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135 .IX Title "EC_GROUP_copy 3"
136 .TH EC_GROUP_copy 3 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 EC_GROUP_copy, EC_GROUP_dup, EC_GROUP_method_of, EC_GROUP_set_generator, EC_GROUP_get0_generator, EC_GROUP_get_order, EC_GROUP_get_cofactor, EC_GROUP_set_curve_name, EC_GROUP_get_curve_name, EC_GROUP_set_asn1_flag, EC_GROUP_get_asn1_flag, EC_GROUP_set_point_conversion_form, EC_GROUP_get_point_conversion_form, EC_GROUP_get0_seed, EC_GROUP_get_seed_len, EC_GROUP_set_seed, EC_GROUP_get_degree, EC_GROUP_check, EC_GROUP_check_discriminant, EC_GROUP_cmp, EC_GROUP_get_basis_type, EC_GROUP_get_trinomial_basis, EC_GROUP_get_pentanomial_basis \- Functions for manipulating EC_GROUP objects.
144 .IX Header "SYNOPSIS"
146 \& #include <openssl/ec.h>
147 \& #include <openssl/bn.h>
149 \& int EC_GROUP_copy(EC_GROUP *dst, const EC_GROUP *src);
150 \& EC_GROUP *EC_GROUP_dup(const EC_GROUP *src);
152 \& const EC_METHOD *EC_GROUP_method_of(const EC_GROUP *group);
154 \& int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, const BIGNUM *order, const BIGNUM *cofactor);
155 \& const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group);
157 \& int EC_GROUP_get_order(const EC_GROUP *group, BIGNUM *order, BN_CTX *ctx);
158 \& int EC_GROUP_get_cofactor(const EC_GROUP *group, BIGNUM *cofactor, BN_CTX *ctx);
160 \& void EC_GROUP_set_curve_name(EC_GROUP *group, int nid);
161 \& int EC_GROUP_get_curve_name(const EC_GROUP *group);
163 \& void EC_GROUP_set_asn1_flag(EC_GROUP *group, int flag);
164 \& int EC_GROUP_get_asn1_flag(const EC_GROUP *group);
166 \& void EC_GROUP_set_point_conversion_form(EC_GROUP *group, point_conversion_form_t form);
167 \& point_conversion_form_t EC_GROUP_get_point_conversion_form(const EC_GROUP *);
169 \& unsigned char *EC_GROUP_get0_seed(const EC_GROUP *x);
170 \& size_t EC_GROUP_get_seed_len(const EC_GROUP *);
171 \& size_t EC_GROUP_set_seed(EC_GROUP *, const unsigned char *, size_t len);
173 \& int EC_GROUP_get_degree(const EC_GROUP *group);
175 \& int EC_GROUP_check(const EC_GROUP *group, BN_CTX *ctx);
177 \& int EC_GROUP_check_discriminant(const EC_GROUP *group, BN_CTX *ctx);
179 \& int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b, BN_CTX *ctx);
181 \& int EC_GROUP_get_basis_type(const EC_GROUP *);
182 \& int EC_GROUP_get_trinomial_basis(const EC_GROUP *, unsigned int *k);
183 \& int EC_GROUP_get_pentanomial_basis(const EC_GROUP *, unsigned int *k1,
184 \& unsigned int *k2, unsigned int *k3);
187 .IX Header "DESCRIPTION"
188 EC_GROUP_copy copies the curve \fBsrc\fR into \fBdst\fR. Both \fBsrc\fR and \fBdst\fR must use the same \s-1EC_METHOD.\s0
190 EC_GROUP_dup creates a new \s-1EC_GROUP\s0 object and copies the content from \fBsrc\fR to the newly created
191 \&\s-1EC_GROUP\s0 object.
