diff options
| -rw-r--r-- | CHANGES | 7 | ||||
| -rw-r--r-- | crypto/ec/ec.h | 6 | ||||
| -rw-r--r-- | crypto/ec/ec_err.c | 3 | ||||
| -rw-r--r-- | crypto/ec/ec_lib.c | 102 |
4 files changed, 108 insertions, 10 deletions
@@ -9,6 +9,13 @@ Changes between 1.0.2s and 1.0.2t [xx XXX xxxx] + *) Compute ECC cofactors if not provided during EC_GROUP construction. Before + this change, EC_GROUP_set_generator would accept order and/or cofactor as + NULL. After this change, only the cofactor parameter can be NULL. It also + does some minimal sanity checks on the passed order. + (CVE-2019-1547) + [Billy Bob Brumley] + *) Document issue with installation paths in diverse Windows builds '/usr/local/ssl' is an unsafe prefix for location to install OpenSSL diff --git a/crypto/ec/ec.h b/crypto/ec/ec.h index 81e6faf6c5..b62613da55 100644 --- a/crypto/ec/ec.h +++ b/crypto/ec/ec.h @@ -1073,6 +1073,7 @@ int EC_KEY_print_fp(FILE *fp, const EC_KEY *key, int off); * The following lines are auto generated by the script mkerr.pl. Any changes * made after this point may be overwritten when the script is next run. */ + void ERR_load_EC_strings(void); /* Error codes for the EC functions. */ @@ -1270,13 +1271,14 @@ void ERR_load_EC_strings(void); # define EC_R_SLOT_FULL 108 # define EC_R_UNDEFINED_GENERATOR 113 # define EC_R_UNDEFINED_ORDER 128 +# define EC_R_UNKNOWN_COFACTOR 152 # define EC_R_UNKNOWN_GROUP 129 # define EC_R_UNKNOWN_ORDER 114 # define EC_R_UNSUPPORTED_FIELD 131 # define EC_R_WRONG_CURVE_PARAMETERS 145 # define EC_R_WRONG_ORDER 130 -#ifdef __cplusplus +# ifdef __cplusplus } -#endif +# endif #endif diff --git a/crypto/ec/ec_err.c b/crypto/ec/ec_err.c index 6fe5baafd4..220541161e 100644 --- a/crypto/ec/ec_err.c +++ b/crypto/ec/ec_err.c @@ -1,6 +1,6 @@ /* crypto/ec/ec_err.c */ /* ==================================================================== - * Copyright (c) 1999-2015 The OpenSSL Project. All rights reserved. + * Copyright (c) 1999-2019 The OpenSSL Project. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions @@ -310,6 +310,7 @@ static ERR_STRING_DATA EC_str_reasons[] = { {ERR_REASON(EC_R_SLOT_FULL), "slot full"}, {ERR_REASON(EC_R_UNDEFINED_GENERATOR), "undefined generator"}, {ERR_REASON(EC_R_UNDEFINED_ORDER), "undefined order"}, + {ERR_REASON(EC_R_UNKNOWN_COFACTOR), "unknown cofactor"}, {ERR_REASON(EC_R_UNKNOWN_GROUP), "unknown group"}, {ERR_REASON(EC_R_UNKNOWN_ORDER), "unknown order"}, {ERR_REASON(EC_R_UNSUPPORTED_FIELD), "unsupported field"}, diff --git a/crypto/ec/ec_lib.c b/crypto/ec/ec_lib.c index cd2c420176..15302322f7 100644 --- a/crypto/ec/ec_lib.c +++ b/crypto/ec/ec_lib.c @@ -294,6 +294,67 @@ int EC_METHOD_get_field_type(const EC_METHOD *meth) return meth->field_type; } +/*- + * Try computing cofactor from the generator order (n) and field cardinality (q). + * This works for all curves of cryptographic interest. + * + * Hasse thm: q + 1 - 2*sqrt(q) <= n*h <= q + 1 + 2*sqrt(q) + * h_min = (q + 1 - 2*sqrt(q))/n + * h_max = (q + 1 + 2*sqrt(q))/n + * h_max - h_min = 4*sqrt(q)/n + * So if n > 4*sqrt(q) holds, there is only one possible value for h: + * h = \lfloor (h_min + h_max)/2 \rceil = \lfloor (q + 1)/n \rceil + * + * Otherwise, zero cofactor and return success. + */ +static int ec_guess_cofactor(EC_GROUP *group) { + int ret = 0; + BN_CTX *ctx = NULL; + BIGNUM *q = NULL; + + /*- + * If the cofactor is too large, we cannot guess it. + * The RHS of below is a strict overestimate of lg(4 * sqrt(q)) + */ + if (BN_num_bits(&group->order) <= (BN_num_bits(&group->field) + 1) / 2 + 3) { + /* default to 0 */ + BN_zero(&group->cofactor); + /* return success */ + return 1; + } + + if ((ctx = BN_CTX_new()) == NULL) + return 0; + + BN_CTX_start(ctx); + if ((q = BN_CTX_get(ctx)) == NULL) + goto err; + + /* set q = 2**m for binary fields; q = p otherwise */ + if (group->meth->field_type == NID_X9_62_characteristic_two_field) { + BN_zero(q); + if (!BN_set_bit(q, BN_num_bits(&group->field) - 1)) + goto err; + } else { + if (!BN_copy(q, &group->field)) + goto err; + } + + /* compute h = \lfloor (q + 1)/n \rceil = \lfloor (q + 1 + n/2)/n \rfloor */ + if (!BN_rshift1(&group->cofactor, &group->order) /* n/2 */ + || !BN_add(&group->cofactor, &group->cofactor, q) /* q + n/2 */ + /* q + 1 + n/2 */ + || !BN_add(&group->cofactor, &group->cofactor, BN_value_one()) + /* (q + 1 + n/2)/n */ + || !BN_div(&group->cofactor, NULL, &group->cofactor, &group->order, ctx)) + goto err; + ret = 1; + err: + BN_CTX_end(ctx); + BN_CTX_free(ctx); + return ret; +} + int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, const BIGNUM *order, const BIGNUM *cofactor) { @@ -302,6 +363,33 @@ int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, return 0; } + /* require group->field >= 1 */ + if (BN_is_zero(&group->field) || BN_is_negative(&group->field)) { + ECerr(EC_F_EC_GROUP_SET_GENERATOR, EC_R_INVALID_FIELD); + return 0; + } + + /*- + * - require order >= 1 + * - enforce upper bound due to Hasse thm: order can be no more than one bit + * longer than field cardinality + */ + if (order == NULL || BN_is_zero(order) || BN_is_negative(order) + || BN_num_bits(order) > BN_num_bits(&group->field) + 1) { + ECerr(EC_F_EC_GROUP_SET_GENERATOR, EC_R_INVALID_GROUP_ORDER); + return 0; + } + + /*- + * Unfortunately the cofactor is an optional field in many standards. + * Internally, the lib uses 0 cofactor as a marker for "unknown cofactor". + * So accept cofactor == NULL or cofactor >= 0. + */ + if (cofactor != NULL && BN_is_negative(cofactor)) { + ECerr(EC_F_EC_GROUP_SET_GENERATOR, EC_R_UNKNOWN_COFACTOR); + return 0; + } + if (group->generator == NULL) { group->generator = EC_POINT_new(group); if (group->generator == NULL) @@ -310,17 +398,17 @@ int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, if (!EC_POINT_copy(group->generator, generator)) return 0; - if (order != NULL) { - if (!BN_copy(&group->order, order)) - return 0; - } else - BN_zero(&group->order); + if (!BN_copy(&group->order, order)) + return 0; - if (cofactor != NULL) { + /* Either take the provided positive cofactor, or try to compute it */ + if (cofactor != NULL && !BN_is_zero(cofactor)) { if (!BN_copy(&group->cofactor, cofactor)) return 0; - } else + } else if (!ec_guess_cofactor(group)) { BN_zero(&group->cofactor); + return 0; + } /*- * Access to the `mont_data` field of an EC_GROUP struct should always be |