86 lines
1.9 KiB
C
86 lines
1.9 KiB
C
/* authdecrypt.c,v 3.1 1993/07/06 01:07:44 jbj Exp
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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_LONGS ((NOCRYPT_OCTETS)/sizeof(U_LONG))
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#define BLOCK_LONGS ((BLOCK_OCTETS)/sizeof(U_LONG))
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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_char DEScache_dkeys[]; /* cached decryption keys */
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extern u_char 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_LONG authdecryptions;
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extern U_LONG authkeyuncached;
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extern U_LONG authdecryptok;
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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_LONG *pkt;
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int length; /* length of variable data in octets */
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{
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register const U_LONG *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_LONG work[2];
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authdecryptions++;
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if (keyno == 0)
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keys = 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 = 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_LONG);
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pd = pkt + longlen; /* points at NOCRYPT area */
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work[0] = *(pd + NOCRYPT_LONGS);
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work[1] = *(pd + NOCRYPT_LONGS + 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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authdecryptok++;
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return 1;
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}
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return 0;
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}
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