85 lines
1.9 KiB
C
85 lines
1.9 KiB
C
/* $NetBSD: authdecrypt.c,v 1.2 1998/01/09 03:15:54 perry Exp $ */
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/*
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* authdecrypt - routine to decrypt a packet to see if this guy knows our key.
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*/
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#include "ntp_stdlib.h"
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/*
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* For our purposes an NTP packet looks like:
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*
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* a variable amount of unencrypted data, multiple of 8 bytes, followed by:
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* NOCRYPT_OCTETS worth of unencrypted data, followed by:
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* BLOCK_OCTETS worth of ciphered checksum.
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*/
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#define NOCRYPT_OCTETS 4
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#define BLOCK_OCTETS 8
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#define NOCRYPT_int32S ((NOCRYPT_OCTETS)/sizeof(u_int32))
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#define BLOCK_int32S ((BLOCK_OCTETS)/sizeof(u_int32))
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/*
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* Imported from the key data base module
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*/
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extern u_long cache_keyid; /* cached key ID */
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extern u_long DEScache_dkeys[]; /* cached decryption keys */
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extern u_long DESzerodkeys[]; /* zero key decryption keys */
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/*
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* Stat counters, imported from data base module
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*/
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extern u_int32 authdecryptions;
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extern u_int32 authkeyuncached;
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int
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DESauthdecrypt(keyno, pkt, length)
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u_long keyno;
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const u_int32 *pkt;
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int length; /* length of variable data in octets */
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{
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register const u_int32 *pd;
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register int i;
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register u_char *keys;
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register int longlen;
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u_int32 work[2];
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authdecryptions++;
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if (keyno == 0)
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keys = (u_char *)DESzerodkeys;
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else {
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if (keyno != cache_keyid) {
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authkeyuncached++;
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if (!authhavekey(keyno))
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return 0;
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}
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keys = (u_char *)DEScache_dkeys;
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}
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/*
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* Get encryption block data in host byte order and decrypt it.
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*/
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longlen = length / sizeof(u_int32);
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pd = pkt + longlen; /* points at NOCRYPT area */
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work[0] = *(pd + NOCRYPT_int32S);
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work[1] = *(pd + NOCRYPT_int32S + 1);
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if (longlen & 0x1) {
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DESauth_des(work, keys);
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work[0] ^= *(--pd);
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}
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for (i = longlen/2; i > 0; i--) {
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DESauth_des(work, keys);
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work[1] ^= *(--pd);
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work[0] ^= *(--pd);
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}
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/*
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* Success if the encryption data is zero
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*/
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if ((work[0] == 0) && (work[1] == 0))
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return 1;
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return 0;
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}
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