Add code that loops through every requested certificate and finds out
the corresponding SingleResponse in the OCSP response. This code is the
skeleton for the verification of each SingleResponse. However, at this
stage the verification code is very minimal.
The function follows RFC 6960 and uses either the responder's name or
the responder's hash of their key as available in the OCSP response to
locate the correct issuer certificate.
To avoid code duplication, some functionality from x509_crt.c module
was moved to x509.c and made public in x509.h.
Add the main skeleton code of a function
x509_ocsp_find_response_issuer_crt() that traverses the certs field in
the OCSP response and other user supplied certificates to find the OCSP
response's issuer. At the momment, the helper function is unimplemented
Add the main OCSP response verification function
mbedtls_x509_ocsp_verify_response() to the header file x509_ocsp.h and
a simple definition to x509_ocsp.c. At this stage, the verification
function only checks the response status and the timestamp and sets the
verification flags accordingly.
Also, new verification errors and flags are added as macros. These
values will be used in subsequent commits.
Rework the function mbedtls_x509_ocsp_response_info() to ensure that
it follows the example of similar functions in other X.509 components.
That is, the function should return the number of bytes written to the
provided buffer and in case of error return a negative value.
Rename the following functions in x509_ocsp.h and x509_ocsp.c to fit
the calling convention in other X.509 components (e.g CRL and CRT):
* mbedtls_x509_ocsp_parse_response -> mbedtls_x509_ocsp_response_parse
* mbedtls_x509_ocsp_parse_response_file -> mbedtls_x509_ocsp_response_parse_file
Return a mores specific error code MBEDTLS_ERR_X509_INVALID_DATE +
MBEDTLS_ERR_ASN1_UNEXPECTED_TAG instead of simply
MBEDTLS_ERR_X509_INVALID_DATE to help debugging.
This commit only adds the test code for
mbedtls_x509_ocsp_parse_response() and an initial set of negative tests
So far, the tests introduced are manually crafted malicious OCSP
responses that tests several error conditions in the initial part of
the response structure including the response status, producedAt date,
ResponderID, part of the tsbResponseData, etc.
Factor common code into a new function x509_ocsp_get_md(). The function
takes in a pointer to the DER-encoded buffer, parses the octet string
containing some hash value and then checks that the length corresponds
to the expected length for each md algorithm.
The responseType indicates a large portion of the syntax of an OCSP
response message. At this stage we only support OCSP Basic, so this
change ensure that the parser returns a failure code if the
responseType does not match the OID id-pkix-ocsp-basic.
Add missing dependency checks to check_config.h and documentation to
config.h. Note that SHA-1 is required for OCSP as RFC 6960 Section
4.4.2 specifies that the ResponderID byKey is the SHA-1 hash of the
responder's public key. That is, without SHA-1 we might not be able to
tell who signed the OCSP response.
Assign the type of response_id used in the OCSP response ID is recorded
before the actual ID is initialised. In this way, if the initialisation
call to a Name ID fails, the function mbedtls_x509_ocsp_response_free()
calls the correct free() function on the response ID avoiding potential
memory leaks.
Add 1 to a temporary buffer in x509_ocsp_info_certs() which is used to
construct the printing prefix to write an informational string of the
OCSP response for the user. The additional element added to the buffer
contains the \0 character. The missing element would cause a heap
overread of 1 when concatenating the prefix string with itself.
Add missing return statement in x509_ocsp_get_response() that would
otherwise allow the code to continue executing even though a parsing
failure has already been found.
Add a check at the beginning of the function
mbedtls_x509_ocsp_response_free() to ensure that the pointer passed to
is not NULL. This prevent a NULL pointer dereference that could lead to
crashes.
The new MBEDTLS_X509_OCSP_PARSE_C is a feature macro that can be
controlled from the config.h file to enable/disable the OCSP X509
feature at compile time.
Relocate the new OCSP and CRL X509 related errors to x509.h as the
error message generation scripts cannot handle these anywhere else.
Also, update the error.c file with the new human-readable strings
for the OCSP and CRL errors.
This patch removes several bound checks that were redundant due to the
structure of the code in which each function parses the top-level
components of ASN.1 structures and helper functions parse the sub-
components.
