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Annotation of src/usr.bin/ssh/deattack.c, Revision 1.1

1.1     ! dugsong     1: /*
        !             2:  * $Id: deattack.c,v 1.9 1998/06/27 00:02:22 futo Exp $ Cryptographic attack
        !             3:  * detector for ssh - source code (C)1998 CORE-SDI, Buenos Aires Argentina
        !             4:  * Ariel Futoransky(futo@core-sdi.com) <http://www.core-sdi.com>
        !             5:  */
        !             6:
        !             7: #include "includes.h"
        !             8: #include "deattack.h"
        !             9: #include "ssh.h"
        !            10: #include "getput.h"
        !            11: #include "xmalloc.h"
        !            12:
        !            13: /* SSH Constants */
        !            14: #define SSH_MAXBLOCKS (32 * 1024)
        !            15: #define SSH_BLOCKSIZE (8)
        !            16:
        !            17: /* Hashing constants */
        !            18: #define HASH_MINSIZE (8 * 1024)
        !            19: #define HASH_ENTRYSIZE (2)
        !            20: #define HASH_FACTOR(x) ((x)*3/2)
        !            21: #define HASH_UNUSEDCHAR (0xff)
        !            22: #define HASH_UNUSED (0xffff)
        !            23: #define HASH_IV     (0xfffe)
        !            24:
        !            25: #define HASH_MINBLOCKS  (7*SSH_BLOCKSIZE)
        !            26:
        !            27:
        !            28: /* Hash function (Input keys are cipher results) */
        !            29: #define HASH(x) GET_32BIT(x)
        !            30:
        !            31: #define CMP(a,b) (memcmp(a, b, SSH_BLOCKSIZE))
        !            32:
        !            33:
        !            34: void
        !            35: crc_update(u_int32_t * a, u_int32_t b)
        !            36: {
        !            37:   b ^= *a;
        !            38:   *a = crc32((unsigned char *) &b, sizeof(b));
        !            39: }
        !            40:
        !            41: /*
        !            42:    check_crc
        !            43:    detects if a block is used in a particular pattern
        !            44:  */
        !            45:
        !            46: int
        !            47: check_crc(unsigned char *S, unsigned char *buf, u_int32_t len, unsigned char *IV)
        !            48: {
        !            49:   u_int32_t          crc;
        !            50:   unsigned char  *c;
        !            51:
        !            52:   crc = 0;
        !            53:   if (IV && !CMP(S, IV))
        !            54:   {
        !            55:     crc_update(&crc, 1);
        !            56:     crc_update(&crc, 0);
        !            57:   }
        !            58:   for (c = buf; c < buf + len; c += SSH_BLOCKSIZE)
        !            59:   {
        !            60:     if (!CMP(S, c))
        !            61:     {
        !            62:       crc_update(&crc, 1);
        !            63:       crc_update(&crc, 0);
        !            64:     } else
        !            65:     {
        !            66:       crc_update(&crc, 0);
        !            67:       crc_update(&crc, 0);
        !            68:     }
        !            69:   }
        !            70:
        !            71:   return (crc == 0);
        !            72: }
        !            73:
        !            74:
        !            75: /*
        !            76:    detect_attack
        !            77:    Detects a crc32 compensation attack on a packet
        !            78:  */
        !            79: int
        !            80: detect_attack(unsigned char *buf, u_int32_t len, unsigned char *IV)
        !            81: {
        !            82:   static u_int16_t  *h = (u_int16_t *) NULL;
        !            83:   static u_int16_t   n = HASH_MINSIZE / HASH_ENTRYSIZE;
        !            84:   register u_int32_t i, j;
        !            85:   u_int32_t          l;
        !            86:   register unsigned char *c;
        !            87:   unsigned char  *d;
        !            88:
        !            89:
        !            90:   assert(len <= (SSH_MAXBLOCKS * SSH_BLOCKSIZE));
        !            91:   assert(len % SSH_BLOCKSIZE == 0);
        !            92:
        !            93:   for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2);
        !            94:
        !            95:   if (h == NULL)
        !            96:   {
        !            97:     debug("Installing crc compensation attack detector.");
        !            98:     n = l;
        !            99:     h = (u_int16_t *) xmalloc(n * HASH_ENTRYSIZE);
        !           100:   } else
        !           101:   {
        !           102:     if (l > n)
        !           103:     {
        !           104:       n = l;
        !           105:       h = (u_int16_t *) xrealloc(h, n * HASH_ENTRYSIZE);
        !           106:     }
        !           107:   }
        !           108:
        !           109:
        !           110:   if (len <= HASH_MINBLOCKS)
        !           111:   {
        !           112:     for (c = buf; c < buf + len; c += SSH_BLOCKSIZE)
        !           113:     {
        !           114:       if (IV && (!CMP(c, IV)))
        !           115:       {
        !           116:        if ((check_crc(c, buf, len, IV)))
        !           117:          return (DEATTACK_DETECTED);
        !           118:        else
        !           119:          break;
        !           120:       }
        !           121:       for (d = buf; d < c; d += SSH_BLOCKSIZE)
        !           122:       {
        !           123:        if (!CMP(c, d))
        !           124:        {
        !           125:          if ((check_crc(c, buf, len, IV)))
        !           126:            return (DEATTACK_DETECTED);
        !           127:          else
        !           128:            break;
        !           129:        }
        !           130:       }
        !           131:     }
        !           132:     return (DEATTACK_OK);
        !           133:   }
        !           134:   memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
        !           135:
        !           136:   if (IV)
        !           137:     h[HASH(IV) & (n - 1)] = HASH_IV;
        !           138:
        !           139:
        !           140:   for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++)
        !           141:   {
        !           142:     for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
        !           143:         i = (i + 1) & (n - 1))
        !           144:     {
        !           145:       if (h[i] == HASH_IV)
        !           146:       {
        !           147:        if (!CMP(c, IV))
        !           148:        {
        !           149:          if (check_crc(c, buf, len, IV))
        !           150:            return (DEATTACK_DETECTED);
        !           151:          else
        !           152:            break;
        !           153:        }
        !           154:       } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE))
        !           155:       {
        !           156:        if (check_crc(c, buf, len, IV))
        !           157:          return (DEATTACK_DETECTED);
        !           158:        else
        !           159:          break;
        !           160:       }
        !           161:     }
        !           162:     h[i] = j;
        !           163:   }
        !           164:
        !           165:   return (DEATTACK_OK);
        !           166: }