Since mbedtls_mpi_random() is not specific to ECC code, move it from
the ECP module to the bignum module.
This increases the code size in builds without short Weierstrass
curves (including builds without ECC at all) that do not optimize out
unused functions.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Rename mbedtls_ecp_gen_privkey_sw to mbedtls_mpi_random since it has
no particular connection to elliptic curves beyond the fact that its
operation is defined by the deterministic ECDSA specification. This is
a generic function that generates a random MPI between 1 inclusive and
N exclusive.
Slightly generalize the function to accept a different lower bound,
which adds a negligible amount of complexity.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Add unit tests for private key generation on short Weierstrass curves.
These tests validate that the result is within the desired range.
Additionally, they validate that after performing many iterations, the
range is covered to an acceptable extent: for tiny ranges, all values
must be reached; for larger ranges, all value bits must reach both 0
and 1.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
mbedtls_ecp_gen_privkey_mx generates a random number with a certain
top bit set. Depending on the size, it would either generate a number
with that top bit being random, then forcibly set the top bit to
1 (when high_bit is not a multiple of 8); or generate a number with
that top bit being 0, then set the top bit to 1 (when high_bit is a
multiple of 8). Change it to always generate the top bit randomly
first.
This doesn't make any difference in practice: the probability
distribution is the same either way, and no supported or plausible
curve has a size of the form 8n+1 anyway. But it slightly simplifies
reasoning about the behavior of this function.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Don't calculate the bit-size of the initially generated random number.
This is not necessary to reach the desired distribution of private
keys, and creates a (tiny) side channel opportunity.
This changes the way the result is derived from the random number, but
does not affect the resulting distribution.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
The library rejected an RNG input of all-bits-zero, which led to the
key 2^{254} (for Curve25519) having a 31/32 chance of being generated
compared to other keys. This had no practical impact because the
probability of non-compliance was 2^{-256}, but needlessly
complicated the code.
The exception was added in 98e28a74e3 to
avoid the case where b - 1 wraps because b is 0. Instead, change the
comparison code to avoid calculating b - 1.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Test the exact output from known RNG input. This is overly
constraining, but ensures that the code has good properties.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
If a fallback is not explicitly configured in the
mbedtls_test_rnd_buf_info structure, fail after the buffer is
exhausted.
There is no intended behavior change in this commit: all existing uses
of mbedtls_test_rnd_buffer_rand() have been updated to set
mbedtls_test_rnd_std_rand as the fallback.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
For Montgomery keys, n_bits is actually the position of the highest
bit and not the number of bits, which would be 1 more (fence vs
posts). Rename the variable accordingly to lessen the confusion.
No semantic change.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Put the Montgomery and short Weierstrass implementations of
mbedtls_ecp_gen_privkey into their own function which can be tested
independently, but will not be part of the public ABI/API.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Prepare to isolate the Montgomery and short Weierstrass
implementations of mbedtls_ecp_gen_privkey into their own function.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Make input/output format documentation easier to find:
- Add direct reference to the steps from the input/output functions
- Move the format description directly to the step constants
Signed-off-by: Janos Follath <janos.follath@arm.com>
- Transformed setup description to a more explicit pseudocode based
approach.
- Explained implicit vs explicit key confirmation
Signed-off-by: Janos Follath <janos.follath@arm.com>
This step is not necessarily a memory-hard function. Memory-hard
functions are the best of the breed at the moment, but that's due to
current hardware designs, and CPU-hard-but-not-memory-hard functions
like PBKDF2 are acceptable as well. We're using “key stretching” as the
generic term for such functions.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The key derivation operation passed to psa_pake_set_password_mhf() might
enter an error state before the function returns. If this happens, the
user needs to know about it so that they can properly abort it.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The type of the key derivation operation was incorrect.
Also neither the PAKE nor key_derivation algorithm knows how many bytes
to transfer at this stage.
There is no optimal or recommended size, PAKEs don't mandate it either
(with the exception of OPAQUE, but that uses it internally and won't be
using this interface).
Adding an input length parameter to allow the application to control how
many bytes the PAKE takes from the key derivation.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Using memory hard functions with PAKEs is the more secure option. It
should be as convenient and efficient to use as less secure options, but
so far it required creating an additional temporary key object.
With psa_pake_set_password_mhf() this eliminates the need for this.
Similarly we could add a convenience function to supply the password
directly from character strings, but that would make the less secure
option more convenient again and therfore we are not doing it now.
Signed-off-by: Janos Follath <janos.follath@arm.com>
PAKE constructions that have multiple key shares will always consume and
produce the key shares in numerical order. So using PSA_PAKE_DATA_XXX_X
would demand step-sequence validation, and provides no functional
utility over having only PSA_PAKE_DATA_XXX.
Signed-off-by: Janos Follath <janos.follath@arm.com>
If PSA_PAKE_OUTPUT_SIZE takes cipher_suite as a parameter and it is a
structure it can't be a compile-time constant anymore.
Reintroducing psa_pake_primitive_t, because it can be constructed as an
integral type and holds enough information to allow PSA_PAKE_OUTPUT_SIZE
calculating accurate estimates on the output size in compile time.
Signed-off-by: Janos Follath <janos.follath@arm.com>
There are too many parameters to the setup function. This makes it hard
to figure out how to call the function and read code that calls the
function. This also opens the suspicion that there's yet another
parameter that we're missing.
Signed-off-by: Janos Follath <janos.follath@arm.com>
"Data" is too vague, renaming it to psa_pake_step_t. It is still
somewhat vague, but at least consistent with the naming used in key
derivation.
Signed-off-by: Janos Follath <janos.follath@arm.com>
__DOXYGEN_ONLY__ blocks were only used to typeset the PSA specification
back when it was extracted from Mbed TLS headers. They are no longer
used and should be removed.
The PSA Crypto Driver API is still under development and might be
extracted from Mbed TLS headers, leaving them there for now.
Signed-off-by: Janos Follath <janos.follath@arm.com>
It is the size of something that has no a priori reason to consist of 8
bits. This should be psa_pake_family_t, both for documentation (and
possibly static analysis) and in case 8 bits turn out not to be enough.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Identifier value was not consistent with PSA conventions (last byte is
reserved for hash algorithms or used in algorithms parametrized by
a hash).
Signed-off-by: Janos Follath <janos.follath@arm.com>
The cipher suite now defines the algorithm itself as well. Passing the
algorithm separately is redundant and error prone.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Making the cipher suite struct internal made a number of types and
macros in the interface unused.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Hiding the structure of the cipher suite implementation allows for
greater flexibility.
To preserve maximum flexibility, the constructor is replaced by
individual setter/getter functions.
Convenience macros and or functions can be added later.
Signed-off-by: Janos Follath <janos.follath@arm.com>
In the key types API, PSA Crypto uses ECC to denote Elliptic curve
cryptography and DH to denote Finite Field Diffie-Hellman.
Change PSA_PAKE_PRIMITIVE_TYPE_XXX macros to be aligned.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The macro PSA_PAKE_KEY_SHARE_SIZE has been removed, we need to remove
references to it from the documentation as well.
Signed-off-by: Janos Follath <janos.follath@arm.com>
There were remnants of the PSA specification wording in the
documentation that can be confusing in Mbed TLS.
We need to make it clear what the consequences of being implementation
defined are in Mbed TLS.
Signed-off-by: Janos Follath <janos.follath@arm.com>
