/* $NetBSD: authdecrypt.c,v 1.3 1998/03/06 18:17:13 christos Exp $ */ /* * authdecrypt - routine to decrypt a packet to see if this guy knows our key. */ #include "ntp_stdlib.h" /* * For our purposes an NTP packet looks like: * * a variable amount of unencrypted 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 */ extern u_int32 cache_keyid; /* cached key ID */ extern u_int32 DEScache_dkeys[]; /* cached decryption keys */ extern u_int32 DESzerodkeys[]; /* zero key decryption keys */ /* * Stat counters, imported from data base module */ extern u_int32 authdecryptions; extern u_int32 authkeyuncached; int DESauthdecrypt(keyno, pkt, length) u_int32 keyno; const u_int32 *pkt; int length; /* length of variable data in octets */ { register const u_int32 *pd; register int i; register u_char *keys; register int longlen; u_int32 work[2]; authdecryptions++; if (keyno == 0) keys = (u_char *)DESzerodkeys; else { if (keyno != cache_keyid) { authkeyuncached++; if (!authhavekey(keyno)) return 0; } keys = (u_char *)DEScache_dkeys; } /* * Get encryption block data in host byte order and decrypt it. */ longlen = length / sizeof(u_int32); pd = pkt + longlen; /* points at NOCRYPT area */ work[0] = *(pd + NOCRYPT_int32S); work[1] = *(pd + NOCRYPT_int32S + 1); if (longlen & 0x1) { DESauth_des(work, keys); work[0] ^= *(--pd); } for (i = longlen/2; i > 0; i--) { DESauth_des(work, keys); work[1] ^= *(--pd); work[0] ^= *(--pd); } /* * Success if the encryption data is zero */ if ((work[0] == 0) && (work[1] == 0)) return 1; return 0; }