XChaCha20 Python3 CLI tool

Hi all,

DJB's XChaCha20 stream cipher is pretty cool for Text messages (SMS),
if you have also a proper encoder for the binary output.

So I decided to convert my Go Code to Python3.

Here is the program to play with, base64 encoded.

$ ./xchacha20.py
Error: Incorrect number of arguments
Usage: ./xchacha20.py <keyfile> <noncefile> < infile > outfile

XChaCha20 encryption/decryption tool

Arguments:
  keyfile    Path to the file containing the key in hexadecimal format
  noncefile  Path to the file containing the nonce in hexadecimal format

The program reads from stdin and writes to stdout. Use input/output redirection for files.

Examples:
  Encryption: ./xchacha20.py key.hex nonce.hex < plaintext.txt > encrypted.bin
  Decryption: ./xchacha20.py key.hex nonce.hex < encrypted.bin > decrypted.txt

Note: The key should be 32 hex bytes (64 characters) long.
      The nonce should be 24 hex bytes (48 characters) long.
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==


$ openssl rand -hex 32 > key
$ openssl rand -hex 24 > nonce
$ echo -n 'Hello World!' | xchacha20 key nonce | hexdump -Cv
00000000  01 eb 7f 2e d5 e9 a4 e0  c8 e4 e2 d6 |............|
0000000c

--
Regards
Stefan