[PM-5731] feat: implement assertion without signature

src/Core/Models/View/Fido2CredentialView.cs

@@ -1,5 +1,6 @@
 using Bit.Core.Enums;
 using Bit.Core.Models.Domain;
+using Bit.Core.Utilities;
 
 namespace Bit.Core.Models.View
 {
@@ -32,6 +33,11 @@ namespace Bit.Core.Models.View
             set => Counter = value.ToString();
         }
 
+        public byte[] UserHandleValue {
+            get => UserHandle == null ? null : CoreHelpers.Base64UrlDecode(UserHandle);
+            set => UserHandle = value == null ? null : CoreHelpers.Base64UrlEncode(value);
+        }
+
         public override string SubTitle => UserName;
         public override List<KeyValuePair<string, LinkedIdType>> LinkedFieldOptions => new List<KeyValuePair<string, LinkedIdType>>();
         public bool IsDiscoverable => bool.TryParse(Discoverable, out var isDiscoverable) && isDiscoverable;

src/Core/Services/Fido2AuthenticatorService.cs

@@ -2,6 +2,7 @@
 using Bit.Core.Models.View;
 using Bit.Core.Enums;
 using Bit.Core.Utilities.Fido2;
+using System.Buffers.Binary;
 
 namespace Bit.Core.Services
 {
@@ -10,13 +11,15 @@ namespace Bit.Core.Services
         private INativeLogService _logService;
         private ICipherService _cipherService;
         private ISyncService _syncService;
+        private ICryptoFunctionService _cryptoFunctionService;
         private IFido2UserInterface _userInterface;
         
-        public Fido2AuthenticatorService(INativeLogService logService, ICipherService cipherService, ISyncService syncService, IFido2UserInterface userInterface)
+        public Fido2AuthenticatorService(INativeLogService logService, ICipherService cipherService, ISyncService syncService, ICryptoFunctionService cryptoFunctionService, IFido2UserInterface userInterface)
         {
             _logService = logService;
             _cipherService = cipherService;
             _syncService = syncService;
+            _cryptoFunctionService = cryptoFunctionService;
             _userInterface = userInterface;
         }
         
@@ -77,10 +80,33 @@ namespace Bit.Core.Services
                     ++selectedFido2Credential.CounterValue;
                 }
 
+                await _cipherService.UpdateLastUsedDateAsync(selectedCipher.Id);
                 var encrypted = await _cipherService.EncryptAsync(selectedCipher);
                 await _cipherService.SaveWithServerAsync(encrypted);
 
-                
+                var authenticatorData = await GenerateAuthData(
+                    rpId: selectedFido2Credential.RpId,
+                    userPresence: true,
+                    userVerification: userVerified,
+                    counter: selectedFido2Credential.CounterValue);
+
+                // const signature = await generateSignature({
+                //     authData: authenticatorData,
+                //     clientDataHash: params.hash,
+                //     privateKey: await getPrivateKeyFromFido2Credential(selectedFido2Credential),
+                // });
+
+                // TODO: IMPLEMENT this
+                return new Fido2AuthenticatorGetAssertionResult
+                {
+                    SelectedCredential = new Fido2AuthenticatorGetAssertionSelectedCredential
+                    {
+                        Id = GuidToRawFormat(selectedCredentialId),
+                        UserHandle = selectedFido2Credential.UserHandleValue
+                    },
+                    AuthenticatorData = authenticatorData,
+                    Signature = new byte[8]
+                };
             } catch {
                 _logService.Info(
                     "[Fido2Authenticator] Aborting because no matching credentials were found in the vault."
@@ -88,13 +114,6 @@ namespace Bit.Core.Services
 
                 throw new UnknownError();
             }
-
-            // TODO: IMPLEMENT this
-            return new Fido2AuthenticatorGetAssertionResult
-            {
-                AuthenticatorData = new byte[32],
-                Signature = new byte[8]
-            };
         }
 
     private async Task<List<CipherView>> FindCredentialsById(PublicKeyCredentialDescriptor[] credentials, string rpId)
@@ -137,9 +156,63 @@ namespace Bit.Core.Services
         );
     }
 
