Biblio

Direct Memory Access (DMA) attacks can allow attackers to access memory directly, bypassing OS supervision or software protections. In this work, we put forth and benchmark a cryptographically secure attestation scheme, which detects DMA attacks. In fact, our scheme detects any attack in a more general class of attacks which we call "direct injection". We prove security of our scheme under a realistic machine model which extends in a non-trivial manner a cryptographic model proposed by Lipton, Ostrovsky, and Zikas (ICALP 2016.) Despite the fact that our scheme, in its current form, protects against write-only attacks, both our security model and our scheme can be extended to allow the attacker to have additional read access to memory—thereby capturing leakage—as well as detecting more types of memory corruptions such as bit flips.

In a secret sharing scheme a dealer shares a secret s among n parties such that an adversary corrupting up to t parties does not learn s, while any t+1 parties can efficiently recover s. Over a long period of time all parties may be corrupted thus violating the threshold, which is accounted for in Proactive Secret Sharing (PSS). PSS schemes periodically rerandomize (refresh) the shares of the secret and invalidate old ones. PSS retains confidentiality even when all parties are corrupted over the lifetime of the secret, but no more than t during a certain window of time, called the refresh period. Existing PSS schemes only guarantee secrecy in the presence of an honest majority with less than n2 total corruptions during a refresh period; an adversary corrupting a single additional party, even if only passively, obtains the secret. This work is the first feasibility result demonstrating PSS tolerating a dishonest majority, it introduces the first PSS scheme secure against t passive adversaries without recovery of lost shares, it can also recover from honest faulty parties losing their shares, and when tolerating e faults the scheme tolerates t passive corruptions. A non-robust version of the scheme can tolerate t active adversaries, and mixed adversaries that control a combination of passively and actively corrupted parties that are a majority, but where less than n/2-e of such corruptions are active. We achieve these high thresholds with O(n4) communication when sharing a single secret, and O(n3) communication when sharing multiple secrets in batches.