NetBSD/lib/libntp/authencrypt.c

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/* $NetBSD: authencrypt.c,v 1.3 1998/03/06 18:17:13 christos Exp $ */
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/*
* authencrypt - compute and encrypt the mac field in an NTP packet
*/
#include "ntp_stdlib.h"
/*
* For our purposes an NTP packet looks like:
*
* a variable amount of encrypted data, multiple of 8 bytes, followed by:
* NOCRYPT_OCTETS worth of unencrypted data, followed by:
* BLOCK_OCTETS worth of ciphered checksum.
*/
#define NOCRYPT_OCTETS 4
#define BLOCK_OCTETS 8
#define NOCRYPT_int32S ((NOCRYPT_OCTETS)/sizeof(u_int32))
#define BLOCK_int32S ((BLOCK_OCTETS)/sizeof(u_int32))
/*
* Imported from the key data base module
*/
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extern u_int32 cache_keyid; /* cached key ID */
extern u_int32 DEScache_ekeys[]; /* cached decryption keys */
extern u_int32 DESzeroekeys[]; /* zero key decryption keys */
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/*
* Stat counters from the database module
*/
extern u_int32 authencryptions;
extern u_int32 authkeyuncached;
extern u_int32 authnokey;
int
DESauthencrypt(keyno, pkt, length)
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u_int32 keyno;
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u_int32 *pkt;
int length; /* length of encrypted portion of packet */
{
register u_int32 *pd;
register int i;
register u_char *keys;
register int len;
u_int32 work[2];
authencryptions++;
if (keyno == 0) {
keys = (u_char *)DESzeroekeys;
} else {
if (keyno != cache_keyid) {
authkeyuncached++;
if (!authhavekey(keyno)) {
authnokey++;
return 0;
}
}
keys = (u_char *)DEScache_ekeys;
}
/*
* Do the encryption. Work our way forward in the packet, eight
* bytes at a time, encrypting as we go. Note that the byte order
* issues are handled by the DES routine itself
*/
pd = pkt;
work[0] = work[1] = 0;
len = length / sizeof(u_int32);
for (i = (len/2); i > 0; i--) {
work[0] ^= *pd++;
work[1] ^= *pd++;
DESauth_des(work, keys);
}
if (len & 0x1) {
work[0] ^= *pd++;
DESauth_des(work, keys);
}
/*
* Space past the keyid and stick the result back in the mac field
*/
pd += NOCRYPT_int32S;
*pd++ = work[0];
*pd = work[1];
return 4 + BLOCK_OCTETS; /* return size of key and MAC */
}