/* * lib80211 crypt: host-based WEP encryption implementation for lib80211 * * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi> * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. See README and COPYING for * more details. */ #include <linux/err.h> #include <linux/module.h> #include <linux/init.h> #include <linux/slab.h> #include <linux/random.h> #include <linux/scatterlist.h> #include <linux/skbuff.h> #include <linux/mm.h> #include <asm/string.h> #include <net/lib80211.h> #include <linux/crypto.h> #include <linux/crc32.h> MODULE_AUTHOR("Jouni Malinen"); MODULE_DESCRIPTION("lib80211 crypt: WEP"); MODULE_LICENSE("GPL"); struct lib80211_wep_data { u32 iv; #define WEP_KEY_LEN 13 u8 key[WEP_KEY_LEN + 1]; u8 key_len; u8 key_idx; struct crypto_blkcipher *tx_tfm; struct crypto_blkcipher *rx_tfm; }; static void *lib80211_wep_init(int keyidx) { struct lib80211_wep_data *priv; priv = kzalloc(sizeof(*priv), GFP_ATOMIC); if (priv == NULL) goto fail; priv->key_idx = keyidx; priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); if (IS_ERR(priv->tx_tfm)) { printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate " "crypto API arc4\n"); priv->tx_tfm = NULL; goto fail; } priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC); if (IS_ERR(priv->rx_tfm)) { printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate " "crypto API arc4\n"); priv->rx_tfm = NULL; goto fail; } /* start WEP IV from a random value */ get_random_bytes(&priv->iv, 4); return priv; fail: if (priv) { if (priv->tx_tfm) crypto_free_blkcipher(priv->tx_tfm); if (priv->rx_tfm) crypto_free_blkcipher(priv->rx_tfm); kfree(priv); } return NULL; } static void lib80211_wep_deinit(void *priv) { struct lib80211_wep_data *_priv = priv; if (_priv) { if (_priv->tx_tfm) crypto_free_blkcipher(_priv->tx_tfm); if (_priv->rx_tfm) crypto_free_blkcipher(_priv->rx_tfm); } kfree(priv); } /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */ static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len, u8 *key, int keylen, void *priv) { struct lib80211_wep_data *wep = priv; u32 klen, len; u8 *pos; if (skb_headroom(skb) < 4 || skb->len < hdr_len) return -1; len = skb->len - hdr_len; pos = skb_push(skb, 4); memmove(pos, pos + 4, hdr_len); pos += hdr_len; klen = 3 + wep->key_len; wep->iv++; /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N) * can be used to speedup attacks, so avoid using them. */ if ((wep->iv & 0xff00) == 0xff00) { u8 B = (wep->iv >> 16) & 0xff; if (B >= 3 && B < klen) wep->iv += 0x0100; } /* Prepend 24-bit IV to RC4 key and TX frame */ *pos++ = (wep->iv >> 16) & 0xff; *pos++ = (wep->iv >> 8) & 0xff; *pos++ = wep->iv & 0xff; *pos++ = wep->key_idx << 6; return 0; } /* Perform WEP encryption on given skb that has at least 4 bytes of headroom * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted, * so the payload length increases with 8 bytes. * * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data)) */ static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv) { struct lib80211_wep_data *wep = priv; struct blkcipher_desc desc = { .tfm = wep->tx_tfm }; u32 crc, klen, len; u8 *pos, *icv; struct scatterlist sg; u8 key[WEP_KEY_LEN + 3]; /* other checks are in lib80211_wep_build_iv */ if (skb_tailroom(skb) < 4) return -1; /* add the IV to the frame */ if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv)) return -1; /* Copy the IV into the first 3 bytes of the key */ skb_copy_from_linear_data_offset(skb, hdr_len, key, 3); /* Copy rest of the WEP key (the secret part) */ memcpy(key + 3, wep->key, wep->key_len); len = skb->len - hdr_len - 4; pos = skb->data + hdr_len + 4; klen = 3 + wep->key_len; /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */ crc = ~crc32_le(~0, pos, len); icv = skb_put(skb, 4); icv[0] = crc; icv[1] = crc >> 8; icv[2] = crc >> 16; icv[3] = crc >> 24; crypto_blkcipher_setkey(wep->tx_tfm, key, klen); sg_init_one(&sg, pos, len + 4); return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4); } /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of * the frame: IV (4 bytes), encrypted payload (including SNAP header), * ICV (4 bytes). len includes both IV and ICV. * * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on * failure. If frame is OK, IV and ICV will be removed. */ static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv) { struct lib80211_wep_data *wep = priv; struct blkcipher_desc desc = { .tfm = wep->rx_tfm }; u32 crc, klen, plen; u8 key[WEP_KEY_LEN + 3]; u8 keyidx, *pos, icv[4]; struct scatterlist sg; if (skb->len < hdr_len + 8) return -1; pos = skb->data + hdr_len; key[0] = *pos++; key[1] = *pos++; key[2] = *pos++; keyidx = *pos++ >> 6; if (keyidx != wep->key_idx) return -1; klen = 3 + wep->key_len; /* Copy rest of the WEP key (the secret part) */ memcpy(key + 3, wep->key, wep->key_len); /* Apply RC4 to data and compute CRC32 over decrypted data */ plen = skb->len - hdr_len - 8; crypto_blkcipher_setkey(wep->rx_tfm, key, klen); sg_init_one(&sg, pos, plen + 4); if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4)) return -7; crc = ~crc32_le(~0, pos, plen); icv[0] = crc; icv[1] = crc >> 8; icv[2] = crc >> 16; icv[3] = crc >> 24; if (memcmp(icv, pos + plen, 4) != 0) { /* ICV mismatch - drop frame */ return -2; } /* Remove IV and ICV */ memmove(skb->data + 4, skb->data, hdr_len); skb_pull(skb, 4); skb_trim(skb, skb->len - 4); return 0; } static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv) { struct lib80211_wep_data *wep = priv; if (len < 0 || len > WEP_KEY_LEN) return -1; memcpy(wep->key, key, len); wep->key_len = len; return 0; } static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv) { struct lib80211_wep_data *wep = priv; if (len < wep->key_len) return -1; memcpy(key, wep->key, wep->key_len); return wep->key_len; } static char *lib80211_wep_print_stats(char *p, void *priv) { struct lib80211_wep_data *wep = priv; p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len); return p; } static struct lib80211_crypto_ops lib80211_crypt_wep = { .name = "WEP", .init = lib80211_wep_init, .deinit = lib80211_wep_deinit, .build_iv = lib80211_wep_build_iv, .encrypt_mpdu = lib80211_wep_encrypt, .decrypt_mpdu = lib80211_wep_decrypt, .encrypt_msdu = NULL, .decrypt_msdu = NULL, .set_key = lib80211_wep_set_key, .get_key = lib80211_wep_get_key, .print_stats = lib80211_wep_print_stats, .extra_mpdu_prefix_len = 4, /* IV */ .extra_mpdu_postfix_len = 4, /* ICV */ .owner = THIS_MODULE, }; static int __init lib80211_crypto_wep_init(void) { return lib80211_register_crypto_ops(&lib80211_crypt_wep); } static void __exit lib80211_crypto_wep_exit(void) { lib80211_unregister_crypto_ops(&lib80211_crypt_wep); } module_init(lib80211_crypto_wep_init); module_exit(lib80211_crypto_wep_exit);