NAME

       EVP_PKEY_size, EVP_PKEY_bits, EVP_PKEY_security_bits - EVP_PKEY information functions

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_PKEY_size(const EVP_PKEY *pkey);
        int EVP_PKEY_bits(const EVP_PKEY *pkey);
        int EVP_PKEY_security_bits(const EVP_PKEY *pkey);

DESCRIPTION

       EVP_PKEY_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_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_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_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_size(), EVP_PKEY_bits() and EVP_PKEY_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_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_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_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)

COPYRIGHT

       Copyright 2020 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>.

1.1.1f                                             2025-02-05                                EVP_PKEY_SIZE(3SSL)