/* $OpenBSD: dh.c,v 1.57 2015/05/27 23:39:18 dtucker Exp $ */ /* * Copyright (c) 2000 Niels Provos. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "includes.h" #include /* MIN */ #include #include #include #include #include #include #include #include "dh.h" #include "pathnames.h" #include "log.h" #include "misc.h" #include "ssherr.h" #include "crypto-wrap.h" static int parse_prime(int linenum, char *line, struct dhgroup *dhg) { char *cp, *arg; char *strsize, *gen, *prime; const char *errstr = NULL; long long n; int r; dhg->p = dhg->g = NULL; cp = line; if ((arg = strdelim(&cp)) == NULL) return 0; /* Ignore leading whitespace */ if (*arg == '\0') arg = strdelim(&cp); if (!arg || !*arg || *arg == '#') return 0; /* time */ if (cp == NULL || *arg == '\0') goto truncated; arg = strsep(&cp, " "); /* type */ if (cp == NULL || *arg == '\0') goto truncated; /* Ensure this is a safe prime */ n = strtonum(arg, 0, 5, &errstr); if (errstr != NULL || n != MODULI_TYPE_SAFE) { error("moduli:%d: type is not %d", linenum, MODULI_TYPE_SAFE); goto fail; } arg = strsep(&cp, " "); /* tests */ if (cp == NULL || *arg == '\0') goto truncated; /* Ensure prime has been tested and is not composite */ n = strtonum(arg, 0, 0x1f, &errstr); if (errstr != NULL || (n & MODULI_TESTS_COMPOSITE) || !(n & ~MODULI_TESTS_COMPOSITE)) { error("moduli:%d: invalid moduli tests flag", linenum); goto fail; } arg = strsep(&cp, " "); /* tries */ if (cp == NULL || *arg == '\0') goto truncated; n = strtonum(arg, 0, 1<<30, &errstr); if (errstr != NULL || n == 0) { error("moduli:%d: invalid primality trial count", linenum); goto fail; } strsize = strsep(&cp, " "); /* size */ if (cp == NULL || *strsize == '\0' || (dhg->size = (int)strtonum(strsize, 0, 64*1024, &errstr)) == 0 || errstr) { error("moduli:%d: invalid prime length", linenum); goto fail; } /* The whole group is one bit larger */ dhg->size++; gen = strsep(&cp, " "); /* gen */ if (cp == NULL || *gen == '\0') goto truncated; prime = strsep(&cp, " "); /* prime */ if (cp != NULL || *prime == '\0') { truncated: error("moduli:%d: truncated", linenum); goto fail; } if ((r = sshbn_from_hex(gen, &dhg->g)) != 0 || (r = sshbn_from_hex(prime, &dhg->p)) != 0) { goto fail; } if (sshbn_bits(dhg->p) != dhg->size) { error("moduli:%d: prime has wrong size: actual %zu listed %zu", linenum, sshbn_bits(dhg->p), dhg->size - 1); goto fail; } if (sshbn_cmp(dhg->g, sshbn_value_1()) <= 0) { error("moduli:%d: generator is invalid", linenum); goto fail; } return 1; fail: sshbn_free(dhg->g); sshbn_free(dhg->p); dhg->g = dhg->p = NULL; return 0; } struct sshdh * choose_dh(u_int min, u_int wantbits, u_int max) { FILE *f; char line[4096]; u_int best, bestcount, which, linenum; int r; struct dhgroup dhg; struct sshdh *dh = NULL; if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL && (f = fopen(_PATH_DH_PRIMES, "r")) == NULL) { logit("WARNING: %s does not exist, using fixed modulus", _PATH_DH_MODULI); goto fallback; } linenum = 0; best = bestcount = 0; while (fgets(line, sizeof(line), f)) { linenum++; if (!parse_prime(linenum, line, &dhg)) continue; sshbn_free(dhg.g); sshbn_free(dhg.p); if (dhg.size > max || dhg.size < min) continue; if ((dhg.size > wantbits && dhg.size < best) || (dhg.size > best && best < wantbits)) { best = dhg.size; bestcount = 0; } if (dhg.size == best) bestcount++; } rewind(f); if (bestcount == 0) { fclose(f); logit("WARNING: no suitable primes in %s", _PATH_DH_PRIMES); goto fallback; } linenum = 0; which = arc4random_uniform(bestcount); while (fgets(line, sizeof(line), f)) { if (!parse_prime(linenum, line, &dhg)) continue; if ((dhg.size > max || dhg.size < min) || dhg.size != best || linenum++ != which) { sshbn_free(dhg.g); sshbn_free(dhg.p); continue; } break; } fclose(f); if (linenum != which+1) { logit("WARNING: line %d disappeared in %s, giving up", which, _PATH_DH_PRIMES); fallback: if ((r = dh_new_group_fallback(max, &dh)) != 0) fatal("%s: dh_new_group_fallback: %s", __func__, ssh_err(r)); return dh; } return (sshdh_new_group(dhg.g, dhg.p)); } /* diffie-hellman-groupN-sha1 */ int dh_pub_is_valid(struct sshdh *dh, struct sshbn *dh_pub) { size_t i; size_t n; int r, freeme = 0, bits_set = 0; struct sshbn *dh_p = NULL, *tmp = NULL; if (dh_pub == NULL) { if ((dh_pub = sshdh_pubkey(dh)) == NULL) return SSH_ERR_ALLOC_FAIL; freeme = 1; } n = sshbn_bits(dh_pub); if (sshbn_cmp(dh_pub, sshbn_value_1()) != 