TLS used to prefer larger curves, under the idea that a larger curve has a
higher security strength and is therefore harder to attack. However, brute
force attacks are not a practical concern, so this was not particularly
meaningful. If a curve is considered secure enough to be allowed, then we
might as well use it.
So order curves by resource usage. The exact definition of what this means
is purposefully left open. It may include criteria such as performance and
memory usage. Risk of side channels could be a factor as well, although it
didn't affect the current choice.
The current list happens to exactly correspond to the numbers reported by
one run of the benchmark program for "full handshake/s" on my machine.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
We stated that curves were listed "in order of preference", but we never
explained what the preference was, so this was not meaningful.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
MBEDTLS_ECP_WINDOW_SIZE is a compromise between memory usage (growing based
on the value) and performance (faster with larger values). There are
disminishing returns as the value grows larger. Based on Manuel's benchmarks
recorded in https://github.com/ARMmbed/mbedtls/issues/4127, 4 is a good
compromise point, with larger values bringing little advantage. So reduce
the default from 6 to 4.
Document the default value as in optimized for performance mostly, but don't
document the specific value, so we may change it later or make it
platform-dependent.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Upgrade the default list of hashes and curves allowed for TLS. The list is
now aligned with X.509 certificate verification: hashes and curves with at
least 255 bits (Curve25519 included), and RSA 2048 and above.
Remove MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE which would no
longer do anything.
Document more precisely what is allowed by default.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Upgrade the default X.509 certificate verification profile
mbedtls_x509_crt_profile_default to the former value of
mbedtls_x509_crt_profile_next, which is hashes and curves with at least 255
bits (Curve25519 included), and RSA 2048 and above.
Document more precisely what goes into the default profile.
Keep the "next" profile unchanged for now.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
mbedtls_dhm_get_value can be seen as either a copy function or a getter
function. Given the name and the semantics, it's more of a getter, even if
it "gets" by doing a copy. Therefore, put the context first, and the
selector next, leaving the output for last.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
The Mbed TLS code relies heavily on reading certain fields of
mbedtls_ecp_group directly. Make these fields public. Require
that MBEDTLS_ECP_ALT alternative implementations have them.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Add two functions mbedtls_dhm_get_len() and mbedtls_dhm_get_bitlen() to
query the length of the modulus in bytes or bits.
Remove the len field: the cost of calling mbedtls_dhm_get_len() each time
it's needed is negligible, and this improves the abstraction of the DHM
module.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
MBEDTLS_ECP_MAX_BITS doesn't make sense as a configuration option: it
must not be smaller than the largest supported curve, and it's useless
to set it to a larger value. So unconditionally set it to the size of
the largest supported curve. Remove it from the build configuration.
Alternative implementations must no longer need define this macro.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Conflicts:
include/mbedtls/ssl.h
include/psa/crypto_struct.h
Conflicts fixed by using the code from development branch
and manually re-applying the MBEDTLS_PRIVATE wrapping.
Mbed OS now provides POSIX-like time functions, although not alarm() nor
signal(). It is possible to implement MBEDTLS_TIMING_ALT on Mbed OS, so
we should not artificially prevent this in check-config. Remove the the
check that prevents implementing MBEDTLS_TIMING_ALT on Mbed OS.
Note that this limitation originally was added in the following commit,
although there isn't much context around why the restriction was
imposed: 63e7ebaaa1 ("Add material for generating yotta module"). In
2015, Mbed OS was quite a different thing: no RTOS, no threads, just an
asynchronous event loop model. I'd suppose the asynchronous event loop
model made it difficult before to implement MBEDTLS_TIMING_C on Mbed OS,
but that is no longer the case.
Fixes#4633
Signed-off-by: Jaeden Amero <jaeden.amero@arm.com>
Removing reference to RFC 7748 as it is more confusing than helpful. (It
decodes the scalars after masking which is not part of the encoding we
want to specify. Also, it has the explanation what it means by little
endian in a preceding section that is not trivial to find.)
We also explicitly specify constraint on leading zeroes.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The expression "the masking is omitted" assumes familiarity with
Montgomery curve private key format and even then can be confusing and
ambiguous or confusing.
Describe directly what format we mean and add some more background
information and reference to the standard as well.
Signed-off-by: Janos Follath <janos.follath@arm.com>
4-space indent is only guaranteed to result in a code block if there's a
blank line just before (details vary depending on the markdown
implementation, and doxygen isn't exactly markdown anyway). In a bullet
list, you need 8 spaces since the list itself is a nested construct
which takes a 4-space indent (even though you don't have to indent
continuation lines inside a bullet point by 4 spaces, 1 is enough).
Using \code...\encode which is rendering as intended.
Signed-off-by: Janos Follath <janos.follath@arm.com>
This level of detail can be confusing and could require even more detail
to clear it up. Simplifying it instead in alignment wiht the
documentation of existing setup functions.
Signed-off-by: Janos Follath <janos.follath@arm.com>
This reverts commit 03a5fd7780026b2ca0b4728352ded930f5a7cff9.
We're already calling the output of a PAKE a "shared secret". The
password is a shared secret (for PAKE where the verifier knows a
password-equivalent secret), but calling it "shared secret" or even just
"secret" would be confusing.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Technically this function takes a low entropy secret as an input which
might or might not be the password. Using the term "secret" in the
function name is less misleading.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The password stretching (using slow and/or memory hard hashes) in PAKEs
usually serves two purposes:
- Defending against server compromise impersonation attacks. J-PAKE is an
augmented PAKE and as such, stores a password-equivalent and defending
against this class of attacks is out of scope.
- Preventing offline dictionary attacks. J-PAKE is proven to be zero
knowledge and leaks no information beyond the fact if the passwords
matched and offline dictionary attack is not possible.
In summary: J-PAKE does not benefit from pasword stretching and is
unlikely to be an input. This part of the API is not necessary at this
point and can be added later.
Signed-off-by: Janos Follath <janos.follath@arm.com>
We are not confident about the stability of the PAKE interface (it is
just a proposal, not part of the standard yet). So we should explicitly
document it as experimental, subject to change.
Signed-off-by: Janos Follath <janos.follath@arm.com>
At this point this is a proposed PAKE interface for the PSA Crypto API
and not part of the official standard. Place the interface in
crypto_extra.h to make this clear.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The API has PSA_ALG_GCM and not PSA_ALG_AEAD_GCM, PSA_ALG_MD5 and not
PSA_ALG_HASH_MD5, etc., so PSA_ALG_PAKE_JPAKE should be PSA_ALG_JPAKE as
well.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The caller is likely to receive the inputs on the wire, and having a
known size for which they can confidently reject longer inputs would be
helpful in cases where the application can't just use the input in
place.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Define the size macros to 0 rather than empty. That will lead to fewer
weird errors when we start implementing.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Remove padding parameters as mbedtls_rsa_init()
cannot return an error code when padding
parameters are invalid.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
