Merge branch 'develop'

.swift-format

@@ -0,0 +1,15 @@
+{
+    "fileScopedDeclarationPrivacy": {
+        "accessLevel": "private"
+    },
+    "indentBlankLines": true,
+    "indentation": {
+        "spaces": 4
+    },
+    "lineLength": 9999,
+    "maximumBlankLines": 1,
+    "multiElementCollectionTrailingCommas": false,
+    "rules": {
+        "FileScopedDeclarationPrivacy": true
+    }
+}

Package.swift

@@ -1,18 +1,28 @@
-// swift-tools-version: 5.10
+// swift-tools-version: 6.0
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
 
 let package = Package(
     name: "KeychainKit",
-    platforms: [.macOS(.v10_15), .iOS(.v13)],
+    defaultLocalization: "en",
+    platforms: [.macOS(.v12), .iOS(.v15)],
     products: [
-        .library(name: "KeychainKit", targets: ["KeychainKit"]),
+        .library(name: "KeychainKit", targets: ["KeychainKit"])
     ],
     dependencies: [
+        .package(url: "https://github.com/angd-dev/localizable.git", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0")
     ],
     targets: [
-        .target(name: "KeychainKit")
+        .target(
+            name: "KeychainKit",
+            dependencies: [
+                .product(name: "Localizable", package: "localizable")
+            ],
+            resources: [
+                .process("Resources/Localizable.xcstrings")
+            ]
+        )
     ]
 )

README.md

@@ -10,11 +10,6 @@ It supports optional authentication via `LAContext`, allowing integration with F
 
 KeychainKit does not hide the complexity of Keychain operations but provides a clean API and convenient error handling via a custom `KeychainError` type.
 
-## Requirements
-
-- **Swift**: 5.10+
-- **Platforms**: macOS 10.15+, iOS 13.0+
-
 ## Installation
 
 To add KeychainKit to your project, use Swift Package Manager (SPM).
@@ -24,7 +19,7 @@ To add KeychainKit to your project, use Swift Package Manager (SPM).
 1. Open your project in Xcode.
 2. Navigate to the `File` menu and select `Add Package Dependencies`.
 3. Enter the repository URL: `https://github.com/angd-dev/keychain-kit.git`
-4. Choose the version to install (e.g., `2.1.0`).
+4. Choose the version to install (e.g., `3.0.0`).
 5. Add the library to your target module.
 
 ### Adding to Package.swift
@@ -38,7 +33,7 @@ import PackageDescription
 let package = Package(
     name: "YourProject",
     dependencies: [
-        .package(url: "https://github.com/angd-dev/keychain-kit.git", from: "2.1.0")
+        .package(url: "https://github.com/angd-dev/keychain-kit.git", from: "3.0.0")
     ],
     targets: [
         .target(
@@ -53,7 +48,7 @@ let package = Package(
 
 ## Additional Resources
 
-For more information and usage examples, see the [documentation](https://docs.angd.dev/?package=keychain-kit&version=2.1.0).
+For more information and usage examples, see the [documentation](https://docs.angd.dev/?package=keychain-kit&version=3.0.0).
 
 ## License
 

Sources/KeychainKit/Classes/KeychainStorage.swift

@@ -2,10 +2,11 @@ import Foundation
 import LocalAuthentication
 import Security
 
-/// A type-safe storage abstraction over the Keychain service.
+/// A service that provides access and management for keychain items.
 ///
-/// Supports storing, retrieving, and deleting generic data associated with
+/// This type provides direct access to the system keychain using `Security` and
-/// accounts and services, with optional local authentication context support.
+/// `LocalAuthentication` frameworks. It supports querying, inserting, deleting, and checking item
+/// existence, while handling authentication contexts and access controls automatically.
 ///
 /// ## Topics
 ///
@@ -18,36 +19,31 @@ import Security
 /// - ``service``
 /// - ``context``
 ///
-/// ### Retrieving Values
+/// ### Instance Methods
 ///
-/// - ``get(_:)``
+/// - ``get(by:)->Data?``
-///
+/// - ``insert(_:by:)-(Data,_)``
-/// ### Storing Values
+/// - ``delete(by:)``
-///
+/// - ``exists(by:)``
-/// - ``set(_:for:)``
-///
-/// ### Deleting Values
-///
-/// - ``delete(_:)``
 public final class KeychainStorage<
     Account: KeychainAccountProtocol,
     Service: KeychainServiceProtocol
->: KeychainStorageProtocol {
+>: KeychainStorageProtocol, @unchecked Sendable {
     // MARK: - Properties
     
-    /// The service metadata associated with this Keychain storage instance.
+    /// The service descriptor associated with this keychain storage.
     public let service: Service?
     
