File encryption done right

About

Kestrel is a data-at-rest file encryption program that lets you encrypt files to anyone with a public key.

Features and Advantages

• Encrypt files using a public key or a password.
• Strong security and privacy guarantees. Uses X25519, ChaCha20-Poly1305 and the Noise Protocol. Guarantees sender authentication.
• Secure defaults with zero configuration needed.
• Supports files of any size.
• Keys are simple strings that are easy to manage and copy-paste.
• Private keys are always encrypted.
• Single binary that is easy to run anywhere.
• Supports Linux, macOS, Windows.

Disadvantages

• Does not handle signatures. You can't sign files with this. However, sender authentication is guaranteed.
• Does not solve the key distribution problem. You have to acquire known-good public keys through some other means.

Security Properties

• Sender authentication: When you successfully decrypt a file, you can be certain that it came from someone that you know and that it hasn't been tampered with in any way.
• Metadata protection: Encrypted files contain absolutely zero information about the sender or recipient.
• Deniability: Unlike using a digital signature for authentication, Kestrel provides sender authentication without non-repudiation. You are not cryptographically bound to the messages that you send. If the recipient tries to reveal a message, you are able to deny that you sent that message.
• Partial forward secrecy: An attacker must compromise the recipient's private key in order to decrypt a file. Someone else getting their private key compromised doesn't affect the files that they had previously sent to you.

Kestrel uses a combination of the Noise Protocol and a chunked file encryption scheme. Read the security documentation for more details.

Advantages compared to other applications

GPG

GPG is a massively complex tool with many use cases, features, and shortcomings. In general, Kestrel provides better default security guarantees with no configuration required. In particular, by default, GPG does not provide sender authentication or metadata protection. Sender authentication can be added by including signatures, but this removes deniability. In contrast, Kestrel includes sender authentication while preserving deniability and protecting metadata.

age

age is a newer tool with strong defaults and is much less complex than GPG. However, age does not provide sender authentication. A successfully decrypted file could have come from anyone, including from an attacker that replaced the file with a malicious copy. Kestrel fixes this by showing you the exact sender of a file.

Installation

Tested on Linux, macOS, Windows

Download from the Official Site

Or grab the GitHub release

If you have cargo you can also use cargo install --locked kestrel-cli

Usage Examples

Generate a new private key $ kestrel key gen -o keyring.txt Key name: alice New password: Confirm password: $ cat keyring.txt [Key] Name = alice PublicKey = mI4mKm85lXzbYdHhDW7hX8yWDIuSwRuzjATP/w4mZxwm+Dck PrivateKey = AAHr9qFFlOx1ujtQg8bQ8I5GTzwWmBjRU8Cf0VAK2CuRKNNlsW4XWCu2GEzFQuqNb1UrkLev7+Qn9OgS5xwVOR3j

Encrypt a file $ kestrel encrypt example.txt --to alice --from alice -k keyring.txt

Decrypt a file $ kestrel decrypt example.txt.ktl -t alice -k keyring.txt

Encrypt a file using a password $ kestrel pass enc example.txt

Set the environment variable KESTREL_KEYRING to use a default keyring file.

Usage

``` USAGE: kestrel encrypt FILE -t NAME -f NAME [-o FILE] [-k KEYRING] kestrel decrypt FILE -t NAME [-o FILE] [-k KEYRING] kestrel key generate -o FILE kestrel key change-pass PRIVATE-KEY kestrel key extract-pub PRIVATE-KEY kestrel password encrypt|decrypt FILE [-o FILE]

Aliases enc, dec, pass, and gen can be used as encrypt, decrypt,
password, and generate respectively.
Option -k is required unless KESTREL_KEYRING env var is set.

OPTIONS: -t, --to Recipient key name. Decrypt requires a private key. -f, --from Sender key name. Must be a private key. -o, --output Output file name. -k, --keyring Location of a keyring file. -h, --help Print help information. -v, --version Print version information. ```

Documentation

View the documentation

Source code for the documentation can be found in the kestrel-doc repository.

Contributing

Patches welcome. Please send feedback and bug reports for any issues that you may have.

License

BSD 3 Clause

Security Warning

To the best of my knowledge, Kestrel is secure. However, this software has not yet undergone a formal security audit. Swim at your own risk.