Picocrypt

Picocrypt is a very tiny (hence "Pico"), very simple, yet very secure file encryption tool. It uses the modern XChaCha20-Poly1305 cipher suite as well as Argon2, making it about as secure and modern of an encryption tool as you'll ever get your hands on. Picocrypt's focus is security, so it might be slightly slower and less attractive visually than others.

Download

You can run the raw Python source file, compile it yourself, or download the portable .exe (for Windows) that I've precompiled and optimized beyond imagination (recommended, because it's just 4MB in size) here. If you're compiling from source or running the raw Python file, the following two dependencies will be automatically installed via pip if not already installed: argon2-cffi and pycryptodome.

Why Picocrypt?

Why should you use Picocrypt, instead of Bitlocker, NordLocker, VeraCrypt, or 7-Zip? Here are some reasons why you should switch to Picocrypt:

• The only safe encryption is the one you do yourself. Don't trust cloud providers to "encrypt" your data, because you'll never know if they do it or not. Picocrypt is meant to be the simplest tool to allow you to take control over your confidential data and protect it with the most secure modern standards available.
• Unlike NordLocker, Bitlocker, and many cloud storage providers, Picocrypt is FOSS (free open-source software) and can be audited. You can verify for yourself that there aren't any backdoors or flaws.
• Picocrypt is portable and tiny (just 4MB!). It's much lighter than NordLocker (>100MB) and VeraCrypt (>30MB). The raw Python file can run any machine and the standalone .exe can run on any Windows PC from 7 and up.
• It's infinitely easier to use than VeraCrypt (no need to create volumes) and a 5-year-old could use Picocrypt.
• Picocrypt is built for security, using modern standards and the most secure settings. See Security below for more info.
• It supports file integrity checking through Poly1305, which means that you would know if a hacker has maliciously modified your data.

Instructions

Picocrypt is about as simple as it gets. Just select a file, enter a password, and start. If you want to encrypt multiple files, add them to an archive or zip file. There are some additional options that you can use for more control:

• File metadata (editable for encryption, readonly for decryption): Use this to store notes, information, and text along with the file (it won't be encrypted). For example, you can put a description of the file before sending it to someone. When the person you sent it to selects the file in Picocrypt, your description will be shown to that person.
• Keep decrypted output even if it's corrupted or modified (decryption only): Picocrypt automatically checks for integrity upon decryption. If the file has been modified or is corrupted, Picocrypt will delete the output. If you want to keep the corrupt or modified data after decryption, check this option.
• Securely erase and delete original file (encryption only): If checked, Picocrypt will generate pseudo-random data and write it to the original file while encrypting, effectively wiping the original file. The file will be deleted once encryption is complete.

Security

Security is Picocrypt's sole focus. I was in need of a secure, reliable, and future-proof encryption tool that didn't require bloatware and containers, but I couldn't find one, so I created Picocrypt. Picocrypt uses XChaCha20-Poly1305, which is a revision of the eSTREAM winner, Salsa20. XChaCha20-Poly1305 has been through a significant amount of cryptanalysis and was selected by security engineers at Google to be used in modern TLS suites. It's considered to be the future of symmetric encryption, and makes Picocrypt more secure than Bitlocker, NordLocker, and 7-Zip. It's used by Cloudflare, Google, and many other forward-thinking companies.

For key derivation, Picocrypt uses Argon2ID, winner of the PHC (Password Hashing Competition), which was completed in 2015. Argon2ID is even slower than Scrypt and Bcrypt (for those that don't understand crypto, this is a good thing), making GPU, ASIC, and FPGA attacks impractical due to the huge amount of RAM that is used and written to during the key derivation.

For key checking and CRCs, SHA3_512 (standardized Keccak) is used. Before decrypting, Picocrypt checks whether the password is correct by comparing the derived key to a SHA3_512 hash stored in the encrypted file. SHA3 is the latest standard for hashing recommended by the NIST. It's a modern and well-designed hash function that's open-source, unpatented, and royalty-free.

XChaCha20-Poly1305, Argon2, and SHA3 are well recognized within the cryptography community and are all considered to be mature and future-proof.

I did not write the crypto for Picocrypt. Picocrypt uses two Python libraries, argon2-cffi and pycryptodome, both of which are well known and popular within the Python community. Picocrypt also uses Python's standard hashlib for SHA3_512. For people who want to know how Picocrypt handles the crypto, or for the paranoid, here is a breakdown of how Picocrypt protects your data:

1. A 16-byte salt (for Argon2) and a 24-byte nonce (for XChaCha20) is generated using a CSPRNG (Python's os.urandom())
2. The encryption/decryption key is generated through Argon2ID using the salt above and the following parameters:
   • Time cost: 8
   • Memory cost: 2^30 (1GiB)
   • Parallelism: 8
3. If decrypting, compare the derived key with the SHA3_512 hash of the correct key stored in the ciphertext. If encrypting, compute the SHA3_512 of the derived key and add to ciphertext.
4. Encryption/decryption start, reading in 1MB chunks at a time. For each chunk, it is first encrypted by XChaCha20, and then a CRC (using SHA3_512) is updated.
5. If 'Secure wipe' is enabled, CSPRNG data is written over the original file in chunks of 1MB to securely wipe the file.
6. When encryption/decryption is finished, the MAC tag (Poly1305) will be added to the ciphertext or verified, depending on if you're encrypting or decrypting. If 'Secure wipe' is enabled, the original file is deleted.
7. Similar to above, the CRC is either checked or added to the ciphertext depending on the operation.
8. If decrypting, both the CRC and the MAC tag are securely verified using constant-time comparison. If either don't match, decryption is unsuccessful and an error message will be displayed. Otherwise, decryption is considered successful and the process is done.

Limitations

• Max file size is 256GB, due to ChaCha20 itself. The reason for this is because the counter for ChaCha20 will overflow out of the 32-bit range at 256GB. You can split files into chunks for files larger than 256GB.
• Argon2 may take a while to derive, but realize that this is all for security. Security and speed were never friends and there is always a trade-off between security and speed.
• Encryption/decryption is a little slower than other tools. Picocrypt average speeds ~50MB/s on a medium-class CPU, because a digest is constantly being updated with every chunk. Same as above, security and reliability comes at a slight decrease in speed.
• The portable .exe can be detected as a virus, because it uses 7-Zip's self-extracting archive format to bundle Python along with Picocrypt. I've done my best and submitted it as a false positive to a couple antivirus companies to deal with this. If your antivirus is detecting it as a virus, please submit it as a false positive to your antivirus provider.

Contribution

If you manage to find a bug or security issue, please create an Issue. If one of Picocrypt's dependencies gets a critical security patch, let me know and I'll update the code (if necessary) and recompile the .exe for Windows. I'm also open to suggestions and features (you can leave an Issue for that).