It may be possible that an implementation does not
fetch key material until a command like
this is called and such an error may occur if an
off-chip secure storage dependency may have been wiped.
Note that PSA_ERROR_NOT_PERMITTED is not included
because I can't think of a scenario where you have
a valid key handle but aren't allowed to read the
attributes
x0-x3 are skipped such that function parameters to not have to be moved.
MULADDC_INIT and MULADDC_STOP are mostly empty because it is more
efficient to keep everything in registers (and that should easily be
possible). I considered a MULADDC_HUIT implementation, but could not
think of something that would be more efficient than basically 8
consecutive MULADDC_CORE. You could combine the loads and stores, but
it's probably more efficient to interleave them with arithmetic,
depending on the specific microarchitecture. NEON allows to do a
64x64->128 bit multiplication (and optional accumulation) in one
instruction, but is not great at handling carries.
Avoid compiler errors when MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER
is set by using the application ID type.
[Error] psa_crypto_slot_management.c@175,9: used type 'psa_key_id_t' (aka 'psa_key_file_id_t') where arithmetic or pointer type is required
A macro useful for initializing psa_key_id_t, whether
MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER is set or not. Without this
macro, it is necessary to know if
MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER as with it the key ID is
non-scalar and needs to be initialized with {0, 0}, and 0 otherwise when
key ID is scalar.
Adjust the wording to permit multiple handles to a single key - closing
a handle does not necessarily release volatile memory associated with
the key, that only occurs when the last handle is closed.
- Describe the implementation defined behavior for opening multiple
keys, and provide a reference to the relevant section.
- Describe the use of INSUFFICENT_MEMORY error to indicate additional
implementation resource constaints.
- Clarify the distinction between DOES_NOT_EXIST and INVALID_HANDLE
error conditions.
Avoid an error with differing linkages being expressed for
psa_set_key_domain_parameters() between crypto_extra.h and
crypto_struct.h in C++ builds.
[Error] crypto_extra.h@456,14: conflicting declaration of 'psa_status_t psa_set_key_domain_parameters(psa_key_attributes_t*, psa_key_type_t, const uint8_t *, size_t)' with 'C' linkage
Document that a curve returned by mbedtls_ecp_curve_list() or
mbedtls_ecp_grp_id_list() may lack support for ECDH or ECDSA.
Add a corresponding changelog entry, under "API Changes" because we
have changed the behavior: formerly, these functions skipped ECDH-only
curves, although this was not documented.
* crypto/pr/212: (337 commits)
Make TODO comments consistent
Fix PSA tests
Fix psa_generate_random for >1024 bytes
Add tests to generate more random than MBEDTLS_CTR_DRBG_MAX_REQUEST
Fix double free in psa_generate_key when psa_generate_random fails
Fix copypasta in test data
Avoid a lowercase letter in a macro name
Correct some comments
Fix PSA init/deinit in mbedtls_xxx tests when using PSA
Make psa_calculate_key_bits return psa_key_bits_t
Adjust secure element code to the new ITS interface
More refactoring: consolidate attribute validation
Fix policy validity check on key creation.
Add test function for import with a bad policy
Test key creation with an invalid type (0 and nonzero)
Remove "allocated" flag from key slots
Take advantage of psa_core_key_attributes_t internally #2
Store the key size in the slot in memory
Take advantage of psa_core_key_attributes_t internally: key loading
Switch storage functions over to psa_core_key_attributes_t
...
Resolve conflicts by performing the following actions:
- Reject changes to ChangeLog, as Mbed Crypto doesn't have one
- Reject changes to tests/compat.sh, as Mbed Crypto doesn't have it
- Reject changes to programs/fuzz/onefile.c, as Mbed Crypto doesn't have
it
- Resolve minor whitespace differences in library/ecdsa.c by taking the
version from Mbed TLS upstream.
