Results 1 
8 of
8
Substitution Deciphering Based on HMMs with Applications to Compressed Document Processing
 IEEE Transactions on Pattern Analysis and Machine Intelligence
, 2002
"... It has been shown that simple substitution ciphers can be solved using statistical methods such as probabilistic relaxation. However, the utility of such solutions has been limited by their inability to cope with noise encountered in practical applications. In this paper, we propose a new solution ..."
Abstract

Cited by 11 (0 self)
 Add to MetaCart
It has been shown that simple substitution ciphers can be solved using statistical methods such as probabilistic relaxation. However, the utility of such solutions has been limited by their inability to cope with noise encountered in practical applications. In this paper, we propose a new solution to substitution deciphering based on hidden Markov models. We show that our algorithm is more accurate than relaxation and much more robust in the presence of noise, making it useful for applications in compressed document processing. Recovering character interpretations from the sequence of cluster identifiers in a symbolically compressed document can be treated as a cipher problem. Although a significant amount of noise is present in the cluster sequence, enough information can be recovered with a robust deciphering algorithm to accomplish certain document analysis tasks. The feasibility of this approach is demonstrated in a multilingual document duplicate detection system.
Attacking decipherment problems optimally with loworder ngram models
 In Proceedings of EMNLP 2008
, 2008
"... We introduce a method for solving substitution ciphers using loworder letter ngram models. This method enforces global constraints using integer programming, and it guarantees that no decipherment key is overlooked. We carry out extensive empirical experiments showing how decipherment accuracy var ..."
Abstract

Cited by 10 (6 self)
 Add to MetaCart
We introduce a method for solving substitution ciphers using loworder letter ngram models. This method enforces global constraints using integer programming, and it guarantees that no decipherment key is overlooked. We carry out extensive empirical experiments showing how decipherment accuracy varies as a function of cipher length and ngram order. We also make an empirical investigation of Shannonâ€™s (1949) theory of uncertainty in decipherment. 1
How to Break Gifford's Cipher
, 1994
"... We present and implement a ciphertextonly algorithm to break Gifford's cipher, a stream cipher designed in 1984 by David Gifford of MIT and used to encrypt New York Times and Associated Press wire reports. Applying linear algebra over finite fields, we exploit a timespace tradeoff to separately de ..."
Abstract

Cited by 9 (1 self)
 Add to MetaCart
We present and implement a ciphertextonly algorithm to break Gifford's cipher, a stream cipher designed in 1984 by David Gifford of MIT and used to encrypt New York Times and Associated Press wire reports. Applying linear algebra over finite fields, we exploit a timespace tradeoff to separately determine key segments derived from a decomposition of the feedback function. This work, the first proposed attack on Gifford's cipher, illustrates a powerful attack on stream ciphers and shows that Gifford's cipher is illsuited for encrypting broadcast data in the MITbased Boston Community Information System (BCIS). Gifford's cipher is a filter generatora linear feedback shift register with nonlinear output. Our cryptanalytic problem is to determine the secret 64bit initial fill, which is changed for each news article. Representing the feedback function as a binary matrix F , we decompose the vector space of register states into a direct sum of four F invariant subspaces determined fr...
The Cryptanalysis of a Three Rotor Machine Using a Genetic
 Proceedings of the Seventh International Conference on Genetic Algorithms (ICGA97
, 1997
"... This paper describes a method of deciphering messages encrypted with rotor machines utilising a Genetic Algorithm to search the keyspace. A fitness measure based on the phi test for non randomness of text is described and the results show that an unknown three rotor machine can generally be cr ..."
Abstract

Cited by 4 (0 self)
 Add to MetaCart
This paper describes a method of deciphering messages encrypted with rotor machines utilising a Genetic Algorithm to search the keyspace. A fitness measure based on the phi test for non randomness of text is described and the results show that an unknown three rotor machine can generally be cryptanalysed with about 4000 letters of ciphertext. The results are compared to those given using a previously published technique and found to be superior.
Bayesian Inference for Zodiac and Other Homophonic Ciphers
"... We introduce a novel Bayesian approach for deciphering complex substitution ciphers. Our method uses a decipherment model which combines information from letter ngram language models as well as word dictionaries. Bayesian inference is performed on our model using an efficient sampling technique. We ..."
Abstract

Cited by 4 (1 self)
 Add to MetaCart
We introduce a novel Bayesian approach for deciphering complex substitution ciphers. Our method uses a decipherment model which combines information from letter ngram language models as well as word dictionaries. Bayesian inference is performed on our model using an efficient sampling technique. We evaluate the quality of the Bayesian decipherment output on simple and homophonic letter substitution ciphers and show that unlike a previous approach, our method consistently produces almost 100 % accurate decipherments. The new method can be applied on more complex substitution ciphers and we demonstrate its utility by cracking the famous Zodiac408 cipher in a fully automated fashion, which has never been done before. 1
The Applications of Genetic Algorithms in Cryptanalysis
, 1996
"... This thesis describes a method of deciphering messages encrypted with rotor machines utilising a Genetic Algorithm to search the keyspace. A fitness measure based on the phi test for non randomness of text is described and the results show that an unknown three rotor machine can generally be cryptan ..."
Abstract

Cited by 3 (0 self)
 Add to MetaCart
This thesis describes a method of deciphering messages encrypted with rotor machines utilising a Genetic Algorithm to search the keyspace. A fitness measure based on the phi test for non randomness of text is described and the results show that an unknown three rotor machine can generally be cryptanalysed with about 4000 letters of ciphertext. The results are compared to those given using a previously published technique and found to be superior. Acknowledgements I would like to thank my supervisors, Vic RaywardSmith and Geoff McKeown, for their help and encouragement. Contents 1 Introduction 8 2 Statistical Inference 10 2.1 Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : 10 2.2 Uncertainty : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 2.2.1 Rules of Probability : : : : : : : : : : : : : : : : : : : 12 2.2.2 Frequency Probability : : : : : : : : : : : : : : : : : : 15 2.2.3 Subjective Probability : : : : : : : : : : : : : : : : : : 15 2.3 Modelling...
The New C Standard: Sentence 782
"... This is "sentence 782" extracted from the book "The New C Standard: An Economic and Cultural Commentary" ..."
Abstract
 Add to MetaCart
This is "sentence 782" extracted from the book "The New C Standard: An Economic and Cultural Commentary"
How to Break Gifford's Cipher (Extended Abstract)
, 1994
"... We present and implement a ciphertextonly algorithm to break Gifford's cipher, a stream cipher designed in 1984 by David Gifford of MIT and used to encrypt New York Times and Associated Press wire reports. Applying linear algebra over finite fields, we exploit a timespace tradeoff to separately de ..."
Abstract
 Add to MetaCart
We present and implement a ciphertextonly algorithm to break Gifford's cipher, a stream cipher designed in 1984 by David Gifford of MIT and used to encrypt New York Times and Associated Press wire reports. Applying linear algebra over finite fields, we exploit a timespace tradeoff to separately determine key segments derived from a decomposition of the feedback function. This work, the first proposed attack on Gifford's cipher, illustrates a powerful attack on stream ciphers and shows that Gifford's cipher is illsuited for encrypting broadcast data in the MITbased Boston Community Information System (BCIS). Gifford's cipher is a filter generatora linear feedback shift register with nonlinear output. Our cryptanalytic problem is to determine the secret 64bit initial fill, which is changed for each news article. Representing the feedback function as a binary matrix F , we decompose the vector space of register states into a direct sum of four F invariant Support for this res...