-    /// An optional local authentication context used for biometric or passcode protection.
+    /// The authentication context used for keychain operations.
     public let context: LAContext?
     
-    // MARK: - Inits
+    // MARK: - Initialization
     
-    /// Creates a new `KeychainStorage` instance with the given service and authentication context.
+    /// Creates a new keychain storage instance.
     ///
     /// - Parameters:
-    ///   - service: An optional `Service` instance representing the keychain service metadata.
+    ///   - service: The service descriptor that defines the keychain group and access settings.
-    ///   - context: An optional `LAContext` instance for authentication protection.
+    ///   - context: The authentication context used for secure access, or `nil` to use a default one.
     public init(service: Service?, context: LAContext?) {
         self.service = service
         self.context = context
@@ -55,23 +51,20 @@ public final class KeychainStorage<
     
     // MARK: - Methods
     
-    /// Retrieves raw `Data` stored in the keychain for the specified account.
+    /// Retrieves raw data for the given account.
     ///
-    /// - Parameter account: The account identifier used to locate the stored value.
+    /// - Parameter account: The account descriptor identifying the stored item.
-    /// - Returns: The raw data associated with the specified account.
+    /// - Returns: The stored data, or `nil` if no item exists.
-    ///
+    /// - Throws: ``KeychainError/invalidData`` if the retrieved value cannot be cast to `Data`.
-    /// - Throws: ``KeychainError/itemNotFound`` if no matching item is found in the keychain.
+    /// - Throws: ``KeychainError/authenticationFailed`` if user authentication fails.
-    /// - Throws: ``KeychainError/authenticationFailed`` if biometric or device authentication fails.
+    /// - Throws: ``KeychainError/osStatus(_:)`` for unexpected system errors.
-    /// - Throws: ``KeychainError/unexpectedData`` if the retrieved data is missing or corrupted.
+    public func get(by account: Account) throws(KeychainError) -> Data? {
-    /// - Throws: ``KeychainError/unexpectedCode(_:)`` for any other unexpected OSStatus error.
-    public func get(_ account: Account) throws(KeychainError) -> Data {
         var query: [CFString: Any] = [
             kSecClass: kSecClassGenericPassword,
             kSecAttrAccount: account.identifier,
             kSecAttrSynchronizable: account.synchronizable,
             kSecUseDataProtectionKeychain: true,
             kSecMatchLimit: kSecMatchLimitOne,
-            kSecReturnAttributes: true,
             kSecReturnData: true
         ]
         
@@ -79,50 +72,41 @@ public final class KeychainStorage<
         query[kSecAttrAccessGroup] = service?.accessGroup
         query[kSecUseAuthenticationContext] = context
         
-        var queryResult: AnyObject?
+        var result: AnyObject?
-        let status = withUnsafeMutablePointer(to: &queryResult) {
-            SecItemCopyMatching(query as CFDictionary, UnsafeMutablePointer($0))
-        }
         
-        switch status {
+        switch SecItemCopyMatching(query as CFDictionary, &result) {
         case errSecSuccess:
-            guard
+            if let data = result as? Data {
-                let item = queryResult as? [CFString : AnyObject],
+                return data
-                let data = item[kSecValueData] as? Data
+            } else {
-            else { throw KeychainError.unexpectedData }
+                throw .invalidData
-            return data
+            }
         case errSecItemNotFound:
-            throw KeychainError.itemNotFound
+            return nil
-        case errSecAuthFailed:
+        case errSecAuthFailed, errSecInteractionNotAllowed, errSecUserCanceled:
-            throw KeychainError.authenticationFailed
+            throw .authenticationFailed
-        default:
+        case let status:
-            throw KeychainError.unexpectedCode(status)
+            throw .osStatus(status)
         }
     }
     
-    /// Stores raw `Data` in the keychain for the specified account, replacing any existing value.
+    /// Inserts raw data for the given account.
-    ///
-    /// This method first deletes any existing keychain item for the account, then creates a new
-    /// item with the specified data and applies the access control settings from the account's
-    /// protection and flags.
     ///
     /// - Parameters:
-    ///   - value: The raw data to store.
+    ///   - value: The data to store.
-    ///   - account: The account identifier conforming to `KeychainAccountProtocol`.
+    ///   - account: The account descriptor identifying the target item.
-    ///
+    /// - Throws: ``KeychainError/underlying(_:)`` if access control creation fails.
-    /// - Throws: ``KeychainError/unexpectedError(_:)`` if access control creation fails.
+    /// - Throws: ``KeychainError/duplicateItem`` if an item with the same key already exists.
-    /// - Throws: ``KeychainError/unexpectedCode(_:)`` if adding the new item to the keychain fails.
+    /// - Throws: ``KeychainError/osStatus(_:)`` for unexpected system errors.
-    /// - Throws: Any error thrown by ``delete(_:)`` if the existing item cannot be removed.
+    public func insert(_ value: Data, by account: Account) throws(KeychainError) {
-    public func set(_ value: Data, for account: Account) throws(KeychainError) {
-        try delete(account)
-        
         var error: Unmanaged<CFError>?
         let access = SecAccessControlCreateWithFlags(
             nil, account.protection, account.accessFlags, &error
         )
         
