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
 #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
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.
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.
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).
EVP_SignFinal(3), EVP_SealInit(3), EVP_PKEY_sign(3),
  EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3),
  EVP_PKEY_derive(3)
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 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>.