In case of AEAD ciphers, the cipher mode (and not even the entire content
of mbedtls_cipher_info_t) doesn't uniquely determine a psa_algorithm_t
because it doesn't specify the AEAD tag length, which however is included
in psa_algorithm_t identifiers.
This commit adds a tag length value to mbedtls_psa_translate_cipher_mode()
to account for that ambiguity.
This commit adds the header file mbedtls/psa_util.h which contains
static utility functions `mbedtls_psa_xxx()` used in the integration
of PSA Crypto into Mbed TLS.
Warning: These functions are internal only and may change at any time.
Deprecate the module-specific XXX_HW_ACCEL_FAILED and
XXX_FEATURE_UNAVAILABLE errors, as alternative implementations should now
return `MBEDTLS_ERR_PLATFORM_HW_FAILED` and
`MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED`.
Context:
The macro `MBEDTLS_ECP_BUDGET()` is called before performing a
number of potentially time-consuming ECC operations. If restartable
ECC is enabled, it wraps a call to `mbedtls_ecp_check_budget()`
which in turn checks if the requested number of operations can be
performed without exceeding the maximum number of consecutive ECC
operations.
Issue:
The function `mbedtls_ecp_check_budget()` expects a the number
of requested operations to be given as a value of type `unsigned`,
while some calls of the wrapper macro `MBEDTLS_ECP_BUDGET()` use
expressions of type `size_t`.
This rightfully leads to warnings about implicit truncation
from `size_t` to `unsigned` on some compilers.
Fix:
This commit makes the truncation explicit by adding an explicit cast
to `unsigned` in the expansion of the `MBEDTLS_ECP_BUDGET()` macro.
Justification:
Functionally, the new version is equivalent to the previous code.
The warning about truncation can be discarded because, as can be
inferred from `ecp.h`, the number of requested operations is never
larger than 1000.
Rename the PLATFORM HW error, to avoid ABI breakage with Mbed OS.
The value changed as well, as previous value was not in the range of
Mbed TLS low level error codes.
The previous comment in ecp.h that only functions that take a "restart
context" argument can restart was wrong due to ECDH and SSL functions.
Changing that criterion to "document says if can return IN PROGRESS".
This requires updating the documentation of the SSL functions to mention this
explicitly, but it's something we really ought to do anyway, a bit
embarrassing that this wasn't done already - callers need to know what
`MBEDTLS_ERR_SSL_xxx` error codes to special-case. Note that the documentation
of the relevant functions was in a suboptimal state, so it was improved in the
process - it could use some more improvement, but only the changes that helped
cleanly insert the info about the IN_PROGRESS part were done here.
Also, while updating the ecp.h comment, I noticed several functions in the
ECDH module were wrongfully documented as restartable, which is probably a
left-over from the days before `mbedtls_ecdh_enable_restart()` was introduced.
Fixing that as well, to make the criterion used in ecp.h correct.
When using a primality testing function the tolerable error rate depends
on the scheme in question, the required security strength and wether it
is used for key generation or parameter validation. To support all use
cases we need more flexibility than what the old API provides.
The FIPS 186-4 RSA key generation prescribes lower failure probability
in primality testing and this makes key generation slower. We enable the
caller to decide between compliance/security and performance.
This python script calculates the base two logarithm of the formulas in
HAC Fact 4.48 and was used to determine the breakpoints and number of
rounds:
def mrpkt_log_2(k, t):
if t <= k/9.0:
return 3*math.log(k,2)/2+t-math.log(t,2)/2+4-2*math.sqrt(t*k)
elif t <= k/4.0:
c1 = math.log(7.0*k/20,2)-5*t
c2 = math.log(1/7.0,2)+15*math.log(k,2)/4.0-k/2.0-2*t
c3 = math.log(12*k,2)-k/4.0-3*t
return max(c1, c2, c3)
else:
return math.log(1/7.0)+15*math.log(k,2)/4.0-k/2.0-2*t
The Cortex M4, M7 MCUs and the Cortex A CPUs support the ARM DSP
instructions, and especially the umaal instruction which greatly
speed up MULADDC code. In addition the patch switched the ASM
constraints to registers instead of memory, giving the opportunity
for the compiler to load them the best way.
The speed improvement is variable depending on the crypto operation
and the CPU. Here are the results on a Cortex M4, a Cortex M7 and a
Cortex A8. All tests have been done with GCC 6.3 using -O2. RSA uses a
RSA-4096 key. ECDSA uses a secp256r1 curve EC key pair.
+--------+--------+--------+
| M4 | M7 | A8 |
+----------------+--------+--------+--------+
| ECDSA signing | +6.3% | +7.9% | +4.1% |
+----------------+--------+--------+--------+
| RSA signing | +43.7% | +68.3% | +26.3% |
+----------------+--------+--------+--------+
| RSA encryption | +3.4% | +9.7% | +3.6% |
+----------------+--------+--------+--------+
| RSA decryption | +43.0% | +67.8% | +22.8% |
+----------------+--------+--------+--------+
I ran the whole testsuite on the Cortex A8 Linux environment, and it
all passes.
It should be valid to RSASSA-PSS sign a SHA-512 hash with a 1024-bit or
1032-bit RSA key, but with the salt size being always equal to the hash
size, this isn't possible: the key is too small.
To enable use of hashes that are relatively large compared to the key
size, allow reducing the salt size to no less than the hash size minus 2
bytes. We don't allow salt sizes smaller than the hash size minus 2
bytes because that too significantly changes the security guarantees the
library provides compared to the previous implementation which always
used a salt size equal to the hash size. The new calculated salt size
remains compliant with FIPS 186-4.
We also need to update the "hash too large" test, since we now reduce
the salt size when certain key sizes are used. We used to not support
1024-bit keys with SHA-512, but now we support this by reducing the salt
size to 62. Update the "hash too large" test to use a 1016-bit RSA key
with SHA-512, which still has too large of a hash because we will not
reduce the salt size further than 2 bytes shorter than the hash size.
The RSA private key used for the test was generated using "openssl
genrsa 1016" using OpenSSL 1.1.1-pre8.
$ openssl genrsa 1016
Generating RSA private key, 1016 bit long modulus (2 primes)
..............++++++
....++++++
e is 65537 (0x010001)
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
