Merge pull request #94 from readium/fix/lcp-decryptor

Fix LCP decryption of ranges

readium-lcp-swift/Content Protection/LCPDecryptor.swift

@@ -23,6 +23,7 @@ final class LCPDecryptor {
     enum Error: Swift.Error {
         case emptyDecryptedData
         case invalidCBCData
+        case invalidRange(Range<UInt64>)
         case inflateFailed
     }
 
@@ -102,9 +103,11 @@ final class LCPDecryptor {
                             throw LCPDecryptor.Error.emptyDecryptedData
                         }
 
+                        let paddingSize = UInt64(data.last ?? 0)
+
                         return length
                             - AESBlockSize  // Minus IV or previous block
-                            - (AESBlockSize - UInt64(data.count)) % AESBlockSize  // Minus padding part
+                            - paddingSize  // Minus padding part
                 }
             }
         }()
@@ -114,43 +117,36 @@ final class LCPDecryptor {
                 return license.decryptFully(data: resource.read(), isDeflated: resource.link.isDeflated)
             }
 
-            return resource.length.tryFlatMap { totalLength in
-                let length = range.upperBound - range.lowerBound
-                let blockPosition = range.lowerBound % AESBlockSize
-
-                // For beginning of the cipher text, IV used for XOR.
-                // For cipher text in the middle, previous block used for XOR.
-                let readPosition = range.lowerBound - blockPosition
-
-                // Count blocks to read.
-                // First block for IV or previous block to perform XOR.
-                var blocksCount: UInt64 = 1
-                var bytesInFirstBlock = (AESBlockSize - blockPosition) % AESBlockSize
-                if (length < bytesInFirstBlock) {
-                    bytesInFirstBlock = 0
-                }
-                if (bytesInFirstBlock > 0) {
-                    blocksCount += 1
+            return resource.length.tryFlatMap { encryptedLength in
+                guard let rangeFirst = range.first, let rangeLast = range.last else {
+                    throw LCPDecryptor.Error.invalidRange(range)
                 }
 
-                blocksCount += (length - bytesInFirstBlock) / AESBlockSize
-                if (length - bytesInFirstBlock) % AESBlockSize != 0 {
-                    blocksCount += 1
-                }
-
-                let readSize = blocksCount * AESBlockSize
-
-                return resource.read(range: readPosition..<(readPosition + readSize))
-                    .tryMap { encryptedData in
-                        guard var data = try license.decipher(encryptedData) else {
-                            throw LCPDecryptor.Error.emptyDecryptedData
-                        }
-
-                        if (data.count > length) {
-                            data = data[0..<length]
-                        }
-
-                        return data
+                // Encrypted data is shifted by AESBlockSize, because of IV and because the
+                // previous block must be provided to perform XOR on intermediate blocks.
+                let encryptedStart = rangeFirst.floorMultiple(of: AESBlockSize)
+                let encryptedEndExclusive = (rangeLast + 1).ceilMultiple(of: AESBlockSize) + AESBlockSize
+
+                return resource.read(range: encryptedStart..<encryptedEndExclusive).tryMap { encryptedData in
+                    guard let bytes = try license.decipher(encryptedData) else {
+                        throw LCPDecryptor.Error.emptyDecryptedData
+                    }
+
+                    // Exclude the bytes added to match a multiple of AESBlockSize.
+                    let sliceStart = (rangeFirst - encryptedStart)
+
+                    let isLastBlockRead = encryptedLength - encryptedEndExclusive <= AESBlockSize
+                    let rangeLength = isLastBlockRead
+                        // Use decrypted length to ensure `rangeLast` doesn't exceed decrypted length - 1.
+                        ? min(rangeLast, try length.get() - 1) - rangeFirst + 1
+                        // The last block won't be read, so there's no need to compute the length
+                        : rangeLast - rangeFirst + 1
+
+                    // Keep only enough bytes to fit the length-corrected request in order to never
+                    // include padding.
+                    let sliceEnd = sliceStart + rangeLength
+
+                    return bytes[sliceStart..<sliceEnd]
                 }
             }
         }
@@ -199,3 +195,16 @@ private extension R2Link {
     }
 
 }
+
+
+private extension UInt64 {
+
+    func ceilMultiple(of divisor: UInt64) -> UInt64 {
+        divisor * (self / divisor + ((self % divisor == 0) ? 0 : 1))
+    }
+
+    func floorMultiple(of divisor: UInt64) -> UInt64 {
+        divisor * (self / divisor)
+    }
+
+}

readium-lcp-swift/LCPAuthenticating.swift

@@ -75,3 +75,36 @@ public struct LCPAuthenticatedLicense {
     }
 
 }
+
+/// An `LCPAuthenticating` implementation which can directly use a provided clear or hashed
+/// passphrase.
+///
+/// If the provided `passphrase` is incorrect, the given `fallback` authentication is used.
+public class LCPPassphrase: LCPAuthenticating {
+
+    private let passphrase: String
+    private let fallback: LCPAuthenticating?
+
+    public init(_ passphrase: String, fallback: LCPAuthenticating? = nil) {
+        self.passphrase = passphrase
+        self.fallback = fallback
+    }
+
+    public var requiresUserInteraction: Bool {
+        fallback?.requiresUserInteraction ?? false
+    }
+
+    public func requestPassphrase(for license: LCPAuthenticatedLicense, reason: LCPAuthenticationReason, sender: Any?, completion: @escaping (String?) -> Void) {
+        guard reason == .passphraseNotFound else {
+            if let fallback = fallback {
+                fallback.requestPassphrase(for: license, reason: reason, sender: sender, completion: completion)
+            } else {
+                completion(nil)
+            }
+            return
+        }
+
+        completion(passphrase)
+    }
+
+}