         guard let access else {
-            throw KeychainError.unexpectedError(error?.takeUnretainedValue())
+            let error = error?.takeRetainedValue()
+            throw .underlying(error as? NSError)
         }
         
         var query: [CFString: Any] = [
@@ -138,19 +122,22 @@ public final class KeychainStorage<
         query[kSecAttrAccessGroup] = service?.accessGroup
         query[kSecUseAuthenticationContext] = context
         
-        let status = SecItemAdd(query as CFDictionary, nil)
+        switch SecItemAdd(query as CFDictionary, nil) {
-        guard status == noErr else {
+        case errSecSuccess:
-            throw KeychainError.unexpectedCode(status)
+            return
+        case errSecDuplicateItem:
+            throw .duplicateItem
+        case let status:
+            throw .osStatus(status)
         }
     }
     
-    /// Deletes the keychain item associated with the specified account.
+    /// Deletes the item for the given account.
     ///
-    /// If no item exists for the given account, this method completes silently without error.
+    /// - Parameter account: The account descriptor identifying the item to remove.
-    ///
+    /// - Throws: ``KeychainError/authenticationFailed`` if user authentication fails.
-    /// - Parameter account: The account identifier conforming to `KeychainAccountProtocol`.
+    /// - Throws: ``KeychainError/osStatus(_:)`` for unexpected system errors.
-    /// - Throws: ``KeychainError/unexpectedCode(_:)`` if the deletion fails with an unexpected OSStatus.
+    public func delete(by account: Account) throws(KeychainError) {
-    public func delete(_ account: Account) throws(KeychainError) {
         var query: [CFString: Any] = [
             kSecClass: kSecClassGenericPassword,
             kSecAttrAccount: account.identifier,
@@ -162,9 +149,45 @@ public final class KeychainStorage<
         query[kSecAttrAccessGroup] = service?.accessGroup
         query[kSecUseAuthenticationContext] = context
         
-        let status = SecItemDelete(query as CFDictionary)
+        switch SecItemDelete(query as CFDictionary) {
-        guard status == errSecSuccess || status == errSecItemNotFound else {
+        case errSecSuccess, errSecItemNotFound:
-            throw KeychainError.unexpectedCode(status)
+            return
+        case errSecAuthFailed, errSecInteractionNotAllowed, errSecUserCanceled:
+            throw .authenticationFailed
+        case let status:
+            throw .osStatus(status)
+        }
+    }
+    
+    /// Checks whether an item exists for the given account.
+    ///
+    /// - Parameter account: The account descriptor identifying the stored item.
+    /// - Returns: `true` if the item exists; otherwise, `false`.
+    /// - Throws: ``KeychainError/osStatus(_:)`` for unexpected system errors.
+    public func exists(by account: Account) throws(KeychainError) -> Bool {
+        var query: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrAccount: account.identifier,
+            kSecAttrSynchronizable: account.synchronizable,
+            kSecUseDataProtectionKeychain: true,
+            kSecMatchLimit: kSecMatchLimitOne,
+            kSecReturnData: false
+        ]
+        
+        let context = LAContext()
+        context.interactionNotAllowed = true
+        
+        query[kSecAttrService] = service?.identifier
+        query[kSecAttrAccessGroup] = service?.accessGroup
+        query[kSecUseAuthenticationContext] = context
+        
+        switch SecItemCopyMatching(query as CFDictionary, nil) {
+        case errSecSuccess, errSecAuthFailed, errSecInteractionNotAllowed:
+            return true
+        case errSecItemNotFound:
+            return false
+        case let status:
+            throw .osStatus(status)
         }
     }
 }

Sources/KeychainKit/Enums/KeychainError.swift

@@ -1,41 +1,44 @@
 import Foundation
 
-/// Errors that can occur during Keychain operations.
+/// An error that represents a keychain operation failure.
+///
+/// Each case corresponds to a specific system or data error encountered while performing keychain
+/// operations.
 public enum KeychainError: Error, Equatable {
-    /// Authentication failed, e.g., due to biometric or passcode denial.
+    /// Authentication was required but failed or was canceled.
     case authenticationFailed
-    /// No item found matching the query.
-    case itemNotFound
-    /// Unexpected or corrupted data found in Keychain item.
-    case unexpectedData
-    /// An unexpected OSStatus error code returned by Keychain API.
-    case unexpectedCode(OSStatus)
-    /// A generic unexpected error, with optional underlying error info.
-    case unexpectedError(Error?)
     
