MGASA-2020-0469

This update provides security bug fixes and minor enhancements.

Limit the size of calculations performed by mbedtlsmpiexpmod to MBEDTLSMPIMAXSIZE to prevent a potential denial of service when generating Diffie-Hellman key pairs.

A failure of the random generator was ignored in mbedtlsmpifill_random(), which is how most uses of randomization in asymmetric cryptography are implemented. This could cause failures or the silent use of non-random values.

Fix a compliance issue whereby the library did not check the tag on the algorithm parameters (only the size) when comparing the signature in the description part of the cert to the real signature.

Zeroising of local buffers and variables which are used for calculations in mbedtlspkcs5pbkdf2hmac(), mbedtlsinternalsha*process(), mbedtlsinternalmd*process() and mbedtlsinternalripemd160process() functions to erase sensitive data from memory.