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 <linux/crypto.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_blkcipher *tx_tfm; 39 struct crypto_blkcipher *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_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); 52 if (IS_ERR(priv->tx_tfm)) { 53 printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate " 54 "crypto API arc4\n"); 55 priv->tx_tfm = NULL; 56 goto fail; 57 } 58 59 priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); 60 if (IS_ERR(priv->rx_tfm)) { 61 printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate " 62 "crypto API arc4\n"); 63 priv->rx_tfm = NULL; 64 goto fail; 65 } 66 /* start WEP IV from a random value */ 67 get_random_bytes(&priv->iv, 4); 68 69 return priv; 70 71 fail: 72 if (priv) { 73 if (priv->tx_tfm) 74 crypto_free_blkcipher(priv->tx_tfm); 75 if (priv->rx_tfm) 76 crypto_free_blkcipher(priv->rx_tfm); 77 kfree(priv); 78 } 79 return NULL; 80 } 81 82 static void lib80211_wep_deinit(void *priv) 83 { 84 struct lib80211_wep_data *_priv = priv; 85 if (_priv) { 86 if (_priv->tx_tfm) 87 crypto_free_blkcipher(_priv->tx_tfm); 88 if (_priv->rx_tfm) 89 crypto_free_blkcipher(_priv->rx_tfm); 90 } 91 kfree(priv); 92 } 93 94 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */ 95 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len, 96 u8 *key, int keylen, void *priv) 97 { 98 struct lib80211_wep_data *wep = priv; 99 u32 klen, len; 100 u8 *pos; 101 102 if (skb_headroom(skb) < 4 || skb->len < hdr_len) 103 return -1; 104 105 len = skb->len - hdr_len; 106 pos = skb_push(skb, 4); 107 memmove(pos, pos + 4, hdr_len); 108 pos += hdr_len; 109 110 klen = 3 + wep->key_len; 111 112 wep->iv++; 113 114 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key 115 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N) 116 * can be used to speedup attacks, so avoid using them. */ 117 if ((wep->iv & 0xff00) == 0xff00) { 118 u8 B = (wep->iv >> 16) & 0xff; 119 if (B >= 3 && B < klen) 120 wep->iv += 0x0100; 121 } 122 123 /* Prepend 24-bit IV to RC4 key and TX frame */ 124 *pos++ = (wep->iv >> 16) & 0xff; 125 *pos++ = (wep->iv >> 8) & 0xff; 126 *pos++ = wep->iv & 0xff; 127 *pos++ = wep->key_idx << 6; 128 129 return 0; 130 } 131 132 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom 133 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted, 134 * so the payload length increases with 8 bytes. 135 * 136 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data)) 137 */ 138 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv) 139 { 140 struct lib80211_wep_data *wep = priv; 141 struct blkcipher_desc desc = { .tfm = wep->tx_tfm }; 142 u32 crc, klen, len; 143 u8 *pos, *icv; 144 struct scatterlist sg; 145 u8 key[WEP_KEY_LEN + 3]; 146 147 /* other checks are in lib80211_wep_build_iv */ 148 if (skb_tailroom(skb) < 4) 149 return -1; 150 151 /* add the IV to the frame */ 152 if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv)) 153 return -1; 154 155 /* Copy the IV into the first 3 bytes of the key */ 156 skb_copy_from_linear_data_offset(skb, hdr_len, key, 3); 157 158 /* Copy rest of the WEP key (the secret part) */ 159 memcpy(key + 3, wep->key, wep->key_len); 160 161 len = skb->len - hdr_len - 4; 162 pos = skb->data + hdr_len + 4; 163 klen = 3 + wep->key_len; 164 165 /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */ 166 crc = ~crc32_le(~0, pos, len); 167 icv = skb_put(skb, 4); 168 