-    /// Compares two `KeychainError` values for equality.
+    /// An item with the same key already exists in the keychain.
+    case duplicateItem
+    
+    /// The stored or retrieved data has an invalid format.
+    case invalidData
+    
+    /// An unexpected system status code was returned.
     ///
-    /// - Parameters:
+    /// - Parameter status: The underlying `OSStatus` value.
-    ///   - lhs: The first `KeychainError` to compare.
+    case osStatus(OSStatus)
-    ///   - rhs: The second `KeychainError` to compare.
+    
-    /// - Returns: `true` if both errors are of the same case and represent the same error details.
+    /// A lower-level error occurred during encoding, decoding, or other processing.
     ///
-    /// For `.unexpectedError`, the comparison is based on the underlying `NSError` identity,
+    /// - Parameter error: The underlying Foundation error, if available.
-    /// which includes domain and error code.
+    case underlying(NSError?)
-    public static func == (lhs: Self, rhs: Self) -> Bool {
+    
-        switch (lhs, rhs) {
+    /// A localized, human-readable description of the error.
-        case (.authenticationFailed, .authenticationFailed):
+    public var localizedDescription: String {
-            true
+        switch self {
-        case (.itemNotFound, .itemNotFound):
+        case .authenticationFailed:
-            true
+            return .Error.authenticationFailed
-        case (.unexpectedData, .unexpectedData):
+        case .duplicateItem:
-            true
+            return .Error.duplicateItem
-        case (.unexpectedCode(let lCode), .unexpectedCode(let rCode)):
+        case .invalidData:
-            lCode == rCode
+            return .Error.invalidData
-        case (.unexpectedError(let lErr), .unexpectedError(let rErr)):
+        case .osStatus(let status):
-            lErr as NSError? == rErr as NSError?
+            let message = SecCopyErrorMessageString(status, nil)
-        default:
+            return .Error.osStatus(message as? String ?? "")
-            false
+        case .underlying(let error):
+            let message = error?.localizedDescription
+            return .Error.underlying(message ?? "")
         }
     }
 }

Sources/KeychainKit/Extensions/String+Error.swift

@@ -0,0 +1,15 @@
+import Foundation
+import Localizable
+
+extension String {
+    @Localizable(bundle: .module)
+    enum Error {
+        private enum Strings {
+            case authenticationFailed
+            case duplicateItem
+            case invalidData
+            case osStatus(String)
+            case underlying(String)
+        }
+    }
+}

Sources/KeychainKit/Protocols/KeychainAccountProtocol.swift

@@ -1,47 +1,53 @@
 import Foundation
 
-/// A protocol that defines the required properties for a keychain account descriptor.
+/// A type that describes a keychain account configuration for secure item storage and access.
 ///
-/// Types conforming to this protocol provide metadata for configuring secure storage
+/// Conforming types define metadata that determines how the keychain protects, authenticates, and
-/// and access behavior for keychain items.
+/// optionally synchronizes specific items.
-public protocol KeychainAccountProtocol {
+///
-    /// A unique string used to identify the keychain account.
+/// ## Topics
+///
+/// ### Properties
+///
+/// - ``identifier``
+/// - ``protection``
+/// - ``accessFlags``
+/// - ``synchronizable``
+public protocol KeychainAccountProtocol: Sendable {
+    /// A unique string that identifies the keychain account.
     var identifier: String { get }
     
-    /// The keychain data protection level for the account.
+    /// The keychain data protection level assigned to the account.
     ///
-    /// Defaults to `kSecAttrAccessibleAfterFirstUnlock`. You may override it to use other
+    /// Defaults to `kSecAttrAccessibleAfterFirstUnlock`. You can override this to use another
-    /// accessibility levels, such as `kSecAttrAccessibleWhenUnlocked`
+    /// accessibility option, such as `kSecAttrAccessibleWhenUnlocked` or
-    /// or `kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly`.
+    /// `kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly`.
     var protection: CFString { get }
     
-    /// The access control flags used to define authentication requirements.
+    /// The access control flags defining additional authentication requirements.
     ///
-    /// Defaults to `[]` (no additional access control). Can be overridden to specify
+    /// Defaults to an empty set (`[]`). Override this to enforce constraints like `.userPresence`,
-    /// constraints such as `.userPresence`, `.biometryAny`, or `.devicePasscode`.
+    /// `.biometryAny`, or `.devicePasscode`.
     var accessFlags: SecAccessControlCreateFlags { get }
     