193 EC_GROUP_method_of obtains the \s-1EC_METHOD\s0 of \fBgroup\fR.
195 EC_GROUP_set_generator sets curve paramaters that must be agreed by all participants using the curve. These
196 paramaters include the \fBgenerator\fR, the \fBorder\fR and the \fBcofactor\fR. The \fBgenerator\fR is a well defined point on the
197 curve chosen for cryptographic operations. Integers used for point multiplications will be between 0 and
198 n\-1 where n is the \fBorder\fR. The \fBorder\fR multipied by the \fBcofactor\fR gives the number of points on the curve.
200 EC_GROUP_get0_generator returns the generator for the identified \fBgroup\fR.
202 The functions EC_GROUP_get_order and EC_GROUP_get_cofactor populate the provided \fBorder\fR and \fBcofactor\fR parameters
203 with the respective order and cofactors for the \fBgroup\fR.
205 The functions EC_GROUP_set_curve_name and EC_GROUP_get_curve_name, set and get the \s-1NID\s0 for the curve respectively
206 (see \fIEC_GROUP_new\fR\|(3)). If a curve does not have a \s-1NID\s0 associated with it, then EC_GROUP_get_curve_name
209 The asn1_flag value on a curve is used to determine whether there is a specific \s-1ASN1 OID\s0 to describe the curve or not.
210 If the asn1_flag is 1 then this is a named curve with an associated \s-1ASN1 OID.\s0 If not then asn1_flag is 0. The functions
211 EC_GROUP_get_asn1_flag and EC_GROUP_set_asn1_flag get and set the status of the asn1_flag for the curve. If set then
212 the curve_name must also be set.
214 The point_coversion_form for a curve controls how \s-1EC_POINT\s0 data is encoded as \s-1ASN1\s0 as defined in X9.62 (\s-1ECDSA\s0).
215 point_conversion_form_t is an enum defined as follows:
219 \& /** the point is encoded as z||x, where the octet z specifies
220 \& * which solution of the quadratic equation y is */
221 \& POINT_CONVERSION_COMPRESSED = 2,
222 \& /** the point is encoded as z||x||y, where z is the octet 0x02 */
223 \& POINT_CONVERSION_UNCOMPRESSED = 4,
224 \& /** the point is encoded as z||x||y, where the octet z specifies
225 \& * which solution of the quadratic equation y is */
226 \& POINT_CONVERSION_HYBRID = 6
227 \& } point_conversion_form_t;
230 For \s-1POINT_CONVERSION_UNCOMPRESSED\s0 the point is encoded as an octet signifying the \s-1UNCOMPRESSED\s0 form has been used followed by
231 the octets for x, followed by the octets for y.
233 For any given x co-ordinate for a point on a curve it is possible to derive two possible y values. For
234 \&\s-1POINT_CONVERSION_COMPRESSED\s0 the point is encoded as an octet signifying that the \s-1COMPRESSED\s0 form has been used \s-1AND\s0 which of
235 the two possible solutions for y has been used, followed by the octets for x.
237 For \s-1POINT_CONVERSION_HYBRID\s0 the point is encoded as an octet signifying the \s-1HYBRID\s0 form has been used \s-1AND\s0 which of the two
238 possible solutions for y has been used, followed by the octets for x, followed by the octets for y.
240 The functions EC_GROUP_set_point_conversion_form and EC_GROUP_get_point_conversion_form set and get the point_conversion_form
241 for the curve respectively.
243 \&\s-1ANSI X9.62 \s0(\s-1ECDSA\s0 standard) defines a method of generating the curve parameter b from a random number. This provides advantages
244 in that a parameter obtained in this way is highly unlikely to be susceptible to special purpose attacks, or have any trapdoors in it.
245 If the seed is present for a curve then the b parameter was generated in a verifiable fashion using that seed. The OpenSSL \s-1EC\s0 library
246 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
247 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
248 builtin curves within the library provide seed values that can be obtained. It is also possible to set a custom seed using
249 EC_GROUP_set_seed and passing a pointer to a memory block, along with the length of the seed. Again, the \s-1EC\s0 library will not use
250 this seed value, although it will be preserved in any \s-1ASN1\s0 based communications.
