wep.c File Reference

The WEP wireless encryption method (insecure!) More...

#include <ipxe/net80211.h>
#include <ipxe/sec80211.h>
#include <ipxe/crypto.h>
#include <ipxe/arc4.h>
#include <ipxe/crc32.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

Go to the source code of this file.

Data Structures
struct	wep_ctx
	Context for WEP encryption and decryption. More...

Macros
#define	WEP_IV_LEN   3
	Length of WEP initialisation vector. More...
#define	WEP_KID_LEN   1
	Length of WEP key ID byte. More...
#define	WEP_ICV_LEN   4
	Length of WEP ICV checksum. More...
#define	WEP_MAX_KEY   16
	Maximum length of WEP key. More...
#define	WEP_HEADER_LEN   4
	Amount of data placed before the encrypted bytes. More...
#define	WEP_TRAILER_LEN   4
	Amount of data placed after the encrypted bytes. More...
#define	WEP_OVERHEAD   8
	Total WEP overhead bytes. More...

Functions
	FILE_LICENCE (GPL2_OR_LATER)
static int	wep_init (struct net80211_crypto *crypto, const void *key, int keylen, const void *rsc __unused)
	Initialize WEP algorithm. More...
static struct io_buffer *	wep_encrypt (struct net80211_crypto *crypto, struct io_buffer *iob)
	Encrypt packet using WEP. More...
static struct io_buffer *	wep_decrypt (struct net80211_crypto *crypto, struct io_buffer *eiob)
	Decrypt packet using WEP. More...
static int	trivial_init (struct net80211_device *dev)
	Initialize trivial 802.11 security handshaker. More...
static int	trivial_change_key (struct net80211_device *dev)
	Check for key change on trivial 802.11 security handshaker. More...

Variables
struct net80211_crypto wep_crypto	__net80211_crypto
	WEP cryptosystem for 802.11. More...
struct net80211_handshaker trivial_handshaker	__net80211_handshaker
	Trivial 802.11 security handshaker. More...

Detailed Description

The WEP wireless encryption method (insecure!)

The data field in a WEP-encrypted packet contains a 3-byte initialisation vector, one-byte Key ID field (only the bottom two bits are ever used), encrypted data, and a 4-byte encrypted CRC of the plaintext data, called the ICV. To decrypt it, the IV is prepended to the shared key and the data stream (including ICV) is run through the ARC4 stream cipher; if the ICV matches a CRC32 calculated on the plaintext, the packet is valid.

For efficiency and code-size reasons, this file assumes it is running on a little-endian machine.

Definition in file wep.c.

Macro Definition Documentation

WEP_IV_LEN

#define WEP_IV_LEN   3

Length of WEP initialisation vector.

Definition at line 48 of file wep.c.

WEP_KID_LEN

#define WEP_KID_LEN   1

Length of WEP key ID byte.

Definition at line 51 of file wep.c.

WEP_ICV_LEN

#define WEP_ICV_LEN   4

Length of WEP ICV checksum.

Definition at line 54 of file wep.c.

WEP_MAX_KEY

#define WEP_MAX_KEY   16

Maximum length of WEP key.

Definition at line 57 of file wep.c.

WEP_HEADER_LEN

#define WEP_HEADER_LEN   4

Amount of data placed before the encrypted bytes.

Definition at line 60 of file wep.c.

WEP_TRAILER_LEN

#define WEP_TRAILER_LEN   4

Amount of data placed after the encrypted bytes.

Definition at line 63 of file wep.c.

WEP_OVERHEAD

#define WEP_OVERHEAD   8

Total WEP overhead bytes.

Definition at line 66 of file wep.c.

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER

)

wep_init()

static int wep_init ( struct net80211_crypto *  crypto, const void *  key, int  keylen, const void *rsc  __unused  )

static

Initialize WEP algorithm.

Parameters

crypto	802.11 cryptographic algorithm
key	WEP key to use
keylen	Length of WEP key
rsc	Initial receive sequence counter (unused)

Return values

rc	Return status code

Standard key lengths are 5 and 13 bytes; 16-byte keys are occasionally supported as an extension to the standard.

Definition at line 98 of file wep.c.

{
        struct wep_ctx *ctx = crypto->priv;

        ctx->keylen = ( keylen > WEP_MAX_KEY ? WEP_MAX_KEY : keylen );
        memcpy ( ctx->key + WEP_IV_LEN, key, ctx->keylen );

        return 0;
}

References ctx, key, wep_ctx::keylen, memcpy(), net80211_crypto::priv, WEP_IV_LEN, and WEP_MAX_KEY.