-    /// Whether the item should be marked as synchronizable via iCloud Keychain.
+    /// Indicates whether the item is synchronized through iCloud Keychain.
     ///
-    /// Defaults to `false`. Set to `true` if the item should sync across devices.
+    /// Defaults to `false`. Set this to `true` if the item should be available across all devices
+    /// associated with the same iCloud account.
     var synchronizable: Bool { get }
 }
 
 public extension KeychainAccountProtocol {
-    /// Default value for `protection`: accessible after first unlock.
     var protection: CFString { kSecAttrAccessibleAfterFirstUnlock }
     
-    /// Default value for `accessFlags`: no access control constraints.
     var accessFlags: SecAccessControlCreateFlags { [] }
     
-    /// Default value for `synchronizable`: not synchronized across devices.
     var synchronizable: Bool { false }
 }
 
 public extension KeychainAccountProtocol where Self: RawRepresentable, Self.RawValue == String {
-    /// Provides a default `identifier` implementation for `RawRepresentable` types
+    /// A unique string that identifies the keychain account.
-    /// whose `RawValue` is `String`.
     ///
-    /// The `identifier` is derived from the raw string value.
+    /// Derived from the instance’s raw string value.
     var identifier: String { rawValue }
 }

Sources/KeychainKit/Protocols/KeychainServiceProtocol.swift

@@ -1,28 +1,33 @@
 import Foundation
 
-/// A protocol that defines the required properties for a keychain service descriptor.
+/// A type that describes a keychain service used to group and identify stored items.
 ///
-/// Types conforming to this protocol provide an identifier used to distinguish stored items
+/// Conforming types define a unique service identifier and may optionally specify an access group
-/// and may optionally specify an access group to enable keychain sharing between apps.
+/// for sharing keychain data between multiple apps or extensions.
-public protocol KeychainServiceProtocol {
+///
-    /// A unique string used to identify the keychain service.
+/// ## Topics
+///
+/// ### Properties
+///
+/// - ``identifier``
+/// - ``accessGroup``
+public protocol KeychainServiceProtocol: Sendable {
+    /// A unique string that identifies the keychain service.
     var identifier: String { get }
     
-    /// An optional keychain access group identifier to support shared access between apps.
+    /// An optional keychain access group identifier that enables shared access between apps.
     ///
-    /// The default implementation returns `nil`, indicating no access group is specified.
+    /// Defaults to `nil`, meaning no access group is specified.
     var accessGroup: String? { get }
 }
 
 public extension KeychainServiceProtocol {
-    /// The default implementation returns `nil`, indicating that no access group is specified.
     var accessGroup: String? { nil }
 }
 
 public extension KeychainServiceProtocol where Self: RawRepresentable, Self.RawValue == String {
-    /// Provides a default `identifier` implementation for `RawRepresentable` types
+    /// A unique string that identifies the keychain service.
-    /// whose `RawValue` is `String`.
     ///
-    /// The `identifier` is derived from the raw string value.
+    /// Derived from the instance’s raw string value.
     var identifier: String { rawValue }
 }

Sources/KeychainKit/Protocols/KeychainStorageProtocol.swift

@@ -1,13 +1,9 @@
 import Foundation
 
-/// A protocol that defines a type-safe interface for storing and retrieving values
+/// A type that provides access to data stored in the keychain.
-/// in the system keychain.
 ///
-/// This protocol provides generic support for `Data`, `String`, `UUID`, and `Codable` types.
+/// Conforming types define how items are encoded, saved, and accessed securely, using account and
-/// It allows configuring the associated account and service context for each operation.
+/// service descriptors to identify individual entries.
-///
-/// Types conforming to this protocol must specify concrete types for `Account`
-/// and `Service`, which describe keychain item identity and service grouping.
 ///
 /// ## Topics
 ///
@@ -20,205 +16,170 @@ import Foundation
 ///
 /// - ``service``
 ///
-/// ### Retrieving Values
+/// ### Retrieving Items
 ///
-/// - ``get(_:)-2gcee``
+/// - ``get(by:)->Data?``
-/// - ``get(_:)-23z7h``
+/// - ``get(by:)->String?``
-/// - ``get(_:)-4xbe6``
+/// - ``get(by:)->UUID?``
-/// - ``get(_:decoder:)``
+/// - ``get(by:decoder:)``
 ///
-/// ### Storing Values
+/// ### Inserting Items
 ///
-/// - ``set(_:for:)-21dla``
+/// - ``insert(_:by:)-(Data,_)``
-/// - ``set(_:for:)-6nzkf``
+/// - ``insert(_:by:)-(String,_)``
-/// - ``set(_:for:)-2smpc``
+/// - ``insert(_:by:)-(UUID,_)``
-/// - ``set(_:for:encoder:)``
+/// - ``insert(_:by:encoder:)``
 ///
-/// ### Deleting Values
+/// ### Deleting Items
 ///
-/// - ``delete(_:)``
+/// - ``delete(by:)``
-public protocol KeychainStorageProtocol {
+///
-    /// A type that describes a keychain account and its security configuration.
+/// ### Checking Existence
+///
+/// - ``exists(by:)``
+public protocol KeychainStorageProtocol: Sendable {
+    // MARK: - Types
+    
+    /// A type that describes a keychain account used to identify stored items.
     associatedtype Account: KeychainAccountProtocol
     
