The following C# macros do the bulk of the job, at the beginning of the file:

#if NETSTANDARD2_0
#define KeePassUAP
#define KeePassLibSD
using System.Security.Cryptography;
#endif

The following code was removed, else compilation fails with macro KeePassUAP (DiagnosticsExt does not exist anywhere):

#if KeePassUAP
			pb = DiagnosticsExt.GetProcessEntropy();
			MemUtil.Write(ms, pb);

The in-memory data protection has to be changed for dot net standard. The ProtectedData API is Windows only. So, I used instead Microsoft.AspNetCore.DataProtection, which is not platform dependant:

#if NETSTANDARD2_0
using Microsoft.AspNetCore.DataProtection;
#endif

Here's how the two methods ProtectData and UnprotectData are changed to use Microsoft.AspNetCore.DataProtection:

#if NETSTANDARD2_0
		public static byte[] ProtectData(byte[] pb, byte[] pbOptEntropy,
			DataProtectionScope s)
		{
			return g_obProtector.Protect(pb);
		}

		public static byte[] UnprotectData(byte[] pb, byte[] pbOptEntropy,
			DataProtectionScope s)
		{
			return g_obProtector.Unprotect(pb);
		}
#else

• NetStd.sln:
  • KeePassLibStd.csproj: builds a read / write capable dot net standard version of the KeePass lib
  • Kdbx2xml: command line tool used for testing purposes
• KeePass.sln: same as the original KeePass2 solution, with key signing removed for convenience

Dummy kdbx files and the unlocking dummy pass phrase are provided in the DummyDatabases folder.

> dotnet Kdbx2XmlConsole.dll --kdbx kdf-argon2_cipher-chacha20.kdbx --password "Her face was large as that of Memphian sphinx"
1,1097866s to export [kdf-argon2_cipher-chacha20.kdbx] to [kdf-argon2_cipher-chacha20.xml]

>dotnet Kdbx2XmlConsole.dll --kdbx "kdf-argon2_cipher-chacha20.kdbx" --password "Her face was large as that of Memphian sphinx" --mode dup
1,06377s to load [kdf-argon2_cipher-chacha20.kdbx]
1,06377s to save [kdf-argon2_cipher-chacha20.kdbx] to [kdf-argon2_cipher-chacha20.dup.kdbx]

For KDBX files saved with the Argon2 key derivation function (the newer one), the loading/saving time is identical the the regular KeePass2 program. This is because Argon2 uses only managed code, even in KeePass2.

However, for KDBX files saved with the AES KDF, the loading and saving time can be several times longer than with the regular KeePass2 program (e.g. 500% longer). This is because KeePass2 uses native libraries that are much faster than the dot net RijndaelManaged class. When the native libraries are not there (KeePassLibC32.dll / KeePassLibC64.dll), KeePass2 fall backs to pure managed code (RijndaelManaged). In which case the performances are identical with the dot net standard lib.