mbedtls_ctr_drbg_seed() always set the entropy length to the default,
so a call to mbedtls_ctr_drbg_set_entropy_len() before seed() had no
effect. Change this to the more intuitive behavior that
set_entropy_len() sets the entropy length and seed() respects that and
only uses the default entropy length if there was no call to
set_entropy_len().
This removes the need for the test-only function
mbedtls_ctr_drbg_seed_entropy_len(). Just call
mbedtls_ctr_drbg_set_entropy_len() followed by
mbedtls_ctr_drbg_seed(), it works now.
The documentation of CTR_DRBG erroneously claimed that
mbedtls_ctr_drbg_set_entropy_len() had an impact on the initial
seeding. This is in fact not the case: mbedtls_ctr_drbg_seed() forces
the initial seeding to grab MBEDTLS_CTR_DRBG_ENTROPY_LEN bytes of
entropy. Fix the documentation and rewrite the discussion of the
entropy length and the security strength accordingly.
Explain how MBEDTLS_CTR_DRBG_ENTROPY_LEN is set next to the security
strength statement, rather than giving a partial explanation (current
setting only) in the documentation of MBEDTLS_CTR_DRBG_ENTROPY_LEN.
NIST and many other sources call it a "personalization string", and
certainly not "device-specific identifiers" which is actually somewhat
misleading since this is just one of many things that might go into a
personalization string.
Document that a derivation function is used.
Document the security strength of the DRBG depending on the
compile-time configuration and how it is set up. In particular,
document how the nonce specified in SP 800-90A is set.
Mention how to link the ctr_drbg module with the entropy module.
* State explicit whether several numbers are in bits or bytes.
* Clarify whether buffer pointer parameters can be NULL.
* Explain the value of constants that are dependent on the configuration.
To help the build system find the correct include files, paths starting
with "mbedtls/" or "psa/" must be used. Otherwise, you can run into
build failures like the following when building Mbed Crypto as a
submodule.
In file included from chachapoly.c:31:0:
../../include/mbedtls/chachapoly.h:43:10: fatal error: poly1305.h: No such file or directory
#include "poly1305.h"
^~~~~~~~~~~~
compilation terminated.
Includes for ALT implementations are not modified, as the alt headers
are provided by system integrators and not Mbed TLS or Mbed Crypto.
Additional changes to temporarily enable running tests:
ssl_srv.c and test_suite_ecdh use mbedtls_ecp_group_load instead of
mbedtls_ecdh_setup
test_suite_ctr_drbg uses mbedtls_ctr_drbg_update instead of
mbedtls_ctr_drbg_update_ret
a compile time print was added warning in case of 128bit ctr_drbg keys.
This was don't to avoid an actual warning in these cases
(making build with warnings as errors possible).
Additional warnings on the Changelog/headers were set to use the same phrasing
phrasing was approved by Gilles and Janos.
the change is designed to make configuring 128bit keys for ctr_drbg more similar to other configuration options. Tests have been updated accordingly.
also clarified test naming.
Minor documentation improvements:
*Standardized file brief description.
*Separated return statements.
*Reordered tags within documentation blocks so that params and returns are last in block.
*Suggest to specify issue for each return code, where multiple failure return codes are listed.
- Rephrase file/function/parameter/enum/define/error descriptions into full
and clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
- Add full standard name in file description.
GitHub PR: #1316
