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.
This commit adds a static array `cid` to the internal structure
`mbedtls_record` representing encrypted and decrypted TLS records.
The expected evolution of state of this field is as follows:
- When handling an incoming record, the caller of `mbedtls_decrypt_buf()`
has to make sure the CID array field in `mbedtls_record` has been
properly set. Concretely, it will be copied from the CID from the record
header during record parsing.
- During decryption in `mbedtls_decrypt_buf()`, the transforms
incoming CID is compared to the CID in the `mbedtls_record`
structure representing the record to be decrypted.
- For an outgoing TLS record, the caller of `mbedtls_encrypt_buf()`
clears the CID in the `mbedtls_record` structure.
- During encryption in `mbedtls_encrypt_buf()`, the CID field in
`mbedtls_record` will be copied from the out-CID in the transform.
These will be copied from the CID fields in mbedtls_ssl_handshake_params
(outgoing CID) and mbedtls_ssl_context (incoming CID) when the transformation
is set up at the end of the handshake.
* mbedtls_ssl_context gets fields indicating whether the CID extension
should be negotiated in the next handshake, and, if yes, which CID
the user wishes the peer to use.
This information does not belong to mbedtls_ssl_handshake_params
because (a) it is configured prior to the handshake, and (b) it
applies to all subsequent handshakes.
* mbedtls_ssl_handshake_params gets fields indicating the state of CID
negotiation during the handshake. Specifically, it indicates if the
use of the CID extension has been negotiated, and if so, which CID
the peer wishes us to use for outgoing messages.
We called in tinycrypt in the file names, but uecc in config.h, all.sh and
other places, which could be confusing. Just use tinycrypt everywhere because
that's the name of the project and repo where we took the files.
The changes were made using the following commands (with GNU sed and zsh):
sed -i 's/uecc/tinycrypt/g' **/*.[ch] tests/scripts/all.sh
sed -i 's/MBEDTLS_USE_UECC/MBEDTLS_USE_TINYCRYPT/g' **/*.[ch] tests/scripts/all.sh scripts/config.pl
This commit adds tests exercising mutually inverse pairs of
record encryption and decryption transformations for the various
transformation types allowed in TLS: Stream, CBC, and AEAD.
The hash contexts `ssl_transform->md_ctx_{enc/dec}` are not used if
only AEAD ciphersuites are enabled. This commit removes them from the
`ssl_transform` struct in this case, saving a few bytes.
Analogous to the previous commit, but concerning the record decryption
routine `ssl_decrypt_buf`.
An important change regards the checking of CBC padding:
Prior to this commit, the CBC padding check always read 256 bytes at
the end of the internal record buffer, almost always going past the
boundaries of the record under consideration. In order to stay within
the bounds of the given record, this commit changes this behavior by
always reading the last min(256, plaintext_len) bytes of the record
plaintext buffer and taking into consideration the last `padlen` of
these for the padding check. With this change, the memory access
pattern and runtime of the padding check is entirely determined by
the size of the encrypted record, in particular not giving away
any information on the validity of the padding.
The following depicts the different behaviors:
1) Previous CBC padding check
1.a) Claimed padding length <= plaintext length
+----------------------------------------+----+
| Record plaintext buffer | | PL |
+----------------------------------------+----+
\__ PL __/
+------------------------------------...
| read for padding check ...
+------------------------------------...
|
contents discarded
from here
1.b) Claimed padding length > plaintext length
+----------------------------------------+----+
| Record plaintext buffer | PL |
+----------------------------------------+----+
+-------------------------...
| read for padding check ...
+-------------------------...
|
contents discarded
from here
2) New CBC padding check
+----------------------------------------+----+
| Record plaintext buffer | | PL |
+----------------------------------------+----+
\__ PL __/
+---------------------------------------+
| read for padding check |
+---------------------------------------+
|
contents discarded
until here
The previous version of the record encryption function
`ssl_encrypt_buf` takes the entire SSL context as an argument,
while intuitively, it should only depend on the current security
parameters and the record buffer.
Analyzing the exact dependencies, it turned out that in addition
to the currently active `ssl_transform` instance and the record
information, the encryption function needs access to
- the negotiated protocol version, and
- the status of the encrypt-then-MAC extension.
