CA5402: Use CreateEncryptor with the default IV

Property	Value
Rule ID	CA5402
Title	Use CreateEncryptor with the default IV
Category	Security
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 9	No

Cause

The rgbIV could be non-default when using System.Security.Cryptography.SymmetricAlgorithm.CreateEncryptor.

Rule description

Symmetric encryption should always use a non-repeatable initialization vector to prevent dictionary attacks.

This rule is similar to CA5401, but analysis can't determine that the initialization vector is definitely the default.

How to fix violations

Use the default rgbIV value explicitly, that is, use the overload of the System.Security.Cryptography.SymmetricAlgorithm.CreateEncryptor which doesn't have any parameter.

When to suppress warnings

It's safe to suppress a warning from this rule if:

• The rgbIV parameter was generated by System.Security.Cryptography.SymmetricAlgorithm.GenerateIV.
• You're sure that the rgbIV parameter is really random and non-repeatable.
• You're sure that the initialization vector is used.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA5402
// The code that's violating the rule is on this line.
#pragma warning restore CA5402

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA5402.severity = none

For more information, see How to suppress code analysis warnings.

Pseudo-code examples

using System;
using System.Security.Cryptography;

class ExampleClass
{
    public void ExampleMethod(byte[] rgbIV)
    {
        AesCng aesCng  = new AesCng();
        Random r = new Random();

        if (r.Next(6) == 4)
        {
            aesCng.IV = rgbIV;
        }

        aesCng.CreateEncryptor();
    }
}

Solution

using System.Security.Cryptography;

class ExampleClass
{
    public void ExampleMethod()
    {
        AesCng aesCng  = new AesCng();
        aesCng.CreateEncryptor();
    }
}