+    private async Task<byte[]> GenerateAuthData(
+        string rpId,
+        bool userVerification,
+        bool userPresence,
+        int counter
+        // byte[] credentialId,
+        // CryptoKey? cryptoKey - only needed for attestation
+    ) {
+        List<byte> authData = new List<byte>();
+
+        var rpIdHash = await _cryptoFunctionService.HashAsync(rpId, CryptoHashAlgorithm.Sha256);
+        authData.AddRange(rpIdHash);
+
+        var flags = AuthDataFlags(false, false, userVerification, userPresence);
+        authData.Add(flags);
+
+        authData.AddRange([
+            (byte)(counter >> 24),
+            (byte)(counter >> 16),
+            (byte)(counter >> 8),
+            (byte)counter
+        ]);
+
+        return authData.ToArray();
+    }
+
+    private byte AuthDataFlags(bool extensionData, bool attestationData, bool userVerification, bool userPresence) {
+        byte flags = 0;
+
+        if (extensionData) {
+            flags |= 0b1000000;
+        }
+
+        if (attestationData) {
+            flags |= 0b01000000;
+        }
+
+        if (userVerification) {
+            flags |= 0b00000100;
+        }
+
+        if (userPresence) {
+            flags |= 0b00000001;
+        }
+
+        return flags;
+    }
+
+
     private string GuidToStandardFormat(byte[] bytes)
     {
         return new Guid(bytes).ToString();
     }
+
+    private byte[] GuidToRawFormat(string guid)
+    {
+        return Guid.Parse(guid).ToByteArray();
+    }
     }
 }

src/Core/Utilities/Fido2/Fido2AuthenticatorGetAssertionResult.cs

@@ -1,11 +1,19 @@
-using System;
-namespace Bit.Core.Utilities.Fido2
+namespace Bit.Core.Utilities.Fido2
 {
     public class Fido2AuthenticatorGetAssertionResult
     {
         public byte[] AuthenticatorData { get; set; }
 
         public byte[] Signature { get; set; }
+
+        public Fido2AuthenticatorGetAssertionSelectedCredential SelectedCredential { get; set; }
+    }
+
+    public class Fido2AuthenticatorGetAssertionSelectedCredential {
+        public byte[] Id { get; set; }
+
+        #nullable enable
+        public byte[]? UserHandle { get; set; }
     }
 }
 

test/Core.Test/Services/Fido2AuthenticatorTests.cs

@@ -288,6 +288,42 @@ namespace Bit.Core.Test.Services
             ));
         }
 
+        [Theory]
+        [InlineCustomAutoData(new[] { typeof(SutProviderCustomization) })]
+        // Spec: Increment the credential associated signature counter
+        public async Task GetAssertionAsync_ReturnsAssertion(SutProvider<Fido2AuthenticatorService> sutProvider, Fido2AuthenticatorGetAssertionParams aParams, Cipher encryptedCipher) {
+            // Common Arrange
+            var cipherView = CreateCipherView(null, "bitwarden.com", true);
+            aParams.RpId = cipherView.Login.MainFido2Credential.RpId;
+            aParams.AllowCredentialDescriptorList = null;
+            sutProvider.GetDependency<ICipherService>().GetAllDecryptedAsync().Returns(new List<CipherView> { cipherView });
+            sutProvider.GetDependency<IFido2UserInterface>().PickCredentialAsync(Arg.Any<Fido2PickCredentialParams>()).Returns(new Fido2PickCredentialResult {
+                CipherId = cipherView.Id,
+                UserVerified = true
+            });
+
+            // Arrange
+            var rpIdHashMock = RandomBytes(32);
+            sutProvider.GetDependency<ICryptoFunctionService>().HashAsync(aParams.RpId, CryptoHashAlgorithm.Sha256).Returns(rpIdHashMock);
+            cipherView.Login.MainFido2Credential.CounterValue = 9000;
+            
+            // Act
+            var result = await sutProvider.Sut.GetAssertionAsync(aParams);
+
+            // Assert
+            var encAuthData = result.AuthenticatorData;
+            var rpIdHash = encAuthData.Take(32);
+            var flags = encAuthData.Skip(32).Take(1);
+            var counter = encAuthData.Skip(33).Take(4);
+
+            Assert.Equal(result.SelectedCredential.Id, Guid.Parse(cipherView.Login.MainFido2Credential.CredentialId).ToByteArray());
+            Assert.Equal(result.SelectedCredential.UserHandle, CoreHelpers.Base64UrlDecode(cipherView.Login.MainFido2Credential.UserHandle));
+            Assert.Equal(rpIdHash, rpIdHashMock);
+            Assert.Equal(flags, new byte[] { 0b00000101 }); // UP = true, UV = true
+            Assert.Equal(counter, new byte[] { 0, 0, 0x23, 0x29 }); // 9001 in binary big-endian format
+            // TODO: Assert signature...
+        }
+
         [Theory]
         [InlineCustomAutoData(new[] { typeof(SutProviderCustomization) })]
         // Spec: Increment the credential associated signature counter
@@ -331,7 +367,8 @@ namespace Bit.Core.Test.Services
                         new Fido2CredentialView {
                             CredentialId = credentialId ?? Guid.NewGuid().ToString(),
                             RpId = rpId ?? "bitwarden.com",
-                            Discoverable = discoverable.HasValue ? discoverable.ToString() : "true"
+                            Discoverable = discoverable.HasValue ? discoverable.ToString() : "true",
+                            UserHandleValue = RandomBytes(32),
                         }
                     }
                 }