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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_LONGS ((NOCRYPT_OCTETS)/sizeof(U_LONG))
#define BLOCK_LONGS ((BLOCK_OCTETS)/sizeof(U_LONG))
/*
* Imported from the key data base module
*/
extern u_long cache_keyid; /* cached key ID */
extern u_char DEScache_ekeys[]; /* cached decryption keys */
extern u_char DESzeroekeys[]; /* zero key decryption keys */
/*
* Stat counters from the database module
*/
extern U_LONG authencryptions;
extern U_LONG authkeyuncached;
extern U_LONG authnokey;
int
DESauthencrypt(keyno, pkt, length)
u_long keyno;
U_LONG *pkt;
int length; /* length of encrypted portion of packet */
{
register U_LONG *pd;
register int i;
register u_char *keys;
register int len;
U_LONG work[2];
authencryptions++;
if (keyno == 0) {
keys = DESzeroekeys;
} else {
if (keyno != cache_keyid) {
authkeyuncached++;
if (!authhavekey(keyno)) {
authnokey++;
return 0;
}
}
keys = 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_LONG);
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_LONGS;
*pd++ = work[0];
*pd = work[1];
return 4 + BLOCK_OCTETS; /* return size of key and MAC */
}
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