Again with the same data:

• B wishes to send the message 12345 to A. What is the ciphertext?

• Moreover, A receives the ciphertext 12345 from C. What is the corresponding plaintext?

Your answer will be a couple of integers (x,y).

There's a third agent with data and .

A and B wish to send to C the same message :102030

A ciphers the message and finds the number

A ciphers the message and finds the number

What is the value of  ?

Your answer will be a relative number.

B chooses and .

Compute Euler's function and, if the choice of is legitimate, find the public key .

Your answer will be either a couple of integers or the word "impossible" (without the inverted commas).

B chooses and .

Compute Euler's function and, if the choice of is legitimate, find the public key .

Your answer will be either a couple of integers or the word "impossible" (without the inverted commas).

A chooses and .

Compute Euler's function and, if the choice of is legitimate, find the private key .

Your answer will be either a couple of integers or the word "impossible" (without the inverted commas).

A chooses and .

Compute Euler's function and, if the choice of is legitimate, find the private key .

Your answer will be either a couple of integers or the word "impossible" (without the inverted commas).

You receive the following ciphertext: .

Decipher the message knowing that it has been enciphered using an affine transformation on digraphs, using the usual alphabet of 26 letters (a=, b=, etc) and with the following enciphering key:

.

Your answer will be a word (no capital letters).