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Manuel Pégourié-Gonnard authored
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.
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