-    /// A type that identifies a keychain service context (e.g., app or subsystem).
+    /// A type that describes a keychain service used to group stored items.
     associatedtype Service: KeychainServiceProtocol
     
-    /// The service associated with this keychain storage instance.
+    // MARK: - Properties
-    ///
+    
-    /// This value is used as the `kSecAttrService` when interacting with the keychain.
+    /// The keychain service associated with this storage instance.
-    /// If `nil`, the default service behavior is used.
     var service: Service? { get }
     
-    /// Retrieves the value stored in the keychain for the specified account as raw `Data`.
+    // MARK: - Methods
-    ///
-    /// - Parameter account: The keychain account whose value should be retrieved.
-    /// - Returns: The data associated with the given account.
-    /// - Throws: An error if the item is not found, access is denied, or another keychain error occurs.
-    func get(_ account: Account) throws(KeychainError) -> Data
     
-    /// Retrieves the value stored in the keychain for the specified account as a UTF-8 string.
+    /// Retrieves raw data for the given account.
     ///
-    /// - Parameter account: The keychain account whose value should be retrieved.
+    /// - Parameter account: The account descriptor identifying the stored item.
-    /// - Returns: A string decoded from the stored data using UTF-8 encoding.
+    /// - Returns: The stored data, or `nil` if no item exists.
-    /// - Throws: An error if the item is not found, the data is not valid UTF-8,
+    /// - Throws: ``KeychainError`` if the operation fails.
-    ///   or a keychain access error occurs.
+    func get(by account: Account) throws(KeychainError) -> Data?
-    func get(_ account: Account) throws(KeychainError) -> String
     
-    /// Retrieves the value stored in the keychain for the specified account as a `UUID`.
+    /// Inserts raw data for the given account.
-    ///
-    /// - Parameter account: The keychain account whose value should be retrieved.
-    /// - Returns: A UUID decoded from a 16-byte binary representation stored in the keychain.
-    /// - Throws: An error if the item is not found, the data is not exactly 16 bytes,
-    ///   or a keychain access error occurs.
-    func get(_ account: Account) throws(KeychainError) -> UUID
-    
-    /// Retrieves and decodes a value of type `T` stored in the keychain for the specified account.
     ///
     /// - Parameters:
-    ///   - account: The keychain account whose value should be retrieved.
+    ///   - value: The data to store.
-    ///   - decoder: The `JSONDecoder` instance used to decode the stored data.
+    ///   - account: The account descriptor identifying the target item.
-    /// - Returns: A decoded instance of type `T`.
+    /// - Throws: ``KeychainError`` if the operation fails.
-    /// - Throws: An error if the item is not found, decoding fails, or a keychain access error occurs.
+    func insert(_ value: Data, by account: Account) throws(KeychainError)
-    func get<T: Decodable>(_ account: Account, decoder: JSONDecoder) throws(KeychainError) -> T
     
-    /// Stores raw `Data` in the keychain for the specified account.
+    /// Deletes the item for the given account.
     ///
-    /// - Parameters:
+    /// - Parameter account: The account descriptor identifying the item to remove.
-    ///   - value: The data to store in the keychain.
+    /// - Throws: ``KeychainError`` if the operation fails.
-    ///   - account: The keychain account under which the data will be saved.
+    func delete(by account: Account) throws(KeychainError)
-    /// - Throws: An error if storing the data fails.
-    func set(_ value: Data, for account: Account) throws(KeychainError)
     
