Append date offset

Author: florentmorin

README.md

@@ -162,11 +162,11 @@ func metadataOutput(_ output: AVCaptureMetadataOutput,
 
 You can store a code with your preferred method: Core Data, Realm, JSON file, raw data.
 
-You need to store 3 informations:
+You need to store at least 3 informations:
 
 * Code identifier
-* Date of scan / manual input
-* A 128 bits key generated from code identifier and date _(called transportableKey)_
+* Date of scan / manual input (calculation is based on day + month + year)
+* A 128 bits key generated from code identifier, date offset _(if present)_ and date _(called transportableKey)_
 
 So, once you received the code, you need to generate local content like this:
 
@@ -177,6 +177,18 @@ let content = LocalContent(codeId: <# The ID from code #>, date: <# Date of scan
 
 <# Store your data from content #>
 
+```
+If you want to add an offset for each date (ie 1 = morning, 2 = afternoon), it's possible.
+
+You just need to store date offset. Date offset will be used in key calculation.
+
+```swift
+let content = LocalContent(codeId: <# The ID from code #>, date: <# Date of scan #>, dateOffset: <# Offset #>)
+
+// Then, you can use `content.codeId`, `content.date`, `content.dateOffset` and `content.transportableKey`
+
+<# Store your data from content #>
+
 ```
 
 ### Export data from local storage
@@ -186,7 +198,7 @@ Your data are stored locally and you want to share them with other users.
 First, rebuild your content:
 
 ```swift
-let localContent = LocalContent((codeId: <# UUID #>, date: <# Date #>, transportableKey: <# Data #>)
+let localContent = LocalContent(codeId: <# UUID #>, date: <# Date #>, transportableKey: <# Data #>)
 ```
 
 Then, create transportable content with data required for diagnosis:

Sources/QRContactTracingCore/Common/LocalContent.swift

@@ -35,35 +35,51 @@ public struct LocalContent: Identifiable {
     /// Date when code was entered
     public let date: Date
 
+    /// Date offset
+    public let dateOffset: Int?
+    
     /// Transportable key calculated from code id + date
     public let transportableKey: Data
 
     /// A date formatter used for encryption
+    @inline(__always)
     fileprivate static let dateFormatter: DateFormatter = {
         let df = DateFormatter()
         df.dateFormat = "yyyyMMdd"
         return df
     }()
-    
     /// Initializer
     ///
     /// - parameter codeId: Code ID (see `Code.id`)
     /// - parameter date: Date when code was entered (default: now)
-    /// - parameter transportableKey: Transportable key calculated from code id + date
-    public init(codeId: UUID, date: Date = Date(), transportableKey: Data? = nil) {
+    /// - parameter dateOffset: Custom date offset to specify each part of the day is concerned (default: nil)
+    /// - parameter transportableKey: Transportable key calculated from code id + date + date offset
+    public init(codeId: UUID, date: Date = Date(), dateOffset: Int? = nil, transportableKey: Data? = nil) {
         self.codeId = codeId
         self.date = date
-        self.transportableKey = transportableKey ?? Self.buildTransportableKey(id: codeId, date: date)
+        self.dateOffset = dateOffset
+        self.transportableKey = transportableKey ?? Self.buildTransportableKey(id: codeId, date: date, dateOffset: dateOffset)
     }
 }
 
 extension LocalContent {
 
+    @inline(__always)
+    private static func buildPassword(date: Date, dateOffset: Int? = nil) -> String {
+        var password = dateFormatter.string(from: date)
+        
+        if let dateOffset = dateOffset {
+            password = password + String(dateOffset)
+        }
+        
+        return password
+    }
+    
     /// Build transportable key using PBKDF2
     @inline(__always)
-    internal static func buildTransportableKey(id: UUID, date: Date) -> Data {
+    internal static func buildTransportableKey(id: UUID, date: Date, dateOffset: Int? = nil) -> Data {
         let length: Int = kCCKeySizeAES128
-        let password = dateFormatter.string(from: date)
+        let password = buildPassword(date: date, dateOffset: dateOffset)
         let rawPassword: [CChar] = password.cString(using: .utf8)!.dropLast()
         let rawSalt: [CUnsignedChar] = Array(hexadecimalSalt(id))
             .chunked(into: 2)

Sources/QRContactTracingCore/Common/TransportableContent.swift

@@ -35,12 +35,12 @@ public struct TransportableContent: Identifiable {
     /// - parameter clearData: Supplement data that need to be encrypted (stored in `encryptedData`)
     @inline(__always)
     public init?(localContent: LocalContent, clearData: Data) {
-        let key = localContent.transportableKey
+        let iv = localContent.transportableKey
 
         let data = Self.crypt(
             input: clearData,
             key: localContent.key,
-            iv: key,
+            iv: iv,
             operation: CCOperation(kCCEncrypt)
         )
 
@@ -49,7 +49,7 @@ public struct TransportableContent: Identifiable {
         }
 
         self.encryptedData = encryptedData
-        self.key = key
+        self.key = iv
     }
 
     /// Initializer from external data

Tests/QRContactTracingCoreTests/Common/LocalContentTests.swift

@@ -22,6 +22,7 @@ final class LocalContentTests: XCTestCase {
         XCTAssertEqual(scannedContent.codeId, code.id)
         XCTAssertEqual(scannedContent.codeId, identifier)
         XCTAssertEqual(scannedContent.date, date)
+        XCTAssertNil(scannedContent.dateOffset)
 
         let rawContent = LocalContent(codeId: identifier, date: date, transportableKey: key)
 
@@ -30,11 +31,39 @@ final class LocalContentTests: XCTestCase {
         XCTAssertEqual(rawContent.key, code.id.data)
         XCTAssertEqual(rawContent.key, rawContent.codeId.data)
         XCTAssertEqual(rawContent.date, date)
+        XCTAssertNil(rawContent.dateOffset)
         XCTAssertEqual(rawContent.transportableKey, key)
         XCTAssertEqual(rawContent.transportableKey, LocalContent.buildTransportableKey(id: rawContent.codeId, date: rawContent.date))
     }
 
+    func testInitializationWithOffset() {
+        let identifier = UUID()
+        let code = MyCode(id: identifier)
+        let date = Date()
+        let dateOffset = 10
+        
+        let scannedContent = LocalContent(codeId: code.id, date: date, dateOffset: dateOffset)
+        let key = scannedContent.transportableKey
+        
+        XCTAssertEqual(scannedContent.codeId, code.id)
+        XCTAssertEqual(scannedContent.codeId, identifier)
+        XCTAssertEqual(scannedContent.date, date)
+        XCTAssertEqual(scannedContent.dateOffset, dateOffset)
+        
+        let rawContent = LocalContent(codeId: identifier, date: date, dateOffset: dateOffset, transportableKey: key)
+        
+        XCTAssertEqual(rawContent.codeId, code.id)
+        XCTAssertEqual(rawContent.codeId, identifier)
+        XCTAssertEqual(rawContent.key, code.id.data)
+        XCTAssertEqual(rawContent.key, rawContent.codeId.data)
+        XCTAssertEqual(rawContent.date, date)
+        XCTAssertEqual(rawContent.dateOffset, dateOffset)
+        XCTAssertEqual(rawContent.transportableKey, key)
+        XCTAssertEqual(rawContent.transportableKey, LocalContent.buildTransportableKey(id: rawContent.codeId, date: rawContent.date, dateOffset: dateOffset))
+    }
+    
     static var allTests = [
-        ("testInitialization", testInitialization)
+        ("testInitialization", testInitialization),
+        ("testInitializationWithOffset", testInitializationWithOffset)
     ]
 }