Let me give you two simple examples: While the examples above are trivial, they do represent two of the functional pairs that are used with PKC; namely, the ease of multiplication and exponentiation versus the relative difficulty of factoring and calculating logarithms, respectively.The mathematical "trick" in PKC is to find a trap door in the one-way function so that the inverse calculation becomes easy given knowledge of some item of information. It is termed "self-synchronizing" because the decryption process can stay synchronized with the encryption process merely by knowing how far into the n-bit keystream it is. Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream.There are several other references that describe interesting algorithms and even SKC codes dating back decades.
One advantage of the Feistel design is that the encryption and decryption stages are similar, sometimes identical, requiring only a reversal of the key operation, thus dramatically reducing the size of the code (software) or circuitry (hardware) necessary to implement the cipher. Challenge-Handshake Authentication Protocol (CHAP) 5.15. Secure E-mail and S/MIME Secret key cryptography methods employ a single key for both encryption and decryption.Synchronous stream ciphers generate the keystream in a fashion independent of the message stream but by using the same keystream generation function at sender and receiver. Barreto and Brice Odilon Boidje and Pierre-Louis Cayrel and Gilbert Ndollane Dione and Kris Gaj and Cheikh Thiecoumba Gueye and Richard Haeussler and Jean Belo Klamti and Ousmane N'diaye and Duc Tri Nguyen and Edoardo Persichetti and and Jefferson E. Bernstein and Stefan Klbl and Stefan Lucks and Pedro Maat Costa Massolino and Florian Mendel and Kashif Nawaz and Tobias Schneider and Peter Schwabe and Franois-Xavier Standaert and Yosuke Todo and Benot Viguier Karthikeyan Bhargavan and Antoine Delignat-Lavaud and Cédric Fournet and Markulf Kohlweiss and Jianyang Pan and Jonathan Protzenko and Aseem Rastogi and Nikhil Swamy and Santiago Zanella-Béguelin and Jean Karim ZinzindohouéEli Ben-Sasson and Iddo Ben-Tov and Alessandro Chiesa and Ariel Gabizon and Daniel Genkin and Matan Hamilis and Evgenya Pergament and Michael Riabzev and Mark Silberstein and Eran Tromer and Madars Virza The QARMA Block Cipher Family -- Almost MDS Matrices Over Rings With Zero Divisors, Nearly Symmetric Even-Mansour Constructions With Non-Involutory Central Rounds, and Search Heuristics for Low-Latency S-Boxes Roman Oliynykov and Ivan Gorbenko and Oleksandr Kazymyrov and Victor Ruzhentsev and Oleksandr Kuznetsov and Yurii Gorbenko and Oleksandr Dyrda and Viktor Dolgov and Andrii Pushkaryov and Ruslan Mordvinov and Dmytro Kaidalov A New Class of Public Key Cryptosystems Constructed Based on Reed-Solomon Codes, K(XII)SE(1)PKC.-- Along with a presentation of K(XII)SE(1)PKC over the extension field extensively used for present day various storage and transmission systems -- Julia Borghoff and Anne Canteaut and Tim Gneysu and Elif Bilge Kavun and Miroslav Kneević and Lars R. One problem is error propagation; a garbled bit in transmission will result in n garbled bits at the receiving side. With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret.