diff --git a/src/Core/Auth/Models/Api/Request/Accounts/RegisterFinishRequestModel.cs b/src/Core/Auth/Models/Api/Request/Accounts/RegisterFinishRequestModel.cs
index 0ac7dbbcb4..92cafbfe7b 100644
--- a/src/Core/Auth/Models/Api/Request/Accounts/RegisterFinishRequestModel.cs
+++ b/src/Core/Auth/Models/Api/Request/Accounts/RegisterFinishRequestModel.cs
@@ -1,6 +1,7 @@
 #nullable enable
 using Bit.Core.Entities;
 using Bit.Core.Enums;
+using Bit.Core.KeyManagement.Models.Data;
 using Bit.Core.Utilities;
 
 namespace Bit.Core.Auth.Models.Api.Request.Accounts;
@@ -21,18 +22,25 @@ public class RegisterFinishRequestModel : IValidatableObject
     public required string Email { get; set; }
     public string? EmailVerificationToken { get; set; }
 
+    public MasterPasswordAuthenticationData? MasterPasswordAuthenticationData { get; set; }
+    public MasterPasswordUnlockData? MasterPasswordUnlockData { get; set; }
+
+    // PM-28143 - Made to be optional as migrating to MasterPasswordUnlockData
     [StringLength(1000)]
-    public required string MasterPasswordHash { get; set; }
+    public required string? MasterPasswordHash { get; set; }
 
     [StringLength(50)]
     public string? MasterPasswordHint { get; set; }
 
-    public required string UserSymmetricKey { get; set; }
+    // PM-28143 - Remove line below (made optional during migration to MasterPasswordUnlockData
+    public string? UserSymmetricKey { get; set; }
 
     public required KeysRequestModel UserAsymmetricKeys { get; set; }
 
-    public required KdfType Kdf { get; set; }
-    public required int KdfIterations { get; set; }
+    // PM-28143 - Remove line below (made optional during migration to MasterPasswordUnlockData
+    public KdfType? Kdf { get; set; }
+    // PM-28143 - Remove line below (made optional during migration to MasterPasswordUnlockData
+    public int? KdfIterations { get; set; }
     public int? KdfMemory { get; set; }
     public int? KdfParallelism { get; set; }
 
@@ -54,11 +62,13 @@ public class RegisterFinishRequestModel : IValidatableObject
         {
             Email = Email,
             MasterPasswordHint = MasterPasswordHint,
-            Kdf = Kdf,
-            KdfIterations = KdfIterations,
-            KdfMemory = KdfMemory,
-            KdfParallelism = KdfParallelism,
-            Key = UserSymmetricKey,
+            Kdf = MasterPasswordUnlockData?.Kdf.KdfType ?? Kdf ?? throw new Exception($"{nameof(Kdf)} is required"),
+            KdfIterations = MasterPasswordUnlockData?.Kdf.Iterations ?? KdfIterations ?? throw new Exception($"{nameof(KdfIterations)} is required"),
+            KdfMemory = MasterPasswordUnlockData?.Kdf.Memory ?? KdfMemory,
+            KdfParallelism = MasterPasswordUnlockData?.Kdf.Parallelism ?? KdfParallelism,
+            // PM-28827 To be added when MasterPasswordSalt is added to the user column
+            // MasterPasswordSalt = MasterPasswordUnlockData?.Salt ?? Email.ToLower().Trim(),
+            Key = MasterPasswordUnlockData?.MasterKeyWrappedUserKey ?? UserSymmetricKey,
         };
 
         UserAsymmetricKeys.ToUser(user);
@@ -95,6 +105,15 @@ public class RegisterFinishRequestModel : IValidatableObject
 
     public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
     {
-        return KdfSettingsValidator.Validate(Kdf, KdfIterations, KdfMemory, KdfParallelism);
+        var kdf = MasterPasswordUnlockData?.Kdf.KdfType ?? Kdf ?? throw new Exception($"{nameof(Kdf)} not found on RequestModel");
+        var kdfIterations = MasterPasswordUnlockData?.Kdf.Iterations ?? KdfIterations ?? throw new Exception($"{nameof(KdfIterations)} not found on RequestModel");
+        var kdfMemory = MasterPasswordUnlockData?.Kdf.Memory ?? KdfMemory;
+        var kdfParallelism = MasterPasswordUnlockData?.Kdf.Parallelism ?? KdfParallelism;
+
+        // PM-28143 - Remove line below in favor of using the unlock data.
+        return KdfSettingsValidator.Validate(kdf, kdfIterations, kdfMemory, kdfParallelism);
+
+        // PM-28143 - Uncomment
+        // return KdfSettingsValidator.Validate(MasterPasswordUnlockData);
     }
 }
diff --git a/src/Core/Entities/User.cs b/src/Core/Entities/User.cs
index 1ca6606779..75f35b7b32 100644
--- a/src/Core/Entities/User.cs
+++ b/src/Core/Entities/User.cs
@@ -7,8 +7,6 @@ using Bit.Core.KeyManagement.Models.Data;
 using Bit.Core.Utilities;
 using Microsoft.AspNetCore.Identity;
 
-#nullable enable
-
 namespace Bit.Core.Entities;
 
 public class User : ITableObject<Guid>, IStorableSubscriber, IRevisable, ITwoFactorProvidersUser
@@ -51,7 +49,7 @@ public class User : ITableObject<Guid>, IStorableSubscriber, IRevisable, ITwoFac
     public string? Key { get; set; }
     /// <summary>
     /// The raw public key, without a signature from the user's signature key.
-    /// </summary> 
+    /// </summary>
     public string? PublicKey { get; set; }
     /// <summary>
     /// User key wrapped private key.
@@ -102,6 +100,8 @@ public class User : ITableObject<Guid>, IStorableSubscriber, IRevisable, ITwoFac
     public DateTime? LastKeyRotationDate { get; set; }
     public DateTime? LastEmailChangeDate { get; set; }
     public bool VerifyDevices { get; set; } = true;
+    // PM-28827 Uncomment below line.
+    // public string? MasterPasswordSalt { get; set; }
 
     public string GetMasterPasswordSalt()
     {
diff --git a/src/Core/Utilities/KdfSettingsValidator.cs b/src/Core/Utilities/KdfSettingsValidator.cs
index f89e8ddb66..34241eda9f 100644
--- a/src/Core/Utilities/KdfSettingsValidator.cs
+++ b/src/Core/Utilities/KdfSettingsValidator.cs
@@ -36,6 +36,33 @@ public static class KdfSettingsValidator
         }
     }
 
+    public static IEnumerable<ValidationResult> Validate(MasterPasswordUnlockData masterPasswordUnlockData)
+    {
+        switch (masterPasswordUnlockData.Kdf.KdfType)
+        {
+            case KdfType.PBKDF2_SHA256:
+                if (!AuthConstants.PBKDF2_ITERATIONS.InsideRange(masterPasswordUnlockData.Kdf.Iterations))
+                {
+                    yield return new ValidationResult($"KDF iterations must be between {AuthConstants.PBKDF2_ITERATIONS.Min} and {AuthConstants.PBKDF2_ITERATIONS.Max}.");
+                }
+                break;
+            case KdfType.Argon2id:
+                if (!AuthConstants.ARGON2_ITERATIONS.InsideRange(masterPasswordUnlockData.Kdf.Iterations))
+                {
+                    yield return new ValidationResult($"Argon2 iterations must be between {AuthConstants.ARGON2_ITERATIONS.Min} and {AuthConstants.ARGON2_ITERATIONS.Max}.");
+                }
+                else if (!masterPasswordUnlockData.Kdf.Memory.HasValue || !AuthConstants.ARGON2_MEMORY.InsideRange(masterPasswordUnlockData.Kdf.Memory.Value))
+                {
+                    yield return new ValidationResult($"Argon2 memory must be between {AuthConstants.ARGON2_MEMORY.Min}mb and {AuthConstants.ARGON2_MEMORY.Max}mb.");
+                }
+                else if (!masterPasswordUnlockData.Kdf.Parallelism.HasValue || !AuthConstants.ARGON2_PARALLELISM.InsideRange(masterPasswordUnlockData.Kdf.Parallelism.Value))
+                {
+                    yield return new ValidationResult($"Argon2 parallelism must be between {AuthConstants.ARGON2_PARALLELISM.Min} and {AuthConstants.ARGON2_PARALLELISM.Max}.");
+                }
+                break;
+        }
+    }
+
     public static IEnumerable<ValidationResult> Validate(KdfSettings settings)
     {
         return Validate(settings.KdfType, settings.Iterations, settings.Memory, settings.Parallelism);