-    /// Stores a UTF-8 encoded `String` in the keychain for the specified account.
+    /// Checks whether an item exists for the given account.
     ///
-    /// - Parameters:
+    /// - Parameter account: The account descriptor identifying the stored item.
-    ///   - value: The string to store in the keychain.
+    /// - Returns: `true` if the item exists; otherwise, `false`.
-    ///   - account: The keychain account under which the string will be saved.
+    /// - Throws: ``KeychainError`` if the check fails.
-    /// - Throws: An error if storing the string fails.
+    func exists(by account: Account) throws(KeychainError) -> Bool
-    func set(_ value: String, for account: Account) throws(KeychainError)
-    
-    /// Stores a `UUID` in the keychain for the specified account.
-    ///
-    /// - Parameters:
-    ///   - value: The UUID to store in the keychain (stored in 16-byte binary format).
-    ///   - account: The keychain account under which the UUID will be saved.
-    /// - Throws: An error if storing the UUID fails.
-    func set(_ value: UUID, for account: Account) throws(KeychainError)
-    
-    /// Encodes and stores a value of type `T` in the keychain for the specified account.
-    ///
-    /// - Parameters:
-    ///   - value: The value to encode and store.
-    ///   - account: The keychain account under which the encoded data will be saved.
-    ///   - encoder: The `JSONEncoder` used to encode the value.
-    /// - Throws: An error if encoding or storing the value fails.
-    func set<T: Encodable>(_ value: T, for account: Account, encoder: JSONEncoder) throws(KeychainError)
-    
-    /// Deletes the keychain item associated with the specified account.
-    ///
-    /// - Parameter account: The keychain account whose stored value should be deleted.
-    /// - Note: If the item does not exist, the method completes silently without error.
-    /// - Throws: An error only if the item exists but removal fails.
-    func delete(_ account: Account) throws(KeychainError)
 }
 
+// MARK: - Get Extension
+
 public extension KeychainStorageProtocol {
-    /// Retrieves a UTF-8 encoded string stored in the keychain for the specified account.
+    /// Retrieves a UTF-8 string for the given account.
     ///
-    /// - Parameter account: The account identifier used to locate the stored value.
+    /// - Parameter account: The account descriptor identifying the stored item.
-    /// - Returns: A string decoded from the keychain data using UTF-8 encoding.
+    /// - Returns: The decoded string, or `nil` if no item exists.
-    /// - Throws: ``KeychainError/unexpectedData`` if the data cannot be decoded as UTF-8.
+    /// - Throws: ``KeychainError`` if retrieval fails.
-    /// - Throws: Any error thrown by ``KeychainStorageProtocol/get(_:)-2gcee``
+    /// - Throws: ``KeychainError/invalidData`` if the stored data cannot be decoded as UTF-8.
-    ///   if reading the raw data fails.
+    func get(by account: Account) throws(KeychainError) -> String? {
-    func get(_ account: Account) throws(KeychainError) -> String {
+        guard let data = try get(by: account) else { return nil }
-        guard let value = String(data: try get(account), encoding: .utf8) else {
+        guard let string = String(data: data, encoding: .utf8) else {
-            throw KeychainError.unexpectedData
+            throw .invalidData
         }
-        return value
+        return string
     }
     
-    /// Retrieves a `UUID` stored in the keychain for the specified account.
+    /// Retrieves a UUID for the given account.
     ///
-    /// - Parameter account: The account identifier used to locate the stored value.
+    /// - Parameter account: The account descriptor identifying the stored item.
-    /// - Returns: A UUID decoded from the keychain string.
+    /// - Returns: The decoded UUID, or `nil` if no item exists.
-    /// - Throws: ``KeychainError/unexpectedData`` if the stored string is missing or invalid.
+    /// - Throws: ``KeychainError`` if retrieval fails.
-    /// - Throws: Any error thrown by ``KeychainStorageProtocol/get(_:)-23z7h``
+    /// - Throws: ``KeychainError/invalidData`` if the stored value is not a valid UUID string.
-    ///   if reading the string from the keychain fails.
+    func get(by account: Account) throws(KeychainError) -> UUID? {
-    func get(_ account: Account) throws(KeychainError) -> UUID {
+        guard let string: String = try get(by: account) else { return nil }
-        guard let value = UUID(uuidString: try get(account)) else {
+        guard let uuid = UUID(uuidString: string) else {
-            throw KeychainError.unexpectedData
+            throw .invalidData
         }
-        return value
+        return uuid
     }
     
-    /// Retrieves a value of type `T` stored in the keychain and decodes it from JSON using the given decoder.
+    /// Retrieves and decodes a `Decodable` value for the given account.
     ///
     /// - Parameters:
-    ///   - account: The account identifier used to locate the stored value.
+    ///   - account: The account descriptor identifying the stored item.
-    ///   - decoder: The `JSONDecoder` to use for decoding. Defaults to a new instance.
+    ///   - decoder: The JSON decoder used to decode the stored data.
-    /// - Returns: A decoded instance of type `T`.
+    /// - Returns: The decoded value, or `nil` if no item exists.
-    /// - Throws: ``KeychainError/unexpectedError(_:)`` if the data cannot be decoded into the specified type.
+    /// - Throws: ``KeychainError`` if retrieval fails.
-    /// - Throws: Any error thrown by ``KeychainStorageProtocol/get(_:)-2gcee`` if reading the raw data fails.
+    /// - Throws: ``KeychainError/underlying(_:)`` if JSON decoding fails.
     func get<T: Decodable>(
-        _ account: Account,
+        by account: Account,
         decoder: JSONDecoder = .init()
-    ) throws(KeychainError) -> T {
+    ) throws(KeychainError) -> T? {
-        let value: Data = try get(account)
+        guard let data = try get(by: account) else { return nil }
         do {
-            return try decoder.decode(T.self, from: value)
+            return try decoder.decode(T.self, from: data)
         } catch {
-            throw KeychainError.unexpectedError(error)
+            throw .underlying(error as NSError)
         }
     }
+}
 
