This commit replaces the dummy implementation of the CRT acquire/release
framework by a cache-based implementation which remembers frame and PK
associated to a CRT across multiple `acquire/release` pairs.
This commit restructures the parsing of X.509 CRTs in the following way:
First, it introduces a 'frame' structure `mbedtls_x509_crt_frame`, which
contains pointers to some structured fields of a CRT as well as copies of
primitive fields. For example, there's a pointer-length pair delimiting the raw
public key data in the CRT, but there's a C-uint8 to store the CRT version
(not a pointer-length pair delimiting the ASN.1 structure holding the version).
Setting up a frame from a raw CRT buffer does not require any memory outside
of the frame structure itself; it's just attaches a 'template' to the buffer
that allows to inspect the structured parts of the CRT afterwards.
Note that the frame structure does not correspond to a particular ASN.1
structure; for example, it contains pointers to delimit the three parts
of a CRT (TBS, SignatureAlgorithm, Signature), but also pointers to the
fields of the TBS, and pointers into the Extensions substructure of the TBS.
Further, the commit introduces an internal function `x509_crt_parse_frame()`
which sets up a frame from a raw CRT buffer, as well as several small helper
functions which help setting up the more complex structures (Subject, Issuer, PK)
from the frame.
These functions are then put to use to rewrite the existing parsing function
`mbedtls_x509_crt_parse_der_core()` by setting up a CRT frame from the input
buffer, residing on the stack, and afterwards copying the respective fields
to the actual `mbedtls_x509_crt` structure and performing the deeper parsing
through the various helper functions.
At every occasion where we're using `mbedtls_x509_memcasecmp()` we're
checking that the two buffer lengths coincide before making the call.
This commit saves a few bytes of code by moving this length check
to `mbedtls_x509_memcasecmp()`.
This commit adds a new function `mbedtls_asn1_traverse_sequence_of()`
which traverses an ASN.1 SEQUENCE and calls a user-provided callback
for each entry.
It allows to put the following constraints on the tags allowed
in the SEQUENCE:
- A tag mask and mandatory tag value w.r.t. that mask.
A non-matching tag leads to an MBEDTLS_ERR_ASN1_UNEXPECTED_TAG error.
For example, it the mask if 0xFF, this means that only
a single tag will be allowed in the SEQUENCE.
- A tag mask and optional tag value w.r.t. that mask.
A non-matching tag is silently ignored.
The main use for this flexibility is the traversal of the
`SubjectAlternativeNames` extension, where some parts of the
tag are fixed but some are flexible to indicate which type
of name the entry describes.
This is analogous to a previous commit for the `ExtendedKeyUsage`
extension: We aim at not using dynamically allocated linked lists
to represent the components of the `SubjectAlternativeName` extension,
but to traverse the raw ASN.1 data when needed.
This commit adds a field to `mbedtls_x509_crt` containing the raw
ASN.1 buffer bounds of the `SubjectAlternativeNames` extension.
This commit re-implements `mbedtls_x509_crt_check_extended_key_usage()`
to not use the dynamically allocated linked list presentation of the
`ExtendedKeyUsage` but to search for the required usage by traversing
the raw ASN.1 data.
The previous commits replace the use of dynamically allocated linked lists
for X.509 name inspection. This commit is the first in a series which attempts
the same for the `ExtendedKeyUsage` extension. So far, when a CRT is parsed,
the extension is traversed and converted into a dynamically allocated linked
list, which is then search through whenever the usage of a CRT needs to be
checked through `mbedtls_x509_check_extended_key_usage()`.
As a first step, this commit introduces a raw buffer holding the bounds
of the `ExtendedKeyUsage` extension to the `mbedtls_x509_crt` structure.
There are three operations that need to be performed on an X.509 name:
1 Initial traversal to check well-formedness of the ASN.1 structure.
2 Comparison between two X.509 name sequences.
3 Checking whether an X.509 name matches a client's ServerName request.
Each of these tasks involves traversing the nested ASN.1 structure,
In the interest of saving code, we aim to provide a single function
which can perform all of the above tasks.
The existing comparison function is already suitable not only for task 2,
but also for 1: One can simply pass two equal ASN.1 name buffers, in which
case the function will succeed if and only if that buffer is a well-formed
ASN.1 name.
This commit further adds a callback to `mbedtls_x509_name_cmp_raw()` which
is called after each successful step in the simultaneous name traversal and
comparison; it may perform any operation on the current name and potentially
signal that the comparison should be aborted.
With that, task 3 can be implemented by passing equal names and a callback
which aborts as soon as it finds the desired name component.
This commit replaces the previous calls to `mbedtls_x509_name_cmp()`
during CRT verification (to match child and parent, to check whether
a CRT is self-issued, and to match CRLs and CAs) by calls to the new
`mbedtls_x509_name_cmp_raw()` using the raw ASN.1 data; it passes the
raw buffers introduced in the last commits.
The previous name comparison function mbedtls_x509_name_cmp() is now
both unused and unneeded, and is removed.
To make use of the X.509 name comparison function based on raw
ASN.1 data that was introduced in the previous commit, this commit
adds an ASN.1 buffer field `issuer_raw_no_hdr` to `mbedtls_x509_crl`
which delimits the raw contents of the CRLs `Issuer` field.
The previous field `issuer_raw` isn't suitable for that because
it includes the ASN.1 header.
