tree e85d41e1bcdb168d357159113c24721108b96595
parent 16ab76bbe774806079e2d5cab0c4209a4f7b0602
author Janos Follath <janos.follath@arm.com> 1703848498 +0000
committer Dave Rodgman <dave.rodgman@arm.com> 1705937599 +0000

Add warning for PKCS 1.5 decryption

Any timing variance dependant on the output of this function enables a
Bleichenbacher attack. It is extremely difficult to use safely.

In the Marvin attack paper
(https://people.redhat.com/~hkario/marvin/marvin-attack-paper.pdf) the
author suggests that implementations of PKCS 1.5 decryption that don't
include a countermeasure should be considered inherently dangerous.

They suggest that all libraries implement the same countermeasure, as
implementing different countermeasures across libraries enables the
Bleichenbacher attack as well.

This is extremely fragile and therefore we don't implement it. The use
of PKCS 1.5 in Mbed TLS implements the countermeasures recommended in
the TLS standard (7.4.7.1 of RFC 5246) and is not vulnerable.

Add a warning to PKCS 1.5 decryption to warn users about this.

Signed-off-by: Janos Follath <janos.follath@arm.com>