Question answers

Question 1

how to combine compression and encryption

Answer 1

better compress then encrypt since the encryption looks like random numbers and it can not be compressed

Question 2

how to combine the encryption and error correction

Answer 2

error correction should be applied after the encryption either there would difficulties decrypting the message

Question 3

attack on AES

Answer 3

For cryptographers, a cryptographic “break” is anything faster than a brute-force attack – i.e., performing one trial decryption for each possible key in sequence (see Cryptanalysis). A break can thus include results that are infeasible with current technology.

Question 4

E′k(m) = Ek(m)||first bit(m)

Answer 4

this is not IND-cpa secure since the cipher text reveals information about the plain text :
bringing up two message m1 , m2 and recognizing the difference can easily lead t discovering the key