Cipher21

Stream cipher simple application for 2021 year which uses XChaCha20-Poly1305

Using XChaCha20-Poly1305 cipher provides:

• Data integrity
• Authenticated Encryption
• Confidentiality
• Allows stream processing
• three times faster then AES on platforms that lack specialized AES hardware
• 256-bit key
• 192-bit nonce lower the probability of a nonce misuse

1. Rationale

Lack of ready to use simple application for encryption with modern cipher.

2. Installation

• Installed Python 3.6 or higher is required.
• Type in the console pip3 install cipher21.

3. Usage Guide

• detailed parameters description: cipher21 -h
• cipher21 supports 64 hexadecimals keys only which you may create via:
  • > python -c "from os import urandom; print(urandom(32).hex())" > key.hex
  • https://www.random.org/integers/?num=8&min=0&max=65535&col=8&base=16&format=html&rnd=new
• encrypting a file with a hex key fetch from a file: cipher21 -e -k file:key.hex < plain.txt > encrypted.c21
• encrypting a file with a hex key fetch from an env: cipher21 -e -k env:KEY64 < plain.txt > encrypted.c21
• decrypting a file with a hex key fetch from a file: cipher21 -d -k file:key.hex < encrypted.c21 > plain.txt
• compressing and encrypting: mysqldump --all-databases | xz -zc | cipher21 -e -k file:key.hex > db-dump.sql.xz.c21
• decrypting and decompressing: cat db-dump.sql.xz.c21 | cipher21 -d -k file:key.hex | xz -dc | mysql

4. Recommended Designations

• .c21 is a recommended file name extension
• application/cipher21 ia a recommended internet media type

5. Technical details

5.1. Stream Structure

• Stream length must always be a multiple of M == 2^14 == 16384 bytes to hide the exact length of a payload.

 offset | len | description
--------+-----+---------------------------------------------------
      0 |   8 | stream signature: "c21\x1A\x00\xFF\x19\x82"
      8 |  24 | nonce
     32 |   E | XChaCha20-Poly1305 encrypted block (see below)
    -16 |  16 | MAC

constraints:
(8 + 24 + E + 16) % M == 0   =>   E % M == M - 48 == 16336

5.2. Encrypted Block

 offset | len | description
--------+-----+---------------------------------------------
      0 |   8 | little endian unsigned integer of an encryption time in nanoseconds
        |     | since the January 1, 1970, 00:00:00 (UTC), not counting leap seconds
      8 |   D | payload
 -2 - P |   P | randomized padding bytes
     -2 |   2 | little endian unsigned integer P - the padding length

constraints:
(8 + D + P + 2) % M == M - 48
    => (D + P) % M == M - 58
    => P % M == (M - 58 - D) % M
    => P == (2*M - 58 - (D % M)) % M