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Concept

The Code Book

Summary

The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography is a book by Simon Singh, published in 1999 by Fourth Estate and Doubleday. The Code Book describes some illustrative highlights in the history of cryptography, drawn from both of its principal branches, codes and ciphers. Thus the book's title should not be misconstrued as suggesting that the book deals only with codes, and not with ciphers; or that the book is in fact a codebook. Contents The Code Book covers diverse historical topics including the Man in the Iron Mask, Arabic cryptography, Charles Babbage, the mechanisation of cryptography, the Enigma machine, and the decryption of Linear B and other ancient writing systems. Later sections cover the development of public-key cryptography. Some of this material is based on interviews with participants, including persons who worked in secret at GCHQ. The book concludes with a discussion of "Pretty Good Privacy" (PGP), quantum computing, and

Official source

https://en.wikipedia.org/wiki/The_Code_Book

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Cryptography, or cryptology (from κρυπτός "hidden, secret"; and γράφειν graphein, "to write", or -λογία -logia, "study", respectively), is the practice and study of techniques for secure communicatio

Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysi

The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany

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Linear (Hull) and Algebraic Cryptanalysis of the Block Cipher PRESENT

Jorge Nakahara, Pouyan Sepehrdad

The contributions of this paper include the first linear hull and a revisit of the algebraic cryptanalysis of reduced-round variants of the block cipher PRESENT, under known-plaintext and ciphertext- only settings. We introduce a pure algebraic cryptanalysis of 5-round PRESENT and in one of our attacks we recover half of the bits of the key in less than three minutes using an ordinary desktop PC. The PRESENT block cipher is a design by Bogdanov et al., announced in CHES 2007 and aimed at RFID tags and sensor networks. For our linear attacks, we can attack 25-round PRESENT with the whole code book, 296.68 25- round PRESENT encryptions, 240 blocks of memory and 0.61 success rate. Further we can extend the linear attack to 26-round with small success rate. As a further contribution of this paper we computed linear hulls in practice for the original PRESENT cipher, which corroborated and even improved on the predicted bias (and the corresponding attack complexities) of conventional linear relations based on a single linear trail.

Springer Berlin / Heidelberg2009

The National Institute of Standards and Technology (NIST) recently published a Format-Preserving Encryption standard accepting two Feistel structure based schemes called FF1 and FF3. Particularly, FF3 is a tweakable block cipher based on an 8-round Feistel network. In CCS~2016, Bellare et. al. gave an attack to break FF3 (and FF1) with time and data complexity

O(N^5\log(N))

, which is much larger than the code book (but using many tweaks), where

N^2

is domain size to the Feistel network. In this work, we give a new practical total break attack to the FF3 scheme (also known as BPS scheme). Our FF3 attack requires

O(N^{\frac{11}{6}})

chosen plaintexts with time complexity

O(N^{5})

. Our attack was successfully tested with

N\leq2^9

. It is a slide attack (using two tweaks) that exploits the bad domain separation of the FF3 design. Due to this weakness, we reduced the FF3 attack to an attack on 4-round Feistel network. Biryukov et. al. already gave a 4-round Feistel structure attack in SAC~2015. However, it works with chosen plaintexts and ciphertexts whereas we need a known-plaintext attack. Therefore, we developed a new generic known-plaintext attack to 4-round Feistel network that reconstructs the entire tables for all round functions. It works with

N^{\frac{3}{2}} \left( \frac{N}{2} \right)^{\frac{1}{6}}

known plaintexts and time complexity

O(N^{3})

. Our 4-round attack is simple to extend to five and more rounds with complexity

N^{(r-5)N+o(N)}

. It shows that FF1 with

N=7

and FF3 with

7\leq N\leq10

do not offer a 128-bit security. Finally, we provide an easy and intuitive fix to prevent the FF3 scheme from our

O(N^{5})

attack.

2017

Related-Key Attack against Triple Encryption based on Fixed Points

Serge Vaudenay

Triple encryption was proposed to increase the security of single encryption when the key is too short. In the past, there have been several attacks in this encryption mode. When triple encryption is based on two keys, Merkle and Hellman proposed a subtle meet-in-the-middle attack which can break it at a price similar to breaking single encryption (but with nearly all the code book). When triple encryption is based on three keys, Kelsey, Schneier, and Wagner proposed a related-key attack which can break it at a price similar to breaking single encryption. In this paper, we propose a new related-key attack against triple encryption which compares to breaking single encryption in the two cases. Our attack against two-key triple-encryption has exactly the same performances as a meet-in-the-middle on double-encryption. It is based on the discovery of fixed points in a decrypt-encrypt sequence using related keys. In the two-key case, it is comparable to the Merkle-Hellman attack (except that is uses related keys). In the three-key case, it has a higher complexity than the Kelsey-Schneier-Wagner attack but can live with known plaintexts.

SciTePress2011

O(N^5\log(N))