Implement SSL asynchronous private operation for the case of a
signature operation in a server.
This is a first implementation. It is functional, but the code is not
clean, with heavy reliance on goto.
The pk layer can infer the hash length from the hash type. Calculate
it explicitly here anyway because it's needed for debugging purposes,
and it's needed for the upcoming feature allowing the signature
operation to be offloaded to an external cryptographic processor, as
the offloading code will need to know what length hash to copy.
New compile-time option MBEDTLS_SSL_ASYNC_PRIVATE_C, enabling
callbacks to replace private key operations. These callbacks allow the
SSL stack to make an asynchronous call to an external cryptographic
module instead of calling the cryptography layer inside the library.
The call is asynchronous in that it may return the new status code
MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS, in which case the SSL stack returns
and can be later called where it left off.
This commit introduces the configuration option. Later commits will
implement the feature proper.
This function is declared in ssl_internal.h, so this is not a public
API change.
This is in preparation for mbedtls_ssl_handshake_free needing to call
methods from the config structure.
In SSL, don't use mbedtls_pk_ec or mbedtls_pk_rsa on a private
signature or decryption key (as opposed to a public key or a key used
for DH/ECDH). Extract the data (it's the same data) from the public
key object instead. This way the code works even if the private key is
opaque or if there is no private key object at all.
Specifically, with an EC key, when checking whether the curve in a
server key matches the handshake parameters, rely only on the offered
certificate and not on the metadata of the private key.
* public/pr/1380:
Update ChangeLog for #1380
Generate RSA keys according to FIPS 186-4
Generate primes according to FIPS 186-4
Avoid small private exponents during RSA key generation
Change mbedtls_zeroize() implementation to use memset() instead of a
custom implementation for performance reasons. Furthermore, we would
also like to prevent as much as we can compiler optimisations that
remove zeroization code.
The implementation of mbedtls_zeroize() now uses a volatile function
pointer to memset() as suggested by Colin Percival at:
http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
Add a new macro MBEDTLS_UTILS_ZEROIZE that allows users to configure
mbedtls_zeroize() to an alternative definition when defined. If the
macro is not defined, then mbed TLS will use the default definition of
the function.
This commit removes all the static occurrencies of the function
mbedtls_zeroize() in each of the individual .c modules. Instead the
function has been moved to utils.h that is included in each of the
modules.
The new header contains common information across various mbed TLS
modules and avoids code duplication. To start, utils.h currently only
contains the mbedtls_zeroize() function.
The specification requires that P and Q are not too close. The specification
also requires that you generate a P and stick with it, generating new Qs until
you have found a pair that works. In practice, it turns out that sometimes a
particular P results in it being very unlikely a Q can be found matching all
the constraints. So we keep the original behavior where a new P and Q are
generated every round.
The specification requires that numbers are the raw entropy (except for odd/
even) and at least 2^(nbits-0.5). If not, new random bits need to be used for
the next number. Similarly, if the number is not prime new random bits need to
be used.
Attacks against RSA exist for small D. [Wiener] established this for
D < N^0.25. [Boneh] suggests the bound should be N^0.5.
Multiple possible values of D might exist for the same set of E, P, Q. The
attack works when there exists any possible D that is small. To make sure that
the generated key is not susceptible to attack, we need to make sure we have
found the smallest possible D, and then check that D is big enough. The
Carmichael function λ of p*q is lcm(p-1, q-1), so we can apply Carmichael's
theorem to show that D = d mod λ(n) is the smallest.
[Wiener] Michael J. Wiener, "Cryptanalysis of Short RSA Secret Exponents"
[Boneh] Dan Boneh and Glenn Durfee, "Cryptanalysis of RSA with Private Key d Less than N^0.292"
Clang-Msan is known to report spurious errors when MBEDTLS_AESNI_C is
enabled, due to the use of assembly code. The error reports don't
mention AES, so they can be difficult to trace back to the use of
AES-NI. Warn about this potential problem at compile time.
Zeroing out an fd_set before calling FD_ZERO on it is in principle
useless, but without it some memory sanitizers think the fd_set is
still uninitialized after FD_ZERO (e.g. clang-msan/Glibc/x86_64 where
FD_ZERO is implemented in assembly). Make the zeroing conditional on
using a memory sanitizer.
The initialization via FD_SET is not seen by memory sanitizers if
FD_SET is implemented through assembly. Additionally zeroizing the
respective fd_set's before calling FD_SET contents the sanitizers
and comes at a negligible computational overhead.
In mbedtls_ssl_derive_keys, don't call mbedtls_md_hmac_starts in
ciphersuites that don't use HMAC. This doesn't change the behavior of
the code, but avoids relying on an uncaught error when attempting to
start an HMAC operation that hadn't been initialized.
Clarify what MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH and
MBEDTLS_ERR_PK_SIG_LEN_MISMATCH mean. Add comments to highlight that
this indicates that a valid signature is present, unlike other error
codes. See
https://github.com/ARMmbed/mbedtls/pull/1149#discussion_r178130705
Conflict resolution:
* ChangeLog
* tests/data_files/Makefile: concurrent additions, order irrelevant
* tests/data_files/test-ca.opensslconf: concurrent additions, order irrelevant
* tests/scripts/all.sh: one comment change conflicted with a code
addition. In addition some of the additions in the
iotssl-1381-x509-verify-refactor-restricted branch need support for
keep-going mode, this will be added in a subsequent commit.
The relevant ASN.1 definitions for a PKCS#8 encoded Elliptic Curve key are:
PrivateKeyInfo ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey,
attributes [0] IMPLICIT Attributes OPTIONAL
}
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL
}
ECParameters ::= CHOICE {
namedCurve OBJECT IDENTIFIER
-- implicitCurve NULL
-- specifiedCurve SpecifiedECDomain
}
ECPrivateKey ::= SEQUENCE {
version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
privateKey OCTET STRING,
parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
publicKey [1] BIT STRING OPTIONAL
}
Because of the two optional fields, there are 4 possible variants that need to
be parsed: no optional fields, only parameters, only public key, and both
optional fields. Previously mbedTLS was unable to parse keys with "only
parameters". Also, only "only public key" was tested. There was a test for "no
optional fields", but it was labelled incorrectly as SEC.1 and not run because
of a great renaming mixup.
check-names.sh reserves the prefix MBEDTLS_ for macros defined in
config.h so this name (or check-names.sh) had to change.
This is also more flexible because it allows for platforms that don't have
an EINTR equivalent or have multiple such values.
Also, introduce MBEDTLS_EINTR locally in net_sockets.c
for the platform-dependent return code macro used by
the `select` call to indicate that the poll was interrupted
by a signal handler: On Unix, the corresponding macro is EINTR,
while on Windows, it's WSAEINTR.
If the select UNIX system call is interrupted by a signal handler,
it is not automatically restarted but returns EINTR. This commit
modifies the use of select in mbedtls_net_poll from net_sockets.c
to retry the select call in this case.
Found by running:
CC=clang cmake -D CMAKE_BUILD_TYPE="Check"
tests/scripts/depend-pkalgs.pl
(Also tested with same command but CC=gcc)
Another PR will address improving all.sh and/or the depend-xxx.pl scripts
themselves to catch this kind of thing.
library\x509_crt.c(2137): warning C4267: 'function' : conversion from 'size_t' to 'int', possible loss of data
library\x509_crt.c(2265): warning C4267: 'function' : conversion from 'size_t' to 'int', possible loss of data
* development: (557 commits)
Add attribution for #1351 report
Adapt version_features.c
Note incompatibility of truncated HMAC extension in ChangeLog
Add LinkLibraryDependencies to VS2010 app template
Add ChangeLog entry for PR #1382
MD: Make deprecated functions not inline
Add ChangeLog entry for PR #1384
Have Visual Studio handle linking to mbedTLS.lib internally
Mention in ChangeLog that this fixes#1351
Add issue number to ChangeLog
Note in the changelog that this fixes an interoperability issue.
Style fix in ChangeLog
Add ChangeLog entries for PR #1168 and #1362
Add ChangeLog entry for PR #1165
ctr_drbg: Typo fix in the file description comment.
dhm: Fix typo in RFC 5114 constants
tests_suite_pkparse: new PKCS8-v2 keys with PRF != SHA1
data_files/pkcs8-v2: add keys generated with PRF != SHA1
tests/pkcs5/pbkdf2_hmac: extend array to accommodate longer results
tests/pkcs5/pbkdf2_hmac: add unit tests for additional SHA algorithms
...
