147 lines
5.3 KiB
Plaintext
147 lines
5.3 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
RAND_DRBG_set_callbacks,
|
|
RAND_DRBG_get_entropy_fn,
|
|
RAND_DRBG_cleanup_entropy_fn,
|
|
RAND_DRBG_get_nonce_fn,
|
|
RAND_DRBG_cleanup_nonce_fn
|
|
- set callbacks for reseeding
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/rand_drbg.h>
|
|
|
|
|
|
int RAND_DRBG_set_callbacks(RAND_DRBG *drbg,
|
|
RAND_DRBG_get_entropy_fn get_entropy,
|
|
RAND_DRBG_cleanup_entropy_fn cleanup_entropy,
|
|
RAND_DRBG_get_nonce_fn get_nonce,
|
|
RAND_DRBG_cleanup_nonce_fn cleanup_nonce);
|
|
|
|
|
|
=head2 Callback Functions
|
|
|
|
typedef size_t (*RAND_DRBG_get_entropy_fn)(
|
|
RAND_DRBG *drbg,
|
|
unsigned char **pout,
|
|
int entropy,
|
|
size_t min_len, size_t max_len,
|
|
int prediction_resistance);
|
|
|
|
typedef void (*RAND_DRBG_cleanup_entropy_fn)(
|
|
RAND_DRBG *drbg,
|
|
unsigned char *out, size_t outlen);
|
|
|
|
typedef size_t (*RAND_DRBG_get_nonce_fn)(
|
|
RAND_DRBG *drbg,
|
|
unsigned char **pout,
|
|
int entropy,
|
|
size_t min_len, size_t max_len);
|
|
|
|
typedef void (*RAND_DRBG_cleanup_nonce_fn)(
|
|
RAND_DRBG *drbg,
|
|
unsigned char *out, size_t outlen);
|
|
|
|
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
RAND_DRBG_set_callbacks() sets the callbacks for obtaining fresh entropy and
|
|
the nonce when reseeding the given B<drbg>.
|
|
The callback functions are implemented and provided by the caller.
|
|
Their parameter lists need to match the function prototypes above.
|
|
|
|
Setting the callbacks is allowed only if the DRBG has not been initialized yet.
|
|
Otherwise, the operation will fail.
|
|
To change the settings for one of the three shared DRBGs it is necessary to call
|
|
RAND_DRBG_uninstantiate() first.
|
|
|
|
The B<get_entropy>() callback is called by the B<drbg> when it requests fresh
|
|
random input.
|
|
It is expected that the callback allocates and fills a random buffer of size
|
|
B<min_len> <= size <= B<max_len> (in bytes) which contains at least B<entropy>
|
|
bits of randomness.
|
|
The B<prediction_resistance> flag indicates whether the reseeding was
|
|
triggered by a prediction resistance request.
|
|
|
|
The buffer's address is to be returned in *B<pout> and the number of collected
|
|
randomness bytes as return value.
|
|
|
|
If the callback fails to acquire at least B<entropy> bits of randomness,
|
|
it must indicate an error by returning a buffer length of 0.
|
|
|
|
If B<prediction_resistance> was requested and the random source of the DRBG
|
|
does not satisfy the conditions requested by [NIST SP 800-90C], then
|
|
it must also indicate an error by returning a buffer length of 0.
|
|
See NOTES section for more details.
|
|
|
|
The B<cleanup_entropy>() callback is called from the B<drbg> to clear and
|
|
free the buffer allocated previously by get_entropy().
|
|
The values B<out> and B<outlen> are the random buffer's address and length,
|
|
as returned by the get_entropy() callback.
|
|
|
|
The B<get_nonce>() and B<cleanup_nonce>() callbacks are used to obtain a nonce
|
|
and free it again. A nonce is only required for instantiation (not for reseeding)
|
|
and only in the case where the DRBG uses a derivation function.
|
|
The callbacks are analogous to get_entropy() and cleanup_entropy(),
|
|
except for the missing prediction_resistance flag.
|
|
|
|
If the derivation function is disabled, then no nonce is used for instantiation,
|
|
and the B<get_nonce>() and B<cleanup_nonce>() callbacks can be omitted by
|
|
setting them to NULL.
|
|
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
RAND_DRBG_set_callbacks() return 1 on success, and 0 on failure
|
|
|
|
=head1 NOTES
|
|
|
|
It is important that B<cleanup_entropy>() and B<cleanup_nonce>() clear the buffer
|
|
contents safely before freeing it, in order not to leave sensitive information
|
|
about the DRBG's state in memory.
|
|
|
|
A request for prediction resistance can only be satisfied by pulling fresh
|
|
entropy from one of the approved entropy sources listed in section 5.5.2 of
|
|
[NIST SP 800-90C].
|
|
Since the default implementation of the get_entropy callback does not have access
|
|
to such an approved entropy source, a request for prediction resistance will
|
|
always fail.
|
|
In other words, prediction resistance is currently not supported yet by the DRBG.
|
|
|
|
The derivation function is disabled during initialization by calling the
|
|
RAND_DRBG_set() function with the RAND_DRBG_FLAG_CTR_NO_DF flag.
|
|
For more information on the derivation function and when it can be omitted,
|
|
see [NIST SP 800-90A Rev. 1]. Roughly speaking it can be omitted if the random
|
|
source has "full entropy", i.e., contains 8 bits of entropy per byte.
|
|
|
|
Even if a nonce is required, the B<get_nonce>() and B<cleanup_nonce>()
|
|
callbacks can be omitted by setting them to NULL.
|
|
In this case the DRBG will automatically request an extra amount of entropy
|
|
(using the B<get_entropy>() and B<cleanup_entropy>() callbacks) which it will
|
|
utilize for the nonce, following the recommendations of [NIST SP 800-90A Rev. 1],
|
|
section 8.6.7.
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<RAND_DRBG_new(3)>,
|
|
L<RAND_DRBG_reseed(3)>,
|
|
L<RAND_DRBG(7)>
|
|
|
|
=head1 HISTORY
|
|
|
|
The RAND_DRBG functions were added in OpenSSL 1.1.1.
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2017-2020 The OpenSSL Project Authors. All Rights Reserved.
|
|
|
|
Licensed under the OpenSSL license (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
|