It's going to be convenient for each function that can generate a
MBEDTLS_ERR_ECP_IN_PROGRESS on its own (as opposed to just passing it around)
to have its own restart context that they can allocate and free as needed
independently of the restart context of other functions.
For example ecp_muladd() is going to have its own restart_muladd context that
in can managed, then when it calls ecp_mul() this will manage a restart_mul
context without interfering with the caller's context.
So, things need to be renames to avoid future name clashes.
From a user's perspective, you want a "basic operation" to take approximately
the same amount of time regardless of the curve size, especially since max_ops
is a global setting: otherwise if you pick a limit suitable for P-384 then
when you do an operation on P-256 it will return way more often than needed.
Said otherwise, a user is actually interested in actual running time, and we
do the API in terms of "basic ops" for practical reasons (no timers) but then
we should make sure it's a good proxy for running time.
Ok, so the original plan was to make mpi_inv_mod() the smallest block that
could not be divided. Updated plan is that the smallest block will be either:
- ecp_normalize_jac_many() (one mpi_inv_mod() + a number or mpi_mul_mpi()s)
- or the second loop in ecp_precompute_comb()
With default settings, the minimum non-restartable sequence is:
- for P-256: 222M
- for P-384: 341M
This is within a 2-3x factor of originally planned value of 120M. However,
that value can be approached, at the cost of some performance, by setting
ECP_WINDOW_SIZE (w below) lower than the default of 6. For example:
- w=4 -> 166M for any curve (perf. impact < 10%)
- w=2 -> 130M for any curve (perf. impact ~ 30%)
My opinion is that the current state with w=4 is a good compromise, and the
code complexity need to attain 120M is not warranted by the 1.4 factor between
that and the current minimum with w=4 (which is close to optimal perf).
We'll need to store MPIs and other things that allocate memory in this
context, so we need a place to free it. We can't rely on doing it before
returning from ecp_mul() as we might return MBEDTLS_ERR_ECP_IN_PROGRESS (thus
preserving the context) and never be called again (for example, TLS handshake
aborted for another reason). So, ecp_group_free() looks like a good place to
do this, if the restart context is part of struct ecp_group.
This means it's not possible to use the same ecp_group structure in different
threads concurrently, but:
- that's already the case (and documented) for other reasons
- this feature is precisely intended for environments that lack threading
An alternative option would be for the caller to have to allocate/free the
restart context and pass it explicitly, but this means creating new functions
that take a context argument, and putting a burden on the user.
The plan is to count basic operations as follows:
- call to ecp_add_mixed() -> 11
- call to ecp_double_jac() -> 8
- call to mpi_mul_mpi() -> 1
- call to mpi_inv_mod() -> 120
- everything else -> not counted
The counts for ecp_add_mixed() and ecp_double_jac() are based on the actual
number of calls to mpi_mul_mpi() they they make.
The count for mpi_inv_mod() is based on timing measurements on K64F and
LPC1768 boards, and are consistent with the usual very rough estimate of one
inversion = 100 multiplications. It could be useful to repeat that measurement
on a Cortex-M0 board as those have smaller divider and multipliers, so the
result could be a bit different but should be the same order of magnitude.
The documented limitation of 120 basic ops is due to the calls to mpi_inv_mod()
which are currently not interruptible nor planned to be so far.
The fact that self-signed end-entity certs can be explicitly trusted by
putting them in the CA list even if they don't have the CA bit was not
documented though it's intentional, and tested by "Certificate verification #73
(selfsigned trusted without CA bit)" in test_suite_x509parse.data
It is unclear to me whether the restriction that explicitly trusted end-entity
certs must be self-signed is a good one. However, it seems intentional as it is
tested in tests #42 and #43, so I'm not touching it for now.
Allow forcing 64-bit integer type for bignum operations. Also introduce
the macro MBEDTLS_TYPE_UDBL to allow configuration of the double length
integer in unknown compilers.
Rename the macro MBEDTLS_PLATFORM_SETUP_ALT to
MBEDTLS_PLATFORM_SETUP_TEARDOWN_ALT to make the name more descriptive
as this macro enables/disables both functions.
Add the following two functions to allow platform setup and teardown
operations for the full library to be hooked in:
* mbedtls_platform_setup()
* mbedtls_platform_teardown()
An mbedtls_platform_context C structure is also added and two internal
functions that are called by the corresponding setup and teardown
functions above:
* mbedtls_internal_platform_setup()
* mbedtls_internal_plartform_teardown()
Finally, the macro MBEDTLS_PLATFORM_SETUP_ALT is also added to allow
mbedtls_platform_context and internal function to be overriden by the
user as needed for a platform.