-    /// Stores a UTF-8 encoded string in the keychain for the specified account.
+// MARK: - Set Extension
+
+public extension KeychainStorageProtocol {
+    /// Inserts a UTF-8 string for the given account.
     ///
     /// - Parameters:
     ///   - value: The string to store.
-    ///   - account: The account identifier used as the key for storing the value.
+    ///   - account: The account descriptor identifying the target item.
-    /// - Throws: ``KeychainError/unexpectedData`` if the string cannot be encoded as UTF-8.
+    /// - Throws: ``KeychainError`` if the operation fails.
-    /// - Throws: Any error thrown by ``KeychainStorageProtocol/set(_:for:)-21dla``
+    /// - Throws: ``KeychainError/invalidData`` if the string cannot be encoded as UTF-8.
-    ///   if saving the data fails.
+    func insert(_ value: String, by account: Account) throws(KeychainError) {
-    func set(_ value: String, for account: Account) throws(KeychainError) {
         guard let data = value.data(using: .utf8) else {
-            throw KeychainError.unexpectedData
+            throw .invalidData
         }
-        try set(data, for: account)
+        try insert(data, by: account)
     }
     
-    /// Stores a `UUID` value as a UTF-8 encoded string in the keychain for the specified account.
+    /// Inserts a UUID for the given account.
     ///
     /// - Parameters:
     ///   - value: The UUID to store.
-    ///   - account: The account identifier used as the key for storing the value.
+    ///   - account: The account descriptor identifying the target item.
-    /// - Throws: Any error thrown by ``KeychainStorageProtocol/set(_:for:)-6nzkf``
+    /// - Throws: ``KeychainError`` if the operation fails.
-    ///   if saving the data fails.
+    func insert(_ value: UUID, by account: Account) throws(KeychainError) {
-    func set(_ value: UUID, for account: Account) throws(KeychainError) {
+        try insert(value.uuidString, by: account)
-        try set(value.uuidString, for: account)
     }
     
-    /// Stores an `Encodable` value in the keychain as JSON-encoded data for the specified account.
+    /// Encodes and inserts an `Encodable` value for the given account.
     ///
     /// - Parameters:
     ///   - value: The value to encode and store.
-    ///   - account: The account identifier used as the key for storing the value.
+    ///   - account: The account descriptor identifying the target item.
-    ///   - encoder: The JSON encoder to use (default is a new instance).
+    ///   - encoder: The JSON encoder used to encode the value.
-    /// - Throws: ``KeychainError/unexpectedError(_:)`` if encoding the value fails.
+    /// - Throws: ``KeychainError`` if the operation fails.
-    /// - Throws: Any error thrown by ``KeychainStorageProtocol/set(_:for:)-21dla``
+    /// - Throws: ``KeychainError/underlying(_:)`` if JSON encoding fails.
-    ///   if saving the data fails.
+    func insert<T: Encodable>(
-    func set<T: Encodable>(
         _ value: T,
-        for account: Account,
+        by account: Account,
         encoder: JSONEncoder = .init()
     ) throws(KeychainError) {
+        let data: Data
         do {
-            let data = try encoder.encode(value)
+            data = try encoder.encode(value)
-            try set(data, for: account)
-        } catch let error as KeychainError {
-            throw error
         } catch {
-            throw KeychainError.unexpectedError(error)
+            throw .underlying(error as NSError)
         }
+        try insert(data, by: account)
     }
 }

Sources/KeychainKit/Resources/Localizable.xcstrings

@@ -0,0 +1,56 @@
+{
+  "sourceLanguage" : "en",
+  "strings" : {
+    "Error.authenticationFailed" : {
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Authentication failed"
+          }
+        }
+      }
+    },
+    "Error.duplicateItem" : {
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Item already exists"
+          }
+        }
+      }
+    },
+    "Error.invalidData" : {
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Stored item contains invalid or unexpected data"
+          }
+        }
+      }
+    },
+    "Error.osStatus %@" : {
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Unexpected Keychain status: %@"
+          }
+        }
+      }
+    },
+    "Error.underlying %@" : {
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Unexpected error while working with Keychain: %@"
+          }
+        }
+      }
+    }
+  },
+  "version" : "1.0"
+}