* origin/development:
Honor MBEDTLS_CONFIG_FILE in fuzz tests
Test that a shared library build produces a dynamically linked executable
Test that the shared library build with CMake works
Add a test of MBEDTLS_CONFIG_FILE
Exclude DTLS 1.2 only with older OpenSSL
Document the rationale for the armel build
Switch armel build to -Os
Add a build on ARMv5TE in ARM mode
Add changelog entry for ARM assembly fix
bn_mul.h: require at least ARMv6 to enable the ARM DSP code
Adapt ChangeLog
ECP restart: Don't calculate address of sub ctx if ctx is NULL
The methods to import and generate a key in a secure element drivers
were written for an earlier version of the application-side interface.
Now that there is a psa_key_attributes_t structure that combines all
key metadata including its lifetime (location), type, size, policy and
extra type-specific data (domain parameters), pass that to drivers
instead of separate arguments for each piece of metadata. This makes
the interface less cluttered.
Update parameter names and descriptions to follow general conventions.
Document the public-key output on key generation more precisely.
Explain that it is optional in a driver, and when a driver would
implement it. Declare that it is optional in the core, too (which
means that a crypto core might not support drivers for secure elements
that do need this feature).
Update the implementation and the tests accordingly.
Register an existing key in a secure element.
Minimal implementation that doesn't call any driver method and just
lets the application declare whatever it wants.
Pass the key creation method (import/generate/derive/copy) to the
driver methods to allocate or validate a slot number. This allows
drivers to enforce policies such as "this key slot can only be used
for keys generated inside the secure element".
Test the behavior of the getter/setter functions.
Test that psa_get_key_slot_number() reports a slot number for a key in
a secure element, and doesn't report a slot number for a key that is
not in a secure element.
Test that psa_get_key_slot_number() reports the correct slot number
for a key in a secure element.
Add a slot_number field to psa_key_attributes_t and getter/setter
functions. Since slot numbers can have the value 0, indicate the
presence of the field via a separate flag.
In psa_get_key_attributes(), report the slot number if the key is in a
secure element.
When creating a key, for now, applications cannot choose a slot
number. A subsequent commit will add this capability in the secure
element HAL.
Add infrastructure for internal, external and dual-use flags, with a
compile-time check (if static_assert is available) to ensure that the
same numerical value doesn't get declared for two different purposes
in crypto_struct.h (external or dual-use) and
psa_crypto_core.h (internal).
Commit 16b1bd8932 "bn_mul.h: add ARM DSP optimized MULADDC code"
added some ARM DSP instructions that was assumed to always be available
when __ARM_FEATURE_DSP is defined to 1. Unfortunately it appears that
the ARMv5TE architecture (GCC flag -march=armv5te) supports the DSP
instructions, but only in Thumb mode and not in ARM mode, despite
defining __ARM_FEATURE_DSP in both cases.
This patch fixes the build issue by requiring at least ARMv6 in addition
to the DSP feature.
Conflict resolution:
* `scripts/config.pl`:
Take the exclusion of `MBEDTLS_PSA_CRYPTO_SE_C` from the API branch.
Take the removal of `MBEDTLS_PSA_CRYPTO_STORAGE_ITS_C` (obsolete) from
the development branch.
* `tests/scripts/all.sh`:
Multiple instances of factoring a sequence of `config.pl` calls into
a mere `config.pl baremetal` in the development branch, and a change in
the composition of `baremetal` in the API branch. In each case, take the
version from development.
* `tests/suites/test_suite_psa_crypto_slot_management.function`:
A function became non-static in development and disappeared in the API
branch. Keep the version from the API branch. Functions need to be
non-static if they're defined but unused in some configurations,
which is not the case for any function in this file at the moment.
* `tests/suites/test_suite_psa_crypto.function`:
Consecutive changes in the two branches, reconciled.
Resolve conflicts by performing the following operations:
- Reject changes related to building a crypto submodule, since Mbed
Crypto is the crypto submodule.
- Reject X.509, NET, and SSL changes.
- Reject changes to README, as Mbed Crypto is a different project from
Mbed TLS, with a different README.
- Avoid adding mention of ssl-opt.sh in a comment near some modified
code in include/CMakeLists.txt (around where ENABLE_TESTING as added).
- Align config.pl in Mbed TLS with config.pl in Mbed Crypto where PSA
options are concerned, to make future merging easier. There is no
reason for the two to be different in this regard, now that Mbed TLS
always depends on Mbed Crypto. Remaining differences are only the
PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER option and the absence of X.509,
NET, and SSL related options in Mbed Crypto's config.pl.