Fix warnings from gcc -O -Wall about `ret` used uninitialized in
CMAC selftest auxiliary functions. The variable was indeed
uninitialized if the function was called with num_tests=0 (which
never happens).
Use specific instructions for moving bytes around in a word. This speeds
things up, and as a side-effect, slightly lowers code size.
ARIA_P3 and ARIA_P1 are now 1 single-cycle instruction each (those
instructions are available in all architecture versions starting from v6-M).
Note: ARIA_P3 was already translated to a single instruction by Clang 3.8 and
armclang 6.5, but not arm-gcc 5.4 nor armcc 5.06.
ARIA_P2 is already efficiently translated to the minimal number of
instruction (1 in ARM mode, 2 in thumb mode) by all tested compilers
Manually compiled and inspected generated code with the following compilers:
arm-gcc 5.4, clang 3.8, armcc 5.06 (with and without --gnu), armclang 6.5.
Size reduction (arm-none-eabi-gcc -march=armv6-m -mthumb -Os): 5288 -> 5044 B
Effect on executing time of self-tests on a few boards:
FRDM-K64F (Cortex-M4): 444 -> 385 us (-13%)
LPC1768 (Cortex-M3): 488 -> 432 us (-11%)
FRDM-KL64Z (Cortex-M0): 1429 -> 1134 us (-20%)
Measured using a config.h with no cipher mode and the following program with
aria.c and aria.h copy-pasted to the online compiler:
#include "mbed.h"
#include "aria.h"
int main() {
Timer t;
t.start();
int ret = mbedtls_aria_self_test(0);
t.stop();
printf("ret = %d; time = %d us\n", ret, t.read_us());
}
(A similar commit for Arm follows.)
Use specific instructions for moving bytes around in a word. This speeds
things up, and as a side-effect, slightly lowers code size.
ARIA_P3 (aka reverse byte order) is now 1 instruction on x86, which speeds up
key schedule. (Clang 3.8 finds this but GCC 5.4 doesn't.)
I couldn't find an Intel equivalent of ARM's ret16 (aka ARIA_P1), so I made it
two instructions, which is still much better than the code generated with
the previous mask-shift-or definition, and speeds up en/decryption. (Neither
Clang 3.8 nor GCC 5.4 find this.)
Before:
O aria.o ins
s 7976 43,865
2 10520 37,631
3 13040 28,146
After:
O aria.o ins
s 7768 33,497
2 9816 28,268
3 11432 20,829
For measurement method, see previous commit:
"aria: turn macro into static inline function"
This decreases the size with -Os by nearly 1k while
not hurting performance too much with -O2 and -O3
Before:
O aria.o ins
s 8784 41,408
2 11112 37,001
3 13096 27,438
After:
O aria.o ins
s 7976 43,865
2 10520 37,631
3 13040 28,146
(See previous commit for measurement details.)
Besides documenting types better and so on, this give the compiler more room
to optimise either for size or performance.
Here are some before/after measurements of:
- size of aria.o in bytes (less is better)
- instruction count for the selftest function (less is better)
with various -O flags.
Before:
O aria.o ins
s 10896 37,256
2 11176 37,199
3 12248 27,752
After:
O aria.o ins
s 8784 41,408
2 11112 37,001
3 13096 27,438
The new version allows the compiler to reach smaller size with -Os while
maintaining (actually slightly improving) performance with -O2 and -O3.
Measurements were done on x86_64 (but since this is mainly about inlining
code, this should transpose well to other platforms) using the following
helper program and script, after disabling CBC, CFB and CTR in config.h, in
order to focus on the core functions.
==> st.c <==
#include "mbedtls/aria.h"
int main( void ) {
return mbedtls_aria_self_test( 0 );
}
==> p.sh <==
#!/bin/sh
set -eu
ccount () {
(
valgrind --tool=callgrind --dump-line=no --callgrind-out-file=/dev/null --collect-atstart=no --toggle-collect=main $1
) 2>&1 | sed -n -e 's/.*refs: *\([0-9,]*\)/\1/p'
}
printf "O\taria.o\tins\n"
for O in s 2 3; do
GCC="gcc -Wall -Wextra -Werror -Iinclude"
$GCC -O$O -c library/aria.c
$GCC -O1 st.c aria.o -o st
./st
SIZE=$( du -b aria.o | cut -f1 )
INS=$( ccount ./st )
printf "$O\t$SIZE\t$INS\n"
done
We're not absolutely consistent in the rest of the library, but we tend to use
C99-style comments less often.
