Paper 2022/567

FC1: A Powerful, Non-Deterministic, Symmetric Key Cipher

Michele Fabbrini


In this paper we describe a symmetric key algorithm that offers an unprecedented grade of confidentiality. Based on the uniqueness of the modular multiplicative inverse of a positive integer a modulo n and on its computability in a polynomial time, this non-deterministic cipher can easily and quickly handle keys of millions or billions of bits that an attacker does not even know the length of. The algorithm’s primary key is the modulo, while the ciphertext is given by the concatenation of the modular inverse of blocks of plaintext whose length is randomly chosen within a predetermined range. In addition to the full specification, we present a working implementation of it in Julia Programming Language, accompanied by real examples of encryption and decryption.

Available format(s)
Secret-key cryptography
Publication info
Preprint. MINOR revision.
symmetric key ciphernon-deterministic algorithm
Contact author(s)
fc1 @ fabbrini org
2022-05-12: revised
2022-05-10: received
See all versions
Short URL
Creative Commons Attribution


      author = {Michele Fabbrini},
      title = {{FC1}: A Powerful, Non-Deterministic, Symmetric Key Cipher},
      howpublished = {Cryptology ePrint Archive, Paper 2022/567},
      year = {2022},
      note = {\url{}},
      url = {}
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