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_cipher *tx_tfm; 39 struct crypto_cipher *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_cipher("arc4", 0, 0); 52 if (IS_ERR(priv->tx_tfm)) { 53 priv->tx_tfm = NULL; 54 goto fail; 55 } 56 57 priv->rx_tfm = crypto_alloc_cipher("arc4", 0, 0); 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_cipher(priv->tx_tfm); 70 crypto_free_cipher(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_cipher(_priv->tx_tfm); 81 crypto_free_cipher(_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 u32 crc, klen, len; 133 u8 *pos, *icv; 134 u8 key[WEP_KEY_LEN + 3]; 135 int i; 136 137 /* other checks are in lib80211_wep_build_iv */ 138 if (skb_tailroom(skb) < 4) 139 return -1; 140 141 /* add the IV to the frame */ 142 if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv)) 143 return -1; 144 145 /* Copy the IV into the first 3 bytes of the key */ 146 skb_copy_from_linear_data_offset(skb, hdr_len, key, 3); 147 148 /* Copy rest of the WEP key (the secret part) */ 149 memcpy(key + 3, wep->key, wep->key_len); 150 151 len = skb->len - hdr_len - 4; 152 pos = skb->data + hdr_len + 4; 153 klen = 3 + wep->key_len; 154 155 /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */ 156 crc = ~crc32_le(~0, pos, len); 157 icv = skb_put(skb, 4); 158 icv[0] = crc; 159 icv[1] = crc >> 8; 160 icv[2] = crc >> 16; 161 icv[3] = crc >> 24; 162 163 crypto_cipher_setkey(wep->tx_tfm, key, klen); 164 165 for (i = 0; i < len + 4; i++) 166 crypto_cipher_encrypt_one(wep->tx_tfm, pos + i, pos + i); 167 168 return 0; 169 } 170 171 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of 172 * the frame: IV (4 bytes), encrypted payload (including SNAP header), 173 * ICV (4 bytes). len includes both IV and ICV. 174 * 175 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on 176 * failure. If frame is OK, IV and ICV will be removed. 177 */ 178 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv) 179 { 180 struct lib80211_wep_data *wep = priv; 181 u32 crc, klen, plen; 182 u8 key[WEP_KEY_LEN + 3]; 183 u8 keyidx, *pos, icv[4]; 184 int i; 185 186 if (skb->len < hdr_len + 8) 187 return -1; 188 189 pos = skb->data + hdr_len; 190 key[0] = *pos++; 191 key[1] = *pos++; 192 key[2] = *pos++; 193 keyidx = *pos++ >> 6; 194 if (keyidx != wep->key_idx) 195 return -1; 196 197 klen = 3 + wep->key_len; 198 199 /* Copy rest of the WEP key (the secret part) */ 200 memcpy(key + 3, wep->key, wep->key_len); 201 202 /* Apply RC4 to data and compute CRC32 over decrypted data */ 203 plen = skb->len - hdr_len - 8; 204 205 crypto_cipher_setkey(wep->rx_tfm, key, klen); 206 for (i = 0; i < plen + 4; i++) 207 crypto_cipher_decrypt_one(wep->rx_tfm, pos + i, pos + i); 208 209 crc = ~crc32_le(~0, pos, plen); 210 icv[0] = crc; 211 icv[1] = crc >> 8; 212 icv[2] = crc >> 16; 213 icv[3] = crc >> 24; 214 if (memcmp(icv, pos + plen, 4) != 0) { 215 /* ICV mismatch - drop frame */ 216 return -2; 217 } 218 219 /* Remove IV and ICV */ 220 memmove(skb->data + 4, skb->data, hdr_len); 221 skb_pull(skb, 4); 222 skb_trim(skb, skb->len - 4); 223 224 return 0; 225 } 226 227 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv) 228 { 229 struct lib80211_wep_data *wep = priv; 230 231 if (len < 0 || len > WEP_KEY_LEN) 232 return -1; 233 234 memcpy(wep->key, key, len); 235 wep->key_len = len; 236 237 return 0; 238 } 239 240 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv) 241 { 242 struct lib80211_wep_data *wep = priv; 243 244 if (len < wep->key_len) 245 return -1; 246 247 memcpy(key, wep->key, wep->key_len); 248 249 return wep->key_len; 250 } 251 252 static void lib80211_wep_print_stats(struct seq_file *m, void *priv) 253 { 254 struct lib80211_wep_data *wep = priv; 255 seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len); 256 } 257 258 static struct lib80211_crypto_ops lib80211_crypt_wep = { 259 .name = "WEP", 260 .init = lib80211_wep_init, 261 .deinit = lib80211_wep_deinit, 262 .encrypt_mpdu = lib80211_wep_encrypt, 263 .decrypt_mpdu = lib80211_wep_decrypt, 264 .encrypt_msdu = NULL, 265 .decrypt_msdu = NULL, 266 .set_key = lib80211_wep_set_key, 267 .get_key = lib80211_wep_get_key, 268 .print_stats = lib80211_wep_print_stats, 269 .extra_mpdu_prefix_len = 4, /* IV */ 270 .extra_mpdu_postfix_len = 4, /* ICV */ 271 .owner = THIS_MODULE, 272 }; 273 274 static int __init lib80211_crypto_wep_init(void) 275 { 276 return lib80211_register_crypto_ops(&lib80211_crypt_wep); 277 } 278 279 static void __exit lib80211_crypto_wep_exit(void) 280 { 281 lib80211_unregister_crypto_ops(&lib80211_crypt_wep); 282 } 283 284 module_init(lib80211_crypto_wep_init); 285 module_exit(lib80211_crypto_wep_exit); 286