- Align config.h in Mbed Crypto with Mbed TLS's copy, with a few notable
exceptions:
- Leave CMAC on by default.
- Leave storage on by default (including ITS emulation).
- Avoid documenting the PSA Crypto API as is in beta stage in
documentation for MBEDTLS_PSA_CRYPTO_C.
The only remaining differences are a lack of X.509, NET, and SSL
options in Mbed Crypto's config.h, as well as an additional
Mbed-Crypto-specific PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER option.
Documentation for the check params feature and related macros is also
updated to match Mbed TLS's description.
- Reject tests/data_files/Makefile changes to generate DER versions of
CRTs and keys, as none of those are used by Mbed Crypto tests.
- Add the "no PEM and no filesystem" test to all.sh, without ssl-opt.sh
run, as Mbed Crypto doesn't have ssl-opt.sh. Also remove use of PSA
Crypto storage and ITS emulation, since those depend on filesystem
support.
- Reject addition of test when no ciphersuites have MAC to all.sh, as
the option being tested, MBEDTLS_SSL_SOME_MODES_USE_MAC, is not
present in Mbed Crypto.
- Use baremetal config in all.sh, as Mbed Crypto's baremetal
configuration does exclude the net module (as it doesn't exist in Mbed
Crypto)
- Reject cmake_subproject_build changes, continuing to link only
libmbedcrypto.
- Reject changes to visualc and associated templates. Mbed Crypto
doesn't need additional logic to handle submodule-sourced headers.
- Avoid adding fuzzers from Mbed TLS. The only relevant fuzzers are the
privkey and pubkey fuzzers, but non-trivial work would be required to
integrate those into Mbed Crypto (more than is comfortable in a merge
commit).
- Reject addition of Docker wrappers for compat.sh and ssl-opt.sh, as
those are not present in Mbed Crypto.
- Remove calls to SSL-related scripts from basic-in-docker.sh
Fix test errors by performing the following:
- Avoid using a link that Doxygen can't seem to resolve in Mbed Crypto,
but can resolve in Mbed TLS. In documentation for
MBEDTLS_CHECK_PARAMS, don't attempt to link to MBEDTLS_PARAM_FAILED.
* origin/development: (339 commits)
Do not build fuzz on windows
No booleans and import config
Removing space before opening parenthesis
Style corrections
Syntax fix
Fixes warnings from MSVC
Add a linker flag to enable gcov in basic-build-test.sh
Update crypto submodule to a revision with the HAVEGE header changes
Test with MBEDTLS_ECP_RESTARTABLE
Allow TODO in code
Use the docstring in the command line help
Split _abi_compliance_command into smaller functions
Record the commits that were compared
Document how to build the typical argument for -s
Allow running /somewhere/else/path/to/abi_check.py
tests: Limit each log to 10 GiB
Warn if VLAs are used
Remove redundant compiler flag
Consistently spell -Wextra
Fix parsing issue when int parameter is in base 16
...
65528 bits is more than any reasonable key until we start supporting
post-quantum cryptography.
This limit is chosen to allow bit-sizes to be stored in 16 bits, with
65535 left to indicate an invalid value. It's a whole number of bytes,
which facilitates some calculations, in particular allowing a key of
exactly PSA_CRYPTO_MAX_STORAGE_SIZE to be created but not one bit
more.
As a resource usage limit, this is arguably too large, but that's out
of scope of the current commit.
Test that key import, generation and derivation reject overly large
sizes.
Move the "core attributes" to a substructure of psa_key_attribute_t.
The motivation is to be able to use the new structure
psa_core_key_attributes_t internally.
Add a parameter to the key import method of a secure element driver to
make it report the key size in bits. This is necessary (otherwise the
core has no idea what the bit-size is), and making import report it is
easier than adding a separate method (for other key creation methods,
this information is an input, not an output).
Secure element support is not yet usable in the real world. Only part
of the feature is implemented and the part that's implemented is not
sufficient for real-world uses. A lot of error handling is missing,
and there are no tests.
