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Diffstat (limited to 'src/lib/libcrypto/doc/EC_GROUP_copy.pod')
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1 | =pod | ||
2 | |||
3 | =head1 NAME | ||
4 | |||
5 | 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 B<EC_GROUP> objects. | ||
6 | |||
7 | =head1 SYNOPSIS | ||
8 | |||
9 | #include <openssl/ec.h> | ||
10 | #include <openssl/bn.h> | ||
11 | |||
12 | int EC_GROUP_copy(EC_GROUP *dst, const EC_GROUP *src); | ||
13 | EC_GROUP *EC_GROUP_dup(const EC_GROUP *src); | ||
14 | |||
15 | const EC_METHOD *EC_GROUP_method_of(const EC_GROUP *group); | ||
16 | |||
17 | int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, const BIGNUM *order, const BIGNUM *cofactor); | ||
18 | const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group); | ||
19 | |||
20 | int EC_GROUP_get_order(const EC_GROUP *group, BIGNUM *order, BN_CTX *ctx); | ||
21 | int EC_GROUP_get_cofactor(const EC_GROUP *group, BIGNUM *cofactor, BN_CTX *ctx); | ||
22 | |||
23 | void EC_GROUP_set_curve_name(EC_GROUP *group, int nid); | ||
24 | int EC_GROUP_get_curve_name(const EC_GROUP *group); | ||
25 | |||
26 | void EC_GROUP_set_asn1_flag(EC_GROUP *group, int flag); | ||
27 | int EC_GROUP_get_asn1_flag(const EC_GROUP *group); | ||
28 | |||
29 | void EC_GROUP_set_point_conversion_form(EC_GROUP *group, point_conversion_form_t form); | ||
30 | point_conversion_form_t EC_GROUP_get_point_conversion_form(const EC_GROUP *); | ||
31 | |||
32 | unsigned char *EC_GROUP_get0_seed(const EC_GROUP *x); | ||
33 | size_t EC_GROUP_get_seed_len(const EC_GROUP *); | ||
34 | size_t EC_GROUP_set_seed(EC_GROUP *, const unsigned char *, size_t len); | ||
35 | |||
36 | int EC_GROUP_get_degree(const EC_GROUP *group); | ||
37 | |||
38 | int EC_GROUP_check(const EC_GROUP *group, BN_CTX *ctx); | ||
39 | |||
40 | int EC_GROUP_check_discriminant(const EC_GROUP *group, BN_CTX *ctx); | ||
41 | |||
42 | int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b, BN_CTX *ctx); | ||
43 | |||
44 | int EC_GROUP_get_basis_type(const EC_GROUP *); | ||
45 | int EC_GROUP_get_trinomial_basis(const EC_GROUP *, unsigned int *k); | ||
46 | int EC_GROUP_get_pentanomial_basis(const EC_GROUP *, unsigned int *k1, | ||
47 | unsigned int *k2, unsigned int *k3); | ||
48 | |||
49 | =head1 DESCRIPTION | ||
50 | |||
51 | EC_GROUP_copy copies the curve B<src> into B<dst>. Both B<src> and B<dst> must use the same EC_METHOD. | ||
52 | |||
53 | EC_GROUP_dup creates a new EC_GROUP object and copies the content from B<src> to the newly created | ||
54 | EC_GROUP object. | ||
55 | |||
56 | EC_GROUP_method_of obtains the EC_METHOD of B<group>. | ||
57 | |||
58 | EC_GROUP_set_generator sets curve paramaters that must be agreed by all participants using the curve. These | ||
59 | paramaters include the B<generator>, the B<order> and the B<cofactor>. The B<generator> is a well defined point on the | ||
60 | curve chosen for cryptographic operations. Integers used for point multiplications will be between 0 and | ||
61 | n-1 where n is the B<order>. The B<order> multipied by the B<cofactor> gives the number of points on the curve. | ||
62 | |||
63 | EC_GROUP_get0_generator returns the generator for the identified B<group>. | ||
64 | |||
65 | The functions EC_GROUP_get_order and EC_GROUP_get_cofactor populate the provided B<order> and B<cofactor> parameters | ||
66 | with the respective order and cofactors for the B<group>. | ||
67 | |||
68 | The functions EC_GROUP_set_curve_name and EC_GROUP_get_curve_name, set and get the NID for the curve respectively | ||
69 | (see L<EC_GROUP_new(3)|EC_GROUP_new(3)>). If a curve does not have a NID associated with it, then EC_GROUP_get_curve_name | ||
70 | will return 0. | ||
71 | |||
72 | The asn1_flag value on a curve is used to determine whether there is a specific ASN1 OID to describe the curve or not. | ||
73 | If the asn1_flag is 1 then this is a named curve with an associated ASN1 OID. If not then asn1_flag is 0. The functions | ||
74 | 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 | ||
75 | the curve_name must also be set. | ||
76 | |||
77 | The point_conversion_form for a curve controls how EC_POINT data is encoded as ASN1 as defined in X9.62 (ECDSA). | ||
78 | point_conversion_form_t is an enum defined as follows: | ||
79 | |||
80 | typedef enum { | ||
81 | /** the point is encoded as z||x, where the octet z specifies | ||
82 | * which solution of the quadratic equation y is */ | ||
83 | POINT_CONVERSION_COMPRESSED = 2, | ||
84 | /** the point is encoded as z||x||y, where z is the octet 0x02 */ | ||
85 | POINT_CONVERSION_UNCOMPRESSED = 4, | ||
86 | /** the point is encoded as z||x||y, where the octet z specifies | ||
87 | * which solution of the quadratic equation y is */ | ||
88 | POINT_CONVERSION_HYBRID = 6 | ||
89 | } point_conversion_form_t; | ||
90 | |||
91 | |||
92 | For POINT_CONVERSION_UNCOMPRESSED the point is encoded as an octet signifying the UNCOMPRESSED form has been used followed by | ||
93 | the octets for x, followed by the octets for y. | ||
94 | |||
95 | For any given x co-ordinate for a point on a curve it is possible to derive two possible y values. For | ||