icv[0] = crc; 169 icv[1] = crc >> 8; 170 icv[2] = crc >> 16; 171 icv[3] = crc >> 24; 172 173 crypto_blkcipher_setkey(wep->tx_tfm, key, klen); 174 sg_init_one(&sg, pos, len + 4); 175 return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4); 176 } 177 178 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of 179 * the frame: IV (4 bytes), encrypted payload (including SNAP header), 180 * ICV (4 bytes). len includes both IV and ICV. 181 * 182 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on 183 * failure. If frame is OK, IV and ICV will be removed. 184 */ 185 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv) 186 { 187 struct lib80211_wep_data *wep = priv; 188 struct blkcipher_desc desc = { .tfm = wep->rx_tfm }; 189 u32 crc, klen, plen; 190 u8 key[WEP_KEY_LEN + 3]; 191 u8 keyidx, *pos, icv[4]; 192 struct scatterlist sg; 193 194 if (skb->len < hdr_len + 8) 195 return -1; 196 197 pos = skb->data + hdr_len; 198 key[0] = *pos++; 199 key[1] = *pos++; 200 key[2] = *pos++; 201 keyidx = *pos++ >> 6; 202 if (keyidx != wep->key_idx) 203 return -1; 204 205 klen = 3 + wep->key_len; 206 207 /* Copy rest of the WEP key (the secret part) */ 208 memcpy(key + 3, wep->key, wep->key_len); 209 210 /* Apply RC4 to data and compute CRC32 over decrypted data */ 211 plen = skb->len - hdr_len - 8; 212 213 crypto_blkcipher_setkey(wep->rx_tfm, key, klen); 214 sg_init_one(&sg, pos, plen + 4); 215 if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4)) 216 return -7; 217 218 crc = ~crc32_le(~0, pos, plen); 219 icv[0] = crc; 220 icv[1] = crc >> 8; 221 icv[2] = crc >> 16; 222 icv[3] = crc >> 24; 223 if (memcmp(icv, pos + plen, 4) != 0) { 224 /* ICV mismatch - drop frame */ 225 return -2; 226 } 227 228 /* Remove IV and ICV */ 229 memmove(skb->data + 4, skb->data, hdr_len); 230 skb_pull(skb, 4); 231 skb_trim(skb, skb->len - 4); 232 233 return 0; 234 } 235 236 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv) 237 { 238 struct lib80211_wep_data *wep = priv; 239 240 if (len < 0 || len > WEP_KEY_LEN) 241 return -1; 242 243 memcpy(wep->key, key, len); 244 wep->key_len = len; 245 246 return 0; 247 } 248 249 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv) 250 { 251 struct lib80211_wep_data *wep = priv; 252 253 if (len < wep->key_len) 254 return -1; 255 256 memcpy(key, wep->key, wep->key_len); 257 258 return wep->key_len; 259 } 260 261 static char *lib80211_wep_print_stats(char *p, void *priv) 262 { 263 struct lib80211_wep_data *wep = priv; 264 p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len); 265 return p; 266 } 267 268 static struct lib80211_crypto_ops lib80211_crypt_wep = { 269 .name = "WEP", 270 .init = lib80211_wep_init, 271 .deinit = lib80211_wep_deinit, 272 .encrypt_mpdu = lib80211_wep_encrypt, 273 .decrypt_mpdu = lib80211_wep_decrypt, 274 .encrypt_msdu = NULL, 275 .decrypt_msdu = NULL, 276 .set_key = lib80211_wep_set_key, 277 .get_key = lib80211_wep_get_key, 278 .print_stats = lib80211_wep_print_stats, 279 .extra_mpdu_prefix_len = 4, /* IV */ 280 .extra_mpdu_postfix_len = 4, /* ICV */ 281 .owner = THIS_MODULE, 282 }; 283 284 static int __init lib80211_crypto_wep_init(void) 285 { 286 return lib80211_register_crypto_ops(&lib80211_crypt_wep); 287 } 288 289 static void __exit lib80211_crypto_wep_exit(void) 290 { 291 lib80211_unregister_crypto_ops(&lib80211_crypt_wep); 292 } 293 294 module_init(lib80211_crypto_wep_init); 295 module_exit(lib80211_crypto_wep_exit); 296