Mark enums with FlagsAttribute (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1027)

'string.IndexOf(char)' has a method overload that takes a 'StringComparison' parameter. Replace this call in 'Opc.Ua.Security.Certificates.AsnUtils.FromHexString(string)' with a call to 'string.IndexOf(char, System.StringComparison)' for clarity of intent. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1307)

'string.IndexOf(char)' has a method overload that takes a 'StringComparison' parameter. Replace this call in 'Opc.Ua.Security.Certificates.AsnUtils.FromHexString(string)' with a call to 'string.IndexOf(char, System.StringComparison)' for clarity of intent. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1307)

In externally visible method 'X509AuthorityKeyIdentifierExtension.X509AuthorityKeyIdentifierExtension(AsnEncodedData encodedExtension, bool critical)', validate parameter 'encodedExtension' is non-null before using it. If appropriate, throw an 'ArgumentNullException' when the argument is 'null'. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1062)

In externally visible method 'X509CrlNumberExtension.X509CrlNumberExtension(AsnEncodedData encodedExtension, bool critical)', validate parameter 'encodedExtension' is non-null before using it. If appropriate, throw an 'ArgumentNullException' when the argument is 'null'. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1062)

In externally visible method 'X509CRL.X509CRL(IX509CRL crl)', validate parameter 'crl' is non-null before using it. If appropriate, throw an 'ArgumentNullException' when the argument is 'null'. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1062)

In externally visible method 'X509SubjectAltNameExtension.X509SubjectAltNameExtension(AsnEncodedData encodedExtension, bool critical)', validate parameter 'encodedExtension' is non-null before using it. If appropriate, throw an 'ArgumentNullException' when the argument is 'null'. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1062)

Modify 'VerifySignature' to catch a more specific allowed exception type, or rethrow the exception (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1031)

Change the type of parameter 'applicationUri' of method 'X509SubjectAltNameExtension.X509SubjectAltNameExtension(string, IEnumerable<string>)' from 'string' to 'System.Uri', or provide an overload to 'X509SubjectAltNameExtension.X509SubjectAltNameExtension(string, IEnumerable<string>)' that allows 'applicationUri' to be passed as a 'System.Uri' object (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1054)