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/******************************************************************************/
/* File includes */
/* */
#include "airpdcap_system.h"
#include "airpdcap_int.h"
#include "airpdcap_wep.h"
#include "airpdcap_debug.h"
/* */
/******************************************************************************/
extern const UINT32 crc32_table[256];
/* Note: copied from FreeBSD source code, RELENG 6, */
/* sys/net80211/ieee80211_crypto_wep.c, 391 */
INT AirPDcapWepDecrypt(
const UCHAR *seed,
const size_t seed_len,
UCHAR *cypher_text,
const size_t data_len)
{
UINT32 i, j, k, crc;
UINT8 S[256];
UINT8 icv[4];
size_t buflen;
/* Generate key stream (RC4 Pseude-Random Number Generator) */
for (i = 0; i < 256; i++)
S[i] = (UINT8)i;
for (j = i = 0; i < 256; i++) {
j = (j + S[i] + seed[i % seed_len]) & 0xff;
S_SWAP(i, j);
}
/* Apply RC4 to data and compute CRC32 over decrypted data */
crc = ~(UINT32)0;
buflen = data_len;
for (i = j = k = 0; k < buflen; k++) {
i = (i + 1) & 0xff;
j = (j + S[i]) & 0xff;
S_SWAP(i, j);
*cypher_text ^= S[(S[i] + S[j]) & 0xff];
crc = crc32_table[(crc ^ *cypher_text) & 0xff] ^ (crc >> 8);
cypher_text++;
}
crc = ~crc;
/* Encrypt little-endian CRC32 and verify that it matches with the received ICV */
icv[0] = (UINT8)crc;
icv[1] = (UINT8)(crc >> 8);
icv[2] = (UINT8)(crc >> 16);
icv[3] = (UINT8)(crc >> 24);
for (k = 0; k < 4; k++) {
i = (i + 1) & 0xff;
j = (j + S[i]) & 0xff;
S_SWAP(i, j);
if ((icv[k] ^ S[(S[i] + S[j]) & 0xff]) != *cypher_text++) {
/* ICV mismatch - drop frame */
return AIRPDCAP_RET_UNSUCCESS;
}
}
return AIRPDCAP_RET_SUCCESS;
}
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