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263 lines
14 KiB
Plaintext
263 lines
14 KiB
Plaintext
=pod
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=head1 NAME
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EC_GROUP_get0_order, EC_GROUP_order_bits, EC_GROUP_get0_cofactor,
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EC_GROUP_copy, EC_GROUP_dup, EC_GROUP_method_of, EC_GROUP_set_generator,
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EC_GROUP_get0_generator, EC_GROUP_get_order, EC_GROUP_get_cofactor,
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EC_GROUP_set_curve_name, EC_GROUP_get_curve_name, EC_GROUP_set_asn1_flag,
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EC_GROUP_get_asn1_flag, EC_GROUP_set_point_conversion_form,
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EC_GROUP_get_point_conversion_form, EC_GROUP_get0_seed,
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EC_GROUP_get_seed_len, EC_GROUP_set_seed, EC_GROUP_get_degree,
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EC_GROUP_check, EC_GROUP_check_named_curve,
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EC_GROUP_check_discriminant, EC_GROUP_cmp,
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EC_GROUP_get_basis_type, EC_GROUP_get_trinomial_basis,
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EC_GROUP_get_pentanomial_basis, EC_GROUP_get0_field,
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EC_GROUP_get_field_type
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- Functions for manipulating EC_GROUP objects
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=head1 SYNOPSIS
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#include <openssl/ec.h>
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int EC_GROUP_copy(EC_GROUP *dst, const EC_GROUP *src);
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EC_GROUP *EC_GROUP_dup(const EC_GROUP *src);
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int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator,
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const BIGNUM *order, const BIGNUM *cofactor);
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const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group);
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int EC_GROUP_get_order(const EC_GROUP *group, BIGNUM *order, BN_CTX *ctx);
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const BIGNUM *EC_GROUP_get0_order(const EC_GROUP *group);
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int EC_GROUP_order_bits(const EC_GROUP *group);
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int EC_GROUP_get_cofactor(const EC_GROUP *group, BIGNUM *cofactor, BN_CTX *ctx);
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const BIGNUM *EC_GROUP_get0_cofactor(const EC_GROUP *group);
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const BIGNUM *EC_GROUP_get0_field(const EC_GROUP *group);
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void EC_GROUP_set_curve_name(EC_GROUP *group, int nid);
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int EC_GROUP_get_curve_name(const EC_GROUP *group);
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void EC_GROUP_set_asn1_flag(EC_GROUP *group, int flag);
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int EC_GROUP_get_asn1_flag(const EC_GROUP *group);
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void EC_GROUP_set_point_conversion_form(EC_GROUP *group, point_conversion_form_t form);
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point_conversion_form_t EC_GROUP_get_point_conversion_form(const EC_GROUP *group);
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unsigned char *EC_GROUP_get0_seed(const EC_GROUP *group);
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size_t EC_GROUP_get_seed_len(const EC_GROUP *group);
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size_t EC_GROUP_set_seed(EC_GROUP *group, const unsigned char *, size_t len);
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int EC_GROUP_get_degree(const EC_GROUP *group);
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int EC_GROUP_check(const EC_GROUP *group, BN_CTX *ctx);
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int EC_GROUP_check_named_curve(const EC_GROUP *group, int nist_only,
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BN_CTX *ctx);
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int EC_GROUP_check_discriminant(const EC_GROUP *group, BN_CTX *ctx);
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int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b, BN_CTX *ctx);
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int EC_GROUP_get_basis_type(const EC_GROUP *group);
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int EC_GROUP_get_trinomial_basis(const EC_GROUP *group, unsigned int *k);
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int EC_GROUP_get_pentanomial_basis(const EC_GROUP *group, unsigned int *k1,
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unsigned int *k2, unsigned int *k3);
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int EC_GROUP_get_field_type(const EC_GROUP *group);
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The following function has been deprecated since OpenSSL 3.0, and can be
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hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
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see L<openssl_user_macros(7)>:
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const EC_METHOD *EC_GROUP_method_of(const EC_GROUP *group);
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=head1 DESCRIPTION
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EC_GROUP_copy() copies the curve B<src> into B<dst>. Both B<src> and B<dst> must use the same EC_METHOD.
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EC_GROUP_dup() creates a new EC_GROUP object and copies the content from B<src> to the newly created
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EC_GROUP object.
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EC_GROUP_method_of() obtains the EC_METHOD of B<group>.
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This function was deprecated in OpenSSL 3.0, since EC_METHOD is no longer a public concept.
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EC_GROUP_set_generator() sets curve parameters that must be agreed by all participants using the curve. These
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parameters include the B<generator>, the B<order> and the B<cofactor>. The B<generator> is a well defined point on the
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curve chosen for cryptographic operations. Integers used for point multiplications will be between 0 and
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n-1 where n is the B<order>. The B<order> multiplied by the B<cofactor> gives the number of points on the curve.
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EC_GROUP_get0_generator() returns the generator for the identified B<group>.
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EC_GROUP_get_order() retrieves the order of B<group> and copies its value into
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B<order>. It fails in case B<group> is not fully initialized (i.e., its order
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is not set or set to zero).