This commit should be reverted once the feature has stabilized.
In the generic message digest abstraction, instead of storing method
pointers in the per-algorithm data structure and using wrapper
functions as those methods, call the per-algorithm function directly.
This saves some code size (2336B -> 2043B for md with all algorithms
enabled on M0+ with gcc -Os). This should also make it easier to
optimize the case when a single algorithm is supported. In addition,
this is a very slight security improvement since it removes one
opportunity for a buffer overflow to directly turn into letting the
attacker overwrite a pointer to a function pointer.
This commit does not modify the documented API. However, it removes
the possibility for users to define their own hash implementations and
use them by building their own md_info.
Changing mbedtls_md_context to contain a md type identifier rather
than a pointer to an info structure would save a few more bytes and a
few more runtime memory accesses, but would be a major API break since
a lot of code uses `const mbedtls_md_info *` to keep track of which
hash is in use.
In configurations wanting an alternative ripemd160 implementation, We
were including the ordinary Mbed Crypto ripemd160.h instead of the
user-provided ripemd160_alt.h. Use the user-provided header instead.
To help the build system find the correct include files, paths starting
with "mbedtls/" or "psa/" must be used. Otherwise, you can run into
build failures like the following when building Mbed Crypto as a
submodule.
In file included from chachapoly.c:31:0:
../../include/mbedtls/chachapoly.h:43:10: fatal error: poly1305.h: No such file or directory
#include "poly1305.h"
^~~~~~~~~~~~
compilation terminated.
Includes for ALT implementations are not modified, as the alt headers
are provided by system integrators and not Mbed TLS or Mbed Crypto.
Most driver methods are not allowed to modify the persistent data, so
the driver context structure contains a const pointer to it. Pass a
non-const pointer to the persstent data to the driver methods that
need it: init, allocate, destroy.
Pass the driver context to all driver methods except the ones that
operate on an already-setup operation context.
Rename `p_context` arguments to `op_context` to avoid confusion
between contexts.
This slightly increases storage requirements, but works in more use
cases. In particular, it allows drivers to treat choose slot numbers
with a monotonic counter that is incremented each time a key is
created, without worrying about overflow in practice.
Instead of having one giant table containing all possible methods,
represent a driver's method table as a structure containing pointers
to substructures. This way a driver that doesn't implement a certain
class of operations can use NULL for this class as a whole instead of
storing NULL for each method.
* origin/pr/1622: (29 commits)
Do not build fuzz on windows
No booleans and import config
Removing space before opening parenthesis
Style corrections
Syntax fix
Fixes warnings from MSVC
Add a linker flag to enable gcov in basic-build-test.sh
checks MBEDTLS_PEM_PARSE_C
Restore programs/fuzz/Makefile after in-tree cmake
Move fuzz directory to programs
Documentation for corpus generation
Restore tests/fuzz/Makefile after in-tree cmake
Adding ifdefs to avoid warnings for unused globals
Adds LDFLAGS fsanitize=address
Ignore compiled object files and executables
Also clean the fuzz subdirectory
copyediting README.md
Protecting client/server fuzz targts with ifdefs
Makefile support 1
Fuzz README and direct compilation
...
* origin/pr/2632:
Adapt ChangeLog
Avoid use of large stack buffers in mbedtls_x509_write_crt_pem()
Improve documentation of mbedtls_pem_write_buffer()
Perform CRT writing in-place on the output buffer
Adapt x509write_crt.c to coding style
Secure element support has its own source file, and in addition
requires many hooks in other files. This is a nontrivial amount of
code, so make it optional (but default on).
Technically we could have reused the old one for the new API, but then
we had to set an extra field during setup. The new version works when
all the fields that haven't been set explicitely are zero-initialised.
This change affects the psa_key_derivation_s structure. With the buffer
removed from the union, it is empty if MBEDTLS_MD_C is not defined.
We can avoid undefined behaviour by adding a new dummy field that is
always present or make the whole union conditional on MBEDTLS_MD_C.
