A past security review identified MD4 and MD5 support as features that
ought to be disabled by default. (There is zero impact on UEFI Secure
Boot itself from having these algorithms enabled: this was just a side
comment in the review.)
As noted in the resulting commit 7f2006a ("[crypto] Disable MD5 as an
OID-identifiable algorithm by default"), the actual MD5 code will
almost certainly still be present in the binary due to its implicit
use by various features. Disabling MD5 support via config/crypto.h
simply removes the OID-identified algorithm, which prevents it from
being used as an explicitly identified algorithm (e.g. in an X.509
certificate digest).
Match the intent of this review comment by marking the OID-identified
algorithms for MD4 and MD5 as forbidden for UEFI Secure Boot.
Extend this to also disable the "md4sum" command and the use of the
md5WithRSAEncryption OID-identified algorithm. (The "md5sum" command
is left enabled for historical reasons, and we have no definition for
md4WithRSAEncryption anyway.)
Signed-off-by: Michael Brown <mcb30@ipxe.org>
There is nothing OID-specific about the ASN1_OID_CURSOR macro. Rename
to allow it to be used for constructing ASN.1 cursors with arbitrary
contents.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
There are many ways in which the object for a cryptographic algorithm
may be included, even if not explicitly enabled in config/crypto.h.
For example: the MD5 algorithm is required by TLSv1.1 or earlier, by
iSCSI CHAP authentication, by HTTP digest authentication, and by NTLM
authentication.
In the current implementation, inclusion of an algorithm for any
reason will result in the algorithm's ASN.1 object identifier being
included in the "asn1_algorithms" table, which consequently allows the
algorithm to be used for any ASN1-identified purpose. For example: if
the MD5 algorithm is included in order to support HTTP digest
authentication, then iPXE would accept a (validly signed) TLS
certificate using an MD5 digest.
Split the ASN.1 object identifiers into separate files that are
required only if explicitly enabled in config/crypto.h. This allows
an algorithm to be omitted from the "asn1_algorithms" table even if
the algorithm implementation is dragged in for some other purpose.
The end result is that only the algorithms that are explicitly enabled
in config/crypto.h can be used for ASN1-identified purposes such as
signature verification.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
