Can you modify the encryption specified in §5.2.3.2 mixing in the plaintext so that instead of bi = md(kab|ci-1) we use bi = md(kab|pi-1)? how do you decrypt it? why wouldn't the modified scheme be as secure?

Consider a slotted aloha system, where the time slot equals the fixed duration of each packet. assume that there are 4 stations a,b,c,d sharing the medium. (a) stations a,b,c,d receive one packet each from higher layers at times 1.3, 1.5, 2.6,5.7 respectively. show which transmissions take place when, according to the slottedaloha protocol; describe all transmissions until all four packets have been successful.when needed, each station has access to the following sequence of random number, provided by a random number generator and drawn uniformly between 0 and 1: (1) station a draws numbers: 0.31, 0.27, 0.78, 0.9, 0.9, 0.11, 0. (2) station b draws numbers: 0.45, 0.28, 0.11, 0.83, 0.37, 0.22, 0. (3)station c draws numbers: 0.1, 0.2, 0.3, 0.4, 0. (4) station d draws numbers: 0.36, 0.77, 0.9, 0.1, 0.1, 0.1, 0.1, 0. (b) in slotted aloha, a station transmits in each time slot with a given probability. what probabilities would you assign to each of the four stations so as to: (i) maximize the efficiency of the protocol? (ii) maximize fairness among the four stations? (c) will the efficiency increase or decrease if we modify slotted aloha as follows: (i) get rid of slots and allow stations to transmit immediately? (ii) implement carrier sensing? (iii) implement collision detection? (iv) implement collision avoidance?

Petrică, tânăr licean în clasa a ix-a, a primit în dar de la părinţii săi un cont bancar pentru micile sale cheltuieli curente. el este pasionat de internet banking şi îşi verifică cu grijă toate tranzacţiile efectuate. pentru creşterea securităţii tranzacţiilor online, banca îi furnizează lui petrică un număr pe care el va trebui să îl modifice, obţinând un număr tan – număr de autentificare a tranzacţiei (transaction authentication number). regula de obţinere a numărului tan este următoarea: se formează cel mai mic număr par din toate cifrele numărului furnizat de bancă. cerinţă cunoscând numărul n furnizat de bancă, să se determine numărul tan obţinut de petrică. date de intrare fişierul tan.in conţine pe prima linie numărul natural n cu semnificaţia din enunţ. date de ieşire fişierul de ieşire tan.out va conţine o singură linie pe care va fi scris numărul tan cerut. restricţii • 0 < n < 18*1018 • n are cel puţin o cifră pară • numărul tan obţinut nu poate conţine zerouri nesemnificative

Python. primary u.s. interstate highways are numbered 1-99. odd numbers (like the 5 or 95) go north/south, and evens (like the 10 or 90) go east/west. auxiliary highways are numbered 100-999, and service the primary highway indicated by the rightmost two digits. thus, the 405 services the 5, and the 290 services the 90. given a highway number, indicate whether it is a primary or auxiliary highway. if auxiliary, indicate what primary highway it serves. also indicate if the (primary) highway runs north/south or east/west.