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Diffstat (limited to 'doc/man3/RAND_DRBG_set_callbacks.pod')
-rw-r--r-- | doc/man3/RAND_DRBG_set_callbacks.pod | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/doc/man3/RAND_DRBG_set_callbacks.pod b/doc/man3/RAND_DRBG_set_callbacks.pod new file mode 100644 index 000000000000..a927d6a7dacc --- /dev/null +++ b/doc/man3/RAND_DRBG_set_callbacks.pod @@ -0,0 +1,147 @@ +=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 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 speeking 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 HISTORY + +The RAND_DRBG functions were added in OpenSSL 1.1.1. + +=head1 SEE ALSO + +L<RAND_DRBG_new(3)>, +L<RAND_DRBG_reseed(3)>, +L<RAND_DRBG(7)> + +=head1 COPYRIGHT + +Copyright 2017-2018 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 |