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EVP_PKEY_get_size(3)                OpenSSL               EVP_PKEY_get_size(3)



NAME
       EVP_PKEY_get_size, EVP_PKEY_get_bits, EVP_PKEY_get_security_bits,
       EVP_PKEY_bits, EVP_PKEY_security_bits, EVP_PKEY_size - EVP_PKEY
       information functions

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_PKEY_get_size(const EVP_PKEY *pkey);
        int EVP_PKEY_get_bits(const EVP_PKEY *pkey);
        int EVP_PKEY_get_security_bits(const EVP_PKEY *pkey);

        #define EVP_PKEY_bits EVP_PKEY_get_bits
        #define EVP_PKEY_security_bits EVP_PKEY_get_security_bits
        #define EVP_PKEY_size EVP_PKEY_get_size

DESCRIPTION
       EVP_PKEY_get_size() returns the maximum suitable size for the output
       buffers for almost all operations that can be done with pkey.  The
       primary documented use is with EVP_SignFinal(3) and EVP_SealInit(3),
       but it isn't limited there.  The returned size is also large enough for
       the output buffer of EVP_PKEY_sign(3), EVP_PKEY_encrypt(3),
       EVP_PKEY_decrypt(3), EVP_PKEY_derive(3).

       It must be stressed that, unless the documentation for the operation
       that's being performed says otherwise, the size returned by
       EVP_PKEY_get_size() is only preliminary and not exact, so the final
       contents of the target buffer may be smaller.  It is therefore crucial
       to take note of the size given back by the function that performs the
       operation, such as EVP_PKEY_sign(3) (the siglen argument will receive
       that length), to avoid bugs.

       EVP_PKEY_get_bits() returns the cryptographic length of the
       cryptosystem to which the key in pkey belongs, in bits.  Note that the
       definition of cryptographic length is specific to the key cryptosystem.

       EVP_PKEY_get_security_bits() returns the number of security bits of the
       given pkey, bits of security is defined in NIST SP800-57.

RETURN VALUES
       EVP_PKEY_get_size(), EVP_PKEY_get_bits() and
       EVP_PKEY_get_security_bits() return a positive number, or 0 if this
       size isn't available.

NOTES
       Most functions that have an output buffer and are mentioned with
       EVP_PKEY_get_size() have a functionality where you can pass NULL for
       the buffer and still pass a pointer to an integer and get the exact
       size that this function call delivers in the context that it's called
       in.  This allows those functions to be called twice, once to find out
       the exact buffer size, then allocate the buffer in between, and call
       that function again actually output the data.  For those functions, it
       isn't strictly necessary to call EVP_PKEY_get_size() to find out the
       buffer size, but may be useful in cases where it's desirable to know
       the upper limit in advance.

       It should also be especially noted that EVP_PKEY_get_size() shouldn't
       be used to get the output size for EVP_DigestSignFinal(), according to
       "NOTES" in EVP_DigestSignFinal(3).

SEE ALSO
       EVP_SignFinal(3), EVP_SealInit(3), EVP_PKEY_sign(3),
       EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3), EVP_PKEY_derive(3)

HISTORY
       The EVP_PKEY_bits(), EVP_PKEY_security_bits(), and EVP_PKEY_size()
       functions were renamed to include "get" in their names in OpenSSL 3.0,
       respectively.  The old names are kept as non-deprecated alias macros.

COPYRIGHT
       Copyright 2020-2021 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>.



3.0.12                            2023-05-07              EVP_PKEY_get_size(3)