The Meaning of Memory Safety

We give a rigorous characterization of what it means for a programming language to be memory safe, capturing the intuition that memory safety supports local reasoning about state. We formalize this principle in two ways. First, we show how a small memory-safe language validates a noninterference property: a program can neither affect nor be affected by unreachable parts of the state. Second, we extend separation logic, a proof system for heap-manipulating programs, with a memory-safe variant of its frame rule. The new rule is stronger because it applies even when parts of the program are buggy or malicious, but also weaker because it demands a stricter form of separation between parts of the program state. We also consider a number of pragmatically motivated variations on memory safety and the reasoning principles they support. As an application of our characterization, we evaluate the security of a previously proposed dynamic monitor for memory safety of heap-allocated data.Comment: POST'18 final versio

On the Complete Non-Malleability of the Fujisaki-Okamoto Transform

The Fujisaki-Okamoto (FO) transform (CRYPTO 1999 and JoC 2013) turns any weakly (i.e., IND-CPA) secure public-key encryption (PKE) scheme into a strongly (i.e., IND-CCA) secure key encapsulation method (KEM) in the random oracle model (ROM). Recently, the FO transform re-gained momentum as part of CRISTAL-Kyber, selected by the NIST as the PKE winner of the post-quantum cryptography standardization project. Following Fischlin (ICALP 2005), we study the complete non-malleability of KEMs obtained via the FO transform. Intuitively, a KEM is completely non-malleable if no adversary can maul a given public key and ciphertext into a new public key and ciphertext encapsulating a related key for the underlying blockcipher. On the negative side, we find that KEMs derived via FO are not completely non-malleable in general. On the positive side, we show that complete non-malleability holds in the ROM by assuming the underlying PKE scheme meets an additional property, or by a slight tweak of the transformation