In ssl_parse_encrypted_pms, some operational failures from
ssl_decrypt_encrypted_pms lead to diff being set to a value that
depended on some uninitialized unsigned char and size_t values. This didn't
affect the behavior of the program (assuming an implementation with no
trap values for size_t) because all that matters is whether diff is 0,
but Valgrind rightfully complained about the use of uninitialized
memory. Behave nicely and initialize the offending memory.
The code paths in the library are different for decryption and for
signature. Improve the test coverage by doing some error path tests
for decryption in addition to signature.
In ssl_server2, the private key objects are normally local variables
of the main function. However this does not hold for private keys in
the SNI configuration. When async callbacks are used, the test code
transfers the ownership of the private keys to the async callbacks.
Therefore the test code must free the SNI private keys through the
async callbacks (but it must not free the straight private keys this
way since they are not even heap-allocated).
When testing async callbacks with SNI, make all the keys async, not
just the first one. Otherwise the test is fragile with respect to
whether a key is used directly or through the async callbacks.
In the current test code, the object that is used as a public key in
the certificate also contains a private key. However this is because
of the way the stest code is built and does not demonstrate the API in
a useful way. Use mbedtls_pk_check_pair, which is not what real-world
code would do (since the private key would typically be in an external
cryptoprocessor) but is a more representative placeholder.
