We were already rejecting them at the end, due to the fact that with the
usual (x, z) formulas they lead to the result (0, 0) so when we want to
normalize at the end, trying to compute the modular inverse of z will
give an error.
If we wanted to support those points, we'd a special case in
ecp_normalize_mxz(). But it's actually permitted by all sources
(RFC 7748 say we MAY reject 0 as a result) and recommended by some to
reject those points (either to ensure contributory behaviour, or to
protect against timing attack when the underlying field arithmetic is
not constant-time).
Since our field arithmetic is indeed not constant-time, let's reject
those points before they get mixed with sensitive data (in
ecp_mul_mxz()), in order to avoid exploitable leaks caused by the
special cases they would trigger. (See the "May the Fourth" paper
https://eprint.iacr.org/2017/806.pdf)
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
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>
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>
Write a simple unit test for mbedtls_ecp_muladd().
Add just one pair of test cases. #2 fails since PR #3512. Thanks to
Philippe Antoine (catenacyber) for the test case, found by ecfuzzer.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
They did not match their description, probably due to a botched manual
endianness conversion where the nibbles also got swapped.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
mbedtls_ecp_write_key is a mirror function to mbedtls_ecp_read_key, which
writes a private key back into a byte buffer in the correct format.
This is a helpful convenience function, since the byte order is defined
differently between Montgomery and Weierstrass curves. Since this difference
is accounted for in mbedtls_ecp_read_key, it made sense to add
mbedtls_ecp_write_key for the purpose of abstracting this away such that
psa_export_key doesn't need to take byte order into account.
Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
Make check-test-cases.py pass.
Prior to this commit, there were many repeated test descriptions, but
none with the same test data and dependencies and comments, as checked
with the following command:
for x in tests/suites/*.data; do perl -00 -ne 'warn "$ARGV: $. = $seen{$_}\n" if $seen{$_}; $seen{$_}=$.' $x; done
Wherever a test suite contains multiple test cases with the exact same
description, add " [#1]", " [#2]", etc. to make the descriptions
unique. We don't currently use this particular arrangement of
punctuation, so all occurrences of " [#" were added by this script.
I used the following ad hoc code:
import sys
def fix_test_suite(data_file_name):
in_paragraph = False
total = {}
index = {}
lines = None
with open(data_file_name) as data_file:
lines = list(data_file.readlines())
for line in lines:
if line == '\n':
in_paragraph = False
continue
if line.startswith('#'):
continue
if not in_paragraph:
# This is a test case description line.
total[line] = total.get(line, 0) + 1
index[line] = 0
in_paragraph = True
with open(data_file_name, 'w') as data_file:
for line in lines:
if line in total and total[line] > 1:
index[line] += 1
line = '%s [#%d]\n' % (line[:-1], index[line])
data_file.write(line)
for data_file_name in sys.argv[1:]:
fix_test_suite(data_file_name)
If we provide low order element as a public key and the implementation
maps the point in infinity to the origin, we can force the common secret
to be zero.
According to the standard (RFC 7748) this is allowed but in this case
the primitive must not be used in a protocol that requires contributory
behaviour.
Mbed Crypto returns an error when the result is the point in the
infinity and does not map it to the origin. This is safe even if used in
protocols that require contributory behaviour.
This commit adds test cases that verify that Mbed Crypto returns an
error when low order public keys are processed.
The low order elements in the test cases were taken from this website:
https://cr.yp.to/ecdh.html
The tests we had for ECP point multiplication were tailored for test
vectors symulating crypto operations and tested a series of operations
against public test vectors.
This commit adds a test function that exercises a single multiplication.
This is much better suited for negative testing than the preexisting
test.
Only one new test case is added that exercises a fraction of an existing
test, just to make sure that the test is consistent with the existing
test functions.
mbedtls_ecp_read_key() module returned without an error even when
importing keys corresponding to the requested group was not
implemented.
We change this and return an error when the requested group is not
supported and make the remaining import/export functions more robust.
Renamed the tests because they are explicitly testing Curve25519 and
nothing else. Improved test coverage, test documentation and extended
in-code documentation with a specific reference to the standard as well.
The library is able to perform computations and cryptographic schemes on
curves with x coordinate ladder representation. Here we add the
capability to export such points.
The private keys used in ECDH differ in the case of Weierstrass and
Montgomery curves. They have different constraints, the former is based
on big endian, the latter little endian byte order. The fundamental
approach is different too:
- Weierstrass keys have to be in the right interval, otherwise they are
rejected.
- Any byte array of the right size is a valid Montgomery key and it
needs to be masked before interpreting it as a number.
Historically it was sufficient to use mbedtls_mpi_read_binary() to read
private keys, but as a preparation to improve support for Montgomery
curves we add mbedtls_ecp_read_key() to enable uniform treatment of EC
keys.
