| Preface |
| Introduction / 1： |
| Some aspects of secure communication |
| Julius Caesar's cipher |
| Some basic definitions |
| Three stages to decrytion: identification, breaking and setting |
| Codes and ciphers |
| Assessing the strength of a cipher system |
| Error detecting and correcting codes |
| Other methods of concealing messages |
| Modular arithmetic |
| Modular addition and subtraction of letters |
| Gender |
| End matter |
| From Julius Caesar to simple substitution / 2： |
| Julius Caesar ciphers and their solution |
| Simple substitution ciphers |
| How to solve a simple substitution cipher |
| Letter frequencies in languages other than English |
| How many letters are needed to solve a simple substitution cipher? |
| Polyalphabetic systems / 3： |
| Strengthening Julius Caesar: Vigenere ciphers |
| How to solve a Vigenere cipher |
| Indicators |
| Depths |
| Recognising 'depths' |
| How much text do we need to solve a Vigenere cipher? |
| Jefferson's cylinder |
| Jigsaw ciphers / 4： |
| Transpositions |
| Simple transposition |
| Double transposition |
| Other forms of transposition |
| Assessment of the security of transposition ciphers |
| Double encipherment in general |
| Two-letter ciphers / 5： |
| Monograph to digraph |
| MDTM ciphers |
| Digraph to digraph |
| Playfair encipherment |
| Playfair decipherment |
| Cryptanalytic aspects of Playfair |
| Double Playfair |
| Codes / 6： |
| Characteristics of codes |
| One-part and two-part codes |
| Code plus additive |
| Ciphers for spies / 7： |
| Stencil ciphers |
| Book ciphers |
| Letter frequencies in book ciphers |
| Solving a book cipher |
| Disastrous errors in using a book cipher |
| 'Garbo"s ciphers |
| One-time pad |
| Producing random numbers and letters / 8： |
| Random sequences |
| Producing random sequences |
| Coin spinning |
| Throwing dice |
| Lottery type draws |
| Cosmic rays |
| Amplifier noise |
| Pseudo-random sequences |
| Linear recurrences |
| Using a binary stream of key for encipherment |
| Binary linear sequences as key generators |
| Cryptanalysis of a linear recurrence |
| Improving the security of binary keys |
| Pseudo-random number generators |
| The mid-square method |
| Linear congruential generators |
| The Enigma cipher machine / 9： |
| Historical background |
| The original Enigma |
| Encipherment using wired wheels |
| Encipherment by the Enigma |
| The Enigma plugboard |
| The Achilles heel of the Enigma |
| The indicator 'chains' in the Enigma |
| Aligning the chains |
| Identifying R1 and its setting |
| Doubly enciphered Enigma messages |
| The Abwehr Enigma |
| The Hagelin cipher machine / 10： |
| Structure of the Hagelin machine |
| Encipherment on the Hagelin |
| Choosing the cage for the Hagelin |
| The theoretical 'work factor' for the Hagelin |
| Solving the Hagelin from a stretch of key |
| Additional features of the Hagelin machine |
| The slide |
| Identifying the slide in a cipher message |
| Overlapping |
| Solving the Hagelin from cipher texts only |
| Beyond the Enigma / 11： |
| The SZ42: a pre-electronic machine |
| Description of the SZ42 machine |
| Encipherment on the SZ42 |
| Breaking and setting the SZ42 |
| Modifications to the SZ42 |
| Public key cryptography / 12： |
| Security issues |
| Protection of programs and data |
| Encipherment of programs, data and messages |
| The key distribution problem |
| The Diffie-Hellman key exchange system |
| Strength of the Diffie-Hellman system |
| Encipherment and the internet / 13： |
| Generalisation of simple substitution |
| Factorisation of large integers |
| The standard method of factorisation |
| Fermat's 'Little Theorem' |
| The Fermat-Euler Theorem (as needed in the RSA system) |
| Encipherment and decipherment keys in the RSA system |
| The encipherment and decipherment processes in the RSA system |
| How does the key-owner reply to correspondents? |
| The Data Encryption Standard (DES) |
| Security of the DES |
| Chaining |
| Implementation of the DES |
| Using both RSA and DES |
| A salutary note |
| Beyond the DES |
| Authentication and signature verification |
| Elliptic curve cryptography |
| Appendix |
| Solutions to problems |
| References |
| Name index |
| Subject index |
| Preface |
| Introduction / 1： |
| Some aspects of secure communication |
| Julius Caesar's cipher |
| Some basic definitions |
| Three stages to decrytion: identification, breaking and setting |