Change to use C89-style comments everywhere except for end-of-line comments
Those suites were defined in ciphersuite_definitions[] but not included in
ciphersuite_preference[] which meant they couldn't be negotiated unless
explicitly added by the user. Add them so that they're usable by default like
any other suite.
In 2.7.0, we replaced a number of MD functions with deprecated inline
versions. This causes ABI compatibility issues, as the functions are no
longer guaranteed to be callable when built into a shared library.
Instead, deprecate the functions without also inlining them, to help
maintain ABI backwards compatibility.
Add missing MBEDTLS_DEPRECATED_REMOVED guards around the definitions
of mbedtls_aes_decrypt and mbedtls_aes_encrypt.
This fixes the build under -Wmissing-prototypes -Werror.
Fixes#1388
Currently only SHA1 is supported as PRF algorithm for PBKDF2
(PKCS#5 v2.0).
This means that keys encrypted and authenticated using
another algorithm of the SHA family cannot be decrypted.
This deficiency has become particularly incumbent now that
PKIs created with OpenSSL1.1 are encrypting keys using
hmacSHA256 by default (OpenSSL1.0 used PKCS#5 v1.0 by default
and even if v2 was forced, it would still use hmacSHA1).
Enable support for all the digest algorithms of the SHA
family for PKCS#5 v2.0.
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
1. Style issues fixes - remove redundant spacing.
2. Remove depency of `MBEDTLS_RSA_C` in `pk_parse_public_keyfile_rsa()`
tests, as the function itself is dependent on it.
- Rephrase file/function/parameter/enum/define/error descriptions into full
and clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
- Add full standard name in file description.
GitHub PR: #1316
- Rephrase file/function/parameter/enum/define/error descriptions into full
and clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
- Rephrase the descriptions of all md_alg and hashlen parameters.
GitHub PR: #1327
- Rephrase file/function/parameter/enum/define/error descriptions into full
and clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
- Standardize defines documentation
GitHub PR: #1323
- Rephrase function/parameter/enum/define/error descriptions into full and
clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
GitHub PR: #1306
- Rephrase function/parameter/enum/define/error descriptions into full and
clear sentences.
- Make sure to adhering to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.
- Fix iv_len values per the standard.
GitHub PR: #1305
- Separate "\file" blocks from copyright, so that Doxygen doesn't repeat
the copyright information in all the Detailed Descriptions.
- Improve phrasing and clarity of functions, parameters, defines and enums.
GitHub PR: #1292
A new test for mbedtls_timing_alarm(0) was introduced in PR 1136, which also
fixed it on Unix. Apparently test results on MinGW were not checked at that
point, so we missed that this new test was also failing on this platform.
Add MBEDTLS_ERR_XXX_HW_ACCEL_FAILED error codes for all cryptography
modules where the software implementation can be replaced by a hardware
implementation.
This does not include the individual message digest modules since they
currently have no way to return error codes.
This does include the higher-level md, cipher and pk modules since
alternative implementations and even algorithms can be plugged in at
runtime.
This commit allows users to provide alternative implementations of the
ECJPAKE interface through the configuration option MBEDTLS_ECJPAKE_ALT.
When set, the user must add `ecjpake_alt.h` declaring the same
interface as `ecjpake.h`, as well as add some compilation unit which
implements the functionality. This is in line with the preexisting
support for alternative implementations of other modules.
The corner cases fixed include:
* Allocating a buffer of size 0. With this change, the allocator now
returns a NULL pointer in this case. Note that changes in pem.c and
x509_crl.c were required to fix tests that did not work under this
assumption.
* Initialising the allocator with less memory than required for headers.
* Fix header chain checks for uninitialised allocator.
The _ext suffix suggests "new arguments", but the new functions have
the same arguments. Use _ret instead, to convey that the difference is
that the new functions return a value.
Conflict resolution:
* ChangeLog: put the new entries in their rightful place.
