<PackageReference Include="BouncyCastle.Cryptography" Version="2.7.0" />

Org.BouncyCastle.Crypto.Utilities.RsaPkcs1Utilities

static class RsaPkcs1Utilities
namespace Org.BouncyCastle.Crypto.Utilities { internal static class RsaPkcs1Utilities { internal delegate int ValidityCheck (byte[] buf, int off, int len); } }