In this latter case the initialiser macro has to depend on MBEDTLS_MD_C
as well. Furthermore the first structure would be either
psa_hkdf_key_derivation_t or psa_tls12_prf_key_derivation_t both of
which are very deep and would make the initialisation macro difficult
to maintain, therefore we go with the first option.
We want to make the PRF context structure depend on this flag, but
crypto_extra.h is included after crypto_struct.h and having the
option at its original place would not affect crypto_struct.h.
Add the compile time option PSA_PRE_1_0_KEY_DERIVATION. If this is not
turned on, then the function `psa_key_derivation()` is removed.
Most of the tests regarding key derivation haven't been adapted to the
new API yet and some of them have only been adapted partially. When this
new option is turned off, the tests using the old API and test cases
using the old API of partially adapted tests are skipped.
The sole purpose of this option is to make the transition to the new API
smoother. Once the transition is complete it can and should be removed
along with the old API and its implementation.
From the implementation point of view does not make much difference to
constrain the input order.
We constrain it because, this way the code is easier to review, the data
flow easier to understand and the implementations in general are easier
to validate.
* origin/pr/2711:
programs: Make `make clean` clean all programs always
ssl_tls: Enable Suite B with subset of ECP curves
windows: Fix Release x64 configuration
platform: Include stdarg.h where needed
timing: Remove redundant include file
net_sockets: Fix typo in net_would_block()
* origin/pr/2697:
Update crypto submodule
Add all.sh component that exercises invalid_param checks
Remove mbedtls_param_failed from programs
Make it easier to define MBEDTLS_PARAM_FAILED as assert
Make test suites compatible with #include <assert.h>
Pass -m32 to the linker as well
Don't systematically rebuild programs
Update havege.h to the new version in the crypto module.
This is technically an API break, since the type mbedtls_havege_state
is exposed in a public header. However normal applications should not
be affected.
There is no ABI break on platforms where uint32_t and int are treated
identically, which is virtually all of them.
Fix#2598
The elements of the HAVEGE state are manipulated with bitwise
operations, with the expectations that the elements are 32-bit
unsigned integers (or larger). But they are declared as int, and so
the code has undefined behavior. Clang with Asan correctly points out
some shifts that reach the sign bit.
Since these are supposed to be 32-bit unsigned integers, declare them
as uint32_t.
This is technically an API break, since the type mbedtls_havege_state
is exposed in a public header. However normal applications should not
be affected.
* origin/pr/2260:
Update crypto submodule
Remove heading spaces in tests/data_files/Makefile
Re-generate library/certs.c from script
Add new line at the end of test-ca2.key.enc
Use strict syntax to annotate origin of test data in certs.c
Add run to all.sh exercising !MBEDTLS_PEM_PARSE_C + !MBEDTLS_FS_IO
Allow DHM self test to run without MBEDTLS_PEM_PARSE_C
ssl-opt.sh: Auto-skip tests that use files if MBEDTLS_FS_IO unset
Document origin of hardcoded certificates in library/certs.c
Adapt ChangeLog
Rename server1.der to server1.crt.der
Add DER encoded files to git tree
Add build instructions to generate DER versions of CRTs and keys
Document "none" value for ca_path/ca_file in ssl_client2/ssl_server2
ssl_server2: Skip CA setup if `ca_path` or `ca_file` argument "none"
ssl_client2: Skip CA setup if `ca_path` or `ca_file` argument "none"
Correct white spaces in ssl_server2 and ssl_client2
Adapt ssl_client2 to parse DER encoded test CRTs if PEM is disabled
Adapt ssl_server2 to parse DER encoded test CRTs if PEM is disabled
Introduce a new configuration option MBEDTLS_CHECK_PARAMS_ASSERT,
which is disabled by default. When this option is enabled,
MBEDTLS_PARAM_FAILED defaults to assert rather than to a call to
mbedtls_param_failed, and <assert.h> is included.
This fixes#2671 (no easy way to make MBEDTLS_PARAM_FAILED assert)
without breaking backward compatibility. With this change,
`config.pl full` runs tests with MBEDTLS_PARAM_FAILED set to assert,
so the tests will fail if a validation check fails, and programs don't
need to provide their own definition of mbedtls_param_failed().
