We were still reusing the internal HMAC-DRBG of the deterministic ECDSA
for blinding. This meant that with cryptographically low likelyhood the
result was not the same signature as the one the deterministic ECDSA
algorithm has to produce (however it is still a valid ECDSA signature).
To correct this we seed a second HMAC-DRBG with the same seed to restore
correct behavior. We also apply a label to avoid reusing the bits of the
ephemeral key for a different purpose and reduce the chance that they
leak.
This workaround can't be implemented in the restartable case without
penalising the case where external RNG is available or completely
defeating the purpose of the restartable feature, therefore in this case
the small chance of incorrect behavior remains.
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.
* origin/pr/2436:
Use certificates from data_files and refer them
Specify server certificate to use in SHA-1 test
refactor CA and SRV certificates into separate blocks
refactor SHA-1 certificate defintions and assignment
refactor server SHA-1 certificate definition into a new block
define TEST_SRV_CRT_RSA_SOME in similar logic to TEST_CA_CRT_RSA_SOME
server SHA-256 certificate now follows the same logic as CA SHA-256 certificate
add entry to ChangeLog
* restricted/pr/550:
Update query_config.c
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
* public/pr/2429:
Add ChangeLog entry for unused bits in bitstrings
Improve docs for ASN.1 bitstrings and their usage
Add tests for (named) bitstring to suite_asn1write
Fix ASN1 bitstring writing
The test used 3DES as the suite for SSLv3, which now makes the handshake fails
with "no ciphersuite in common", failing the test as well. Use Camellia
instead (as there are not enough AES ciphersuites before TLS 1.2 to
distinguish between the 3 versions).
Document some dependencies, but not all. Just trying to avoid introducing new
issues by using a new cipher here, not trying to make it perfect, which is a
much larger task out of scope of this commit.
Line issue trackers are conceptually a subclass of file issue
trackers: they're file issue trackers where issues arise from checking
each line independently. So make it an actual subclass.
Pylint pointed out the design smell: there was an abstract method that
wasn't always overridden in concrete child classes.
Make check-python-files.sh run pylint on all *.py files (in
directories where they are known to be present), rather than list
files explicitly.
Fix a bug whereby the return status of check-python-files.sh was only
based on the last file passing, i.e. errors in other files were
effectively ignored.
Make check-python-files.sh run pylint unconditionally. Since pylint3
is not critical, make all.sh to skip running check-python-files.sh if
pylint3 is not available.
The pylint configuration in .pylint was a modified version of the
output of `pylint --generate-rcfile` from an unknown version of
pylint. Replace it with a file that only contains settings that are
modified from the default, with an explanation of why each setting is
modified.
The new .pylintrc was written from scratch, based on the output of
pylint on the current version of the files and on a judgement of what
to silence generically, what to silence on a case-by-case basis and
what to fix.
If mbedtls_ecdh_get_params is called with keys belonging to
different groups, make it return an error the second time, rather than
silently interpret the first key as being on the second curve.
This makes the non-regression test added by the previous commit pass.
Add a test case for doing an ECDH calculation by calling
mbedtls_ecdh_get_params on both keys, with keys belonging to
different groups. This should fail, but currently passes.