For the masking the `mbedtls_mpi_set_bit()` function is used. This is
suboptimal but seems to provide the best trade-off at this time.
Alternatives considered:
- Making a copy of the input buffer (less efficient)
- removing the `const` constraint from the input buffer (breaks the api
and makes it less user friendly)
- applying the mask directly to the limbs (violates the api between the
modules and creates and unwanted dependency)
The library is able to perform computations and cryptographic schemes on
curves with x coordinate ladder representation. Here we add the
capability to import such points.
* development-restricted: (578 commits)
Update library version number to 2.13.1
Don't define _POSIX_C_SOURCE in header file
Don't declare and define gmtime()-mutex on Windows platforms
Correct preprocessor guards determining use of gmtime()
Correct documentation of mbedtls_platform_gmtime_r()
Correct typo in documentation of mbedtls_platform_gmtime_r()
Correct POSIX version check to determine presence of gmtime_r()
Improve documentation of mbedtls_platform_gmtime_r()
platform_utils.{c/h} -> platform_util.{c/h}
Don't include platform_time.h if !MBEDTLS_HAVE_TIME
Improve wording of documentation of MBEDTLS_PLATFORM_GMTIME_R_ALT
Fix typo in documentation of MBEDTLS_PLATFORM_GMTIME_R_ALT
Replace 'thread safe' by 'thread-safe' in the documentation
Improve documentation of MBEDTLS_HAVE_TIME_DATE
ChangeLog: Add missing renamings gmtime -> gmtime_r
Improve documentation of MBEDTLS_HAVE_TIME_DATE
Minor documentation improvements
Style: Add missing period in documentation in threading.h
Rename mbedtls_platform_gmtime() to mbedtls_platform_gmtime_r()
Guard decl and use of gmtime mutex by HAVE_TIME_DATE and !GMTIME_ALT
...
- Separate string and hex parameter as unhexify is moved out of the function. It's input should only be hex.
- Fix test mbedtls_ccm_encrypt_and_tag that grows input message buffer with tag
- Add missing expected length parameter in ECP TLS tests
- Add deleted TEST_ASSERT and mbedtls calls that got removed in script based code generation
Summary of merge conflicts:
include/mbedtls/ecdh.h -> documentation style
include/mbedtls/ecdsa.h -> documentation style
include/mbedtls/ecp.h -> alt style, new error codes, documentation style
include/mbedtls/error.h -> new error codes
library/error.c -> new error codes (generated anyway)
library/ecp.c:
- code of an extracted function was changed
library/ssl_cli.c:
- code addition on one side near code change on the other side
(ciphersuite validation)
library/x509_crt.c -> various things
- top fo file: helper structure added near old zeroize removed
- documentation of find_parent_in()'s signature: improved on one side,
added arguments on the other side
- documentation of find_parent()'s signature: same as above
- verify_chain(): variables initialised later to give compiler an
opportunity to warn us if not initialised on a code path
- find_parent(): funcion structure completely changed, for some reason git
tried to insert a paragraph of the old structure...
- merge_flags_with_cb(): data structure changed, one line was fixed with a
cast to keep MSVC happy, this cast is already in the new version
- in verify_restratable(): adjacent independent changes (function
signature on one line, variable type on the next)
programs/ssl/ssl_client2.c:
- testing for IN_PROGRESS return code near idle() (event-driven):
don't wait for data in the the socket if ECP_IN_PROGRESS
tests/data_files/Makefile: adjacent independent additions
tests/suites/test_suite_ecdsa.data: adjacent independent additions
tests/suites/test_suite_x509parse.data: adjacent independent additions
* development: (1059 commits)
Change symlink to hardlink to avoid permission issues
Fix out-of-tree testing symlinks on Windows
Updated version number to 2.10.0 for release
Add a disabled CMAC define in the no-entropy configuration
Adapt the ARIA test cases for new ECB function
Fix file permissions for ssl.h
Add ChangeLog entry for PR#1651
Fix MicroBlaze register typo.
Fix typo in doc and copy missing warning
Fix edit mistake in cipher_wrap.c
Update CTR doc for the 64-bit block cipher
Update CTR doc for other 128-bit block ciphers
Slightly tune ARIA CTR documentation
Remove double declaration of mbedtls_ssl_list_ciphersuites
Update CTR documentation
Use zeroize function from new platform_util
Move to new header style for ALT implementations
Add ifdef for selftest in header file
Fix typo in comments
Use more appropriate type for local variable
...
This curve has special arithmetic on 64 bit platforms and an untested
path lead to trying to free a buffer on the stack.
For the sake of completeness, a test case for a point with non-affine
coordinates has been added as well.