Relative include paths should be avoided. The build system will
determine where to pull in includes from. Specifically, `#include
"../mbedtls/config.h"` shouldn't be used. Use `#include
"mbedtls/config.h` instead, so that the submodule-building makefiles can
change which directory to use to get mbedtls include files from.
Fixes#141
Remove the key creation functions from before the attribute-based API,
i.e. the key creation functions that worked by allocating a slot, then
setting metadata through the handle and finally creating key material.
All of them are copied from (former) CRT and key files in `tests/data_files`.
For files which have been regenerated since they've been copied to `certs.c`,
update the copy.
Add declarations for DER encoded test CRTs to certs.h
Add DER encoded versions of CRTs to certs.c
fix comment in certs.c
Don't use (signed) char for DER encoded certificates
Consistently use `const char *` for test CRTs regardless of encoding
Remove non-sensical and unused PW variable for DER encoded key
Provide test CRTs in PEM and DER fmt, + pick suitable per config
This commit modifies `certs.h` and `certs.c` to start following the
following pattern for the provided test certificates and files:
- Raw test data is named `NAME_ATTR1_ATTR2_..._ATTRn`
For example, there are
`TEST_CA_CRT_{RSA|EC}_{PEM|DER}_{SHA1|SHA256}`.
- Derived test data with fewer attributes, iteratively defined as one
of the raw test data instances which suits the current configuration.
For example,
`TEST_CA_CRT_RSA_PEM`
is one of `TEST_CA_CRT_RSA_PEM_SHA1` or `TEST_CA_CRT_RSA_PEM_SHA256`,
depending on whether SHA-1 and/or SHA-256 are defined in the current
config.
Add missing public declaration of test key password
Fix signedness and naming mismatches
Further improve structure of certs.h and certs.c
Fix definition of mbedtls_test_cas test CRTs depending on config
Remove semicolon after macro string constant in certs.c
This commit modifies mbedtls_ssl_get_peer_cid() to also allow passing
NULL pointers in the arguments for the peer's CID value and length, in
case this information is needed.
For example, some users might only be interested in whether the use of
the CID was negotiated, in which case both CID value and length pointers
can be set to NULL. Other users might only be interested in confirming
that the use of CID was negotiated and the peer chose the empty CID,
in which case the CID value pointer only would be set to NULL.
It doesn't make sense to pass a NULL pointer for the CID length but a
non-NULL pointer for the CID value, as the caller has no way of telling
the length of the returned CID - and this case is therefore forbidden.
This commit modifies the CID configuration API mbedtls_ssl_conf_cid_len()
to allow the configuration of the stack's behaviour when receiving an
encrypted DTLS record with unexpected CID.
Currently, the stack silently ignores DTLS frames with an unexpected CID.
However, in a system which performs CID-based demultiplexing before passing
datagrams to the Mbed TLS stack, unexpected CIDs are a sign of something not
working properly, and users might want to know about it.
This commit introduces an SSL error code MBEDTLS_ERR_SSL_UNEXPECTED_CID
which the stack can return in response to an unexpected CID. It will
conditionally be put to use in subsequent commits.
mbedtls_ssl_context contains pointers in_buf, in_hdr, in_len, ...
which point to various parts of the header of an incoming TLS or
DTLS record; similarly, there are pointers out_buf, ... for
outgoing records.
This commit adds fields in_cid and out_cid which point to where
the CID of incoming/outgoing records should reside, if present,
namely prior to where the record length resides.
Quoting https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-04:
The DTLSInnerPlaintext value is then encrypted and the CID added to
produce the final DTLSCiphertext.
struct {
ContentType special_type = tls12_cid; /* 25 */
ProtocolVersion version;
uint16 epoch;
uint48 sequence_number;
opaque cid[cid_length]; // New field
uint16 length;
opaque enc_content[DTLSCiphertext.length];
} DTLSCiphertext;
For outgoing records, out_cid is set in ssl_update_out_pointers()
based on the settings in the current outgoing transform.
For incoming records, ssl_update_in_pointers() sets in_cid as if no
CID was present, and it is the responsibility of ssl_parse_record_header()
to update the field (as well as in_len, in_msg and in_iv) when parsing
records that do contain a CID. This will be done in a subsequent commit.
