This commit restructures ssl_ciphersuites.h and ssl_ciphersuites.c to
define all ciphersuite helper functions static inline in ssl_ciphersuites.h
if MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE is set, and to otherwise put their
definitions in ssl_ciphersuites.c.
If MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled, the type
mbedtls_ssl_ciphersuite_handle_t
is logically a boolean (concretely realized as `unsigned char`),
containing the invalid handle and the unique valid handle, which
represents the single enabled ciphersuite.
The SSL session structure mbedtls_ssl_session contains an instance
of mbedtls_ssl_ciphersuite_handle_t which is guaranteed to be valid,
and which is hence redundant in any two-valued implementation of
mbedtls_ssl_ciphersuite_handle_t.
This commit replaces read-uses of
mbedtls_ssl_session::ciphersuite_info
by a getter functions which, and defines this getter function
either by just reading the field from the session structure
(in case MBEDTLS_SSL_SINGLE_CIPHERSUITE is disabled), or by
returning the single valid ciphersuite handle (in case
MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled) and removing the
field from mbedtls_ssl_session in this case.
This commit is a step towards the goal of allowing to hardcode the choice
of a single ciphersuite at compile-time. The hoped for benefit of this is
that whereever a ciphersuite attribute is queried and checked against a
compile-time constant, the check can be recognized as either true or false
at compile-time, hence leading to a code-size reduction.
For this to work, the ciphersuite attribute getter functions
mbedtls_ssl_suite_get_xxx() will be modified to return something
the compiler can recognize as a compile-time constant. In particular,
in order to avoid relying on constant propagation abilities of the
compiler, these functions should ideally return constant symbols
(instead of, say, fields in a globally const structure instance).
This puts us in the following situation: On the one hand, there's the
array of ciphersuite information structures defining the attribute of
those ciphersuites the stack knows about. On the other hand, we need
direct access to those fields through constant symbols in the getter
functions.
In order to avoid any duplication of information, this commit exemplifies
how ciphersuites can be conveniently defined on the basis of macro
definitions, and how the corresponding instances of the ciphersuite
information structure can be auto-generated from this.
In the approach, to add support for a ciphersuite with official name
NAME (such as TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8), the following macro
constants need to be defined in ssl_ciphersuites.h:
MBEDTLS_SUITE__ NAME __ID
MBEDTLS_SUITE__ NAME __NAME
MBEDTLS_SUITE__ NAME __CIPHER
MBEDTLS_SUITE__ NAME __MAC
...
To make check-names.sh happy, one also needs a dummy macro
MBEDTLS_SUITE__ NAME()
These ciphersuite attribute values can then be queried via
MBEDTLS_SSL_SUITE_ID( NAME_MACRO )
...
where NAME_MACRO can be any macro expanding to a defined NAME.
Further, a convenience macro
MBEDTLS_SSL_SUITE_INFO( NAME_MACRO )
is provided that again takes a macro NAME_MACRO expanding to a
defined NAME, and itself expands to an instance of
mbedtls_ssl_ciphersuite_info_t using the macro attributes
defined for NAME. This macro is then used in ssl_ciphersuites.c
when defining the array of known ciphersuite information structures,
(a) without duplicating the information, and (b) with increased
readability, because there's only one line for each ciphersuite.
This commit introduces an internal zero-cost abstraction layer for
SSL ciphersuites: Instead of addressing ciphersuites via pointers
to instances of mbedtls_ssl_ciphersuite_t and accessing their fields
directly, this commit introduces an opaque type
mbedtls_ssl_ciphersuite_handle_t,
and getter functions
mbedtls_ssl_suite_get_xxx()
operating on ciphersuite handles.
The role of NULL is played by a new macro constant
MBEDTLS_SSL_CIPHERSUITE_INVALID_HANDLE
which results of functions returning handles can be checked against.
(For example, when doing a lookup of a ciphersuite from a peer-provided
ciphersuite ID in the per's Hello message).
The getter functions have the validity of the handle as a precondition
and are undefined if the handle is invalid.
So far, there's only one implementation of this abstraction layer, namely
mbedtls_ssl_ciphersuite_handle_t being mbedtls_ssl_ciphersuite_t const *
and
getter functions being field accesses.
In subsequent commits, however, the abstraction layer will be useful
to save code in the situation where only a single ciphersuite is enabled.
Previously, ssl.h included ssl_ciphersuites.h to have access to the
helper macros MBEDTLS_KEY_EXCHANGE_XXX_ENABLED, and for no other
reason. This commit moves the definitions of these macros to ssl.h,
thereby removing the dependency of ssl.h on ssl_ciphersuites.h.
This commit introduces a static helper function
`mbedtls_ssl_ciphersuite_uses_srv_cert()`
which determines whether a ciphersuite may make use of server-side CRTs.
This function is in turn uses in `mbedtls_ssl_parse_certificate()` to
skip certificate parsing for ciphersuites which don't involve CRTs.
Note: Ciphersuites not using server-side CRTs don't allow client-side CRTs
either, so it is safe to guard `mbedtls_ssl_{parse/write}_certificate()`
this way.
Note: Previously, the code uses a positive check over the suites
- MBEDTLS_KEY_EXCHANGE_PSK
- MBEDTLS_KEY_EXCHANGE_DHE_PSK
- MBEDTLS_KEY_EXCHANGE_ECDHE_PSK
- MBEDTLS_KEY_EXCHANGE_ECJPAKE,
while now, it uses a negative check over `mbedtls_ssl_ciphersuite_uses_srv_cert()`,
which checks for the suites
- MBEDTLS_KEY_EXCHANGE_RSA
- MBEDTLS_KEY_EXCHANGE_RSA_PSK
- MBEDTLS_KEY_EXCHANGE_DHE_RSA
- MBEDTLS_KEY_EXCHANGE_ECDH_RSA
- MBEDTLS_KEY_EXCHANGE_ECDHE_RSA
- MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA
- MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA
This is equivalent since, together, those are all ciphersuites.
Quoting ssl_ciphersuites.h:
```
typedef enum {
MBEDTLS_KEY_EXCHANGE_NONE = 0,
MBEDTLS_KEY_EXCHANGE_RSA,
MBEDTLS_KEY_EXCHANGE_DHE_RSA,
MBEDTLS_KEY_EXCHANGE_ECDHE_RSA,
MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA,
MBEDTLS_KEY_EXCHANGE_PSK,
MBEDTLS_KEY_EXCHANGE_DHE_PSK,
MBEDTLS_KEY_EXCHANGE_RSA_PSK,
MBEDTLS_KEY_EXCHANGE_ECDHE_PSK,
MBEDTLS_KEY_EXCHANGE_ECDH_RSA,
MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA,
MBEDTLS_KEY_EXCHANGE_ECJPAKE,
} mbedtls_key_exchange_type_t;
```
Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves#1371
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.
The routine `mbedtls_ssl_write_server_key_exchange` heavily depends on
what kind of cipher suite is active: some don't need a
ServerKeyExchange at all, some need (EC)DH parameters but no server
signature, some require both. Each time we want to restrict a certain
piece of code to some class of ciphersuites, it is guarded by a
lengthy concatentation of configuration checks determining whether at
least one of the relevant cipher suites is enabled in the config; on
the code level, it is guarded by the check whether one of these
cipher suites is the active one.
To ease readability of the code, this commit introduces several helper
macros and helper functions that can be used to determine whether a
certain class of ciphersuites (a) is active in the config, and
(b) contains the currently present ciphersuite.
fixes#310
Actually all key exchanges that use a certificate use signatures too, and
there is no key exchange that uses signatures but no cert, so merge those two
flags.