The functions mbedtls_aes_decrypt and mbedtls_aes_encrypt have been
superseded by mbedtls_aes_internal_decrypt and
mbedtls_aes_internal_encrypt, respectively. Alternative
implementations should now only replace the latter, and leave the
maintenance wrapper definitions of the former untouched.
This commit clarifies this in the documentation of the respective
configuration options MBEDTLS_AES_DECRYPT_ALT and
MBEDTLS_AES_ENCRYPT_ALT.
Protecting the ECP hardware acceleratior with mutexes is inconsistent with the
philosophy of the library. Pre-existing hardware accelerator interfaces
leave concurrency support to the underlying platform.
Fixes#863
Document the preconditions on the input and output buffers for
the PKCS1 decryption functions
- mbedtls_rsa_pkcs1_decrypt,
- mbedtls_rsa_rsaes_pkcs1_v15_decrypt
- mbedtls_rsa_rsaes_oaep_decrypt
* restricted/iotssl-1398:
Add ChangeLog entry
Ensure application data records are not kept when fully processed
Add hard assertion to mbedtls_ssl_read_record_layer
Fix mbedtls_ssl_read
Simplify retaining of messages for future processing
There are situations in which it is not clear what message to expect
next. For example, the message following the ServerHello might be
either a Certificate, a ServerKeyExchange or a CertificateRequest. We
deal with this situation in the following way: Initially, the message
processing function for one of the allowed message types is called,
which fetches and decodes a new message. If that message is not the
expected one, the function returns successfully (instead of throwing
an error as usual for unexpected messages), and the handshake
continues to the processing function for the next possible message. To
not have this function fetch a new message, a flag in the SSL context
structure is used to indicate that the last message was retained for
further processing, and if that's set, the following processing
function will not fetch a new record.
This commit simplifies the usage of this message-retaining parameter
by doing the check within the record-fetching routine instead of the
specific message-processing routines. The code gets cleaner this way
and allows retaining messages to be used in other situations as well
without much effort. This will be used in the next commits.
By default, keep allowing SHA-1 in key exchange signatures. Disabling
it causes compatibility issues, especially with clients that use
TLS1.2 but don't send the signature_algorithms extension.
SHA-1 is forbidden in certificates by default, since it's vulnerable
to offline collision-based attacks.
There is now one test case to validate that SHA-1 is rejected in
certificates by default, and one test case to validate that SHA-1 is
supported if MBEDTLS_TLS_DEFAULT_ALLOW_SHA1 is #defined.
Default to forbidding the use of SHA-1 in TLS where it is unsafe: for
certificate signing, and as the signature hash algorithm for the TLS
1.2 handshake signature. SHA-1 remains allowed in HMAC-SHA-1 in the
XXX_SHA ciphersuites and in the PRF for TLS <= 1.1.
For easy backward compatibility for use in controlled environments,
turn on the MBEDTLS_TLS_DEFAULT_ALLOW_SHA1 compiled-time option.
* hanno/sig_hash_compatibility:
Improve documentation
Split long lines
Remember suitable hash function for any signature algorithm.
Introduce macros and functions to characterize certain ciphersuites.
This patch modifies the following 2 functions in the AES module to
change the return type from void to int:
* mbedtls_aes_encrypt() -> mbedtls_internal_aes_encrypt()
* mbedtls_aes_decrypt() -> mbedtls_internal_aes_decrypt()
This change is necessary to allow users of MBEDTLS_AES_ALT,
MBEDTLS_AES_DECRYPT_ALT and MBEDTLS_AES_ENCRYPT_ALT to return an error
code when replacing the default with their own implementation, e.g.
a hardware crypto accelerator.
According to RFC5246 the server can indicate the known Certificate
Authorities or can constrain the aurhorisation space by sending a
certificate list. This part of the message is optional and if omitted,
the client may send any certificate in the response.
The previous behaviour of mbed TLS was to always send the name of all the
CAs that are configured as root CAs. In certain cases this might cause
usability and privacy issues for example:
- If the list of the CA names is longer than the peers input buffer then
the handshake will fail
- If the configured CAs belong to third parties, this message gives away
information on the relations to these third parties
Therefore we introduce an option to suppress the CA list in the
Certificate Request message.
Providing this feature as a runtime option comes with a little cost in
code size and advantages in maintenance and flexibility.
This commit changes `ssl_parse_signature_algorithms_ext` to remember
one suitable ( := supported by client and by our config ) hash
algorithm per signature algorithm.
It also modifies the ciphersuite checking function
`ssl_ciphersuite_match` to refuse a suite if there
is no suitable hash algorithm.
Finally, it adds the corresponding entry to the ChangeLog.