This commit moves these two fields into `ssl_transform` and
changes the signature of `ssl_encrypt_buf` to only use an instance
of `ssl_transform` and an instance of the new `ssl_record` type.
The `ssl_context` instance is *solely* kept for the debugging macros
which need an SSL context instance.
The benefit of the change is twofold:
1) It avoids the need of the MPS to deal with instances of
`ssl_context`. The MPS should only work with records and
opaque security parameters, which is what the change in
this commit makes progress towards.
2) It significantly eases testing of the encryption function:
independent of any SSL context, the encryption function can
be passed some record buffer to encrypt alongside some arbitrary
choice of parameters, and e.g. be checked to not overflow the
provided memory.
This commit adds a structure `mbedtls_record` whose instances
represent (D)TLS records. This structure will be used in the
subsequent adaptions of the record encryption and decryption
routines `ssl_decrypt_buf` and `ssl_encrypt_buf`, which currently
take the entire SSL context as input, but should only use the
record to be acted on as well as the record transformation to use.
The macro constant `MBEDTLS_SSL_MAC_ADD` defined in `ssl_internal.h`
defines an upper bound for the amount of space needed for the record
authentication tag. Its definition distinguishes between the
presence of an ARC4 or CBC ciphersuite suite, in which case the maximum
size of an enabled SHA digest is used; otherwise, `MBEDTLS_SSL_MAC_ADD`
is set to 16 to accomodate AEAD authentication tags.
This assignment has a flaw in the situation where confidentiality is
not needed and the NULL cipher is in use. In this case, the
authentication tag also uses a SHA digest, but the definition of
`MBEDTLS_SSL_MAC_ADD` doesn't guarantee enough space.
The present commit fixes this by distinguishing between the presence
of *some* ciphersuite using a MAC, including those using a NULL cipher.
For that, the previously internal macro `SSL_SOME_MODES_USE_MAC` from
`ssl_tls.c` is renamed and moved to the public macro
`MBEDTLS_SOME_MODES_USE_MAC` defined in `ssl_internal.h`.
Prior to this commit, the security parameter struct `ssl_transform`
contained a `ciphersuite_info` field pointing to the information
structure for the negotiated ciphersuite. However, the only
information extracted from that structure that was used in the core
encryption and decryption functions `ssl_encrypt_buf`/`ssl_decrypt_buf`
was the authentication tag length in case of an AEAD cipher.
The present commit removes the `ciphersuite_info` field from the
`ssl_transform` structure and adds an explicit `taglen` field
for AEAD authentication tag length.
This is in accordance with the principle that the `ssl_transform`
structure should contain the raw parameters needed for the record
encryption and decryption functions to work, but not the higher-level
information that gave rise to them. For example, the `ssl_transform`
structure implicitly contains the encryption/decryption keys within
their cipher contexts, but it doesn't contain the SSL master or
premaster secrets. Likewise, it contains an explicit `maclen`, while
the status of the 'Truncated HMAC' extension -- which determines the
value of `maclen` when the `ssl_transform` structure is created in
`ssl_derive_keys` -- is not contained in `ssl_transform`.
The `ciphersuite_info` pointer was used in other places outside
the encryption/decryption functions during the handshake, and for
these functions to work, this commit adds a `ciphersuite_info` pointer
field to the handshake-local `ssl_handshake_params` structure.
The `ssl_transform` security parameter structure contains opaque
cipher contexts for use by the record encryption/decryption functions
`ssl_decrypt_buf`/`ssl_encrypt_buf`, while the underlying key material
is configured once in `ssl_derive_keys` and is not explicitly dealt with
anymore afterwards. In particular, the key length is not needed
explicitly by the encryption/decryption functions but is nonetheless
stored in an explicit yet superfluous `keylen` field in `ssl_transform`.
This commit removes this field.
This commit improves hygiene and formatting of macro definitions
throughout the library. Specifically:
- It adds brackets around parameters to avoid unintended
interpretation of arguments, e.g. due to operator precedence.
- It adds uses of the `do { ... } while( 0 )` idiom for macros that
can be used as commands.
