1 /* 2 * lib80211 crypt: host-based WEP encryption implementation for lib80211 3 * 4 * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi> 5 * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com> 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License version 2 as 9 * published by the Free Software Foundation. See README and COPYING for 10 * more details. 11 */ 12 13 #include <linux/err.h> 14 #include <linux/module.h> 15 #include <linux/init.h> 16 #include <linux/slab.h> 17 #include <linux/random.h> 18 #include <linux/scatterlist.h> 19 #include <linux/skbuff.h> 20 #include <linux/mm.h> 21 #include <asm/string.h> 22 23 #include <net/lib80211.h> 24 25 #include <crypto/skcipher.h> 26 #include <linux/crc32.h> 27 28 MODULE_AUTHOR("Jouni Malinen"); 29 MODULE_DESCRIPTION("lib80211 crypt: WEP"); 30 MODULE_LICENSE("GPL"); 31 32 struct lib80211_wep_data { 33 u32 iv; 34 #define WEP_KEY_LEN 13 35 u8 key[WEP_KEY_LEN + 1]; 36 u8 key_len; 37 u8 key_idx; 38 struct crypto_skcipher *tx_tfm; 39 struct crypto_skcipher *rx_tfm; 40 }; 41 42 static void *lib80211_wep_init(int keyidx) 43 { 44 struct lib80211_wep_data *priv; 45 46 priv = kzalloc(sizeof(*priv), GFP_ATOMIC); 47 if (priv == NULL) 48 goto fail; 49 priv->key_idx = keyidx; 50 51 priv->tx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); 52 if (IS_ERR(priv->tx_tfm)) { 53 priv->tx_tfm = NULL; 54 goto fail; 55 } 56 57 priv->rx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); 58 if (IS_ERR(priv->rx_tfm)) { 59 priv->rx_tfm = NULL; 60 goto fail; 61 } 62 /* start WEP IV from a random value */ 63 get_random_bytes(&priv->iv, 4); 64 65 return priv; 66 67 fail: 68 if (priv) { 69 crypto_free_skcipher(priv->tx_tfm); 70 crypto_free_skcipher(priv->rx_tfm); 71 kfree(priv); 72 } 73 return NULL; 74 } 75 76 static void lib80211_wep_deinit(void *priv) 77 { 78 struct lib80211_wep_data *_priv = priv; 79 if (_priv) { 80 crypto_free_skcipher(_priv->tx_tfm); 81 crypto_free_skcipher(_priv->rx_tfm); 82 } 83 kfree(priv); 84 } 85 86 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */ 87 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len, 88 u8 *key, int keylen, void *priv) 89 { 90 struct lib80211_wep_data *wep = priv; 91 u32 klen; 92 u8 *pos; 93 94 if (skb_headroom(skb) < 4 || skb->len < hdr_len) 95 return -1; 96 97 pos = skb_push(skb, 4); 98 memmove(pos, pos + 4, hdr_len); 99 pos += hdr_len; 100 101 klen = 3 + wep->key_len; 102 103 wep->iv++; 104 105 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key 106 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N) 107 * can be used to speedup attacks, so avoid using them. */ 108 if ((wep->iv & 0xff00) == 0xff00) { 109 u8 B = (wep->iv >> 16) & 0xff; 110 if (B >= 3 && B < klen) 111 wep->iv += 0x0100; 112 } 113 114 /* Prepend 24-bit IV to RC4 key and TX frame */ 115 *pos++ = (wep->iv >> 16) & 0xff; 116 *pos++ = (wep->iv >> 8) & 0xff; 117 *pos++ = wep->iv & 0xff; 118 *pos++ = wep->key_idx << 6; 119 120 return 0; 121 } 122 123 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom 124 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted, 125 * so the payload length increases with 8 bytes. 126 * 127 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data)) 128 */ 129 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv) 130 { 131 struct lib80211_wep_data *wep = priv; 132 SKCIPHER_REQUEST_ON_STACK(req, wep->tx_tfm); 133 u32 crc, klen, len; 134 u8 *pos, *icv; 135 struct scatterlist sg; 136 u8 key[WEP_KEY_LEN + 3]; 137 int err; 138 139 /* other checks are in lib80211_wep_build_iv */ 140 if (skb_tailroom(skb) < 4) 141 return -1; 142 143 /* add the IV to the frame */ 144 if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv)) 145 return -1; 146 147 /* Copy the IV into the first 3 bytes of the key */ 148 skb_copy_from_linear_data_offset(skb, hdr_len, key, 3); 149 150 /* Copy rest of the WEP key (the secret part) */ 151 memcpy(key + 3, wep->key, wep->key_len); 152 153 len = skb->len - hdr_len - 4; 154 pos = skb->data + hdr_len + 4; 155 klen = 3 + wep->key_len; 156 157 /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */ 158 crc = ~crc32_le(~0, pos, len); 159 icv = skb_put(skb, 4); 160 icv[0] = crc; 161 icv[1] = crc >> 8; 162 icv[2] = crc >> 16; 163 icv[3] = crc >> 24; 164 165 crypto_skcipher_setkey(wep->tx_tfm, key, klen); 166 sg_init_one(&sg, pos, len + 4); 167 skcipher_request_set_tfm(req, wep->tx_tfm); 168 skcipher_request_set_callback(req, 0, NULL, NULL); 169 skcipher_request_set_crypt(req, &sg, &sg, len + 4, NULL); 170 err = crypto_skcipher_encrypt(req); 171 skcipher_request_zero(req); 172 return err; 173 } 174 175 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of 176 * the frame: IV (4 bytes), encrypted payload (including SNAP header), 177 * ICV (4 bytes). len includes both IV and ICV. 178 * 179 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on 180 * failure. If frame is OK, IV and ICV will be removed. 181 */ 182 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv) 183 { 184 struct lib80211_wep_data *wep = priv; 185 SKCIPHER_REQUEST_ON_STACK(req, wep->rx_tfm); 186 u32 crc, klen, plen; 187 u8 key[WEP_KEY_LEN + 3]; 188 u8 keyidx, *pos, icv[4]; 189 struct scatterlist sg; 190 int err; 191 192 if (skb->len < hdr_len + 8) 193 return -1; 194 195 pos = skb->data + hdr_len; 196 key[0] = *pos++; 197 key[1] = *pos++; 198 key[2] = *pos++; 199 keyidx = *pos++ >> 6; 200 if (keyidx != wep->key_idx) 201 return -1; 202 203 klen = 3 + wep->key_len; 204 205 /* Copy rest of the WEP key (the secret part) */ 206 memcpy(key + 3, wep->key, wep->key_len); 207 208 /* Apply RC4 to data and compute CRC32 over decrypted data */ 209 plen = skb->len - hdr_len - 8; 210 211 crypto_skcipher_setkey(wep->rx_tfm, key, klen); 212 sg_init_one(&sg, pos, plen + 4); 213 skcipher_request_set_tfm(req, wep->rx_tfm); 214 skcipher_request_set_callback(req, 0, NULL, NULL); 215 skcipher_request_set_crypt(req, &sg, &sg, plen + 4, NULL); 216 err = crypto_skcipher_decrypt(req); 217 skcipher_request_zero(req); 218 if (err) 219 return -7; 220 221 crc = ~crc32_le(~0, pos, plen); 222 icv[0] = crc; 223 icv[1] = crc >> 8; 224 icv[2] = crc >> 16; 225 icv[3] = crc >> 24; 226 if (memcmp(icv, pos + plen, 4) != 0) { 227 /* ICV mismatch - drop frame */ 228 return -2; 229 } 230 231 /* Remove IV and ICV */ 232 memmove(skb->data + 4, skb->data, hdr_len); 233 skb_pull(skb, 4); 234 skb_trim(skb, skb->len - 4); 235 236 return 0; 237 } 238 239 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv) 240 { 241 struct lib80211_wep_data *wep = priv; 242 243 if (len < 0 || len > WEP_KEY_LEN) 244 return -1; 245 246 memcpy(wep->key, key, len); 247 wep->key_len = len; 248 249 return 0; 250 } 251 252 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv) 253 { 254 struct lib80211_wep_data *wep = priv; 255 256 if (len < wep->key_len) 257 return -1; 258 259 memcpy(key, wep->key, wep->key_len); 260 261 return wep->key_len; 262 } 263 264 static void lib80211_wep_print_stats(struct seq_file *m, void *priv) 265 { 266 struct lib80211_wep_data *wep = priv; 267 seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len); 268 } 269 270 static struct lib80211_crypto_ops lib80211_crypt_wep = { 271 .name = "WEP", 272 .init = lib80211_wep_init, 273 .deinit = lib80211_wep_deinit, 274 .encrypt_mpdu = lib80211_wep_encrypt, 275 .decrypt_mpdu = lib80211_wep_decrypt, 276 .encrypt_msdu = NULL, 277 .decrypt_msdu = NULL, 278 .set_key = lib80211_wep_set_key, 279 .get_key = lib80211_wep_get_key, 280 .print_stats = lib80211_wep_print_stats, 281 .extra_mpdu_prefix_len = 4, /* IV */ 282 .extra_mpdu_postfix_len = 4, /* ICV */ 283 .owner = THIS_MODULE, 284 }; 285 286 static int __init lib80211_crypto_wep_init(void) 287 { 288 return lib80211_register_crypto_ops(&lib80211_crypt_wep); 289 } 290 291 static void __exit lib80211_crypto_wep_exit(void) 292 { 293 lib80211_unregister_crypto_ops(&lib80211_crypt_wep); 294 } 295 296 module_init(lib80211_crypto_wep_init); 297 module_exit(lib80211_crypto_wep_exit); 298