feat: add ProtectedString with XOR obfuscation

MyPassCore/Sources/MyPassCore/Models/ProtectedString.swift

@@ -0,0 +1,32 @@
+import Foundation
+
+public struct ProtectedString: Equatable {
+    private let obfuscated: [UInt8]
+    private let key: [UInt8]
+    public let isProtected: Bool
+
+    public init(_ value: String, isProtected: Bool = true) {
+        self.isProtected = isProtected
+        let bytes = Array(value.utf8)
+        let k = (0 ..< bytes.count).map { _ in UInt8.random(in: 0 ... 255) }
+        self.key = k
+        self.obfuscated = zip(bytes, k).map { $0 ^ $1 }
+    }
+
+    public func reveal() -> String {
+        let bytes = zip(obfuscated, key).map { $0 ^ $1 }
+        return String(bytes: bytes, encoding: .utf8) ?? ""
+    }
+
+    public static func == (lhs: ProtectedString, rhs: ProtectedString) -> Bool {
+        lhs.reveal() == rhs.reveal() && lhs.isProtected == rhs.isProtected
+    }
+}
+
+extension ProtectedString: CustomStringConvertible {
+    public var description: String { isProtected ? "***" : reveal() }
+}
+
+extension ProtectedString: CustomDebugStringConvertible {
+    public var debugDescription: String { "ProtectedString(isProtected: \(isProtected))" }
+}

MyPassCore/Tests/MyPassCoreTests/ProtectedStringTests.swift

@@ -0,0 +1,30 @@
+import XCTest
+@testable import MyPassCore
+
+final class ProtectedStringTests: XCTestCase {
+    func test_reveal_returnsOriginalValue() {
+        let ps = ProtectedString("hunter2", isProtected: true)
+        XCTAssertEqual(ps.reveal(), "hunter2")
+    }
+
+    func test_description_isRedactedWhenProtected() {
+        let ps = ProtectedString("secret", isProtected: true)
+        XCTAssertEqual("\(ps)", "***")
+    }
+
+    func test_description_isPlainWhenNotProtected() {
+        let ps = ProtectedString("visible", isProtected: false)
+        XCTAssertEqual("\(ps)", "visible")
+    }
+
+    func test_equality_matchesByRevealedValue() {
+        let a = ProtectedString("abc", isProtected: true)
+        let b = ProtectedString("abc", isProtected: true)
+        XCTAssertEqual(a, b)
+    }
+
+    func test_debugDescription_neverRevealSecret() {
+        let ps = ProtectedString("topsecret", isProtected: true)
+        XCTAssertFalse(ps.debugDescription.contains("topsecret"))
+    }
+}