Question

AES128 encryption given by the following setting (Note: plaintext, Cipherkey and Ciphertext are Bytes)

a. Plaintext: 00……00 Cipherkey: 00……00 Ciphertext: 66 E9 4B D4 EF 8A 2C 3B 88 4C FA 59 CA 34 2B 2E

b. Plaintext: 00……01 Cipherkey: 00……00 Ciphertext: 58 E2 FC CE FA 7E 30 61 36 7F 1D 57 A4 E7 45 5A

c. Plaintext: 00……00 Cipherkey: 00……01 Ciphertext: 05 45 AA D5 6D A2 A9 7C 36 63 D1 43 2A 3D 1C 84

Please compare the result of the ciphertext from the above questions, and explain what are the difference.

Answer 1

a. Plaintext: 00……00 Cipherkey: 00……00 Ciphertext: 66 E9 4B D4 EF 8A 2C 3B 88 4C FA 59 CA 34 2B 2E

b. Plaintext: 00……01 Cipherkey: 00……00 Ciphertext: 58 E2 FC CE FA 7E 30 61 36 7F 1D 57 A4 E7 45 5A

c. Plaintext: 00……00 Cipherkey: 00……01 Ciphertext: 05 45 AA D5 6D A2 A9 7C 36 63 D1 43 2A 3D 1C 84

From the given question that plaintext is the same for a and c but the cipher key is only changed by a single bit but the ciphertext is completely changed. It shows that a single bit doesn't affect a part of the resulted ciphertext but a complete change. Which shows how powerful is AES encryption.

And comparing a and b the cipher key is same but plain text is only changed by a bit. And as a result, the whole ciphertext is changed.

It shows a single bit change in plaintext or cipher key the resulted cipher text is complelty changed.  This is due to the working of AES 128 bit encryption.

In AES 128. Data is treated as plaintext block. In 128 AES 10 rounds are performed where in each round a new AES key is generated from original aes key.