Cryptology I (Autumn 2007)

Take-home exercises, 5th set

Deadline: October 19th

Task 5a A certain message m was encrypted with three different RSA keys (n1,e1), (n2,e2) and (n3,e3). You'll find both the keys and the ciphertexts c1, c2 and c3 in the file under your name. Find m.
Silver Aabjõe Madis Abel Lidija Agen Erkki Alamäe Alexander Andrusenko Mart Aomets Kalmer Apinis Liisi Haav Roman Jagomägis Andres Kalle Diana Korsmik Magnus Leppik Jelena Makarova Avo Muromägi Jaan Neljandik Long Ngo Long Nguyen Hoang Margus Niitsoo Indrek Priks Kairi Schotter Ivo Seeba Andres Tiko Aleksandr Tkatšenko Ain Uljas Merli Uus Yanjun Yao

Ülesanne 5b A certain message m was encrypted with three different RSA keys (n1,e1), (n2,e2) and (n3,e3). You'll find both the keys and the ciphertexts c1, c2 and c3 in the file under your name. Find m. (Remark: this is different from task 5a.)

Silver Aabjõe Madis Abel Lidija Agen Erkki Alamäe Alexander Andrusenko Mart Aomets Kalmer Apinis Liisi Haav Roman Jagomägis Andres Kalle Diana Korsmik Magnus Leppik Jelena Makarova Avo Muromägi Jaan Neljandik Long Ngo Long Nguyen Hoang Margus Niitsoo Indrek Priks Kairi Schotter Ivo Seeba Andres Tiko Aleksandr Tkatšenko Ain Uljas Merli Uus Yanjun Yao

Ülesanne 5c In the file under your name you'll find a number n that is the product of two large primes and would thus be a suitable RSA module. Unfortunately, one of these primes is smooth. Factor n.

Silver Aabjõe Madis Abel Lidija Agen Erkki Alamäe Alexander Andrusenko Mart Aomets Kalmer Apinis Liisi Haav Roman Jagomägis Andres Kalle Diana Korsmik Magnus Leppik Jelena Makarova Avo Muromägi Jaan Neljandik Long Ngo Long Nguyen Hoang Margus Niitsoo Indrek Priks Kairi Schotter Ivo Seeba Andres Tiko Aleksandr Tkatšenko Ain Uljas Merli Uus Yanjun Yao

Ülesanne 5d Rabin's cryptosystem (whose key you'll find in the file under your name) was used to encrypt the messages m and am+b. The resulting ciphertexts c1 and c2 are in the file below. Also, you'll find the numbers a and b there. Find m.

Silver Aabjõe Madis Abel Lidija Agen Erkki Alamäe Alexander Andrusenko Mart Aomets Kalmer Apinis Liisi Haav Roman Jagomägis Andres Kalle Diana Korsmik Magnus Leppik Jelena Makarova Avo Muromägi Jaan Neljandik Long Ngo Long Nguyen Hoang Margus Niitsoo Indrek Priks Kairi Schotter Ivo Seeba Andres Tiko Aleksandr Tkatšenko Ain Uljas Merli Uus Yanjun Yao

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