EVP_PKEY_GET_SIZE(3ossl) OpenSSL EVP_PKEY_GET_SIZE(3ossl)
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
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(3) returns the maximum suitable size for the output
buffers for almost all operations that can be done with pkey. This
corresponds to the provider parameter OSSL_PKEY_PARAM_MAX_SIZE. 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(3) 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.
This length corresponds to the provider parameter OSSL_PKEY_PARAM_BITS.
EVP_PKEY_get_security_bits() returns the number of security bits of the
given pkey, bits of security is defined in NIST SP800-57. This
corresponds to the provider parameter OSSL_PKEY_PARAM_SECURITY_BITS.
RETURN VALUES
EVP_PKEY_get_size(3), 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(3) 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(3) 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(3) shouldn't
be used to get the output size for EVP_DigestSignFinal(), according to
"NOTES" in EVP_DigestSignFinal(3).
SEE ALSO
provider-keymgmt(7), 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 2020-2023 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>.
3.2.0 2023-11-23 EVP_PKEY_GET_SIZE(3ossl)
openssl 3.2.0 - Generated Thu Nov 30 18:53:55 CST 2023