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EC_GROUP_get_cofactor() retrieves the cofactor of B<group> and copies its value
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into B<cofactor>. It fails in case B<group> is not fully initialized or if the
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cofactor is not set (or set to zero).
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The functions EC_GROUP_set_curve_name() and EC_GROUP_get_curve_name(), set and get the NID for the curve respectively
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(see L<EC_GROUP_new(3)>). If a curve does not have a NID associated with it, then EC_GROUP_get_curve_name
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will return NID_undef.
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The asn1_flag value is used to determine whether the curve encoding uses
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explicit parameters or a named curve using an ASN1 OID: many applications only
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support the latter form. If asn1_flag is B<OPENSSL_EC_NAMED_CURVE> then the
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named curve form is used and the parameters must have a corresponding
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named curve NID set. If asn1_flags is B<OPENSSL_EC_EXPLICIT_CURVE> the
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parameters are explicitly encoded. The functions EC_GROUP_get_asn1_flag() and
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EC_GROUP_set_asn1_flag() get and set the status of the asn1_flag for the curve.
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Note: B<OPENSSL_EC_EXPLICIT_CURVE> was added in OpenSSL 1.1.0, for
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previous versions of OpenSSL the value 0 must be used instead. Before OpenSSL
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1.1.0 the default form was to use explicit parameters (meaning that
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applications would have to explicitly set the named curve form) in OpenSSL
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1.1.0 and later the named curve form is the default.
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The point_conversion_form for a curve controls how EC_POINT data is encoded as ASN1 as defined in X9.62 (ECDSA).
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point_conversion_form_t is an enum defined as follows:
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typedef enum {
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/** the point is encoded as z||x, where the octet z specifies
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* which solution of the quadratic equation y is */
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POINT_CONVERSION_COMPRESSED = 2,
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/** the point is encoded as z||x||y, where z is the octet 0x04 */
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POINT_CONVERSION_UNCOMPRESSED = 4,
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/** the point is encoded as z||x||y, where the octet z specifies
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* which solution of the quadratic equation y is */
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POINT_CONVERSION_HYBRID = 6
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} point_conversion_form_t;
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For POINT_CONVERSION_UNCOMPRESSED the point is encoded as an octet signifying the UNCOMPRESSED form has been used followed by
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the octets for x, followed by the octets for y.
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For any given x coordinate for a point on a curve it is possible to derive two possible y values. For
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POINT_CONVERSION_COMPRESSED the point is encoded as an octet signifying that the COMPRESSED form has been used AND which of
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the two possible solutions for y has been used, followed by the octets for x.
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For POINT_CONVERSION_HYBRID the point is encoded as an octet signifying the HYBRID form has been used AND which of the two
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possible solutions for y has been used, followed by the octets for x, followed by the octets for y.
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The functions EC_GROUP_set_point_conversion_form() and EC_GROUP_get_point_conversion_form(), set and get the point_conversion_form
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for the curve respectively.
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ANSI X9.62 (ECDSA standard) defines a method of generating the curve parameter b from a random number. This provides advantages
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in that a parameter obtained in this way is highly unlikely to be susceptible to special purpose attacks, or have any trapdoors in it.
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If the seed is present for a curve then the b parameter was generated in a verifiable fashion using that seed. The OpenSSL EC library
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does not use this seed value but does enable you to inspect it using EC_GROUP_get0_seed(). This returns a pointer to a memory block
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containing the seed that was used. The length of the memory block can be obtained using EC_GROUP_get_seed_len(). A number of the
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built-in curves within the library provide seed values that can be obtained. It is also possible to set a custom seed using
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EC_GROUP_set_seed() and passing a pointer to a memory block, along with the length of the seed. Again, the EC library will not use
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this seed value, although it will be preserved in any ASN1 based communications.
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EC_GROUP_get_degree() gets the degree of the field.
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For Fp fields this will be the number of bits in p.
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For F2^m fields this will be the value m.
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EC_GROUP_get_field_type() identifies what type of field the EC_GROUP structure supports,
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which will be either F2^m or Fp.
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The function EC_GROUP_check_discriminant() calculates the discriminant for the curve and verifies that it is valid.
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For a curve defined over Fp the discriminant is given by the formula 4*a^3 + 27*b^2 whilst for F2^m curves the discriminant is
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simply b. In either case for the curve to be valid the discriminant must be non zero.
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The function EC_GROUP_check() behaves in the following way:
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For the OpenSSL default provider it performs a number of checks on a curve to verify that it is valid. Checks performed include
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verifying that the discriminant is non zero; that a generator has been defined; that the generator is on the curve and has
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the correct order. For the OpenSSL FIPS provider it uses EC_GROUP_check_named_curve() to conform to SP800-56Ar3.
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The function EC_GROUP_check_named_curve() determines if the group's domain parameters match one of the built-in curves supported by the library.
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The curve name is returned as a B<NID> if it matches. If the group's domain parameters have been modified then no match will be found.
