1=pod 2 3=head1 NAME 4 5EVP_PKEY_CTX_new, EVP_PKEY_CTX_new_id, EVP_PKEY_CTX_new_from_name, 6EVP_PKEY_CTX_new_from_pkey, EVP_PKEY_CTX_dup, EVP_PKEY_CTX_free, 7EVP_PKEY_CTX_is_a 8- public key algorithm context functions 9 10=head1 SYNOPSIS 11 12 #include <openssl/evp.h> 13 14 EVP_PKEY_CTX *EVP_PKEY_CTX_new(EVP_PKEY *pkey, ENGINE *e); 15 EVP_PKEY_CTX *EVP_PKEY_CTX_new_id(int id, ENGINE *e); 16 EVP_PKEY_CTX *EVP_PKEY_CTX_new_from_name(OSSL_LIB_CTX *libctx, 17 const char *name, 18 const char *propquery); 19 EVP_PKEY_CTX *EVP_PKEY_CTX_new_from_pkey(OSSL_LIB_CTX *libctx, 20 EVP_PKEY *pkey, 21 const char *propquery); 22 EVP_PKEY_CTX *EVP_PKEY_CTX_dup(const EVP_PKEY_CTX *ctx); 23 void EVP_PKEY_CTX_free(EVP_PKEY_CTX *ctx); 24 int EVP_PKEY_CTX_is_a(EVP_PKEY_CTX *ctx, const char *keytype); 25 26=head1 DESCRIPTION 27 28The EVP_PKEY_CTX_new() function allocates public key algorithm context using 29the I<pkey> key type and ENGINE I<e>. 30 31The EVP_PKEY_CTX_new_id() function allocates public key algorithm context 32using the key type specified by I<id> and ENGINE I<e>. 33 34The EVP_PKEY_CTX_new_from_name() function allocates a public key algorithm 35context using the library context I<libctx> (see L<OSSL_LIB_CTX(3)>), the 36key type specified by I<name> and the property query I<propquery>. None 37of the arguments are duplicated, so they must remain unchanged for the 38lifetime of the returned B<EVP_PKEY_CTX> or of any of its duplicates. Read 39further about the possible names in L</NOTES> below. 40 41The EVP_PKEY_CTX_new_from_pkey() function allocates a public key algorithm 42context using the library context I<libctx> (see L<OSSL_LIB_CTX(3)>) and the 43algorithm specified by I<pkey> and the property query I<propquery>. None of the 44arguments are duplicated, so they must remain unchanged for the lifetime of the 45returned B<EVP_PKEY_CTX> or any of its duplicates. 46 47EVP_PKEY_CTX_new_id() and EVP_PKEY_CTX_new_from_name() are normally 48used when no B<EVP_PKEY> structure is associated with the operations, 49for example during parameter generation or key generation for some 50algorithms. 51 52EVP_PKEY_CTX_dup() duplicates the context I<ctx>. 53It is not supported for a keygen operation. 54It is however possible to duplicate a context freshly created via any of the 55above C<new> functions, provided L<EVP_PKEY_keygen_init(3)> has not yet been 56called on the source context, and then use the copy for key generation. 57 58EVP_PKEY_CTX_free() frees up the context I<ctx>. 59If I<ctx> is NULL, nothing is done. 60 61EVP_PKEY_is_a() checks if the key type associated with I<ctx> is I<keytype>. 62 63=head1 NOTES 64 65=head2 On B<EVP_PKEY_CTX> 66 67The B<EVP_PKEY_CTX> structure is an opaque public key algorithm context used 68by the OpenSSL high-level public key API. Contexts B<MUST NOT> be shared between 69threads: that is it is not permissible to use the same context simultaneously 70in two threads. 71 72=head2 On Key Types 73 74We mention "key type" in this manual, which is the same 75as "algorithm" in most cases, allowing either term to be used 76interchangeably. There are algorithms where the I<key type> and the 77I<algorithm> of the operations that use the keys are not the same, 78such as EC keys being used for ECDSA and ECDH operations. 79 80Key types are given in two different manners: 81 82=over 4 83 84=item Legacy NID or EVP_PKEY type 85 86This is the I<id> used with EVP_PKEY_CTX_new_id(). 87 88These are B<EVP_PKEY_RSA>, B<EVP_PKEY_RSA_PSS>, B<EVP_PKEY_DSA>, 89B<EVP_PKEY_DH>, B<EVP_PKEY_EC>, B<EVP_PKEY_SM2>, B<EVP_PKEY_X25519>, 90B<EVP_PKEY_X448>, and are used by legacy methods. 91 92=item Name strings 93 94This is the I<name> used with EVP_PKEY_CTX_new_from_name(). 95 96These are names like "RSA", "DSA", and what's available depends on what 97providers are currently accessible. 98 99The OpenSSL providers offer a set of key types available this way, please 100see L<OSSL_PROVIDER-FIPS(7)> and L<OSSL_PROVIDER-default(7)> and related 101documentation for more information. 102 103=back 104 105=head1 RETURN VALUES 106 107EVP_PKEY_CTX_new(), EVP_PKEY_CTX_new_id() and EVP_PKEY_CTX_dup() return either 108the newly allocated B<EVP_PKEY_CTX> structure or B<NULL> if an error occurred. 109 110EVP_PKEY_CTX_free() does not return a value. 111 112EVP_PKEY_CTX_is_a() returns 1 for true and 0 for false. 113 114=head1 SEE ALSO 115 116L<EVP_PKEY_new(3)> 117 118=head1 HISTORY 119 120The EVP_PKEY_CTX_new(), EVP_PKEY_CTX_new_id(), EVP_PKEY_CTX_dup() and 121EVP_PKEY_CTX_free() functions were added in OpenSSL 1.0.0. 122 123The EVP_PKEY_CTX_new_from_name() and EVP_PKEY_CTX_new_from_pkey() functions were 124added in OpenSSL 3.0. 125 126=head1 COPYRIGHT 127 128Copyright 2006-2025 The OpenSSL Project Authors. All Rights Reserved. 129 130Licensed under the Apache License 2.0 (the "License"). You may not use 131this file except in compliance with the License. You can obtain a copy 132in the file LICENSE in the source distribution or at 133L<https://www.openssl.org/source/license.html>. 134 135=cut 136