypto_tfm *tfm, u8 *out, const u8 *in)
 91 {
 92         arc4_crypt(crypto_tfm_ctx(tfm), out, in, 1);
 93 }
 94 
 95 static int ecb_arc4_crypt(struct blkcipher_desc *desc, struct scatterlist *dst,
 96                           struct scatterlist *src, unsigned int nbytes)
 97 {
 98         struct arc4_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
 99         struct blkcipher_walk walk;
100         int err;
101 
102         blkcipher_walk_init(&walk, dst, src, nbytes);
103 
104         err = blkcipher_walk_virt(desc, &walk);
105 
106         while (walk.nbytes > 0) {
107                 u8 *wsrc = walk.src.virt.addr;
108                 u8 *wdst = walk.dst.virt.addr;
109 
110                 arc4_crypt(ctx, wdst, wsrc, walk.nbytes);
111 
112                 err = blkcipher_walk_done(desc, &walk, 0);
113         }
114 
115         return err;
116 }
117 
118 static struct crypto_alg arc4_algs[2] = { {
119         .cra_name               =       "arc4",
120         .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
121         .cra_blocksize          =       ARC4_BLOCK_SIZE,
122         .cra_ctxsize            =       sizeof(struct arc4_ctx),
123         .cra_module             =       THIS_MODULE,
124         .cra_u                  =       {
125                 .cipher = {
126                         .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
127                         .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
128                         .cia_setkey             =       arc4_set_key,
129                         .cia_encrypt            =       arc4_crypt_one,
130                         .cia_decrypt            =       arc4_crypt_one,
131                 },
132         },
133 }, {
134         .cra_name               =       "ecb(arc4)",
135         .cra_priority           =       100,
136         .cra_flags              =       CRYPTO_ALG_TYPE_BLKCIPHER,
137         .cra_blocksize          =       ARC4_BLOCK_SIZE,
138         .cra_ctxsize            =       sizeof(struct arc4_ctx),
139         .cra_alignmask          =       0,
140         .cra_type               =       &crypto_blkcipher_type,
141         .cra_module             =       THIS_MODULE,
142         .cra_u                  =       {
143                 .blkcipher = {
144                         .min_keysize    =       ARC4_MIN_KEY_SIZE,
145                         .max_keysize    =       ARC4_MAX_KEY_SIZE,
146                         .setkey         =       arc4_set_key,
147                         .encrypt        =       ecb_arc4_crypt,
148                         .decrypt        =       ecb_arc4_crypt,
149                 },
150         },
151 } };
152 
153 static int __init arc4_init(void)
154 {
155         return crypto_register_algs(arc4_algs, ARRAY_SIZE(arc4_algs));
156 }
157 
158 static void __exit arc4_exit(void)
159 {
160         crypto_unregister_algs(arc4_algs, ARRAY_SIZE(arc4_algs));
161 }
162 
163 module_init(arc4_init);
164 module_exit(arc4_exit);
165 
166 MODULE_LICENSE("GPL");
167 MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
168 MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");
169 MODULE_ALIAS_CRYPTO("arc4");
170 

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