AES, block cipher standards

This repository implements several cryptographic standards in C.

Primarily, different modes of AES from NIST Special Publication 800-38X.

https://csrc.nist.gov/pubs/sp/800/38/a/final

AES is also implemented in Python to simulate timing attacks by looking at S-box leakage.

Disclaimer

They are not resistant to side-channel attacks, nor necessarily performant. They are primarily for educational use.

Build

To build the binaries, run:

make

The binaries will be in bin. For example, one could run:

./bin/main_128

To run some examples with AES-128.

Test

To run the suite of tests, run:

make test

Advanced Encryption Standard (AES)

• FIPS 197 (2001), i.e. AES

NIST Block Cipher Modes (SP 800-38x Series)

• SP 800-38A — Block Cipher Modes of Operation

  • ECB (Electronic Codebook)
  • CBC (Cipher Block Chaining)
  • CFB (Cipher Feedback)
  • OFB (Output Feedback)
  • CTR (Counter Mode)

• SP 800-38B — CMAC (Cipher-based Message Authentication Code)

• SP 800-38C — CCM (Counter with CBC-MAC)

• SP 800-38D — GCM and GMAC (Galois/Counter Mode)

• SP 800-38E — XTS (XEX-based Tweaked CodeBook mode with CipherText Stealing)

• SP 800-38F — Modes for Key Wrapping

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NIST Algorithm Validation & Reference Docs

• CAVP Test Vectors — Implement test harness to verify correctness
• CMVP — (Optional) Integrate self-tests / validation reporting

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Protocol and Standards Integration

• RFC 5116 — AEAD (Authenticated Encryption with Associated Data) interface

• RFC 5288 — AES-GCM Cipher Suites for TLS

• ISO/IEC JTC 1 SC 27 — High-level review of ISO crypto standards (for comparison and interoperability)

• ANSI X9F — Financial crypto standards (e.g., Triple DES modes, MACing) — optional stretch goal

• IEEE Standards — Optional reference (e.g., secure hardware, P1619 XTS mode)

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Additional Tools & Techniques (Implementation Side)

• Implement padding (PKCS#7) and ciphertext stealing (CTS)
• Write reusable AES primitive to support all modes
• Add unit tests for each mode (including edge cases)
• Integrate CAVP test vectors for validation
• Build benchmarking harness (performance & correctness)
• Add error handling and misuse detection (e.g., nonce reuse detection in GCM)

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AES

Implementation

This repository implements basic implementations of AES128 and AES256 in C, Python.

The core algorithm proceeds by performing S-box, shift, mix, and add_round methods.

• sub_bytes(state, sbox);
• shift_rows(state);
• mix_columns(state);
• add_round_key(state, round_keys + round * AES256_BLOCK_SIZE);

These are permutation and substituions methods performed on a block which is length 16 consisting of uint8 bytes. These can be viewed as polynomials in GF(2^8).

Timing

For each possible value of the first plaintext byte (0x00 to 0xFF):

• Fills the 16-byte AES input block with all zeros except the first byte set to that value.
• runs AES encryption many times (e.g., 10,000) on that same block, measuring the total time taken.
• Records the total elapsed time for these encryptions.
• Outputs a CSV where each line corresponds to a plaintext first byte value and the total time to encrypt 10,000 blocks with that first byte.

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