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If the curve name of the given group is B<NID_undef> (e.g. it has been created by using explicit parameters with no curve name),
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then this method can be used to lookup the name of the curve that matches the group domain parameters. The built-in curves contain
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aliases, so that multiple NID's can map to the same domain parameters. For such curves it is unspecified which of the aliases will be
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returned if the curve name of the given group is NID_undef.
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If B<nist_only> is 1 it will only look for NIST approved curves, otherwise it searches all built-in curves.
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This function may be passed a BN_CTX object in the B<ctx> parameter.
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The B<ctx> parameter may be NULL.
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EC_GROUP_cmp() compares B<a> and B<b> to determine whether they represent the same curve or not.
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The functions EC_GROUP_get_basis_type(), EC_GROUP_get_trinomial_basis() and EC_GROUP_get_pentanomial_basis() should only be called for curves
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defined over an F2^m field. Addition and multiplication operations within an F2^m field are performed using an irreducible polynomial
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function f(x). This function is either a trinomial of the form:
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f(x) = x^m + x^k + 1 with m > k >= 1
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or a pentanomial of the form:
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f(x) = x^m + x^k3 + x^k2 + x^k1 + 1 with m > k3 > k2 > k1 >= 1
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The function EC_GROUP_get_basis_type() returns a NID identifying whether a trinomial or pentanomial is in use for the field. The
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function EC_GROUP_get_trinomial_basis() must only be called where f(x) is of the trinomial form, and returns the value of B<k>. Similarly
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the function EC_GROUP_get_pentanomial_basis() must only be called where f(x) is of the pentanomial form, and returns the values of B<k1>,
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B<k2> and B<k3> respectively.
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=head1 RETURN VALUES
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The following functions return 1 on success or 0 on error: EC_GROUP_copy(), EC_GROUP_set_generator(), EC_GROUP_check(),
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EC_GROUP_check_discriminant(), EC_GROUP_get_trinomial_basis() and EC_GROUP_get_pentanomial_basis().
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EC_GROUP_dup() returns a pointer to the duplicated curve, or NULL on error.
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EC_GROUP_method_of() returns the EC_METHOD implementation in use for the given curve or NULL on error.
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EC_GROUP_get0_generator() returns the generator for the given curve or NULL on error.
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EC_GROUP_get_order() returns 0 if the order is not set (or set to zero) for
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B<group> or if copying into B<order> fails, 1 otherwise.
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EC_GROUP_get_cofactor() returns 0 if the cofactor is not set (or is set to zero) for B<group> or if copying into B<cofactor> fails, 1 otherwise.
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EC_GROUP_get_curve_name() returns the curve name (NID) for B<group> or will return NID_undef if no curve name is associated.
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EC_GROUP_get_asn1_flag() returns the ASN1 flag for the specified B<group> .
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EC_GROUP_get_point_conversion_form() returns the point_conversion_form for B<group>.
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EC_GROUP_get_degree() returns the degree for B<group> or 0 if the operation is not supported by the underlying group implementation.
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EC_GROUP_get_field_type() returns either B<NID_X9_62_prime_field> for prime curves
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or B<NID_X9_62_characteristic_two_field> for binary curves;
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these values are defined in the F<< <openssl/obj_mac.h> >> header file.
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EC_GROUP_check_named_curve() returns the nid of the matching named curve, otherwise it returns 0 for no match, or -1 on error.
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EC_GROUP_get0_order() returns an internal pointer to the group order.
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EC_GROUP_order_bits() returns the number of bits in the group order.
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EC_GROUP_get0_cofactor() returns an internal pointer to the group cofactor.
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EC_GROUP_get0_field() returns an internal pointer to the group field. For curves over GF(p), this is the modulus; for curves
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over GF(2^m), this is the irreducible polynomial defining the field.
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EC_GROUP_get0_seed() returns a pointer to the seed that was used to generate the parameter b, or NULL if the seed is not
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specified. EC_GROUP_get_seed_len() returns the length of the seed or 0 if the seed is not specified.
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EC_GROUP_set_seed() returns the length of the seed that has been set. If the supplied seed is NULL, or the supplied seed length is
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0, the return value will be 1. On error 0 is returned.
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EC_GROUP_cmp() returns 0 if the curves are equal, 1 if they are not equal, or -1 on error.
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EC_GROUP_get_basis_type() returns the values NID_X9_62_tpBasis or NID_X9_62_ppBasis (as defined in F<< <openssl/obj_mac.h> >>) for a
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trinomial or pentanomial respectively. Alternatively in the event of an error a 0 is returned.
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=head1 SEE ALSO
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L<crypto(7)>, L<EC_GROUP_new(3)>,
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L<EC_POINT_new(3)>, L<EC_POINT_add(3)>, L<EC_KEY_new(3)>,
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L<EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)>
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=head1 HISTORY
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EC_GROUP_method_of() was deprecated in OpenSSL 3.0.
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EC_GROUP_get0_field(), EC_GROUP_check_named_curve() and EC_GROUP_get_field_type() were added in OpenSSL 3.0.
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EC_GROUP_get0_order(), EC_GROUP_order_bits() and EC_GROUP_get0_cofactor() were added in OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2013-2023 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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