The libgcrypt RNG implementation uses static buffer allocation which it does
not free. There is no symbol we can catch in leak-detective, hence we explicitly
initialize the RNG during the whitelisted gcrypt_plugin_create() function.
The performance impact is not measurable, as the compiler loads these variables
in xmm registers in unrolled loops anyway.
However, we avoid loading these sensitive keys onto the stack. This happens for
larger key schedules, where the register count is insufficient. If that key
material is not on the stack, we can avoid to wipe it explicitly after
crypto operations.
While the required members are aligned in the struct as required, on 32-bit
platforms the allocator aligns the structures itself to 8 bytes only. This
results in non-aligned struct members, and invalid memory accesses.
CTR can be parallelized, and we do so by queueing instructions to the processor
pipeline. While we have enough registers for 128-bit decryption, the register
count is insufficient to hold all variables with larger key sizes. Nonetheless
is 4-way parallelism faster, depending on key size between ~10% and ~25%.
CBC decryption can be parallelized, and we do so by queueing instructions
to the processor pipeline. While we have enough registers for 128-bit
decryption, the register count is insufficient to hold all variables with
larger key sizes. Nonetheless is 4-way parallelism faster, roughly by ~8%.
This allows us to unroll loops, and use local (register) variables for the
key schedule. This improves performance slightly for encryption, but a lot
for reorderable decryption (>30%).
We don't have any where plain or associated data is not a multiple of the block
size, but it is likely to find bugs here. Also, we miss some ICV12 test vectors
using 128- and 192-bit key sizes.
We previously didn't pass the key size during algorithm registration, but this
resulted in benchmarking with the "default" key size the crypter uses when
passing 0 as key size.
We previously checked for older library versions without locking support at
all. But newer libraries can be built in single-threading mode as well, where
we have to care about the locking.
With OpenSSL commit 929b0d70c19f60227f89fac63f22a21f21950823 setting an empty
key fails if no previous key has been set on that HMAC.
In 9138f49e we explicitly added the check we remove now, as HMAC_Update()
might crash if HMAC_Init_ex() has not been called yet. To avoid that, we
set and check a flag locally to let any get_mac() call fail if set_key() has
not yet been called.
Martin Willi