NAME

       EVP_PKEY_CTX_new, EVP_PKEY_CTX_new_id, EVP_PKEY_CTX_new_from_name,
       EVP_PKEY_CTX_new_from_pkey, EVP_PKEY_CTX_dup, EVP_PKEY_CTX_free, EVP_PKEY_CTX_is_a -
       public key algorithm context functions

SYNOPSIS

        #include <openssl/evp.h>

        EVP_PKEY_CTX *EVP_PKEY_CTX_new(EVP_PKEY *pkey, ENGINE *e);
        EVP_PKEY_CTX *EVP_PKEY_CTX_new_id(int id, ENGINE *e);
        EVP_PKEY_CTX *EVP_PKEY_CTX_new_from_name(OSSL_LIB_CTX *libctx,
                                                 const char *name,
                                                 const char *propquery);
        EVP_PKEY_CTX *EVP_PKEY_CTX_new_from_pkey(OSSL_LIB_CTX *libctx,
                                                 EVP_PKEY *pkey,
                                                 const char *propquery);
        EVP_PKEY_CTX *EVP_PKEY_CTX_dup(const EVP_PKEY_CTX *ctx);
        void EVP_PKEY_CTX_free(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_CTX_is_a(EVP_PKEY_CTX *ctx, const char *keytype);

DESCRIPTION

       The EVP_PKEY_CTX_new() function allocates public key algorithm context using the pkey key
       type and ENGINE e.

       The EVP_PKEY_CTX_new_id() function allocates public key algorithm context using the key
       type specified by id and ENGINE e.

       The EVP_PKEY_CTX_new_from_name() function allocates a public key algorithm context using
       the library context libctx (see OSSL_LIB_CTX(3)), the key type specified by name and the
       property query propquery.  None of the arguments are duplicated, so they  must remain
       unchanged for the lifetime of the returned EVP_PKEY_CTX or of any of its duplicates.  Read
       further about the possible names in "NOTES" below.

       The EVP_PKEY_CTX_new_from_pkey() function allocates a public key algorithm context using
       the library context libctx (see OSSL_LIB_CTX(3)) and the algorithm specified by pkey and
       the property query propquery. None of the arguments are duplicated, so they must remain
       unchanged for the lifetime of the returned EVP_PKEY_CTX or any of its duplicates.

       EVP_PKEY_CTX_new_id() and EVP_PKEY_CTX_new_from_name() are normally used when no EVP_PKEY
       structure is associated with the operations, for example during parameter generation or
       key generation for some algorithms.

       EVP_PKEY_CTX_dup() duplicates the context ctx. It is not supported for a keygen operation.

       EVP_PKEY_CTX_free() frees up the context ctx.  If ctx is NULL, nothing is done.

       EVP_PKEY_is_a() checks if the key type associated with ctx is keytype.

NOTES

   On EVP_PKEY_CTX
       The EVP_PKEY_CTX structure is an opaque public key algorithm context used by the OpenSSL
       high-level public key API. Contexts MUST NOT be shared between threads: that is it is not
       permissible to use the same context simultaneously in two threads.

   On Key Types
       We mention "key type" in this manual, which is the same as "algorithm" in most cases,
       allowing either term to be used interchangeably.  There are algorithms where the key type
       and the algorithm of the operations that use the keys are not the same, such as EC keys
       being used for ECDSA and ECDH operations.

       Key types are given in two different manners:

       Legacy NID or EVP_PKEY type
           This is the id used with EVP_PKEY_CTX_new_id().

           These are EVP_PKEY_RSA, EVP_PKEY_RSA_PSS, EVP_PKEY_DSA, EVP_PKEY_DH, EVP_PKEY_EC,
           EVP_PKEY_SM2, EVP_PKEY_X25519, EVP_PKEY_X448, and are used by legacy methods.

       Name strings
           This is the name used with EVP_PKEY_CTX_new_from_name().

           These are names like "RSA", "DSA", and what's available depends on what providers are
           currently accessible.

           The OpenSSL providers offer a set of key types available this way, please see
           OSSL_PROVIDER-FIPS(7) and OSSL_PROVIDER-default(7) and related documentation for more
           information.

RETURN VALUES

       EVP_PKEY_CTX_new(), EVP_PKEY_CTX_new_id() and EVP_PKEY_CTX_dup() return either the newly
       allocated EVP_PKEY_CTX structure or NULL if an error occurred.

       EVP_PKEY_CTX_free() does not return a value.

       EVP_PKEY_CTX_is_a() returns 1 for true and 0 for false.

SEE ALSO

       EVP_PKEY_new(3)

HISTORY

       The EVP_PKEY_CTX_new(), EVP_PKEY_CTX_new_id(), EVP_PKEY_CTX_dup() and EVP_PKEY_CTX_free()
       functions were added in OpenSSL 1.0.0.

       The EVP_PKEY_CTX_new_from_name() and EVP_PKEY_CTX_new_from_pkey() functions were added in
       OpenSSL 3.0.

COPYRIGHT

       Copyright 2006-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.