diff --git a/src/Core/Abstractions/IFido2AuthenticatorService.cs b/src/Core/Abstractions/IFido2AuthenticatorService.cs
new file mode 100644
index 0000000000..b6b160928f
--- /dev/null
+++ b/src/Core/Abstractions/IFido2AuthenticatorService.cs
@@ -0,0 +1,9 @@
+using Bit.Core.Utilities.Fido2;
+
+namespace Bit.Core.Abstractions
+{
+    public interface IFido2AuthenticatorService
+    {
+        Task<Fido2AuthenticatorGetAssertionResult> GetAssertionAsync(Fido2AuthenticatorGetAssertionParams assertionParams);
+    }
+}
diff --git a/src/Core/Services/Fido2AuthenticatorService.cs b/src/Core/Services/Fido2AuthenticatorService.cs
new file mode 100644
index 0000000000..d0747f3fbe
--- /dev/null
+++ b/src/Core/Services/Fido2AuthenticatorService.cs
@@ -0,0 +1,18 @@
+using Bit.Core.Abstractions;
+using Bit.Core.Utilities.Fido2;
+
+namespace Bit.Core.Services
+{
+    public class Fido2AuthenticatorService : IFido2AuthenticatorService
+    {
+        public Task<Fido2AuthenticatorGetAssertionResult> GetAssertionAsync(Fido2AuthenticatorGetAssertionParams assertionParams)
+        {
+            // TODO: IMPLEMENT this
+            return Task.FromResult(new Fido2AuthenticatorGetAssertionResult
+            {
+                AuthenticatorData = new byte[32],
+                Signature = new byte[8]
+            });
+        }
+    }
+}
diff --git a/src/Core/Utilities/Fido2/Fido2AuthenticatorGetAssertionParams.cs b/src/Core/Utilities/Fido2/Fido2AuthenticatorGetAssertionParams.cs
index ab6fe1e3ab..803815c926 100644
--- a/src/Core/Utilities/Fido2/Fido2AuthenticatorGetAssertionParams.cs
+++ b/src/Core/Utilities/Fido2/Fido2AuthenticatorGetAssertionParams.cs
@@ -2,11 +2,21 @@
 {
     public class Fido2AuthenticatorGetAssertionParams
     {
+        /** The caller’s RP ID, as determined by the user agent and the client. */
         public string RpId { get; set; }
 
-        public string CredentialId { get; set; }
+        /** The hash of the serialized client data, provided by the client. */
+        public byte[] Hash {get; set;}
 
-        public string Counter { get; set; }
+        public PublicKeyCredentialDescriptor[] AllowCredentialDescriptorList {get; set;}
+
+        /** The effective user verification requirement for assertion, a Boolean value provided by the client. */
+        public bool RequireUserVerification {get; set;}
+        
+        /** CTAP2 authenticators support setting this to false, but we only support the WebAuthn authenticator model which does not have that option. */
+        // public bool RequireUserPresence {get; set;} // Always required
+
+        public object Extensions {get; set;}
     }
 }
 
diff --git a/src/Core/Utilities/Fido2/PublicKeyCredentialDescriptor.cs b/src/Core/Utilities/Fido2/PublicKeyCredentialDescriptor.cs
new file mode 100644
index 0000000000..07e3d601b4
--- /dev/null
+++ b/src/Core/Utilities/Fido2/PublicKeyCredentialDescriptor.cs
@@ -0,0 +1,9 @@
+namespace Bit.Core.Utilities.Fido2
+{
+    public class PublicKeyCredentialDescriptor {
+        public byte[] Id {get; set;}
+        public string[] Transports;
+        public string Type;
+    }
+}
+
diff --git a/test/Core.Test/Services/Fido2AuthenticatorTests.cs b/test/Core.Test/Services/Fido2AuthenticatorTests.cs
new file mode 100644
index 0000000000..f81cf35496
--- /dev/null
+++ b/test/Core.Test/Services/Fido2AuthenticatorTests.cs
@@ -0,0 +1,38 @@
+using Bit.Core.Abstractions;
+using Bit.Core.Exceptions;
+using Bit.Core.Services;
+using Bit.Core.Test.AutoFixture;
+using Bit.Test.Common.AutoFixture;
+using Bit.Test.Common.AutoFixture.Attributes;
+using NSubstitute;
+using NSubstitute.ExceptionExtensions;
+using Xunit;
+
+namespace Bit.Core.Test.Services
+{
+    public class Fido2AuthenticatorTests
+    {
+        [Theory]
+        public async Task GetAssertionAsync_Throws_InputIsMissingSupportedAlgorithm(Fido2AuthenticatorService sut)
+        {
+            await Assert.ThrowsAsync<NotFoundException>(async () => await sut.GetAssertionAsync(new Fido2AuthenticatorGetAssertionParams()));
+        }
+
+        // it("should throw error when input does not contain any supported algorithms", async () => {
+        //     const result = async () =>
+        //     await authenticator.makeCredential(invalidParams.unsupportedAlgorithm, tab);
+
+        //     await expect(result).rejects.toThrowError(Fido2AuthenticatorErrorCode.NotSupported);
+        // });
+
+        private Fido2AuthenticatorGetAssertionParams GetAssertionParams()
+        {
+            return new Fido2AuthenticatorGetAssertionParams
+            {
+                RpId = "test",
+                Counter = 0,
+                CredentialId = new byte[32]
+            };
+        }
+    }
+}