252 EC_GROUP_get_degree gets the degree of the field. For Fp fields this will be the number of bits in p. For F2^m fields this will be
255 The function EC_GROUP_check_discriminant calculates the discriminant for the curve and verifies that it is valid.
256 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
257 simply b. In either case for the curve to be valid the discriminant must be non zero.
259 The function EC_GROUP_check performs a number of checks on a curve to verify that it is valid. Checks performed include
260 verifying that the discriminant is non zero; that a generator has been defined; that the generator is on the curve and has
263 EC_GROUP_cmp compares \fBa\fR and \fBb\fR to determine whether they represent the same curve or not.
265 The functions EC_GROUP_get_basis_type, EC_GROUP_get_trinomial_basis and EC_GROUP_get_pentanomial_basis should only be called for curves
266 defined over an F2^m field. Addition and multiplication operations within an F2^m field are performed using an irreducible polynomial
267 function f(x). This function is either a trinomial of the form:
269 f(x) = x^m + x^k + 1 with m > k >= 1
271 or a pentanomial of the form:
273 f(x) = x^m + x^k3 + x^k2 + x^k1 + 1 with m > k3 > k2 > k1 >= 1
275 The function EC_GROUP_get_basis_type returns a \s-1NID\s0 identifying whether a trinomial or pentanomial is in use for the field. The
276 function EC_GROUP_get_trinomial_basis must only be called where f(x) is of the trinomial form, and returns the value of \fBk\fR. Similary
277 the function EC_GROUP_get_pentanomial_basis must only be called where f(x) is of the pentanomial form, and returns the values of \fBk1\fR,
278 \&\fBk2\fR and \fBk3\fR respectively.
280 .IX Header "RETURN VALUES"
281 The following functions return 1 on success or 0 on error: EC_GROUP_copy, EC_GROUP_set_generator, EC_GROUP_check,
282 EC_GROUP_check_discriminant, EC_GROUP_get_trinomial_basis and EC_GROUP_get_pentanomial_basis.
284 EC_GROUP_dup returns a pointer to the duplicated curve, or \s-1NULL\s0 on error.
286 EC_GROUP_method_of returns the \s-1EC_METHOD\s0 implementation in use for the given curve or \s-1NULL\s0 on error.
288 EC_GROUP_get0_generator returns the generator for the given curve or \s-1NULL\s0 on error.
290 EC_GROUP_get_order, EC_GROUP_get_cofactor, EC_GROUP_get_curve_name, EC_GROUP_get_asn1_flag, EC_GROUP_get_point_conversion_form
291 and EC_GROUP_get_degree return the order, cofactor, curve name (\s-1NID\s0), \s-1ASN1\s0 flag, point_conversion_form and degree for the
292 specified curve respectively. If there is no curve name associated with a curve then EC_GROUP_get_curve_name will return 0.
294 EC_GROUP_get0_seed returns a pointer to the seed that was used to generate the parameter b, or \s-1NULL\s0 if the seed is not
295 specified. EC_GROUP_get_seed_len returns the length of the seed or 0 if the seed is not specified.
297 EC_GROUP_set_seed returns the length of the seed that has been set. If the supplied seed is \s-1NULL,\s0 or the supplied seed length is
298 0, the return value will be 1. On error 0 is returned.
300 EC_GROUP_cmp returns 0 if the curves are equal, 1 if they are not equal, or \-1 on error.
302 EC_GROUP_get_basis_type returns the values NID_X9_62_tpBasis or NID_X9_62_ppBasis (as defined in <openssl/obj_mac.h>) for a
303 trinomial or pentanomial respectively. Alternatively in the event of an error a 0 is returned.
305 .IX Header "SEE ALSO"
306 \&\fIcrypto\fR\|(3), \fIec\fR\|(3), \fIEC_GROUP_new\fR\|(3),
307 \&\fIEC_POINT_new\fR\|(3), \fIEC_POINT_add\fR\|(3), \fIEC_KEY_new\fR\|(3),
308 \&\fIEC_GFp_simple_method\fR\|(3), \fId2i_ECPKParameters\fR\|(3)