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Python implementation of Ascon

This is a Python3 implementation of Ascon, a family of lightweight cryptographic algorithms. ascon.py includes the authenticated encryption and hash function variants as specified in NIST SP 800-232 (initial public draft).

https://github.com/meichlseder/pyascon

Ascon

Ascon is a family of authenticated encryption (AEAD) and hashing algorithms designed to be lightweight and easy to implement, even with added countermeasures against side-channel attacks. It was designed by a team of cryptographers from Graz University of Technology, Infineon Technologies, and Radboud University: Christoph Dobraunig, Maria Eichlseder, Florian Mendel, and Martin Schläffer.

Ascon has been selected as the standard for lightweight cryptography in the NIST Lightweight Cryptography competition (2019–2023) and as the primary choice for lightweight authenticated encryption in the final portfolio of the CAESAR competition (2014–2019).

Find more information, including the specification and more implementations here:

https://ascon.iaik.tugraz.at/

Algorithms

This is a simple reference implementation of Ascon as specified in NIST's draft standard, NIST SP 800-232, which includes

  • Authenticated encryption ascon_encrypt(key, nonce, associateddata, plaintext, variant="Ascon-AEAD128") (and similarly decrypt):

    • Ascon-AEAD128

  • Hashing algorithms ascon_hash(message, variant="Ascon-Hash256", hashlength=32) including 3 hash function variants with slightly different interfaces:

    • Ascon-Hash256 with fixed 256-bit output
    • Ascon-XOF128 with variable output lengths (specified with hashlength)
    • Ascon-CXOF128 with variable output lengths (hashlength) and supporting a customization string as an additional input (to be implemented)

Older Algorithm Variants

Older versions of ascon.py implement Ascon v1.2 as submitted to the NIST LWC competition and published in the Journal of Cryptology, as well as additional functionality for message authentication. These versions can be found in commit (TODO), including

  • Authenticated encryption:

    • Ascon-128
    • Ascon-128a
    • Ascon-80pq

  • Hashing algorithms:

    • Ascon-Hash
    • Ascon-Hasha
    • Ascon-Xof
    • Ascon-Xofa

  • Message authentication codes ascon_mac(key, message, variant="Ascon-Mac", taglength=16) for 5 MAC variants (from https://eprint.iacr.org/2021/1574, not part of the LWC proposal) with fixed 128-bit (Mac) or variable (Prf) output lengths, including a variant for short messages of up to 128 bits (PrfShort).

    • Ascon-Mac
    • Ascon-Maca
    • Ascon-Prf
    • Ascon-Prfa
    • Ascon-PrfShort

Files

  • ascon.py: Implements all family members as well as the underlying permutation:

    • ascon_encryption()/ascon_decrypt() for authenticated encryption,
    • ascon_hash() for hashing,
    • ascon_mac() for message authentication,
    • ascon_permutation() for the underlying permutation.

    By default, prints the results of encrypting and hashing some example strings.

    • debug = True|False: Set this variable to print the intermediate state after each phase of the encryption/hashing process.
    • debugpermutation = True|False: Set this variable to print the intermediate state after each step of the permutation's round function.

  • genkat.py: Produces result files for the Known Answer Tests (KATs) defined for the NIST LWC competition (call for algorithms, test vector generation code).

    Call with the name of the target algorithm (see above) as first parameter, default is Ascon-AEAD128:

    python3 genkat.py Ascon-AEAD128

    Results are written to

    • LWC_AEAD_KAT_{klenbits}_{nlenbits}.txt for authenticated encryption,
    • LWC_HASH_KAT_{hlenbits}.txt for hashing,
    • LWC_XOF_KAT_{hlenbits}.txt for extendable-output hashing (custom KAT configuration),
    • LWC_CXOF_KAT_{hlenbits}.txt for customizable-input extendable-output hashing (custom KAT configuration), and
    • LWC_AUTH_KAT_128_128.txt for various message authentication codes.

    Additionally, a JSON version of the same data is written to the corresponding .json files. Note that this may overwrite KATs for other variants which share the same parameters (in the AUTH case).

  • writer.py: Helper code for genkat.py that specifies the text and JSON encoding.