883 research outputs found
Reducing branch delay to zero in pipelined processors
A mechanism to reduce the cost of branches in pipelined processors is described and evaluated. It is based on the use of multiple prefetch, early computation of the target address, delayed branch, and parallel execution of branches. The implementation of this mechanism using a branch target instruction memory is described. An analytical model of the performance of this implementation makes it possible to measure the efficiency of the mechanism with a very low computational cost. The model is used to determine the size of cache lines that maximizes the processor performance, to compare the performance of the mechanism with that of other schemes, and to analyze the performance of the mechanism with two alternative cache organizations.Peer ReviewedPostprint (published version
Strongly Secure and Efficient Data Shuffle On Hardware Enclaves
Mitigating memory-access attacks on the Intel SGX architecture is an
important and open research problem. A natural notion of the mitigation is
cache-miss obliviousness which requires the cache-misses emitted during an
enclave execution are oblivious to sensitive data. This work realizes the
cache-miss obliviousness for the computation of data shuffling. The proposed
approach is to software-engineer the oblivious algorithm of Melbourne shuffle
on the Intel SGX/TSX architecture, where the Transaction Synchronization
eXtension (TSX) is (ab)used to detect the occurrence of cache misses. In the
system building, we propose software techniques to prefetch memory data prior
to the TSX transaction to defend the physical bus-tapping attacks. Our
evaluation based on real implementation shows that our system achieves superior
performance and lower transaction abort rate than the related work in the
existing literature.Comment: Systex'1
Permuting operations on strings: Their permutations and their primes
We study some length-preserving operations on strings that permute the symbol positions in strings. These operations include some well-known examples (reversal, circular or cyclic shift, shuffle, twist, operations induced by the Josephus problem) and some new ones based on Archimedes spiral. Such a permuting operation gives rise to a family of similar permutations. We investigate the structure and the order of the cyclic group generated by such a permutation . We call an integer -prime if consists of a single cycle of length (). Then we show some properties of these -primes, particularly, how -primes are related to -primes as well as to ordinary prime numbers
DR.SGX: Hardening SGX Enclaves against Cache Attacks with Data Location Randomization
Recent research has demonstrated that Intel's SGX is vulnerable to various
software-based side-channel attacks. In particular, attacks that monitor CPU
caches shared between the victim enclave and untrusted software enable accurate
leakage of secret enclave data. Known defenses assume developer assistance,
require hardware changes, impose high overhead, or prevent only some of the
known attacks. In this paper we propose data location randomization as a novel
defensive approach to address the threat of side-channel attacks. Our main goal
is to break the link between the cache observations by the privileged adversary
and the actual data accesses by the victim. We design and implement a
compiler-based tool called DR.SGX that instruments enclave code such that data
locations are permuted at the granularity of cache lines. We realize the
permutation with the CPU's cryptographic hardware-acceleration units providing
secure randomization. To prevent correlation of repeated memory accesses we
continuously re-randomize all enclave data during execution. Our solution
effectively protects many (but not all) enclaves from cache attacks and
provides a complementary enclave hardening technique that is especially useful
against unpredictable information leakage
Permutations, Representations, and Partition Algebras: A Random Walk through Algebraic Statistics
My thesis examines a class of functions on the symmetric group called permutation statistics using tools from representation theory. In 2014, Axel Hultman gave formulas for computing expected values of permutation statistics sampled via random walks. I present analogous formulas for computing variances of these statistics involving Kronecker coefficients – certain numbers that arise in the representation theory of the symmetric group. I also explore deep connections between the study of moments of permutation statistics and the representation theory of the partition algebras, a family of algebras introduced by Paul Martin in 1991. By harnessing these partition algebras, I derive a new polynomial describing the mean statistic of the 2nd moment of the number of inversions of a permutation
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