89 lines
1.9 KiB
C
89 lines
1.9 KiB
C
/*
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* authencrypt - compute and encrypt the mac field in an NTP packet
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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 encrypted 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_ekeys[]; /* cached decryption keys */
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extern u_char DESzeroekeys[]; /* zero key decryption keys */
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/*
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* Stat counters from the database module
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*/
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extern U_LONG authencryptions;
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extern U_LONG authkeyuncached;
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extern U_LONG authnokey;
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int
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DESauthencrypt(keyno, pkt, length)
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u_long keyno;
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U_LONG *pkt;
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int length; /* length of encrypted portion of packet */
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{
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register U_LONG *pd;
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register int i;
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register u_char *keys;
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register int len;
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U_LONG work[2];
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authencryptions++;
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if (keyno == 0) {
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keys = DESzeroekeys;
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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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authnokey++;
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return 0;
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}
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}
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keys = DEScache_ekeys;
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}
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/*
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* Do the encryption. Work our way forward in the packet, eight
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* bytes at a time, encrypting as we go. Note that the byte order
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* issues are handled by the DES routine itself
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*/
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pd = pkt;
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work[0] = work[1] = 0;
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len = length / sizeof(U_LONG);
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for (i = (len/2); i > 0; i--) {
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work[0] ^= *pd++;
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work[1] ^= *pd++;
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DESauth_des(work, keys);
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}
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if (len & 0x1) {
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work[0] ^= *pd++;
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DESauth_des(work, keys);
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}
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/*
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* Space past the keyid and stick the result back in the mac field
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*/
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pd += NOCRYPT_LONGS;
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*pd++ = work[0];
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*pd = work[1];
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return 4 + BLOCK_OCTETS; /* return size of key and MAC */
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}
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