=head1 NAME
-rand - Psdeudo-random number generator
+rand - pseudo-random number generator
=head1 SYNOPSIS
#include <openssl/rand.h>
- int RAND_bytes(unsigned char *buf,int num);
- int RAND_pseudo_bytes(unsigned char *buf,int num);
+ int RAND_set_rand_engine(ENGINE *engine);
- void RAND_seed(const void *buf,int num);
- void RAND_add(const void *buf,int num,int entropy);
- void RAND_screen(void);
+ 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_load_file(const char *file, long max_bytes);
int RAND_write_file(const char *file);
- char *RAND_file_name(char *file,int num);
+ const char *RAND_file_name(char *file, size_t num);
- void RAND_set_rand_method(RAND_METHOD *meth);
- RAND_METHOD *RAND_get_rand_method(void);
+ 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 recommended
+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
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)>. Its state can be saved in a seed file
-(see L<RAND_load_file(3)>) to avoid having to go through the seeding
-process whenever the application is started.
+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)> describes how to obtain random data from the PRNG.
+L<RAND_bytes(3)|RAND_bytes(3)> describes how to obtain random data from the
+PRNG.
=head1 INTERNALS
The algorithm is as follows.
There is global state made up of a 1023 byte buffer (the 'state'), a
-working hash function ('md') and a counter ('count').
+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 16 bytes (or less for
+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'
function and xor).
When bytes are extracted from the RNG, the following process is used.
-For each group of 8 bytes (or less), we do the following,
+For each group of 10 bytes (or less), we do the following:
-Input into the hash function the top 8 bytes from 'md', the bytes that
-are to be overwritten by the random bytes, and bytes from the 'state'
-(incrementing looping index). From this hash function output (which
-is kept in 'md'), the top (upto) 8 bytes are returned to the caller
-and the bottom (upto) 8 bytes are xored into the 'state'.
+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
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 8 bytes given to the caller to
+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()>).
+L<RAND_add(3)|RAND_add(3)>).
=head1 SEE ALSO
-BN_rand(3), RAND_add(3), RAND_load_file(3), RAND_bytes(3),
-RAND_set_rand_method(3), RAND_cleanup(3)
+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
projects / openssl.git / blobdiff