1) { /* pub_exp <= 1 */ logit("invalid public DH value: <= 1"); r = SSH_ERR_INVALID_FORMAT; goto out; } if ((dh_p = sshdh_p(dh)) == NULL) { error("%s: sshdh_p failed", __func__); r = SSH_ERR_ALLOC_FAIL; goto out; } if ((tmp = sshbn_new()) == NULL) { error("%s: sshbn_new failed", __func__); r = SSH_ERR_ALLOC_FAIL; goto out; } if ((r = sshbn_sub(tmp, dh_p, sshbn_value_1())) != 0) { error("%s: sshbn_sub: %s", __func__, ssh_err(r)); r = SSH_ERR_LIBCRYPTO_ERROR; goto out; } if ((r = sshbn_cmp(dh_pub, tmp)) != -1) { /* pub_exp > p-2 */ logit("invalid public DH value: >= p-1"); r = SSH_ERR_INVALID_FORMAT; goto out; } for (i = 0; i <= n; i++) if (sshbn_is_bit_set(dh_pub, i)) bits_set++; debug2("bits set: %d/%zu", bits_set, sshbn_bits(dh_p)); /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */ if (bits_set <= 1) { logit("invalid public DH value (%d/%zu)", bits_set, sshbn_bits(dh_p)); r = SSH_ERR_INVALID_FORMAT; goto out; } /* success */ r = 0; out: sshbn_free(dh_p); sshbn_free(tmp); if (freeme) sshbn_free(dh_pub); return r; } int dh_gen_key(struct sshdh *dh, u_int need) { size_t pbits; struct sshbn *dh_p; int r; if ((dh_p = sshdh_p(dh)) == NULL) { error("%s: sshdh_p failed", __func__); return 0; } if (need == 0 || (pbits = sshbn_bits(dh_p)) == 0 || need > INT_MAX / 2 || 2 * need > pbits) { sshbn_free(dh_p); return SSH_ERR_INVALID_ARGUMENT; } if ((r = sshdh_generate(dh, MIN(need * 2, pbits - 1))) != 0 || (r = dh_pub_is_valid(dh, NULL)) != 0) return r; return 0; } int dh_new_group1(struct sshdh **dhp) { static char *gen = "2", *group1 = "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381" "FFFFFFFF" "FFFFFFFF"; return sshdh_new_group_hex(gen, group1, dhp); } int dh_new_group14(struct sshdh **dhp) { static char *gen = "2", *group14 = "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D" "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F" "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D" "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B" "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9" "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510" "15728E5A" "8AACAA68" "FFFFFFFF" "FFFFFFFF"; return sshdh_new_group_hex(gen, group14, dhp); } /* * 4k bit fallback group used by DH-GEX if moduli file cannot be read. * Source: MODP group 16 from RFC3526. */ int dh_new_group_fallback(int max, struct sshdh **dhp) { static char *gen = "2", *group16 = "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1" "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD" "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245" "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED" "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D" "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F" "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D" "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B" "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9" "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510" "15728E5A" "8AAAC42D" "AD33170D" "04507A33" "A85521AB" "DF1CBA64" "ECFB8504" "58DBEF0A" "8AEA7157" "5D060C7D" "B3970F85" "A6E1E4C7" "ABF5AE8C" "DB0933D7" "1E8C94E0" "4A25619D" "CEE3D226" "1AD2EE6B" "F12FFA06" "D98A0864" "D8760273" "3EC86A64" "521F2B18" "177B200C" "BBE11757" "7A615D6C" "770988C0" "BAD946E2" "08E24FA0" "74E5AB31" "43DB5BFC" "E0FD108E" "4B82D120" "A9210801" "1A723C12" "A787E6D7" "88719A10" "BDBA5B26" "99C32718" "6AF4E23C" "1A946834" "B6150BDA" "2583E9CA" "2AD44CE8" "DBBBC2DB" "04DE8EF9" "2E8EFC14" "1FBECAA6" "287C5947" "4E6BC05D" "99B2964F" "A090C3A2" "233BA186" "515BE7ED" "1F612970" "CEE2D7AF" "B81BDD76" "2170481C" "D0069127" "D5B05AA9" "93B4EA98" "8D8FDDC1" "86FFB7DC" "90A6C08F" "4DF435C9" "34063199" "FFFFFFFF" "FFFFFFFF"; if (max < 4096) { debug3("requested max size %d, using 2k bit group 14", max); return dh_new_group14(dhp); } debug3("using 4k bit group 16"); return sshdh_new_group_hex(gen, group16, dhp); } /* * Estimates the group order for a Diffie-Hellman group that has an * attack complexity approximately the same as O(2**bits). * Values from NIST Special Publication 800-57: Recommendation for Key * Management Part 1 (rev 3) limited by the recommended maximum value * from RFC4419 section 3. */ u_int dh_estimate(int bits) { if (bits <= 112) return 2048; if (bits <= 128) return 3072; if (bits <= 192) return 7680; return 8192; }