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>
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>