This commit provides a new function `mbedtls_x509_name_cmp_raw()`
to x509.c for comparing to X.509 names by traversing the raw ASN.1
data (as opposed to using the dynamically allocated linked list
of `mbedtls_x509_name` structures). It has external linkage because
it will be needed in `x509_crt` and `x509_crl`, but is marked
internal and hence not part of the public API.
The function `mbedtls_x509_sig_alg_gets()` previously needed the
raw ASN.1 OID string even though it is implicit in the PK and MD
parameters.
This commit modifies `mbedtls_x509_sig_alg_gets()` to infer the OID
and remove it from the parameters.
This will be needed for the new X.509 CRT structure which will
likely not store the signature OID.
Care has to be taken to handle the case of RSASSA-PSS correctly,
where the hash algorithm in the OID list is set to MBEDTLS_MD_NONE
because it's only determined by the algorithm parameters.
This commit introduces a macro `MBEDTLS_ASN1_IS_STRING_TAG`
that can be used to check if an ASN.1 tag is among the list
of string tags:
- MBEDTLS_ASN1_BMP_STRING
- MBEDTLS_ASN1_UTF8_STRING
- MBEDTLS_ASN1_T61_STRING
- MBEDTLS_ASN1_IA5_STRING
- MBEDTLS_ASN1_UNIVERSAL_STRING
- MBEDTLS_ASN1_PRINTABLE_STRING
- MBEDTLS_ASN1_BIT_STRING
If `MBEDTLS_SSL_KEEP_PEER_CERTIFICATE` is not set, `mbedtls_ssl_session`
contains the digest of the peer's certificate for the sole purpose of
detecting a CRT change on renegotiation. Hence, it is not needed if
renegotiation is disabled.
This commit removes the `peer_cert_digest` fields (and friends) from
`mbedtls_ssl_session` if
`!MBEDTLS_SSL_KEEP_PEER_CERTIFICATE + !MBEDTLS_SSL_RENEGOTIATION`,
which is a sensible configuration for constrained devices.
Apart from straightforward replacements of
`if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)`
by
`if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE) && \
defined(MBEDTLS_SSL_RENEGOTIATION)`,
there's one notable change: On the server-side, the CertificateVerify
parsing function is a no-op if the client hasn't sent a certificate.
So far, this was determined by either looking at the peer CRT or the
peer CRT digest in the SSL session structure (depending on the setting
of `MBEDTLS_SSL_KEEP_PEER_CERTIFICATE`), which now no longer works if
`MBEDTLS_SSL_KEEP_PEER_CERTIFICATE` is unset. Instead, this function
now checks whether the temporary copy of the peer's public key within
the handshake structure is initialized or not (which is also a
beneficial simplification in its own right, because the pubkey is
all the function needs anyway).
`MBEDTLS_SSL__ECP_RESTARTABLE` is only defined if
`MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED` is set, which
requires `MBEDTLS_X509_PARSE_C` to be set (this is checked
in `check_config.`). The additional `MBEDTLS_X509_PARSE_C`
guard around the `ecrs_peer_cert` field is therefore not
necessary; moreover, it's misleading, because it hasn't
been used consistently throughout the code.
When removing the (session-local) copy of the peer's CRT chain, we must
keep a handshake-local copy of the peer's public key, as (naturally) every
key exchange will make use of that public key at some point to verify that
the peer actually owns the corresponding private key (e.g., verify signatures
from ServerKeyExchange or CertificateVerify, or encrypt a PMS in a RSA-based
exchange, or extract static (EC)DH parameters).
This commit adds a PK context field `peer_pubkey` to the handshake parameter
structure `mbedtls_handshake_params_init()` and adapts the init and free
functions accordingly. It does not yet make actual use of the new field.
This commit adds an ASN.1 buffer field `pk_raw` to `mbedtls_x509_crt`
which stores the bounds of the raw public key data within an X.509 CRT.
This will be useful in subsequent commits to extract the peer's public
key from its certificate chain.
`mbedtls_ssl_parse_certificate()` parses the peer's certificate chain
directly into the `peer_cert` field of the `mbedtls_ssl_session`
structure being established. To allow to optionally remove this field
from the session structure, this commit changes this to parse the peer's
chain into a local variable instead first, which can then either be freed
after CRT verification - in case the chain should not be stored - or
mapped to the `peer_cert` if it should be kept. For now, only the latter
is implemented.
A subsequent commit will need this function in the session ticket
and session cache implementations. As the latter are server-side,
this commit also removes the MBEDTLS_SSL_CLI_C guard.
For now, the function is declared in ssl_internal.h and hence not
part of the public API.
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;
```
Introduce MBEDTLS_X509_INFO to indicate the availability of the
mbedtls_x509_*_info() function and closely related APIs. When this is
not defined, also omit name and description from
mbedtls_oid_descriptor_t, and omit OID arrays, macros, and types that
are entirely unused. This saves several KB of code space.
Change-Id: I056312613379890e0d70e1d08c34171287c0aa17
Some TLS-only code paths were not protected by an #ifdef and while some
compiler are happy to just silently remove them, armc5 complains:
Warning: #111-D: statement is unreachable
Let's make armc5 happy.
This is enabled by default as we generally enable things by default unless
there's a reason not to (experimental, deprecated, security risk).
We need a compile-time option because, even though the functions themselves
can be easily garbage-collected by the linker, implementing them will require
saving 64 bytes of Client/ServerHello.random values after the handshake, that
would otherwise not be needed, and people who don't need this feature
shouldn't have to pay the price of increased RAM usage.