Referenced by trivial_change_key().

wep_encrypt()

static struct io_buffer* wep_encrypt ( struct net80211_crypto *  crypto, struct io_buffer *  iob  )

static

Encrypt packet using WEP.

Parameters

crypto	802.11 cryptographic algorithm
iob	I/O buffer of plaintext packet

Return values

eiob	Newly allocated I/O buffer for encrypted packet, or NULL

If memory allocation fails, NULL is returned.

Definition at line 118 of file wep.c.

{
        struct wep_ctx *ctx = crypto->priv;
        struct io_buffer *eiob;
        struct ieee80211_frame *hdr;
        const int hdrlen = IEEE80211_TYP_FRAME_HEADER_LEN;
        int datalen = iob_len ( iob ) - hdrlen;
        int newlen = hdrlen + datalen + WEP_OVERHEAD;
        u32 iv, icv;

        eiob = alloc_iob ( newlen );
        if ( ! eiob )
                return NULL;

        memcpy ( iob_put ( eiob, hdrlen ), iob->data, hdrlen );
        hdr = eiob->data;
        hdr->fc |= IEEE80211_FC_PROTECTED;

        /* Calculate IV, put it in the header (with key ID byte = 0), and
           set it up at the start of the encryption key. */
        iv = random() & 0xffffff; /* IV in bottom 3 bytes, top byte = KID = 0 */
        memcpy ( iob_put ( eiob, WEP_HEADER_LEN ), &iv, WEP_HEADER_LEN );
        memcpy ( ctx->key, &iv, WEP_IV_LEN );

        /* Encrypt the data using RC4 */
        cipher_setkey ( &arc4_algorithm, &ctx->arc4, ctx->key,
                        ctx->keylen + WEP_IV_LEN );
        cipher_encrypt ( &arc4_algorithm, &ctx->arc4, iob->data + hdrlen,
                         iob_put ( eiob, datalen ), datalen );

        /* Add ICV */
        icv = ~crc32_le ( ~0, iob->data + hdrlen, datalen );
        cipher_encrypt ( &arc4_algorithm, &ctx->arc4, &icv,
                         iob_put ( eiob, WEP_ICV_LEN ), WEP_ICV_LEN );

        return eiob;
}

References alloc_iob(), arc4_algorithm, cipher_encrypt, cipher_setkey(), crc32_le(), ctx, io_buffer::data, datalen, hdr, IEEE80211_FC_PROTECTED, IEEE80211_TYP_FRAME_HEADER_LEN, iob_len(), iob_put, iv, memcpy(), NULL, net80211_crypto::priv, random(), WEP_HEADER_LEN, WEP_ICV_LEN, WEP_IV_LEN, and WEP_OVERHEAD.

wep_decrypt()

static struct io_buffer* wep_decrypt ( struct net80211_crypto *  crypto, struct io_buffer *  eiob  )

static

Decrypt packet using WEP.

Parameters

crypto	802.11 cryptographic algorithm
eiob	I/O buffer of encrypted packet

Return values

iob	Newly allocated I/O buffer for plaintext packet, or NULL

If a consistency check for the decryption fails (usually indicating an invalid key), NULL is returned.

Definition at line 167 of file wep.c.

{
        struct wep_ctx *ctx = crypto->priv;
        struct io_buffer *iob;
        struct ieee80211_frame *hdr;
        const int hdrlen = IEEE80211_TYP_FRAME_HEADER_LEN;
        int datalen = iob_len ( eiob ) - hdrlen - WEP_OVERHEAD;
        int newlen = hdrlen + datalen;
        u32 iv, icv, crc;

        iob = alloc_iob ( newlen );
        if ( ! iob )
                return NULL;

        memcpy ( iob_put ( iob, hdrlen ), eiob->data, hdrlen );
        hdr = iob->data;
        hdr->fc &= ~IEEE80211_FC_PROTECTED;

        /* Strip off IV and use it to initialize cryptosystem */
        memcpy ( &iv, eiob->data + hdrlen, 4 );
        iv &= 0xffffff;         /* ignore key ID byte */
        memcpy ( ctx->key, &iv, WEP_IV_LEN );

        /* Decrypt the data using RC4 */
        cipher_setkey ( &arc4_algorithm, &ctx->arc4, ctx->key,
                        ctx->keylen + WEP_IV_LEN );
        cipher_decrypt ( &arc4_algorithm, &ctx->arc4, eiob->data + hdrlen +
                         WEP_HEADER_LEN, iob_put ( iob, datalen ), datalen );

