As has been previously done for ciphersuites, this commit introduces
a zero-cost abstraction layer around the type
mbedtls_md_info const *
whose valid values represent implementations of message digest algorithms.
Access to a particular digest implementation can be requested by name or
digest ID through the API mbedtls_md_info_from_xxx(), which either returns
a valid implementation or NULL, representing failure.
This commit replaces such uses of `mbedtls_md_info const *` by an abstract
type `mbedtls_md_handle_t` whose valid values represent digest implementations,
and which has a designated invalid value MBEDTLS_MD_INVALID_HANDLE.
The purpose of this abstraction layer is to pave the way for builds which
support precisely one digest algorithm. In this case, mbedtls_md_handle_t
can be implemented as a two-valued type, with one value representing the
invalid handle, and the unique valid value representing the unique enabled
digest.
pkcs11_sign() reuses *sig to store the header and hash, but those might
be larger than the actual sig, causing a buffer overflow.
An overflow can occur when using raw sigs with hashlen > siglen, or when
the RSA key is less than 664 bits long (or less when using hashes
shorter than SHA512)
As siglen is always within the 'low realm' < 32k, an overflow of asnlen
+ hashlen is not possible.
This restores previous functionality, and thus still allows only RSA to be
used through PKCS#11.
Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Signed-off-by: Paul Bakker <p.j.bakker@polarssl.org>
