Menu > Articles de la revue de presse : - l'ensemble [tous | francophone] - par mots clé [tous] - par site [tous] - le tagwall [voir] - Top bi-hebdo de la revue de presse [Voir]

---

S'abonner au fil RSS global de la revue de presse

---

Présentation : The New Scientist has reported on recently declassified letters that were exchanged between John Nash and the NSA in the mid 50 s pertaining to his ideas of building cryptosystems that are essentially unbreakable in practice. At that time the one time pad of Shannon was well-known but Nash, like Shannon himself, hit upon the idea that the inconvenience of managing keys in a perfectly secure cryptosystem could be traded for one where the key space is so large that it cannot be searched in a feasible amount of time. Nash quotes the unicity distance as a measure of how much ciphertext is required to determine the key uniquely, which is infinite for the one time pad but small for a cipher with a fixed key. Even so, quickly obtaining the small amount of ciphertext to uniquely determine the key in principle does not mean that the task of recovering that unique key is computationally easy. Nash outlined his ideas for building a computationally secure cipher to the NSA in a handwritten letter, and proposed a cipher to meet these criteria, a snippet of which is shown below he would not be winning any awards for his cursive . image Nash made the prophetic remark that substitutions ciphers can be broken piecemeal with partial information accumulating, and that the game of cipher breaking by skilled teams is essentially a thing of the past. In short, and with hindsight then, people that could break the Enigma would not be prepared to break RSA, or other cryptosystems based on computationally difficult problems from number theory. The scale had changed. It seems that the NSA broke the cipher that was proposed by Nash, or did not think it interesting or practical. In any case, they did not wish to pursue the ideas expressed by Nash, and told him as much. Nash s letter was written about 20 years before the ideas of pubic key cryptography became mainstream in the mid 70 s. The New Scientist article related Nash s proposal for an effectively unbreakable cipher to one of the The Millennium Problems, proposed by the Clay Mathematics Institute. Each problem or challenge if you prefer carries a prize of 1 million dollars for a solution, and a cipher that would require exponential work to solve implies a solution for the P vs. NP problem.






Les derniers articles du site "No Tricks" :

- Some Mindmaps Online
- The 12 Bonk Rule
- Some more Satellite Risks
- John Nash on modern Cryptography
- Chrome headed to be 1 Browser
- Crypto from Tesco
- Xobni becomes Smartr
- Yoda Pie Chart - there is no Try
- 150,000 reads of my Scribd documents
- SHA post as SPAM magnet

---

S'abonner au fil RSS global de la revue de presse

---