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 priv->tx_tfm = NULL; 54 goto fail; 55 } 56 57 priv->rx_tfm = crypto_alloc_blkcipher("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 if (priv->tx_tfm) 70 crypto_free_blkcipher(priv->tx_tfm); 71 if (priv->rx_tfm) 72 crypto_free_blkcipher(priv->rx_tfm); 73 kfree(priv); 74 } 75 return NULL; 76 } 77 78 static void lib80211_wep_deinit(void *priv) 79 { 80 struct lib80211_wep_data *_priv = priv; 81 if (_priv) { 82 if (_priv->tx_tfm) 83 crypto_free_blkcipher(_priv->tx_tfm); 84 if (_priv->rx_tfm) 85 crypto_free_blkcipher(_priv->rx_tfm); 86 } 87 kfree(priv); 88 } 89 90 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */ 91 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len, 92 u8 *key, int keylen, void *priv) 93 { 94 struct lib80211_wep_data *wep = priv; 95 u32 klen; 96 u8 *pos; 97 98 if (skb_headroom(skb) < 4 || skb->len < hdr_len) 99 return -1; 100 101 pos = skb_push(skb, 4); 102 memmove(pos, pos + 4, hdr_len); 103 pos += hdr_len; 104 105 klen = 3 + wep->key_len; 106 107 wep->iv++; 108 109 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key 110 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N) 111 * can be used to speedup attacks, so avoid using them. */ 112 if ((wep->iv & 0xff00) == 0xff00) { 113 u8 B = (wep->iv >> 16) & 0xff; 114 if (B >= 3 && B < klen) 115 wep->iv += 0x0100; 116 } 117 118 /* Prepend 24-bit IV to RC4 key and TX frame */ 119 *pos++ = (wep->iv >> 16) & 0xff; 120 *pos++ = (wep->iv >> 8) & 0xff; 121 *pos++ = wep->iv & 0xff; 122 *pos++ = wep->key_idx << 6; 123 124 return 0; 125 } 126 127 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom 128 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted, 129 * so the payload length increases with 8 bytes. 130 * 131 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data)) 132 */ 133 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv) 134 { 135 struct lib80211_wep_data *wep = priv; 136 struct blkcipher_desc desc = { .tfm = wep->tx_tfm }; 137 u32 crc, klen, len; 138 u8 *pos, *icv; 139 struct scatterlist sg; 140 u8 key[WEP_KEY_LEN + 3]; 141 142 /* other checks are in lib80211_wep_build_iv */ 143 if (skb_tailroom(skb) < 4) 144 return -1; 145 146 /* add the IV to the frame */ 147 if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv)) 148 return -1; 149 150 /* Copy the IV into the first 3 bytes of the key */ 151 skb_copy_from_linear_data_offset(skb, hdr_len, key, 3); 152 153 /* Copy rest of the WEP key (the secret part) */ 154 memcpy(key + 3, wep->key, wep->key_len); 155 156 len = skb->len - hdr_len - 4; 157 pos = skb->data + hdr_len + 4; 158 klen = 3 + wep->key_len; 159 160 /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */ 161 crc = ~crc32_le(~0, pos, len); 162 icv = skb_put(skb, 4); 163 icv[0] = crc; 164 icv[1] = crc >> 8; 165 icv[2] = crc >> 16; 166 icv[3] = crc >> 24; 167 168 crypto_blkcipher_setkey(wep->tx_tfm, key, klen); 169 sg_init_one(&sg, pos, len + 4); 170 return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4); 171 } 172 173 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of 174 * the frame: IV (4 bytes), encrypted payload (including SNAP header), 175 * ICV (4 bytes). len includes both IV and ICV. 176 * 177 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on 178 * failure. If frame is OK, IV and ICV will be removed. 179 */ 180 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv) 181 { 182 struct lib80211_wep_data *wep = priv; 183 struct blkcipher_desc desc = { .tfm = wep->rx_tfm }; 184 u32 crc, klen, plen; 185 u8 key[WEP_KEY_LEN + 3]; 186 u8 keyidx, *pos, icv[4]; 187 struct scatterlist sg; 188 189 if (skb->len < hdr_len + 8) 190 return -1; 191 192 pos = skb->data + hdr_len; 193 key[0] = *pos++; 194 key[1] = *pos++; 195 key[2] = *pos++; 196 keyidx = *pos++ >> 6; 197 if (keyidx != wep->key_idx) 198 return -1; 199 200 klen = 3 + wep->key_len; 201 202 /* Copy rest of the WEP key (the secret part) */ 203 memcpy(key + 3, wep->key, wep->key_len); 204 205 /* Apply RC4 to data and compute CRC32 over decrypted data */ 206 plen = skb->len - hdr_len - 8; 207 208 crypto_blkcipher_setkey(wep->rx_tfm, key, klen); 209 sg_init_one(&sg, pos, plen + 4); 210 if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4)) 211 return -7; 212 213 crc = ~crc32_le(~0, pos, plen); 214 icv[0] = crc; 215 icv[1] = crc >> 8; 216 icv[2] = crc >> 16; 217 icv[3] = crc >> 24; 218 if (memcmp(icv, pos + plen, 4) != 0) { 219 /* ICV mismatch - drop frame */ 220 return -2; 221 } 222 223 /* Remove IV and ICV */ 224 memmove(skb->data + 4, skb->data, hdr_len); 225 skb_pull(skb, 4); 226 skb_trim(skb, skb->len - 4); 227 228 return 0; 229 } 230 231 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv) 232 { 233 struct lib80211_wep_data *wep = priv; 234 235 if (len < 0 || len > WEP_KEY_LEN) 236 return -1; 237 238 memcpy(wep->key, key, len); 239 wep->key_len = len; 240 241 return 0; 242 } 243 244 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv) 245 { 246 struct lib80211_wep_data *wep = priv; 247 248 if (len < wep->key_len) 249 return -1; 250 251 memcpy(key, wep->key, wep->key_len); 252 253 return wep->key_len; 254 } 255 256 static void lib80211_wep_print_stats(struct seq_file *m, void *priv) 257 { 258 struct lib80211_wep_data *wep = priv; 259 seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len); 260 } 261 262 static struct lib80211_crypto_ops lib80211_crypt_wep = { 263 .name = "WEP", 264 .init = lib80211_wep_init, 265 .deinit = lib80211_wep_deinit, 266 .encrypt_mpdu = lib80211_wep_encrypt, 267 .decrypt_mpdu = lib80211_wep_decrypt, 268 .encrypt_msdu = NULL, 269 .decrypt_msdu = NULL, 270 .set_key = lib80211_wep_set_key, 271 .get_key = lib80211_wep_get_key, 272 .print_stats = lib80211_wep_print_stats, 273 .extra_mpdu_prefix_len = 4, /* IV */ 274 .extra_mpdu_postfix_len = 4, /* ICV */ 275 .owner = THIS_MODULE, 276 }; 277 278 static int __init lib80211_crypto_wep_init(void) 279 { 280 return lib80211_register_crypto_ops(&lib80211_crypt_wep); 281 } 282 283 static void __exit lib80211_crypto_wep_exit(void) 284 { 285 lib80211_unregister_crypto_ops(&lib80211_crypt_wep); 286 } 287 288 module_init(lib80211_crypto_wep_init); 289 module_exit(lib80211_crypto_wep_exit); 290