mirror of
https://github.com/nillerusr/source-engine.git
synced 2024-12-28 09:03:01 +00:00
176 lines
6.1 KiB
Plaintext
176 lines
6.1 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
rand - pseudo-random number generator
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/rand.h>
|
|
|
|
int RAND_set_rand_engine(ENGINE *engine);
|
|
|
|
int RAND_bytes(unsigned char *buf, int num);
|
|
int RAND_pseudo_bytes(unsigned char *buf, int num);
|
|
|
|
void RAND_seed(const void *buf, int num);
|
|
void RAND_add(const void *buf, int num, int entropy);
|
|
int RAND_status(void);
|
|
|
|
int RAND_load_file(const char *file, long max_bytes);
|
|
int RAND_write_file(const char *file);
|
|
const char *RAND_file_name(char *file, size_t num);
|
|
|
|
int RAND_egd(const char *path);
|
|
|
|
void RAND_set_rand_method(const RAND_METHOD *meth);
|
|
const RAND_METHOD *RAND_get_rand_method(void);
|
|
RAND_METHOD *RAND_SSLeay(void);
|
|
|
|
void RAND_cleanup(void);
|
|
|
|
/* For Win32 only */
|
|
void RAND_screen(void);
|
|
int RAND_event(UINT, WPARAM, LPARAM);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
Since the introduction of the ENGINE API, the recommended way of controlling
|
|
default implementations is by using the ENGINE API functions. The default
|
|
B<RAND_METHOD>, as set by RAND_set_rand_method() and returned by
|
|
RAND_get_rand_method(), is only used if no ENGINE has been set as the default
|
|
"rand" implementation. Hence, these two functions are no longer the recommened
|
|
way to control defaults.
|
|
|
|
If an alternative B<RAND_METHOD> implementation is being used (either set
|
|
directly or as provided by an ENGINE module), then it is entirely responsible
|
|
for the generation and management of a cryptographically secure PRNG stream. The
|
|
mechanisms described below relate solely to the software PRNG implementation
|
|
built in to OpenSSL and used by default.
|
|
|
|
These functions implement a cryptographically secure pseudo-random
|
|
number generator (PRNG). It is used by other library functions for
|
|
example to generate random keys, and applications can use it when they
|
|
need randomness.
|
|
|
|
A cryptographic PRNG must be seeded with unpredictable data such as
|
|
mouse movements or keys pressed at random by the user. This is
|
|
described in L<RAND_add(3)|RAND_add(3)>. Its state can be saved in a seed file
|
|
(see L<RAND_load_file(3)|RAND_load_file(3)>) to avoid having to go through the
|
|
seeding process whenever the application is started.
|
|
|
|
L<RAND_bytes(3)|RAND_bytes(3)> describes how to obtain random data from the
|
|
PRNG.
|
|
|
|
=head1 INTERNALS
|
|
|
|
The RAND_SSLeay() method implements a PRNG based on a cryptographic
|
|
hash function.
|
|
|
|
The following description of its design is based on the SSLeay
|
|
documentation:
|
|
|
|
First up I will state the things I believe I need for a good RNG.
|
|
|
|
=over 4
|
|
|
|
=item 1
|
|
|
|
A good hashing algorithm to mix things up and to convert the RNG 'state'
|
|
to random numbers.
|
|
|
|
=item 2
|
|
|
|
An initial source of random 'state'.
|
|
|
|
=item 3
|
|
|
|
The state should be very large. If the RNG is being used to generate
|
|
4096 bit RSA keys, 2 2048 bit random strings are required (at a minimum).
|
|
If your RNG state only has 128 bits, you are obviously limiting the
|
|
search space to 128 bits, not 2048. I'm probably getting a little
|
|
carried away on this last point but it does indicate that it may not be
|
|
a bad idea to keep quite a lot of RNG state. It should be easier to
|
|
break a cipher than guess the RNG seed data.
|
|
|
|
=item 4
|
|
|
|
Any RNG seed data should influence all subsequent random numbers
|
|
generated. This implies that any random seed data entered will have
|
|
an influence on all subsequent random numbers generated.
|
|
|
|
=item 5
|
|
|
|
When using data to seed the RNG state, the data used should not be
|
|
extractable from the RNG state. I believe this should be a
|
|
requirement because one possible source of 'secret' semi random
|
|
data would be a private key or a password. This data must
|
|
not be disclosed by either subsequent random numbers or a
|
|
'core' dump left by a program crash.
|
|
|
|
=item 6
|
|
|
|
Given the same initial 'state', 2 systems should deviate in their RNG state
|
|
(and hence the random numbers generated) over time if at all possible.
|
|
|
|
=item 7
|
|
|
|
Given the random number output stream, it should not be possible to determine
|
|
the RNG state or the next random number.
|
|
|
|
=back
|
|
|
|
The algorithm is as follows.
|
|
|
|
There is global state made up of a 1023 byte buffer (the 'state'), a
|
|
working hash value ('md'), and a counter ('count').
|
|
|
|
Whenever seed data is added, it is inserted into the 'state' as
|
|
follows.
|
|
|
|
The input is chopped up into units of 20 bytes (or less for
|
|
the last block). Each of these blocks is run through the hash
|
|
function as follows: The data passed to the hash function
|
|
is the current 'md', the same number of bytes from the 'state'
|
|
(the location determined by in incremented looping index) as
|
|
the current 'block', the new key data 'block', and 'count'
|
|
(which is incremented after each use).
|
|
The result of this is kept in 'md' and also xored into the
|
|
'state' at the same locations that were used as input into the
|
|
hash function. I
|
|
believe this system addresses points 1 (hash function; currently
|
|
SHA-1), 3 (the 'state'), 4 (via the 'md'), 5 (by the use of a hash
|
|
function and xor).
|
|
|
|
When bytes are extracted from the RNG, the following process is used.
|
|
For each group of 10 bytes (or less), we do the following:
|
|
|
|
Input into the hash function the local 'md' (which is initialized from
|
|
the global 'md' before any bytes are generated), the bytes that are to
|
|
be overwritten by the random bytes, and bytes from the 'state'
|
|
(incrementing looping index). From this digest output (which is kept
|
|
in 'md'), the top (up to) 10 bytes are returned to the caller and the
|
|
bottom 10 bytes are xored into the 'state'.
|
|
|
|
Finally, after we have finished 'num' random bytes for the caller,
|
|
'count' (which is incremented) and the local and global 'md' are fed
|
|
into the hash function and the results are kept in the global 'md'.
|
|
|
|
I believe the above addressed points 1 (use of SHA-1), 6 (by hashing
|
|
into the 'state' the 'old' data from the caller that is about to be
|
|
overwritten) and 7 (by not using the 10 bytes given to the caller to
|
|
update the 'state', but they are used to update 'md').
|
|
|
|
So of the points raised, only 2 is not addressed (but see
|
|
L<RAND_add(3)|RAND_add(3)>).
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<BN_rand(3)|BN_rand(3)>, L<RAND_add(3)|RAND_add(3)>,
|
|
L<RAND_load_file(3)|RAND_load_file(3)>, L<RAND_egd(3)|RAND_egd(3)>,
|
|
L<RAND_bytes(3)|RAND_bytes(3)>,
|
|
L<RAND_set_rand_method(3)|RAND_set_rand_method(3)>,
|
|
L<RAND_cleanup(3)|RAND_cleanup(3)>
|
|
|
|
=cut
|