w2-aes

Week 2: AES in CBC and CTR modes

In this project, we have two encryption/decryption systems:

• AES in CBC mode
• AES in counter mode (CTR)

In both cases the 16-byte encryption IV is chosen at random and is prepended to the ciphertext.

For CBC encryption, we use the PKCS7 padding scheme.

In this assignment, we are given an AES key and a ciphertext (both are hex encoded) and our goal is to recover the plaintext.

We use an existing crypto library, aes-soft, for its built-in AES function, and we only implement the CBC and CTR modes.

Problem 1

• CBC key: 140b41b22a29beb4061bda66b6747e14
• CBC Ciphertext 1:

4ca00ff4c898d61e1edbf1800618fb2828a226d160dad07883d04e008a7897ee2e4b7465d5290d0c0e6c6822236e1daafb94ffe0c5da05d9476be028ad7c1d81

Problem 2

• CBC key: 140b41b22a29beb4061bda66b6747e14
• CBC Ciphertext 2:

5b68629feb8606f9a6667670b75b38a5b4832d0f26e1ab7da33249de7d4afc48e713ac646ace36e872ad5fb8a512428a6e21364b0c374df45503473c5242a253

Problem 3

• CTR key: 36f18357be4dbd77f050515c73fcf9f2
• CTR Ciphertext 1:

69dda8455c7dd4254bf353b773304eec0ec7702330098ce7f7520d1cbbb20fc388d1b0adb5054dbd7370849dbf0b88d393f252e764f1f5f7ad97ef79d59ce29f5f51eeca32eabedd9afa9329

Problem 4

• CTR key: 36f18357be4dbd77f050515c73fcf9f2
• CTR Ciphertext 2:

770b80259ec33beb2561358a9f2dc617e46218c0a53cbeca695ae45faa8952aa0e311bde9d4e01726d3184c34451