AesGcmStrict 1.0.2

dotnet add package AesGcmStrict --version 1.0.2
NuGet\Install-Package AesGcmStrict -Version 1.0.2
This command is intended to be used within the Package Manager Console in Visual Studio, as it uses the NuGet module's version of Install-Package.
<PackageReference Include="AesGcmStrict" Version="1.0.2" />
For projects that support PackageReference, copy this XML node into the project file to reference the package.
paket add AesGcmStrict --version 1.0.2
#r "nuget: AesGcmStrict, 1.0.2"
#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package.
// Install AesGcmStrict as a Cake Addin
#addin nuget:?package=AesGcmStrict&version=1.0.2

// Install AesGcmStrict as a Cake Tool
#tool nuget:?package=AesGcmStrict&version=1.0.2

AesGcmStrict (.NET) NuGet

by Stan Drapkin

AesGcmStrict class:

  • Wraps AesGcm and enforces AesGcm Tag to be exactly 16 bytes. Use AesGcmStrict instead of AesGcm.
  • AesGcm allows truncated Tags: any AesGcm-provided Tag truncated to ex. 12 bytes will successfully decrypt.

Example of the problem:

Span<byte> plaintext = Encoding.UTF8.GetBytes("Hello World!");
Span<byte> key = new byte[32];
Span<byte> nonce = new byte[12];
Span<byte> ciphertext = new byte[plaintext.Length];
Span<byte> tag = new byte[16]; // generating a 16-byte Tag!

using var gcm = new AesGcm(key);

Console.WriteLine(Encoding.UTF8.GetString(plaintext));

gcm.Encrypt(nonce, plaintext, ciphertext, tag);
plaintext.Clear();
tag = tag.Slice(0, 12); // truncating the Tag to ex. 12 bytes
gcm.Decrypt(nonce, ciphertext, tag, plaintext); // decrypts successfully (PROBLEM)
Console.WriteLine(Encoding.UTF8.GetString(plaintext));

Most users of AesGcm might expect ~128 bits of Tag-security, but effectively get only ~96 bits at best.

How to fix with AesGcmStrict:

  1. Add the namespace: using SecurityDriven;
  2. Replace AesGcm with AesGcmStrict

Same example with AesGcmStrict:

// using SecurityDriven;
Span<byte> plaintext = Encoding.UTF8.GetBytes("Hello World!");
Span<byte> key = new byte[32];
Span<byte> nonce = new byte[12];
Span<byte> ciphertext = new byte[plaintext.Length];
Span<byte> tag = new byte[16]; // generating a 16-byte Tag!

using var gcm = new AesGcmStrict(key); // switching to AesGcmStrict

Console.WriteLine(Encoding.UTF8.GetString(plaintext));

gcm.Encrypt(nonce, plaintext, ciphertext, tag);
plaintext.Clear();
tag = tag.Slice(0, 12); // truncating the Tag to ex. 12 bytes
gcm.Decrypt(nonce, ciphertext, tag, plaintext); // throws ArgumentException (tag must be 16 bytes)
Console.WriteLine(Encoding.UTF8.GetString(plaintext));
Product Compatible and additional computed target framework versions.
.NET net5.0 was computed.  net5.0-windows was computed.  net6.0 is compatible.  net6.0-android was computed.  net6.0-ios was computed.  net6.0-maccatalyst was computed.  net6.0-macos was computed.  net6.0-tvos was computed.  net6.0-windows was computed.  net7.0 was computed.  net7.0-android was computed.  net7.0-ios was computed.  net7.0-maccatalyst was computed.  net7.0-macos was computed.  net7.0-tvos was computed.  net7.0-windows was computed.  net8.0 was computed.  net8.0-android was computed.  net8.0-browser was computed.  net8.0-ios was computed.  net8.0-maccatalyst was computed.  net8.0-macos was computed.  net8.0-tvos was computed.  net8.0-windows was computed. 
.NET Core netcoreapp3.0 was computed.  netcoreapp3.1 was computed. 
.NET Standard netstandard2.1 is compatible. 
MonoAndroid monoandroid was computed. 
MonoMac monomac was computed. 
MonoTouch monotouch was computed. 
Tizen tizen60 was computed. 
Xamarin.iOS xamarinios was computed. 
Xamarin.Mac xamarinmac was computed. 
Xamarin.TVOS xamarintvos was computed. 
Xamarin.WatchOS xamarinwatchos was computed. 
Compatible target framework(s)
Included target framework(s) (in package)
Learn more about Target Frameworks and .NET Standard.
  • .NETStandard 2.1

    • No dependencies.
  • net6.0

    • No dependencies.

NuGet packages

This package is not used by any NuGet packages.

GitHub repositories

This package is not used by any popular GitHub repositories.

Version Downloads Last updated
1.0.2 497 6/30/2022

Replacement for System.Security.Cryptography.AesGcm.