* library/x509write_crt.c: the change in development was whitespace
only, so use the one from the iotssl-1251 feature branch.
This commit adds some explicit downcasts from `size_t` to `uint8_t` in
the RSASSA signature encoding function `rsa_rsassa_pkcs1_v15_encode`.
The truncation is safe as it has been checked beforehand that the
respective values are in the range of a `uint8_t`.
1) `mbedtls_rsa_import_raw` used an uninitialized return
value when it was called without any input parameters.
While not sensible, this is allowed and should be a
succeeding no-op.
2) The MPI test for prime generation missed a return value
check for a call to `mbedtls_mpi_shift_r`. This is neither
critical nor new but should be fixed.
3) Both the RSA keygeneration example program and the
RSA test suites contained code initializing an RSA context
after a potentially failing call to CTR DRBG initialization,
leaving the corresponding RSA context free call in the
cleanup section of the respective function orphaned.
While this defect existed before, Coverity picked up on
it again because of newly introduced MPI's that were
also wrongly initialized only after the call to CTR DRBG
init. The commit fixes both the old and the new issue
by moving the initializtion of both the RSA context and
all MPI's prior to the first potentially failing call.
The function `mbedtls_rsa_complete` is supposed to guarantee that
RSA operations will complete without failure. In contrast, it does
not ensure consistency of parameters, which is the task of the
checking functions `rsa_check_pubkey` and `rsa_check_privkey`.
Previously, the maximum allowed size of the RSA modulus was checked
in `mbedtls_rsa_check_pubkey`. However, exceeding this size would lead
to failure of some RSA operations, hence this check belongs to
`mbedtls_rsa_complete` rather than `mbedtls_rsa_check_pubkey`.
This commit moves it accordingly.
The function `pk_get_rsapubkey` originally performed some basic
sanity checks (e.g. on the size of public exponent) on the parsed
RSA public key by a call to `mbedtls_rsa_check_pubkey`.
This check was dropped because it is not possible to thoroughly
check full parameter sanity (i.e. that (-)^E is a bijection on Z/NZ).
Still, for the sake of not silently changing existing behavior,
this commit puts back the call to `mbedtls_rsa_check_pubkey`.
- Adapt the change in all.sh to the new keep-going mode
- Restore alphabetical order of configuration flags for
alternative implementations in config.h and rebuild
library/version_features.c
`mbedtls_rsa_deduce_primes` implicitly casts the result of a call to
`mbedtls_mpi_lsb` to a `uint16_t`. This is safe because of the size
of MPI's used in the library, but still may have compilers complain
about it. This commit makes the cast explicit.
Conflict resolution: additions in the same places as
upstream-public/pr/865, both adding into lexicographically sorted
lists, resolved by taking the additions in lexicographic order.
* development:
Timing self test: shorten redundant tests
Timing self test: increased duration
Timing self test: increased tolerance
Timing unit tests: more protection against infinite loops
Unit test for mbedtls_timing_hardclock
New timing unit tests
selftest: allow excluding a subset of the tests
selftest: allow running a subset of the tests
selftest: refactor to separate the list of tests from the logic
Timing self test: print some diagnosis information
mbedtls_timing_get_timer: don't use uninitialized memory
timing interface documentation: minor clarifications
Timing: fix mbedtls_set_alarm(0) on Unix/POSIX
* public/pr/1136:
Timing self test: shorten redundant tests
Timing self test: increased duration
Timing self test: increased tolerance
Timing unit tests: more protection against infinite loops
Unit test for mbedtls_timing_hardclock
New timing unit tests
selftest: allow excluding a subset of the tests
selftest: allow running a subset of the tests
selftest: refactor to separate the list of tests from the logic
Timing self test: print some diagnosis information
mbedtls_timing_get_timer: don't use uninitialized memory
timing interface documentation: minor clarifications
Timing: fix mbedtls_set_alarm(0) on Unix/POSIX
1. Surround the generate keys with
`#if ! defined(MBEDTLS_CMAC_ALT) || defined(MBEDTLS_SELF_TEST)`
to resolve build issue when `MBEDTLS_SELF_TEST` is defined for
alternative CMAC as well
2. Update ChangeLog
Increase the duration of the self test, otherwise it tends to fail on
a busy machine even with the recently upped tolerance. But run the
loop only once, it's enough for a simple smoke test.
mbedtls_timing_self_test fails annoyingly often when running on a busy
machine such as can be expected of a continous integration system.
