Committing ChaCha20-BLAKE3, XChaCha20-BLAKE3, and XChaCha20-BLAKE3-SIV AEAD implementations using libsodium and BLAKE3.

This library does several things for you:

• Derives a 256-bit encryption key and 256-bit MAC key based on the key and nonce.
• Supports additional data in the calculation of the authentication tag, unlike most Encrypt-then-MAC implementations.
• Appends the authentication tag to the ciphertext.
• Compares the authentication tags in constant time during decryption and only returns plaintext if they match.
• Offers access to an SIV implementation that does not take a nonce.

The popular AEADs in use today, such as (X)ChaCha20-Poly1305, AES-GCM, AES-GCM-SIV, XSalsa20-Poly1305, AES-OCB, and so on, are not key or message committing. This means it is possible to decrypt a ciphertext using multiple keys without an authentication error, which can lead to partitioning oracle attacks and deanonymisation in certain online scenarios. Furthermore, if an attacker knows the key, then they can find other messages that have the same tag.

This library was created because there are currently no standardised committing AEAD schemes, adding the commitment property to a non-committing AEAD requires using a MAC, and Encrypt-then-MAC offers improved security guarantees.

Finally, (X)ChaCha20-BLAKE3 is a good combination for an Encrypt-then-MAC scheme because:

1. ChaCha20 has a higher security margin than AES, performs well on older devices, and runs in constant time, unlike AES.
2. BLAKE3 is fast and evolved from BLAKE, which received a significant amount of cryptanalysis, even more than Keccak (the SHA3 finalist), as part of the SHA3 competition.

You can find the NuGet package here. The easiest way to install this is via the NuGet Package Manager in Visual Studio, as explained here. JetBrains Rider also has a package manager, and instructions can be found here.

1. Install the Sodium.Core and Blake3.NET NuGet packages for your project in Visual Studio.
2. Download the latest release.
3. Move the downloaded .dll file into your project folder.
4. Click on the Project tab and Add Project Reference... in Visual Studio.
5. Go to Browse, click the Browse button, and select the downloaded .dll file.
6. Add using ChaCha20Blake3; to the top of each code file that will use the library.

The libsodium library requires the Visual C Redistributable for Visual Studio 2015-2019 to work on Windows. If you want your program to be portable, then you must keep the relevant (x86 or x64) vcruntime140.dll file in the same folder as your executable on Windows.

⚠️WARNING: Never reuse a nonce with the same key.

const string filePath = "C:\\Users\\samuel-lucas6\\Pictures\\test.jpg";
const string version = "application v1.0.0";

// The message does not have to be a file
byte[] message = File.ReadAllBytes(filePath);

// The nonce should be a counter that gets incremented for each message encrypted using the same key
byte[] nonce = new byte[ChaCha20BLAKE3.NonceSize];

// The key can be randomly generated using a CSPRNG or derived using a KDF (e.g. Argon2, HKDF, etc)
byte[] key = SodiumCore.GetRandomBytes(ChaCha20BLAKE3.KeySize);

// The additional data can be null but is ideal for file headers, version numbers, timestamps, etc
byte[] additionalData = Encoding.UTF8.GetBytes(version);

// Encrypt the message
byte[] ciphertext = ChaCha20BLAKE3.Encrypt(message, nonce, key, additionalData);

// Decrypt the ciphertext
byte[] plaintext = ChaCha20BLAKE3.Decrypt(ciphertext, nonce, key, additionalData);

⚠️WARNING: Never reuse a nonce with the same key.

const string filePath = "C:\\Users\\samuel-lucas6\\Pictures\\test.jpg";
const string version = "application v1.0.0";

// The message does not have to be a file
byte[] message = File.ReadAllBytes(filePath);

// The nonce can be a counter or randomly generated using a CSPRNG
// Increment or randomly generate the nonce for each message encrypted using the same key
byte[] nonce = SodiumCore.GetRandomBytes(XChaCha20BLAKE3.NonceSize);

// The key can be randomly generated using a CSPRNG or derived using a KDF (e.g. Argon2, HKDF, etc)
byte[] key = SodiumCore.GetRandomBytes(XChaCha20BLAKE3.KeySize);

// The additional data can be null but is ideal for file headers, version numbers, timestamps, etc
byte[] additionalData = Encoding.UTF8.GetBytes(version);

// Encrypt the message
byte[] ciphertext = XChaCha20BLAKE3.Encrypt(message, nonce, key, additionalData);

// Decrypt the ciphertext
byte[] plaintext = XChaCha20BLAKE3.Decrypt(ciphertext, nonce, key, additionalData);

⚠️WARNING: Never reuse a key. As a precaution, you can use at least 16 bytes of unique, random data as part of the additional data to act as a nonce.

const string filePath = "C:\\Users\\samuel-lucas6\\Pictures\\test.jpg";

// The message does not have to be a file
byte[] message = File.ReadAllBytes(filePath);

// The key can be randomly generated using a CSPRNG or derived using a KDF (e.g. Argon2, HKDF, etc)
byte[] key = SodiumCore.GetRandomBytes(XChaCha20BLAKE3SIV.KeySize);

// The additional data can be null, used as a nonce, and/or used for file headers, version numbers, timestamps, etc
byte[] additionalData = SodiumCore.GetRandomBytes(XChaCha20BLAKE3SIV.KeySize / 2);

// Encrypt the message
byte[] ciphertext = XChaCha20BLAKE3SIV.Encrypt(message, key, additionalData);

// Decrypt the ciphertext
byte[] plaintext = XChaCha20BLAKE3SIV.Decrypt(ciphertext, key, additionalData);

The following benchmarks were done using BenchmarkDotNet in a .NET 6 console application with 16 bytes of additional data.

In sum, ChaCha20-BLAKE3 performs similarly to ChaCha20-Poly1305 and is even faster with large inputs. Whilst it is slower with small messages, I would argue that the additional security makes up for any performance loss.