Finally, the code around the invocations of ssl_decrypt_buf()
and ssl_encrypt_buf() is adapted to transfer the CID from the
input/output buffer to the CID field in the internal record
structure (which is what ssl_{encrypt/decrypt}_buf() uses).
Note that mbedtls_ssl_in_hdr_len() doesn't need change because
it infers the header length as in_iv - in_hdr, which will account
for the CID for records using such.
Using the Connection ID extension increases the maximum record expansion
because
- the real record content type is added to the plaintext
- the plaintext may be padded with an arbitrary number of
zero bytes, in order to prevent leakage of information
through package length analysis. Currently, we always
pad the plaintext in a minimal way so that its length
is a multiple of 16 Bytes.
This commit adapts the various parts of the library to account
for that additional source of record expansion.
Context:
The CID draft does not require that the length of CIDs used for incoming
records must not change in the course of a connection. Since the record
header does not contain a length field for the CID, this means that if
CIDs of varying lengths are used, the CID length must be inferred from
other aspects of the record header (such as the epoch) and/or by means
outside of the protocol, e.g. by coding its length in the CID itself.
Inferring the CID length from the record's epoch is theoretically possible
in DTLS 1.2, but it requires the information about the epoch to be present
even if the epoch is no longer used: That's because one should silently drop
records from old epochs, but not the entire datagrams to which they belong
(there might be entire flights in a single datagram, including a change of
epoch); however, in order to do so, one needs to parse the record's content
length, the position of which is only known once the CID length for the epoch
is known. In conclusion, it puts a significant burden on the implementation
to infer the CID length from the record epoch, which moreover mangles record
processing with the high-level logic of the protocol (determining which epochs
are in use in which flights, when they are changed, etc. -- this would normally
determine when we drop epochs).
Moreover, with DTLS 1.3, CIDs are no longer uniquely associated to epochs,
but every epoch may use a set of CIDs of varying lengths -- in that case,
it's even theoretically impossible to do record header parsing based on
the epoch configuration only.
We must therefore seek a way for standalone record header parsing, which
means that we must either (a) fix the CID lengths for incoming records,
or (b) allow the application-code to configure a callback to implement
an application-specific CID parsing which would somehow infer the length
of the CID from the CID itself.
Supporting multiple lengths for incoming CIDs significantly increases
complexity while, on the other hand, the restriction to a fixed CID length
for incoming CIDs (which the application controls - in contrast to the
lengths of the CIDs used when writing messages to the peer) doesn't
appear to severely limit the usefulness of the CID extension.
Therefore, the initial implementation of the CID feature will require
a fixed length for incoming CIDs, which is what this commit enforces,
in the following way:
In order to avoid a change of API in case support for variable lengths
CIDs shall be added at some point, we keep mbedtls_ssl_set_cid(), which
includes a CID length parameter, but add a new API mbedtls_ssl_conf_cid_len()
which applies to an SSL configuration, and which fixes the CID length that
any call to mbetls_ssl_set_cid() which applies to an SSL context that is bound
to the given SSL configuration must use.
While this creates a slight redundancy of parameters, it allows to
potentially add an API like mbedtls_ssl_conf_cid_len_cb() later which
could allow users to register a callback which dynamically infers the
length of a CID at record header parsing time, without changing the
rest of the API.
The function mbedtls_ssl_hdr_len() returns the length of the record
header (so far: always 13 Bytes for DTLS, and always 5 Bytes for TLS).
With the introduction of the CID extension, the lengths of record
headers depends on whether the records are incoming or outgoing,
and also on the current transform.
Preparing for this, this commit splits mbedtls_ssl_hdr_len() in two
-- so far unmodified -- functions mbedtls_ssl_in_hdr_len() and
mbedtls_ssl_out_hdr_len() and replaces the uses of mbedtls_ssl_hdr_len()
according to whether they are about incoming or outgoing records.
There is no need to change the signature of mbedtls_ssl_{in/out}_hdr_len()
in preparation for its dependency on the currently active transform,
since the SSL context is passed as an argument, and the currently
active transform is referenced from that.
