The signature of mbedtls_mpi_cmp_mpi_ct() meant to support using it in
place of mbedtls_mpi_cmp_mpi(). This meant full comparison functionality
and a signed result.
To make the function more universal and friendly to constant time
coding, we change the result type to unsigned. Theoretically, we could
encode the comparison result in an unsigned value, but it would be less
intuitive.
Therefore we won't be able to represent the result as unsigned anymore
and the functionality will be constrained to checking if the first
operand is less than the second. This is sufficient to support the
current use case and to check any relationship between MPIs.
The only drawback is that we need to call the function twice when
checking for equality, but this can be optimised later if an when it is
needed.
The documentation of HMAC_DRBG erroneously claimed that
mbedtls_hmac_drbg_set_entropy_len() had an impact on the initial
seeding. This is in fact not the case: mbedtls_hmac_drbg_seed() forces
the entropy length to its chosen value. Fix the documentation.
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.
* State explicit whether several numbers are in bits or bytes.
* Clarify whether buffer pointer parameters can be NULL.
* Minor wording and formatting improvements.
Explain what how entropy input length is determined from the
configuration, and how this in turn determines the security strength.
Explain how the nonce is obtained during initialization.
* State explicit whether several numbers are in bits or bytes.
* Clarify whether buffer pointer parameters can be NULL.
* Clarify some terminology.
* Minor wording and formatting improvements.
* restricted/pr/581:
Remove unnecessary empty line
Add a test for signing content with a long ECDSA key
Add documentation notes about the required size of the signature buffers
Add missing MBEDTLS_ECP_C dependencies in check_config.h
Change size of preallocated buffer for pk_sign() calls
* origin/pr/2612:
Adjust backport's documentation to account for missing features
Backport a doxygen note from development for `mbedtls_ssl_conf_max_frag_len()`
Update change log
Reword ssl_conf_max_frag_len documentation for clarity
* restricted/pr/529:
Fix order of sections in the ChangeLog
Fix failure in SSLv3 per-version suites test
Adjust DES exclude lists in test scripts
Clarify 3DES changes in ChangeLog
Fix documentation for 3DES removal
Exclude 3DES tests in test scripts
Fix wording of ChangeLog and 3DES_REMOVE docs
Reduce priority of 3DES ciphersuites
Refactor the function mbedtls_asn1_write_bitstring() that removes
trailing 0s at the end of DER encoded bitstrings. The function is
implemented according to Hanno Becker's suggestions.
This commit also changes the functions x509write_crt_set_ns_cert_type
and crt_set_key_usage to call the new function as the use named
bitstrings instead of the regular bitstrings.
Alternative implementations are often hardware accelerators and might
not need an RNG for blinding. But if they do, then we make them misuse
the RNG in the deterministic case.
There are several way around this:
- Exposing a lower level function for replacement. This would be the
optimal solution, but litters the API and is not backward compatible.
- Introducing a new compile time option for replacing the deterministic
function. This would mostly cover the same code as
MBEDTLS_ECDSA_DETERMINISTIC and would be yet another compile time flag.
- Reusing the existing MBEDTLS_ECDSA_DETERMINISTIC macro. This changes
the algorithm used by the PK layer from deterministic to randomised if
the alternative implementation is present.
This commit implements the third option. This is a temporary solution
and should be fixed at the next device driver API change.
`mbedtls_ecdsa_sign_det` reuses the internal HMAC-DRBG instance to
implement blinding. The advantage of this is that the algorithm is
deterministic too, not just the resulting signature. The drawback is
that the blinding is always the same for the same key and message.
This diminishes the efficiency of blinding and leaks information about
the private key.
A function that takes external randomness fixes this weakness.
Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves#1371