        /* Strip off ICV and verify it */
        cipher_decrypt ( &arc4_algorithm, &ctx->arc4, eiob->data + hdrlen +
                         WEP_HEADER_LEN + datalen, &icv, WEP_ICV_LEN );
        crc = ~crc32_le ( ~0, iob->data + hdrlen, datalen );
        if ( crc != icv ) {
                DBGC ( crypto, "WEP %p CRC mismatch: expect %08x, get %08x\n",
                       crypto, icv, crc );
                free_iob ( iob );
                return NULL;
        }
        return iob;
}

References alloc_iob(), arc4_algorithm, cipher_decrypt, cipher_setkey(), crc32_le(), ctx, io_buffer::data, datalen, DBGC, free_iob(), hdr, IEEE80211_FC_PROTECTED, IEEE80211_TYP_FRAME_HEADER_LEN, iob_len(), iob_put, iv, memcpy(), NULL, net80211_crypto::priv, WEP_HEADER_LEN, WEP_ICV_LEN, WEP_IV_LEN, and WEP_OVERHEAD.

trivial_init()

static int trivial_init ( struct net80211_device *  dev )

static

Initialize trivial 802.11 security handshaker.

Parameters

dev	802.11 device
ctx	Security handshaker

This simply fetches a WEP key from netX/key, and if it exists, installs WEP cryptography on the 802.11 device. No real handshaking is performed.

Definition at line 229 of file wep.c.

{
        u8 key[WEP_MAX_KEY];    /* support up to 128-bit keys */
        int len;
        int rc;

        if ( dev->associating &&
             dev->associating->crypto == NET80211_CRYPT_NONE )
                return 0;       /* no crypto? OK. */

        len = fetch_raw_setting ( netdev_settings ( dev->netdev ),
                                  &net80211_key_setting, key, WEP_MAX_KEY );

        if ( len <= 0 ) {
                DBGC ( dev, "802.11 %p cannot do WEP without a key\n", dev );
                return -EACCES;
        }

        /* Full 128-bit keys are a nonstandard extension, but they're
           utterly trivial to support, so we do. */
        if ( len != 5 && len != 13 && len != 16 ) {
                DBGC ( dev, "802.11 %p invalid WEP key length %d\n",
                       dev, len );
                return -EINVAL;
        }

        DBGC ( dev, "802.11 %p installing %d-bit WEP\n", dev, len * 8 );

        rc = sec80211_install ( &dev->crypto, NET80211_CRYPT_WEP, key, len,
                                NULL );
        if ( rc < 0 )
                return rc;

        return 0;
}

References net80211_device::associating, net80211_device::crypto, net80211_wlan::crypto, DBGC, EACCES, EINVAL, fetch_raw_setting(), key, len, NET80211_CRYPT_NONE, NET80211_CRYPT_WEP, net80211_device::netdev, netdev_settings(), NULL, rc, sec80211_install(), and WEP_MAX_KEY.

trivial_change_key()

static int trivial_change_key ( struct net80211_device *  dev )

static

Check for key change on trivial 802.11 security handshaker.

Parameters

dev	802.11 device
ctx	Security handshaker

Definition at line 271 of file wep.c.

{
        u8 key[WEP_MAX_KEY];
        int len;
        int change = 0;

        /* If going from WEP to clear, or something else to WEP, reassociate. */
        if ( ! dev->crypto || ( dev->crypto->init != wep_init ) )
                change ^= 1;

        len = fetch_raw_setting ( netdev_settings ( dev->netdev ),
                                  &net80211_key_setting, key, WEP_MAX_KEY );
        if ( len <= 0 )
                change ^= 1;

        /* Changing crypto type => return nonzero to reassociate. */
        if ( change )
                return -EINVAL;

        /* Going from no crypto to still no crypto => nothing to do. */
        if ( len <= 0 )
                return 0;

        /* Otherwise, reinitialise WEP with new key. */
        return wep_init ( dev->crypto, key, len, NULL );
}

References net80211_device::crypto, EINVAL, fetch_raw_setting(), net80211_crypto::init, key, len, net80211_device::netdev, netdev_settings(), NULL, wep_init(), and WEP_MAX_KEY.

Variable Documentation

__net80211_crypto

struct net80211_crypto wep_crypto __net80211_crypto

Initial value:

= {
        .algorithm = NET80211_CRYPT_WEP,
        .init = wep_init,
        .encrypt = wep_encrypt,
        .decrypt = wep_decrypt,
        .priv_len = sizeof ( struct wep_ctx ),
}

WEP cryptosystem for 802.11.

Definition at line 211 of file wep.c.

__net80211_handshaker

struct net80211_handshaker trivial_handshaker __net80211_handshaker

Initial value:

= {
        .protocol = NET80211_SECPROT_NONE,
        .init = trivial_init,
        .change_key = trivial_change_key,
        .priv_len = 0,
}

Trivial 802.11 security handshaker.

Definition at line 299 of file wep.c.