An Alternative to Arithmetic Coding with Local Decodability
msra(2010)
摘要
We describe a simple, but powerful local encoding technique, implying two surprising results: 1. We show how to represent a vector of n values from using dn log2 e bits, such that reading or writing any entry takes O(1) time. This demonstrates, for instance, an \equivalence" between decimal and binary computers, and has been a central toy problem in the eld of succinct data structures. Previous solutions required space of n log 2 + n= lg O(1) n bits for constant access. 2. Given a stream of n bits arriving online (for any n, not known in advance), we can output a prex-free encoding that uses n+log 2 n+O(lg lgn) bits. The encoding and decoding algorithms only require O(lgn) bits of memory, and run in constant time per word. This result is interesting in cryptographic applications, as prex-free codes are the simplest counter-measure to exten- sions attacks on hash functions, message authentication codes and pseudorandom functions. Our result refutes a conjecture of (Maurer, Sjodin 2005) on the hardness of online prex-free encodings.
更多查看译文
关键词
arithmetic coding,hash function,succinct data structure,message authentication code
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络