Picocrypt is a very tiny (hence "Pico"), very simple, yet very secure file encryption tool. It uses the modern ChaCha20-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. It's very simple to use, which allows anyone to start encrypting private files, no matter what level of experience they have with computers. 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 under /src or download the portable .exe (for Windows) that I've precompiled and optimized beyond imagination here (recommended, because it's just 3MB and fully portable). If you're compiling from source or running the raw Python file, the following three dependencies will be automatically installed via pip if not already installed: argon2-cffi, pycryptodome, and reedsolo. See the /src folder for more info.

Note: For some reason, there's an outdated and useless tool called PicoCrypt on the Internet, which was last updated in 2005. PicoCrypt is not related to Picocrypt (this project). Make sure you only download Picocrypt from this Github repository to ensure that you download the correct, authentic, and backdoor-free software.

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 and its dependencies are 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 3MB!). 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. Picocrypt floats your boat without any bloat.
• It's infinitely easier to use than VeraCrypt (no need to create volumes) and a 5-year-old could probably use Picocrypt. All you need to do is select a file and enter a password.
• Picocrypt is built for security, using modern standards and 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. This is useful for transfering sensitive data where authenticity is crucial.
• Picocrypt supports anti-corruption through Reed-Solomon. Unlike other encryption tools, Picocrypt can actively protect your files by adding extra Reed-Solomon bytes, so if your file gets corrupted (ie. hard drive failure), Picocrypt can still fix the errors and decrypt your files. None of Bitlocker, NordLocker, VeraCrypt, or 7-Zip has this ability.

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 and select it. 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 corrupted or modified data after decryption, check this option. Also, if this option is checked and the Reed-Solomon feature was used on the encrypted file, Picocrypt will attempt to recover as much of the file as possible during decryption, if it is corrupted.
• 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. This method is better than just deleting the original file, because the original file can still be recovered by hackers using special software. Picocrypt overwrites the original file making sure that it's impossibe to retrieve the original file after deletion.
• Prevent corruption using Reed-Solomon (encryption only): This feature is very useful if you are planning on archiving important data on a cloud provider or external hard drive for a long time. If checked, Picocrypt will use the Reed-Solomon error correction code to add 13 extra bytes for every 128 bytes to prevent file corruption. This means that up to ~5% (13/128/2) of your file can corrupt, and Picocrypt will still be able to correct it and decrypt your files with no corruption. Note that decryption is very slow because Picocrypt is reassembling and (if necessary) correcting broken bytes. The output will also be ~10% larger.

Security

Security is Picocrypt's primary 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. That's why I created Picocrypt, which 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 Argon2(id), winner of the PHC (Password Hashing Competition), which was completed in 2015. Argon2 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 corruption checks, SHA3-512 (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. You can rely on these ciphers and algorithms to protect your data, as they are all modern and have undergone a large amount of cryptanalysis.

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 anti-corruption is checked, the 1MB chunk will be split into 128 byte chunks and 13 additional Reed-Solomon (parity) bytes will be added. If decrypting, decode the encoded 1MB chunk to get the raw data.
6. If 'Secure wipe' is enabled, CSPRNG data is written over the original file in chunks of 1MB to securely wipe the file.
7. 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.
8. Similar to above, the CRC is either checked or added to the ciphertext depending on the operation.
9. If decrypting, both the CRC and the MAC tag are verified. 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.

Note: the list above is heavily simplified. A lot more is actually happening.

Limitations

• Max file size is 256GB, due to ChaCha20 cipher itself. The reason for this is that 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 help the community and 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 the security problem is severe or critical and could potentially be exploited by hackers if published, please contact me privately through the contacts section in my website: https://evansu.cc. 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).