mirror of https://github.com/openssl/openssl.git
62 lines
1.7 KiB
Plaintext
62 lines
1.7 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
BN_num_bits, BN_num_bytes, BN_num_bits_word - get BIGNUM size
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/bn.h>
|
|
|
|
int BN_num_bytes(const BIGNUM *a);
|
|
|
|
int BN_num_bits(const BIGNUM *a);
|
|
|
|
int BN_num_bits_word(BN_ULONG w);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
BN_num_bytes() returns the size of a B<BIGNUM> in bytes.
|
|
|
|
BN_num_bits_word() returns the number of significant bits in a word.
|
|
If we take 0x00000432 as an example, it returns 11, not 16, not 32.
|
|
Basically, except for a zero, it returns I<floor(log2(w))+1>.
|
|
|
|
BN_num_bits() returns the number of significant bits in a B<BIGNUM>,
|
|
following the same principle as BN_num_bits_word().
|
|
|
|
BN_num_bytes() is a macro.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
The size.
|
|
|
|
=head1 NOTES
|
|
|
|
Some have tried using BN_num_bits() on individual numbers in RSA keys,
|
|
DH keys and DSA keys, and found that they don't always come up with
|
|
the number of bits they expected (something like 512, 1024, 2048,
|
|
...). This is because generating a number with some specific number
|
|
of bits doesn't always set the highest bits, thereby making the number
|
|
of I<significant> bits a little lower. If you want to know the "key
|
|
size" of such a key, either use functions like RSA_size(), DH_size()
|
|
and DSA_size(), or use BN_num_bytes() and multiply with 8 (although
|
|
there's no real guarantee that will match the "key size", just a lot
|
|
more probability).
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<DH_size(3)>, L<DSA_size(3)>,
|
|
L<RSA_size(3)>
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2000-2017 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
|
|
L<https://www.openssl.org/source/license.html>.
|
|
|
|
=cut
|