ChaCha20

A C implementation of the ChaCha20 stream cipher (RFC 7539), usable as a command-line tool.

Usage

./chacha20 -e <file> -k <key_file> [options]   # encrypt
./chacha20 -d <file> -k <key_file> [options]   # decrypt

Options:

Option	Description	Default
-e, --encrypt	Input file to encrypt	-
-d, --decrypt	Input file to decrypt	-
-k, --key	Path to a 256-bit (32-byte) binary key file	-
-o, --output	Output file	data.chacha20
--help	Show help	-

Examples:

./chacha20 -e myfile.txt -k key.bin -o encrypted.chacha20
./chacha20 --decrypt encrypted.chacha20 --key key.bin -o decrypted.txt

Encrypted format

The output file starts with a 12-byte randomly generated nonce, followed by the ciphertext:

| uint8_t[12] | uint8_t[]  |
|    nonce    | ciphertext |

References

• RFC 7539: ChaCha20 and Poly1305 for IETF Protocols
• ChaCha, a variant of Salsa20. Daniel J. Bernstein