7 - EVP_PKEY EC keytype and algorithm support
11 The B<EC> keytype is implemented in OpenSSL's default provider.
13 =head2 Common EC parameters
15 The normal way of specifying domain parameters for an EC curve is via the
16 curve name "group". For curves with no curve name, explicit parameters can be
17 used that specify "field-type", "p", "a", "b", "generator" and "order".
18 Explicit parameters are supported for backwards compatibility reasons, but they
19 are not compliant with multiple standards (including RFC5915) which only allow
22 The following KeyGen/Gettable/Import/Export types are available for the
23 built-in EC algorithm:
27 =item "group" (B<OSSL_PKEY_PARAM_GROUP_NAME>) <UTF8 string>
31 =item "field-type" (B<OSSL_PKEY_PARAM_EC_FIELD_TYPE>) <UTF8 string>
33 The value should be either "prime-field" or "characteristic-two-field",
34 which correspond to prime field Fp and binary field F2^m.
36 =item "p" (B<OSSL_PKEY_PARAM_EC_P>) <unsigned integer>
38 For a curve over Fp I<p> is the prime for the field. For a curve over F2^m I<p>
39 represents the irreducible polynomial - each bit represents a term in the
40 polynomial. Therefore, there will either be three or five bits set dependent on
41 whether the polynomial is a trinomial or a pentanomial.
43 =item "a" (B<OSSL_PKEY_PARAM_EC_A>) <unsigned integer>
45 =item "b" (B<OSSL_PKEY_PARAM_EC_B>) <unsigned integer>
47 =item "seed" (B<OSSL_PKEY_PARAM_EC_SEED>) <octet string>
49 I<a> and I<b> represents the coefficients of the curve
50 For Fp: y^2 mod p = x^3 +ax + b mod p OR
51 For F2^m: y^2 + xy = x^3 + ax^2 + b
53 I<seed> is an optional value that is for information purposes only.
54 It represents the random number seed used to generate the coefficient I<b> from a
57 =item "generator" (B<OSSL_PKEY_PARAM_EC_GENERATOR>) <octet string>
59 =item "order" (B<OSSL_PKEY_PARAM_EC_ORDER>) <unsigned integer>
61 =item "cofactor" (B<OSSL_PKEY_PARAM_EC_COFACTOR>) <unsigned integer>
63 The I<generator> is a well defined point on the curve chosen for cryptographic
64 operations. The encoding conforms with Sec. 2.3.3 of the SECG SEC 1 ("Elliptic Curve
65 Cryptography") standard. See EC_POINT_oct2point().
66 Integers used for point multiplications will be between 0 and
68 I<cofactor> is an optional value.
69 I<order> multiplied by the I<cofactor> gives the number of points on the curve.
71 =item "decoded-from-explicit" (B<OSSL_PKEY_PARAM_EC_DECODED_FROM_EXPLICIT_PARAMS>) <integer>
73 Gets a flag indicating whether the key or parameters were decoded from explicit
74 curve parameters. Set to 1 if so or 0 if a named curve was used.
76 =item "use-cofactor-flag" (B<OSSL_PKEY_PARAM_USE_COFACTOR_ECDH>) <integer>
78 Enable Cofactor DH (ECC CDH) if this value is 1, otherwise it uses normal EC DH
79 if the value is zero. The cofactor variant multiplies the shared secret by the
80 EC curve's cofactor (note for some curves the cofactor is 1).
82 =item "encoding" (B<OSSL_PKEY_PARAM_EC_ENCODING>) <UTF8 string>
84 Set the format used for serializing the EC group parameters.
85 Valid values are "explicit" or "named_curve". The default value is "named_curve".
87 =item "point-format" (B<OSSL_PKEY_PARAM_EC_POINT_CONVERSION_FORMAT>) <UTF8 string>
89 Sets or gets the point_conversion_form for the I<key>. For a description of
90 point_conversion_forms please see L<EC_POINT_new(3)>. Valid values are
91 "uncompressed" or "compressed". The default value is "uncompressed".
93 =item "group-check" (B<OSSL_PKEY_PARAM_EC_GROUP_CHECK_TYPE>) <UTF8 string>
95 Sets or Gets the type of group check done when EVP_PKEY_param_check() is called.
96 Valid values are "default", "named" and "named-nist".
97 The "named" type checks that the domain parameters match the inbuilt curve parameters,
98 "named-nist" is similar but also checks that the named curve is a nist curve.
99 The "default" type does domain parameter validation for the OpenSSL default provider,
100 but is equivalent to "named-nist" for the OpenSSL fips provider.
102 =item "include-public" (B<OSSL_PKEY_PARAM_EC_INCLUDE_PUBLIC>) <integer>
104 Setting this value to 0 indicates that the public key should not be included when
105 encoding the private key. The default value of 1 will include the public key.
