NAME
EC_GROUP_check_discriminant,
EC_GROUP_check —
partially check validity of
EC_GROUP objects
SYNOPSIS
#include
<openssl/bn.h>
#include <openssl/ec.h>
Deprecated:
int
EC_GROUP_check_discriminant(const
EC_GROUP *group, BN_CTX *ctx);
int
EC_GROUP_check(const EC_GROUP
*group, BN_CTX *ctx);
DESCRIPTION
These functions are deprecated. Only standardized curves built into the library should be used, see EC_GROUP_new_by_curve_name(3). For builtin curves far more thorough checks than the minimal checks performed by these functions have been performed.
These functions have an optional ctx argument which is used to avoid the cost of repeated allocation of auxiliary BIGNUM objects.
EC_GROUP_check_discriminant()
can be called after
EC_GROUP_new_curve_GFp(3) to verify that
group's parameters have non-zero discriminant 4a^3 +
27b^2 modulo p. Assuming that p is a prime number
larger than three this implies that the Weierstrass equation defines an
elliptic curve.
EC_GROUP_check()
partially verifies that group represents an an
elliptic curve and that generator is a point on the
curve whose order divides order. It checks with
EC_GROUP_check_discriminant() that the discriminant
is non-zero and then verifies that that order is
non-zero and that the product generator
* order is the point at
infinity. This implies that order is an integer
multiple of the generator's
order. The verification that p
is a prime and that order is the
generator's order are skipped because they are too
expensive.
RETURN VALUES
EC_GROUP_check_discriminant() returns 1 on
success and 0 on failure. Failure modes include that the discriminant is
zero modulo p and memory allocation failure.
EC_GROUP_check() returns 1 on success and
0 on failure.
ERRORS
Diagnostics for EC_GROUP_check() that can
be retrieved with
ERR_get_error(3),
ERR_GET_REASON(3), and
ERR_reason_error_string(3) include:
EC_R_DISCRIMINANT_IS_ZERO"discriminant is zero"EC_GROUP_check_discriminant() failed because the discriminant is zero or for some other reason.EC_R_UNDEFINED_GENERATOR"undefined generator"- no generator is set on group, for example because a call to EC_GROUP_set_generator(3) is missing.
EC_R_POINT_IS_NOT_ON_CURVE"point is not on curve"- a generator is set, but it is not a point on the curve represented by group.
EC_R_UNDEFINED_ORDER"undefined order"- the order set on group is zero.
EC_R_INVALID_GROUP_ORDER"invalid group order"- generator * order is not the point at infinity.
SEE ALSO
BN_CTX_new(3), BN_is_zero(3), crypto(3), d2i_ECPKParameters(3), EC_GROUP_get_curve_name(3), EC_GROUP_new_by_curve_name(3), EC_GROUP_new_curve_GFp(3), EC_KEY_METHOD_new(3), EC_KEY_new(3), EC_POINT_add(3), EC_POINT_get_affine_coordinates(3), EC_POINT_new(3), EC_POINT_point2oct(3), ECDH_compute_key(3), ECDSA_SIG_new(3)
HISTORY
EC_GROUP_check() and
EC_GROUP_check_discriminant() first appeared in
OpenSSL 0.9.8 and have been available since OpenBSD
4.5.