ChaCha20-BLAKE3

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

Features

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.

Justification

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.

Installation

NuGet

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.

Manual

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.

Notes

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.

Usage

ChaCha20-BLAKE3

⚠️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);

XChaCha20-BLAKE3

⚠️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);

XChaCha20-BLAKE3-SIV

⚠️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);

Benchmarks

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.

512 bytes

Method	Mean	Error	StdDev
ChaCha20-BLAKE3.Encrypt	1.504 us	0.0027 us	0.0024 us
ChaCha20-BLAKE3.Decrypt	1.530 us	0.0067 us	0.0060 us
XChaCha20-BLAKE3.Encrypt	1.601 us	0.0012 us	0.0010 us
XChaCha20-BLAKE3.Decrypt	1.610 us	0.0068 us	0.0060 us
XChaCha20-BLAKE3-SIV.Encrypt	1.593 us	0.0086 us	0.0080 us
XChaCha20-BLAKE3-SIV.Decrypt	1.610 us	0.0009 us	0.0008 us
ChaCha20-Poly1305.Encrypt	785.9 ns	4.59 ns	4.29 ns
ChaCha20-Poly1305.Decrypt	793.6 ns	1.25 ns	0.98 ns
XChaCha20-Poly1305.Encrypt	865.1 ns	1.24 ns	0.97 ns
XChaCha20-Poly1305.Decrypt	888.1 ns	4.23 ns	3.75 ns

16 KiB

Method	Mean	Error	StdDev
ChaCha20-BLAKE3.Encrypt	25.49 us	0.039 us	0.032 us
ChaCha20-BLAKE3.Decrypt	24.91 us	0.026 us	0.024 us
XChaCha20-BLAKE3.Encrypt	25.75 us	0.042 us	0.039 us
XChaCha20-BLAKE3.Decrypt	24.99 us	0.051 us	0.048 us
XChaCha20-BLAKE3-SIV.Encrypt	23.76 us	0.030 us	0.028 us
XChaCha20-BLAKE3-SIV.Decrypt	23.88 us	0.024 us	0.022 us
ChaCha20-Poly1305.Encrypt	16.62 us	0.049 us	0.041 us
ChaCha20-Poly1305.Decrypt	16.66 us	0.096 us	0.090 us
XChaCha20-Poly1305.Encrypt	16.76 us	0.069 us	0.058 us
XChaCha20-Poly1305.Decrypt	16.70 us	0.020 us	0.017 us

32 KiB

Method	Mean	Error	StdDev
ChaCha20-BLAKE3.Encrypt	40.38 us	0.060 us	0.056 us
ChaCha20-BLAKE3.Decrypt	39.58 us	0.035 us	0.033 us
XChaCha20-BLAKE3.Encrypt	40.53 us	0.038 us	0.032 us
XChaCha20-BLAKE3.Decrypt	39.50 us	0.048 us	0.045 us
XChaCha20-BLAKE3-SIV.Encrypt	36.02 us	0.673 us	0.661 us
XChaCha20-BLAKE3-SIV.Decrypt	36.91 us	0.034 us	0.032 us
ChaCha20-Poly1305.Encrypt	32.87 us	0.051 us	0.043 us
ChaCha20-Poly1305.Decrypt	32.92 us	0.187 us	0.175 us
XChaCha20-Poly1305.Encrypt	32.85 us	0.046 us	0.039 us
XChaCha20-Poly1305.Decrypt	33.03 us	0.093 us	0.087 us

64 KiB

Method	Mean	Error	StdDev
ChaCha20-BLAKE3.Encrypt	63.93 us	0.098 us	0.091 us
ChaCha20-BLAKE3.Decrypt	62.47 us	0.142 us	0.133 us
XChaCha20-BLAKE3.Encrypt	64.31 us	0.141 us	0.131 us
XChaCha20-BLAKE3.Decrypt	62.67 us	0.084 us	0.078 us
XChaCha20-BLAKE3-SIV.Encrypt	59.08 us	0.053 us	0.049 us
XChaCha20-BLAKE3-SIV.Decrypt	60.09 us	0.052 us	0.049 us
ChaCha20-Poly1305.Encrypt	65.33 us	0.182 us	0.142 us
ChaCha20-Poly1305.Decrypt	65.75 us	0.529 us	0.494 us
XChaCha20-Poly1305.Encrypt	65.43 us	0.236 us	0.197 us
XChaCha20-Poly1305.Decrypt	65.79 us	0.584 us	0.546 us

128 KiB

Method	Mean	Error	StdDev
ChaCha20-BLAKE3.Encrypt	208.2 us	2.65 us	2.48 us
ChaCha20-BLAKE3.Decrypt	196.0 us	2.56 us	2.39 us
XChaCha20-BLAKE3.Encrypt	208.1 us	2.94 us	2.60 us
XChaCha20-BLAKE3.Decrypt	197.1 us	2.65 us	2.35 us
XChaCha20-BLAKE3-SIV.Encrypt	206.1 us	2.82 us	2.64 us
XChaCha20-BLAKE3-SIV.Decrypt	196.4 us	3.14 us	2.93 us
ChaCha20-Poly1305.Encrypt	182.0 us	1.15 us	1.08 us
ChaCha20-Poly1305.Decrypt	180.9 us	1.49 us	1.39 us
XChaCha20-Poly1305.Encrypt	180.9 us	1.13 us	1.00 us
XChaCha20-Poly1305.Decrypt	181.1 us	1.45 us	1.29 us

32 MiB

Method	Mean	Error	StdDev
ChaCha20-BLAKE3.Encrypt	44.08 ms	0.814 ms	0.937 ms
ChaCha20-BLAKE3.Decrypt	42.88 ms	0.736 ms	0.653 ms
XChaCha20-BLAKE3.Encrypt	41.90 ms	0.812 ms	0.967 ms
XChaCha20-BLAKE3.Decrypt	42.31 ms	0.653 ms	0.579 ms
XChaCha20-BLAKE3-SIV.Encrypt	42.35 ms	0.821 ms	1.008 ms
XChaCha20-BLAKE3-SIV.Decrypt	42.39 ms	0.694 ms	0.649 ms
ChaCha20-Poly1305.Encrypt	49.07 ms	0.289 ms	0.271 ms
ChaCha20-Poly1305.Decrypt	48.68 ms	0.171 ms	0.143 ms
XChaCha20-Poly1305.Encrypt	49.02 ms	0.150 ms	0.140 ms
XChaCha20-Poly1305.Decrypt	48.77 ms	0.195 ms	0.173 ms