* restricted/pr/553:
Fix mbedtls_ecdh_get_params with new ECDH context
Add changelog entry for mbedtls_ecdh_get_params robustness
Fix ecdh_get_params with mismatching group
Add test case for ecdh_get_params with mismatching group
Add test case for ecdh_calc_secret
Fix typo in documentation
* restricted/pr/550:
Update query_config.c
Fix failure in SSLv3 per-version suites test
Adjust DES exclude lists in test scripts
Clarify 3DES changes in ChangeLog
Fix documentation for 3DES removal
Exclude 3DES tests in test scripts
Fix wording of ChangeLog and 3DES_REMOVE docs
Reduce priority of 3DES ciphersuites
As there are some definitions that are defined regardless of
whether MBEDTLS_ECP_RESTARTABLE is defined or not, these definitions
need to be moved outside the MBEDTLS_ECP_ALT guards. This is a simple
move as MBEDTLS_ECP_ALT and MBEDTLS_ECP_RESTARTABLE are mutually
exclusive options.
Document when a context must be initialized or not, when it must be
set up or not, and whether it needs a private key or a public key will
do.
The implementation is sometimes more liberal than the documentation,
accepting a non-set-up context as a context that can't perform the
requested information. This preserves backward compatibility.
For mbedtls_pk_parse_key and mbedtls_pk_parse_keyfile, the password is
optional. Clarify what this means: NULL is ok and means no password.
Validate parameters and test accordingly.
A 0-length buffer for the key is a legitimate edge case. Ensure that
it works, even with buf=NULL. Document the key and keylen parameters.
There are already test cases for parsing an empty buffer. A subsequent
commit will add tests for writing to an empty buffer.
The previous introduction of constant deprecation macros
in platform_util.h lead to failure of tests/scrips/check-names.sh
because the regular expressions in the latter choked on the brackets
in the part `__attribute__((deprecated))` of the definition of the
helper type `mbedtls_deprecated_{numeric|string}_constant_t`.
Postponing any further study and potential robustness improvements
in check-names.sh to another time, this commit circumvents this
problem by temporarily abbreviating `__attribute__((deprecated))`
as `MBEDTLS_DEPRECATED`, which doesn't lead to problems with
check-names.sh.
This commit introduces macros
* MBEDTLS_DEPRECATED_STRING_CONSTANT
* MBEDTLS_DEPRECATED_NUMERIC_CONSTANT
to platform_util.h which can be used to deprecate public macro constants.
Their definition is essentially taken from dhm.h where the
MBEDTLS_DEPRECATED_STRING_CONSTANT was used to deprecate
insecure hardcoded DHM primes.
Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves#1371
- Be specific about the constraints: be a readable/writable buffer of length
X, be an initialized context, be a context initialized and bound to a key...
- Always use full sentences with all the required pronouns.
It's better if the macro receives the condition as an expression rather than a
string - that way it can choose to use it as is or stringify it. Also, the
documentation states that the parameter is an expression, not a string.
The test framework for validation of parameters depends on the macro
MBEDTLS_PARAM_FAILED() being set to its default value when building the
library. So far the test framework attempted to define this macro but this was
the wrong place - this definition wouldn't be picked by the library.
Instead, a different approach is taken: skip those tests when the macro is
defined in config.h, as in that case we have no way to know if it will indeed
end up calling mbedtls_param_failed() as we need it to.
This commit was tested by manually ensuring that aes_invalid_params:
- passes (and is not skipped) in the default configuration
- is skipped when MBEDTLS_PARAM_FAILED() is defined in config.h
The previous prototype gave warnings are the strings produced by #cond and
__FILE__ are const, so we shouldn't implicitly cast them to non-const.
While at it modifying most example programs:
- include the header that has the function declaration, so that the definition
can be checked to match by the compiler
- fix whitespace
- make it work even if PLATFORM_C is not defined:
- CHECK_PARAMS is not documented as depending on PLATFORM_C and there is
no reason why it should
- so, remove the corresponding #if defined in each program...
