Anna and Benoît exchange messages using the following coding table.

Moreover, they use as message unit the tetratagrams (blocks of four letters) that they encode as a number in the following

way:

For example, the word "TEST" becomes the number .

They use the Elgamal cryptosystem with public domain .

Anna's public and private keys are .

Benoît's public and private keys are .

Anna receives the message from Benoît. To which four-letter word this message correponds to ?

Your answer will be a four-letter word in capital letters.

I am given the number and I decide to choose randomly a number between and . What is the probability that will be an acceptable public key for the RSA cryptosystem?

Your answer will be a number with three significant digits.

Nicolas wants to use the RSA cryptosystem and chooses the following data:

, , .

Is his data legitimate ?

Albert and Barnabe exchange information using the RSA cryptosystem. They

wish to check their identities using the authentification procedure.

Their information is given below. Barnabe receives the ciphered signature

Your answer will be "yes" or "no" (without the inverted commas).