ca5379.md

title	description	ms.date	author	ms.author	f1_keywords
CA5379: Ensure key derivation function algorithm is sufficiently strong (code analysis)	Provides information about code analysis rule CA5379, including causes, how to fix violations, and when to suppress it.	05/07/2020	LLLXXXCCC	linche	CA5379 DoNotUseWeakKDFAlgorithm

CA5379: Ensure key derivation function algorithm is sufficiently strong

Property	Value
Rule ID	CA5379
Title	Ensure key derivation function algorithm is sufficiently strong
Category	Security
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 8	No

Cause

Use of one of the following algorithms when instantiating xref:System.Security.Cryptography.Rfc2898DeriveBytes?displayProperty=nameWithType:

• xref:System.Security.Cryptography.MD5?displayProperty=nameWithType
• xref:System.Security.Cryptography.SHA1?displayProperty=nameWithType
• An algorithm that the rule can't determine at compile time

Rule description

The xref:System.Security.Cryptography.Rfc2898DeriveBytes class defaults to using the xref:System.Security.Cryptography.HashAlgorithmName.SHA1 algorithm. When instantiating an xref:System.Security.Cryptography.Rfc2898DeriveBytes object, you should specify a hash algorithm of xref:System.Security.Cryptography.HashAlgorithmName.SHA256 or higher. Note that xref:System.Security.Cryptography.Rfc2898DeriveBytes.HashAlgorithm?displayProperty=nameWithType property only has a get accessor.

How to fix violations

Because xref:System.Security.Cryptography.MD5 or xref:System.Security.Cryptography.SHA1 are vulnerable to collisions, use xref:System.Security.Cryptography.SHA256 or higher for the xref:System.Security.Cryptography.Rfc2898DeriveBytes class.

Older versions of .NET Framework or .NET Core may not allow you to specify a key derivation function hash algorithm. In such cases, you need to upgrade the target framework version of .NET to use a stronger algorithm.

When to suppress warnings

It is not recommended to suppress this rule except for application compatibility reasons.

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 CA5379
// The code that's violating the rule is on this line.
#pragma warning restore CA5379

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

[*.{cs,vb}]
dotnet_diagnostic.CA5379.severity = none

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

Pseudo-code examples

Specify hash algorithm in constructor violation

using System.Security.Cryptography;

class ExampleClass
{
    public void ExampleMethod(byte[] password, byte[] salt, int iterations, HashAlgorithmName hashAlgorithm)
    {
        var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, salt, iterations, HashAlgorithmName.MD5);
    }
}

Specify hash algorithm in derived class' constructor violation

using System.Security.Cryptography;

class DerivedClass : Rfc2898DeriveBytes
{
    public DerivedClass (byte[] password, byte[] salt, int iterations, HashAlgorithmName hashAlgorithm) : base(password, salt, iterations, hashAlgorithm)
    {
    }
}

class ExampleClass
{
    public void ExampleMethod(byte[] password, byte[] salt, int iterations, HashAlgorithmName hashAlgorithm)
    {
        var derivedClass = new DerivedClass(password, salt, iterations, HashAlgorithmName.MD5);
    }
}

Set hash algorithm property in derived classes violation

using System.Security.Cryptography;

class DerivedClass : Rfc2898DeriveBytes
{
    public DerivedClass (byte[] password, byte[] salt, int iterations, HashAlgorithmName hashAlgorithm) : base(password, salt, iterations, hashAlgorithm)
    {
    }

    public HashAlgorithmName HashAlgorithm { get; set;}
}

class ExampleClass
{
    public void ExampleMethod(byte[] password, byte[] salt, int iterations, HashAlgorithmName hashAlgorithm)
    {
        var derivedClass = new DerivedClass(password, salt, iterations, HashAlgorithmName.MD5);
        derivedClass.HashAlgorithm = HashAlgorithmName.SHA256;
    }
}

Solution

using System.Security.Cryptography;

class ExampleClass
{
    public void ExampleMethod(byte[] password, byte[] salt, int iterations, HashAlgorithmName hashAlgorithm)
    {
        var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, salt, iterations, HashAlgorithmName.SHA256);
    }
}