96 | POINT_CONVERSION_COMPRESSED the point is encoded as an octet signifying that the COMPRESSED form has been used AND which of | ||
97 | the two possible solutions for y has been used, followed by the octets for x. | ||
98 | |||
99 | For POINT_CONVERSION_HYBRID the point is encoded as an octet signifying the HYBRID form has been used AND which of the two | ||
100 | possible solutions for y has been used, followed by the octets for x, followed by the octets for y. | ||
101 | |||
102 | The functions EC_GROUP_set_point_conversion_form and EC_GROUP_get_point_conversion_form set and get the point_conversion_form | ||
103 | for the curve respectively. | ||
104 | |||
105 | ANSI X9.62 (ECDSA standard) defines a method of generating the curve parameter b from a random number. This provides advantages | ||
106 | in that a parameter obtained in this way is highly unlikely to be susceptible to special purpose attacks, or have any trapdoors in it. | ||
107 | 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 | ||
108 | 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 | ||
109 | 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 | ||
110 | builtin curves within the library provide seed values that can be obtained. It is also possible to set a custom seed using | ||
111 | 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 | ||
112 | this seed value, although it will be preserved in any ASN1 based communications. | ||
113 | |||
114 | 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 | ||
115 | the value m. | ||
116 | |||
117 | The function EC_GROUP_check_discriminant calculates the discriminant for the curve and verifies that it is valid. | ||
118 | 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 | ||
119 | simply b. In either case for the curve to be valid the discriminant must be non zero. | ||
120 | |||
121 | The function EC_GROUP_check performs a number of checks on a curve to verify that it is valid. Checks performed include | ||
122 | verifying that the discriminant is non zero; that a generator has been defined; that the generator is on the curve and has | ||
123 | the correct order. | ||
124 | |||
125 | EC_GROUP_cmp compares B<a> and B<b> to determine whether they represent the same curve or not. | ||
126 | |||
127 | The functions EC_GROUP_get_basis_type, EC_GROUP_get_trinomial_basis and EC_GROUP_get_pentanomial_basis should only be called for curves | ||
128 | defined over an F2^m field. Addition and multiplication operations within an F2^m field are performed using an irreducible polynomial | ||
129 | function f(x). This function is either a trinomial of the form: | ||
130 | |||
131 | f(x) = x^m + x^k + 1 with m > k >= 1 | ||
132 | |||
133 | or a pentanomial of the form: | ||
134 | |||
135 | f(x) = x^m + x^k3 + x^k2 + x^k1 + 1 with m > k3 > k2 > k1 >= 1 | ||
136 | |||
137 | The function EC_GROUP_get_basis_type returns a NID identifying whether a trinomial or pentanomial is in use for the field. The | ||
138 | 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 | ||
139 | 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>, | ||
140 | B<k2> and B<k3> respectively. | ||
141 | |||
142 | =head1 RETURN VALUES | ||
143 | |||
144 | The following functions return 1 on success or 0 on error: EC_GROUP_copy, EC_GROUP_set_generator, EC_GROUP_check, | ||
145 | EC_GROUP_check_discriminant, EC_GROUP_get_trinomial_basis and EC_GROUP_get_pentanomial_basis. | ||
146 | |||
147 | EC_GROUP_dup returns a pointer to the duplicated curve, or NULL on error. | ||
148 | |||
149 | EC_GROUP_method_of returns the EC_METHOD implementation in use for the given curve or NULL on error. | ||
150 | |||
151 | EC_GROUP_get0_generator returns the generator for the given curve or NULL on error. | ||
152 | |||
153 | EC_GROUP_get_order, EC_GROUP_get_cofactor, EC_GROUP_get_curve_name, EC_GROUP_get_asn1_flag, EC_GROUP_get_point_conversion_form | ||
154 | and EC_GROUP_get_degree return the order, cofactor, curve name (NID), ASN1 flag, point_conversion_form and degree for the | ||
155 | specified curve respectively. If there is no curve name associated with a curve then EC_GROUP_get_curve_name will return 0. | ||
156 | |||
157 | 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 | ||
158 | specified. EC_GROUP_get_seed_len returns the length of the seed or 0 if the seed is not specified. | ||
159 | |||
160 | 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 | ||
161 | 0, the return value will be 1. On error 0 is returned. | ||
162 | |||
163 | EC_GROUP_cmp returns 0 if the curves are equal, 1 if they are not equal, or -1 on error. | ||
164 | |||
165 | 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 | ||
166 | trinomial or pentanomial respectively. Alternatively in the event of an error a 0 is returned. | ||
167 | |||
168 | =head1 SEE ALSO | ||
169 | |||
170 | L<crypto(3)|crypto(3)>, L<ec(3)|ec(3)>, L<EC_GROUP_new(3)|EC_GROUP_new(3)>, | ||
171 | L<EC_POINT_new(3)|EC_POINT_new(3)>, L<EC_POINT_add(3)|EC_POINT_add(3)>, L<EC_KEY_new(3)|EC_KEY_new(3)>, | ||
172 | L<EC_GFp_simple_method(3)|EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)|d2i_ECPKParameters(3)> | ||
173 | |||
174 | =cut | ||