In the case of x509_ocsp_get_response(), the parsing of the OCTET
STRING was moved to its caller function as the main job of
x509_ocsp_get_response() is to parse the BasicOCSPResponse structure,
so the OCTET STRING is considered a top-level component similar to an
EXPLICIT tag
Populate the function x509_ocsp_get_certs() to parse the OPTIONAL list
of certificates in the BasicOCSPResponse ASN.1 structure of the OCSP
response:
certs [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL
x509_ocsp_get_certs() only parses the SEQUENCE OF (the EXPLICIT tag is
parsed by the caller) and delegates the actual parsing of the
certificate to the x509_crt.c module.
NOTE: The parsing of certificates in x509_ocsp.c is currently very
inefficient in terms of space as x509_ocsp.c and x509_crt.c both make
an internal copy of the buffer passed to them. This will be optimised
in the future.
Populate the function x509_ocsp_get_sig_alg() that parses the
signatureAlgorithm from the BasicOCSPResponse ASN.1 structure. The
parsing is actually done by the preexisting functions:
* mbedtls_x509_get_alg()
* mbedtls_x509_get_sig_alg()
This is only placeholder code that does not actually check that the
extensions are at least well formed. Therefore, the function
x509_ocsp_get_extensions() has been marked as TODO.
Strictly speaking, the CRLReason is a concept imported from the CRL
profile defined in RFC 5280 Section 5.3.1. However, this is a CRL
extension that is not implemented in mbed TLS. Therefore, this patch
introduces the relevant macros with revocation reasons and error return
codes in x509_crt.h. Also the function x509_ocsp_get_crl_reason() to
parse the CRLReason. If necessary, this code can later be migrated to
x509_crl.c.
The CRL reason ASN1. structure is specified in RFC 5280 Section 5.3.1
as follows:
CRLReason ::= ENUMERATED {
unspecified (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
-- value 7 is not used
removeFromCRL (8),
privilegeWithdrawn (9),
aACompromise (10) }
Populate the function x509_ocsp_get_revoked_info() with code to parse the
following ASN.1 structure:
RevokedInfo ::= SEQUENCE {
revocationTime GeneralizedTime,
revocationReason [0] EXPLICIT CRLReason OPTIONAL }
x509_ocsp_get_revoked_info() parses the top level SEQUENCE and the EXPLICIT
OPTIONAL tag, but delegates the parsing of GeneralizedTime and
CRL reason (if present) to x509_ocsp_get_generalized_time() and
x509_ocsp_get_crl_reason() respectively.
Populate the function x509_ocsp_get_cert_status() with code that parses
the following ASN.1 structure:
CertStatus ::= CHOICE {
good [0] IMPLICIT NULL,
revoked [1] IMPLICIT RevokedInfo,
unknown [2] IMPLICIT UnknownInfo }
x509_ocsp_get_cert_status() parses the top level CHOICE and IMPLICIT
components. In the case of status good and unknown, their value is both
expected to be NULL because according to RFC 6960 Section 4.2:
UnknownInfo ::= NULL
Therefore, no further parsing is needed here. In the case of status
revoked, the parsing of Revoked info is delegated to a helper function.
Populate the function x509_ocsp_get_cert_id() that parses the following
ASN.1 structure:
CertID ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
issuerNameHash OCTET STRING, -- Hash of issuer's DN
issuerKeyHash OCTET STRING, -- Hash of issuer's public key
serialNumber CertificateSerialNumber }
x509_ocsp_get_cert_id() parses the top-level SEQUENCE component and
calls the following helpers for the actual contents of the CertID:
* mbedtls_x509_get_md_alg(): Parses the hashAlgorithm
* x509_ocsp_get_octet_string(): Parses the OCTET STRINGs
issuerNameHash and issuerKeyHash, but does not actually check
that the length or hashes are actually correct or correspond
to the expected length given the hashAlgorithm
* mbedtls_x509_get_serial: Parses the serialNumber
Populate the function x509_ocsp_get_single_response() that parses the
following ASN.1 structure:
SingleResponse ::= SEQUENCE {
certID CertID,
certStatus CertStatus,
thisUpdate GeneralizedTime,
nextUpdate [0] EXPLICIT GeneralizedTime OPTIONAL,
singleExtensions [1] EXPLICIT Extensions OPTIONAL }
x509_ocsp_get_single_response() parses the top-level SEQUENCE and the
two explicit tags. Note that the tagged values at the end of the
SingleResponse are optional so this function takes care of the
following cases using a switch statement:
* nextUpdate only
* nextUpdate followed by SingleExtensions
* singleExtensions only