Increase the tolerances in the delay test, to reduce the chance of
failures that are only due to missing a deadline on a busy machine.
Print some not-very-nice-looking but helpful diagnosis information if
the timing selftest fails. Since the failures tend to be due to heavy
system load that's hard to reproduce, this information is necessary to
understand what's going on.
mbedtls_timing_get_timer with reset=1 is called both to initialize a
timer object and to reset an already-initialized object. In an
initial call, the content of the data structure is indeterminate, so
the code should not read from it. This could crash if signed overflows
trap, for example.
As a consequence, on reset, we can't return the previously elapsed
time as was previously done on Windows. Return 0 as was done on Unix.
The POSIX/Unix implementation of mbedtls_set_alarm did not set the
mbedtls_timing_alarmed flag when called with 0, which was inconsistent
with what the documentation implied and with the Windows behavior.
* restricted/pr/403:
Correct record header size in case of TLS
Don't allocate space for DTLS header if DTLS is disabled
Improve debugging output
Adapt ChangeLog
Add run-time check for handshake message size in ssl_write_record
Add run-time check for record content size in ssl_encrypt_buf
Add compile-time checks for size of record content and payload
* development:
Don't split error code description across multiple lines
Register new error code in error.h
Move deprecation to separate section in ChangeLog
Extend scope of ERR_RSA_UNSUPPORTED_OPERATION error code
Adapt RSA test suite
Adapt ChangeLog
Deprecate usage of RSA primitives with wrong key type
* restricted/pr/397:
Don't split error code description across multiple lines
Register new error code in error.h
Move deprecation to separate section in ChangeLog
Extend scope of ERR_RSA_UNSUPPORTED_OPERATION error code
Adapt RSA test suite
Adapt ChangeLog
Deprecate usage of RSA primitives with wrong key type
In a previous PR (Fix heap corruption in implementation of truncated HMAC
extension #425) the place where MAC is computed was changed from the end of
the SSL I/O buffer to a local buffer (then (part of) the content of the local
buffer is either copied to the output buffer of compare to the input buffer).
Unfortunately, this change was made only for TLS 1.0 and later, leaving SSL
3.0 in an inconsistent state due to ssl_mac() still writing to the old,
hard-coded location, which, for MAC verification, resulted in later comparing
the end of the input buffer (containing the computed MAC) to the local buffer
(uninitialised), most likely resulting in MAC verification failure, hence no
interop (even with ourselves).
This commit completes the move to using a local buffer by using this strategy
for SSL 3.0 too. Fortunately ssl_mac() was static so it's not a problem to
change its signature.
Fix missing definition of mbedtls_zeroize when MBEDTLS_FS_IO is
disabled in the configuration.
Introduced by e7707228b4
Merge remote-tracking branch 'upstream-public/pr/1062' into development
In case truncated HMAC must be used but the Mbed TLS peer hasn't been updated
yet, one can use the compile-time option MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT to
temporarily fall back to the old, non-compliant implementation of the truncated
HMAC extension.
The truncated HMAC extension as described in
https://tools.ietf.org/html/rfc6066.html#section-7 specifies that when truncated
HMAC is used, only the HMAC output should be truncated, while the HMAC key
generation stays unmodified. This commit fixes Mbed TLS's behavior of also
truncating the key, potentially leading to compatibility issues with peers
running other stacks than Mbed TLS.
Details:
The keys for the MAC are pieces of the keyblock that's generated from the
master secret in `mbedtls_ssl_derive_keys` through the PRF, their size being
specified as the size of the digest used for the MAC, regardless of whether
truncated HMAC is enabled or not.
/----- MD size ------\ /------- MD size ----\
Keyblock +----------------------+----------------------+------------------+---
now | MAC enc key | MAC dec key | Enc key | ...
(correct) +----------------------+----------------------+------------------+---
In the previous code, when truncated HMAC was enabled, the HMAC keys
were truncated to 10 bytes:
/-10 bytes-\ /-10 bytes-\
Keyblock +-------------+-------------+------------------+---
previously | MAC enc key | MAC dec key | Enc key | ...