107 See also L<EVP_KEYEXCH-ECDH(7)> for the related
108 B<OSSL_EXCHANGE_PARAM_EC_ECDH_COFACTOR_MODE> parameter that can be set on a
111 =item "pub" (B<OSSL_PKEY_PARAM_PUB_KEY>) <octet string>
113 The public key value in EC point format.
115 =item "priv" (B<OSSL_PKEY_PARAM_PRIV_KEY>) <unsigned integer>
117 The private key value.
119 =item "encoded-pub-key" (B<OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY>) <octet string>
121 Used for getting and setting the encoding of an EC public key. The public key
122 is expected to be a point conforming to Sec. 2.3.4 of the SECG SEC 1 ("Elliptic
123 Curve Cryptography") standard.
125 =item "qx" (B<OSSL_PKEY_PARAM_EC_PUB_X>) <unsigned integer>
127 Used for getting the EC public key X component.
129 =item "qy" (B<OSSL_PKEY_PARAM_EC_PUB_Y>) <unsigned integer>
131 Used for getting the EC public key Y component.
133 =item (B<OSSL_PKEY_PARAM_DEFAULT_DIGEST>) <UTF8 string>
135 Getter that returns the default digest name.
136 (Currently returns "SHA256" as of OpenSSL 3.0).
140 The following Gettable types are also available for the built-in EC algorithm:
144 =item "basis-type" (B<OSSL_PKEY_PARAM_EC_CHAR2_TYPE>) <UTF8 string>
146 Supports the values "tpBasis" for a trinomial or "ppBasis" for a pentanomial.
147 This field is only used for a binary field F2^m.
149 =item "m" (B<OSSL_PKEY_PARAM_EC_CHAR2_M>) <integer>
151 =item "tp" (B<OSSL_PKEY_PARAM_EC_CHAR2_TP_BASIS>) <integer>
153 =item "k1" (B<OSSL_PKEY_PARAM_EC_CHAR2_PP_K1>) <integer>
155 =item "k2" (B<OSSL_PKEY_PARAM_EC_CHAR2_PP_K2>) <integer>
157 =item "k3" (B<OSSL_PKEY_PARAM_EC_CHAR2_PP_K3>) <integer>
159 These fields are only used for a binary field F2^m.
160 I<m> is the degree of the binary field.
162 I<tp> is the middle bit of a trinomial so its value must be in the
165 I<k1>, I<k2> and I<k3> are used to get the middle bits of a pentanomial such
166 that m > k3 > k2 > k1 > 0
172 An B<EVP_PKEY> context can be obtained by calling:
175 EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL);
177 An B<EVP_PKEY> ECDSA or ECDH key can be generated with a "P-256" named group by
180 pkey = EVP_EC_gen("P-256");
184 EVP_PKEY *key = NULL;
185 OSSL_PARAM params[2];
187 EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL);
189 EVP_PKEY_keygen_init(gctx);
191 params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
193 params[1] = OSSL_PARAM_construct_end();
194 EVP_PKEY_CTX_set_params(gctx, params);
196 EVP_PKEY_generate(gctx, &key);
198 EVP_PKEY_print_private(bio_out, key, 0, NULL);
201 EVP_PKEY_CTX_free(gctx);
203 An B<EVP_PKEY> EC CDH (Cofactor Diffie-Hellman) key can be generated with a
204 "K-571" named group by calling:
207 EVP_PKEY *key = NULL;
208 OSSL_PARAM params[3];
210 EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL);
212 EVP_PKEY_keygen_init(gctx);
214 params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
217 * This curve has a cofactor that is not 1 - so setting CDH mode changes
218 * the behaviour. For many curves the cofactor is 1 - so setting this has
221 params[1] = OSSL_PARAM_construct_int(OSSL_PKEY_PARAM_USE_COFACTOR_ECDH,
223 params[2] = OSSL_PARAM_construct_end();
224 EVP_PKEY_CTX_set_params(gctx, params);
226 EVP_PKEY_generate(gctx, &key);
227 EVP_PKEY_print_private(bio_out, key, 0, NULL);
230 EVP_PKEY_CTX_free(gctx);
237 L<provider-keymgmt(7)>,
238 L<EVP_SIGNATURE-ECDSA(7)>,
239 L<EVP_KEYEXCH-ECDH(7)>
243 Copyright 2020-2022 The OpenSSL Project Authors. All Rights Reserved.
245 Licensed under the Apache License 2.0 (the "License"). You may not use
246 this file except in compliance with the License. You can obtain a copy
247 in the file LICENSE in the source distribution or at
248 L<https://www.openssl.org/source/license.html>.