Simple OTP

This is an easy-to-use tool to encrypt and decrypt data. It uses one-time pad encryption.

Definition (One-Time Pad):

"The one-time pad is a private-key encryption scheme where the key is a string of truly random bits equal in length to the message. The encryption is performed by computing the bitwise XOR of the message and the key. The one-time pad is perfectly secure when the key is chosen uniformly at random, is used only once, and kept secret."

— from Introduction to Modern Cryptography
Jonathan Katz and Yehuda Lindell, 2nd ed. (Section 2.4.1)

How to Compile

Extremely simple, this project has no dependencies, just libc.

1. Inside project root, run:

make

2. To install system-wide:

sudo make install

All binaries are compiled into the src/ directory. After compilation, you will find:

• otp: the main OTP tool
• genkey: used to generate cryptographically secure random keys

Usages

 Simple OTP 2.0.0 (c) 2022-2025 trusted-ws 

 Usage: otp <filename> <keyfile> <output> [options]

 Required arguments:
   <filename>             Path of file to be encrypted.
   <keyfile>              Path of key file.
   <output>               Output filename.

 Unique arguments:
   --show <filename>      Show details of encrypted file (OTP only).
   --help / -h            Show this message.
   --version              Show the version.

 Optional arguments:
   --force / -f           Force overwriting when the output file exists.
   --description <text>   Set a description text to the encrypted file.
   --no-warnings          Suppress warning messages during execution.
   --ignore-otp-filetype  Ignore OTP filetype header during encryption.

 Notes:
   If the key size is smaller than the plaintext, the key will be reused cyclically.

   You are free to use this software as you wish, but we highly recommend following
   best practices whilst using OTP, such as employing a truly random key as long as
   plaintext, never reusing keys, securely distributing and storing keys, and
   destroying them after use.

Extras

Encrypted files generated without the --ignore-otp-filetype flag include a custom binary header that defines a unique file type. To allow the file command to recognize these files, you can use the simple_otp_type.magic file located in the project root directory.

1. To install it you can:

# make sure to have a backup:
sudo cp /etc/magic /etc/magic.bak

# install with:
sudo tee -a /etc/magic < simple_otp_type.magic

2. Recompile file database:

sudo file -C -m /etc/magic

References:

• Claude Shannon, "Communication Theory of Secrecy Systems,"
  Bell System Technical Journal, vol. 28, no. 4, pp. 656–715, 1949.
  https://ieeexplore.ieee.org/document/6769090

• Jonathan Katz and Yehuda Lindell, Introduction to Modern Cryptography,
  2nd ed., CRC Press, 2014. ISBN: 978-1466570269