(wrong) +-------------+-------------+------------------+---
The reason for this was that a single variable `transform->maclen` was used for
both the keysize and the size of the final MAC, and its value was reduced from
the MD size to 10 bytes in case truncated HMAC was negotiated.
This commit fixes this by introducing a temporary variable `mac_key_len` which
permanently holds the MD size irrespective of the presence of truncated HMAC,
and using this temporary to obtain the MAC key chunks from the keyblock.
Previously, MAC validation for an incoming record proceeded as follows:
1) Make a copy of the MAC contained in the record;
2) Compute the expected MAC in place, overwriting the presented one;
3) Compare both.
This resulted in a record buffer overflow if truncated MAC was used, as in this
case the record buffer only reserved 10 bytes for the MAC, but the MAC
computation routine in 2) always wrote a full digest.
For specially crafted records, this could be used to perform a controlled write of
up to 6 bytes past the boundary of the heap buffer holding the record, thereby
corrupting the heap structures and potentially leading to a crash or remote code
execution.
This commit fixes this by making the following change:
1) Compute the expected MAC in a temporary buffer that has the size of the
underlying message digest.
2) Compare to this to the MAC contained in the record, potentially
restricting to the first 10 bytes if truncated HMAC is used.
A similar fix is applied to the encryption routine `ssl_encrypt_buf`.
* development: (30 commits)
update README file (#1144)
Fix typo in asn1.h
Improve leap year test names in x509parse.data
Correctly handle leap year in x509_date_is_valid()
Renegotiation: Add tests for SigAlg ext parsing
Parse Signature Algorithm ext when renegotiating
Minor style fix
config.pl get: be better behaved
config.pl get: don't rewrite config.h; detect write errors
Fixed "config.pl get" for options with no value
Fix typo and bracketing in macro args
Ensure failed test_suite output is sent to stdout
Remove use of GNU sed features from ssl-opt.sh
Fix typos in ssl-opt.sh comments
Add ssl-opt.sh test to check gmt_unix_time is good
Extend ssl-opt.h so that run_test takes function
Always print gmt_unix_time in TLS client
Restored note about using minimum functionality in makefiles
Note in README that GNU make is required
Fix changelog for ssl_server2.c usage fix
...
Fix the x509_get_subject_alt_name() function to not accept invalid
tags. The problem was that the ASN.1 class for tags consists of two
bits. Simply doing bit-wise and of the CONTEXT_SPECIFIC macro with the
input tag has the potential of accepting tag values 0x10 (private)
which would indicate that the certificate has an incorrect format.
This commit fixes a comparison of ssl_session->encrypt_then_mac against the
ETM-unrelated constant MBEDTLS_SSL_EXTENDED_MS_DISABLED. Instead,
MBEDTLS_SSL_ETM_DISABLED should be used.
The typo is has no functional effect since both constants have the same value 0.
Remove a check introduced in the previous buffer overflow fix with keys of
size 8N+1 which the subsequent fix for buffer start calculations made
redundant.
Added a changelog entry for the buffer start calculation fix.
For a key of size 8N+1, check that the first byte after applying the
public key operation is 0 (it could have been 1 instead). The code was
incorrectly doing a no-op check instead, which led to invalid
signatures being accepted. Not a security flaw, since you would need the
private key to craft such an invalid signature, but a bug nonetheless.
The check introduced by the previous security fix was off by one. It
fixed the buffer overflow but was not compliant with the definition of
PSS which technically led to accepting some invalid signatures (but
not signatures made without the private key).
I don't think this can cause a crash as the member accessed is in the
beginning of the context, so wouldn't be outside of valid memory if the actual
context was RSA.
Also, the mismatch will be caught later when checking signature, so the cert
chain will be rejected anyway.
Fix buffer overflow in RSA-PSS signature verification when the hash is
too large for the key size. Found by Seth Terashima, Qualcomm.
Added a non-regression test and a positive test with the smallest
permitted key size for a SHA-512 hash.
The function mbedtls_ecp_gen_keypair_base did not wipe the stack buffer used to
hold the private exponent before returning. This commit fixes this by not using
a stack buffer in the first place but instead calling mpi_fill_random directly
to acquire the necessary random MPI.