- and add missing #defines for mbedtls_exit when needed
The result has been tested (make all test with -Werror) with the following
configurations:
- full with CHECK_PARAMS with PLATFORM_C
- full with CHECK_PARAMS without PLATFORM_C
- full without CHECK_PARAMS without PLATFORM_C
- full without CHECK_PARAMS with PLATFORM_C
Additionally, it has been manually tested that adding
mbedtls_aes_init( NULL );
near the normal call to mbedtls_aes_init() in programs/aes/aescrypt2.c has the
expected effect when running the program.
It was inconsistent between files: sometimes 3 arguments, sometimes one.
Align to 1 argument for the macro and 3 for the function, because:
- we don't need 3 arguments for the macro, it can add __FILE__ and __LINE__
in its expansion, while the function needs them as parameters to be correct;
- people who re-defined the macro should have flexibility, and 3 arguments
can give the impression they they don't have as much as they actually do;
- the design document has the macro with 1 argument, so let's stick to that.
The function called through the macro MBEDTLS_PARAM_FAILED() must be supplied by
users and makes no sense as a library function, apart from debug and test.
The SSL module accesses ECDH context members directly to print debug
information. This can't work with the new context, where we can't make
assumptions about the implementation of the context. This commit adds
new debug functions to complete the encapsulation of the ECDH context
and work around the problem.
We want to support alternative software implementations and we extend
the ECDH context to enable this. The actual functional change that makes
use of the new context is out of scope for this commit.
Changing the context breaks the API and therefore it has to be
excluded from the default configuration by a compile time flag.
We add the compile time flag to the module header instead of
`config.h`, because this is not a standalone feature, it only
enables adding new implementations in the future.
The new context features a union of the individual implementations
and a selector that chooses the implementation in use. An alternative
is to use an opaque context and function pointers, like for example the
PK module does it, but it is more dangerous, error prone and tedious to
implement.
We leave the group ID and the point format at the top level of the
structure, because they are very simple and adding an abstraction
layer around them away does not come with any obvious benefit.
Other alternatives considered:
- Using the module level replacement mechanism in the ECP module. This
would have made the use of the replacement feature more difficult and
the benefit limited.
- Replacing our Montgomery implementations with a new one directly. This
would have prevented using Montgomery curves across implementations.
(For example use implementation A for Curve448 and implementation B for
Curve22519.) Also it would have been inflexible and limited to
Montgomery curves.
- Encoding the implementation selector and the alternative context in
`mbedtls_ecp_point` somehow and rewriting `mbedtls_ecp_mul()` to
dispatch between implementations. This would have been a dangerous and
ugly hack, and very likely to break legacy applications.
- Same as above just with hardcoding the selector and using a compile
time option to make the selection. Rejected for the same reasons as
above.
- Using the PK module to provide to provide an entry point for
alternative implementations. Like most of the above options this
wouldn't have come with a new compile time option, but conceptually
would have been very out of place and would have meant much more work to
complete the abstraction around the context.
In retrospect:
- We could have used the group ID as the selector, but this would have
made the code less flexible and only marginally simpler. On the other
hand it would have allowed to get rid of the compile time option if a
tight integration of the alternative is possible. (It does not seem
possible at this point.)
- We could have used the same approach we do in this commit to the
`mbedtls_ecp_point` structure. Completing the abstraction around this
structure would have been a much bigger and much riskier code change
with increase in memory footprint, potential decrease in performance
and no immediate benefit.
In the future we want to support alternative ECDH implementations. We
can't make assumptions about the structure of the context they might
use, and therefore shouldn't access the members of
`mbedtls_ecdh_context`.
Currently the lifecycle of the context can't be done without direct
manipulation. This commit adds `mbedtls_ecdh_setup()` to complete
covering the context lifecycle with functions.
`mbedtls_ecp_tls_read_group()` both parses the group ID and loads the
group into the structure provided. We want to support alternative
implementations of ECDH in the future and for that we need to parse the
group ID without populating an `mbedtls_ecp_group` structure (because
alternative implementations might not use that).
This commit moves the part that parses the group ID to a new function.
There is no need to test the new function directly, because the tests
for `mbedtls_ecp_tls_read_group()` are already implicitly testing it.
There is no intended change in behaviour in this commit.
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`.
