The basis for the Lucky 13 family of attacks is for an attacker to be able to
distinguish between (long) valid TLS-CBC padding and invalid TLS-CBC padding.
Since our code sets padlen = 0 for invalid padding, the length of the input to
the HMAC function, and the location where we read the MAC, give information
about that.
A local attacker could gain information about that by observing via a
cache attack whether the bytes at the end of the record (at the location of
would-be padding) have been read during MAC verification (computation +
comparison).
Let's make sure they're always read.
The basis for the Lucky 13 family of attacks is for an attacker to be able to
distinguish between (long) valid TLS-CBC padding and invalid TLS-CBC padding.
Since our code sets padlen = 0 for invalid padding, the length of the input to
the HMAC function gives information about that.
Information about this length (modulo the MD/SHA block size) can be deduced
from how much MD/SHA padding (this is distinct from TLS-CBC padding) is used.
If MD/SHA padding is read from a (static) buffer, a local attacker could get
information about how much is used via a cache attack targeting that buffer.
Let's get rid of this buffer. Now the only buffer used is the internal MD/SHA
one, which is always read fully by the process() function.
As a protection against the Lucky Thirteen attack, the TLS code for
CBC decryption in encrypt-then-MAC mode performs extra MAC
calculations to compensate for variations in message size due to
padding. The amount of extra MAC calculation to perform was based on
the assumption that the bulk of the time is spent in processing
64-byte blocks, which is correct for most supported hashes but not for
SHA-384. Correct the amount of extra work for SHA-384 (and SHA-512
which is currently not used in TLS, and MD2 although no one should
care about that).
We naturally added the new Curve448 ECP group ID in alphabetical order in
the mbedtls_ecp_group_id enum. However, this causes binary incompatibility
issues as previous binaries will use values for groups that now have a
different meaning. For example, MBEDTLS_ECP_DP_SECP192K1, old value 10,
would mean Curve448 (MBEDTLS_ECP_DP_CURVE448) and the wrong group ID used.
Fix the binary compatibility issue by adding new enum entries to the end of
the enum, even though this isn't so great for readbility as the list is no
longer in alphabetical order. However, the list wasn't perfectly in
alphabetical order before anyway.