readium-lcp-swiftTests/Content Protection/LCPDecryptorTests.swift

@@ -0,0 +1,83 @@
+//
+//  Copyright 2020 Readium Foundation. All rights reserved.
+//  Use of this source code is governed by the BSD-style license
+//  available in the top-level LICENSE file of the project.
+//
+
+import XCTest
+import R2Shared
+import PDFKit
+@testable import ReadiumLCP
+
+class LCPDecryptorTests: XCTestCase {
+
+    let fixtures = Fixtures()
+    var service: LCPService!
+    var encryptedResource: Resource!
+    var clearData: Data!
+
+    override func setUpWithError() throws {
+        service = R2MakeLCPService()
+
+        let fetcher = ArchiveFetcher(archive: try DefaultArchiveFactory().open(url: self.fixtures.url(for: "daisy.lcpdf"), password: nil))
+        encryptedResource = fetcher.get(Link(
+            href: "/publication.pdf",
+            properties: Properties([
+                "encrypted": [
+                    "scheme": "http://readium.org/2014/01/lcp",
+                    "profile": "http://readium.org/lcp/basic-profile",
+                    "algorithm": "http://www.w3.org/2001/04/xmlenc#aes256-cbc"
+                ]
+            ])
+        ))
+
+        clearData = try Data(contentsOf: fixtures.url(for: "daisy.pdf"))
+    }
+
+    /// Checks that we can decrypt the full content successfully.
+    func testDecryptFull() throws {
+        retrieveLicense(path: "daisy.lcpdf", passphrase: "test") { license in
+            let decryptedResource = LCPDecryptor(license: license).decrypt(resource: self.encryptedResource)
+
+            XCTAssertEqual(try decryptedResource.read().get(), self.clearData)
+        }
+    }
+
+    /// Checks that we can decrypt various ranges successfully.
+    func testDecryptRanges() throws {
+        retrieveLicense(path: "daisy.lcpdf", passphrase: "test") { license in
+            let decryptedResource = LCPDecryptor(license: license).decrypt(resource: self.encryptedResource)
+
+            // These ranges seem arbirtrary, but some of them were failing before the fix in the
+            // same commit.
+            let ranges: [Range<UInt64>] = [
+                0..<2048,  // 2048
+                817152..<819200,  // 2048
+                819200..<819856,  // 656
+                0..<16384,  // 16384
+                819792..<819856, // 64
+                819565..<819856  // 291
+            ]
+
+            for range in ranges {
+                let intRange = Int(range.lowerBound)..<Int(range.upperBound)
+                let decrypted = try decryptedResource.read(range: range).get()
+                let clear = self.clearData[intRange]
+                XCTAssertEqual(decrypted, clear, "Failed to decrypt range \(intRange)")
+            }
+        }
+    }
+
+    private func retrieveLicense(path: String, passphrase: String, completion: @escaping (LCPLicense) throws -> Void) {
+        let completionExpectation = expectation(description: "License opened")
+
+        let url = fixtures.url(for: path)
+        service.retrieveLicense(from: url, authentication: LCPPassphrase(passphrase)) { result in
+            try! completion((try! result.get())!)
+            completionExpectation.fulfill()
+        }
+
+        waitForExpectations(timeout: 10, handler: nil)
+    }
+
+}

readium-lcp-swiftTests/Fixtures.swift

@@ -0,0 +1,32 @@
+//
+//  Copyright 2020 Readium Foundation. All rights reserved.
+//  Use of this source code is governed by the BSD-style license
+//  available in the top-level LICENSE file of the project.
+//
+
+import Foundation
+import XCTest
+
+class Fixtures {
+
+    let path: String?
+
+    init(path: String? = nil) {
+        self.path = path
+    }
+
+    private lazy var bundle = Bundle(for: type(of: self))
+
+    func url(for filepath: String) -> URL {
+        return try! XCTUnwrap(bundle.resourceURL?.appendingPathComponent("Fixtures/\(path ?? "")/\(filepath)"))
+    }
+
+    func data(at filepath: String) -> Data {
+        return try! XCTUnwrap(try? Data(contentsOf: url(for: filepath)))
+    }
+
+    func json<T>(at filepath: String) -> T {
+        return try! XCTUnwrap(JSONSerialization.jsonObject(with: data(at: filepath)) as? T)
+    }
+
+}

readium-lcp-swiftTests/Info.plist

@@ -3,7 +3,7 @@
 <plist version="1.0">
 <dict>
 	<key>CFBundleDevelopmentRegion</key>
-	<string>en</string>
+	<string>$(DEVELOPMENT_LANGUAGE)</string>
 	<key>CFBundleExecutable</key>
 	<string>$(EXECUTABLE_NAME)</string>
 	<key>CFBundleIdentifier</key>
@@ -13,7 +13,7 @@
 	<key>CFBundleName</key>
 	<string>$(PRODUCT_NAME)</string>
 	<key>CFBundlePackageType</key>
-	<string>BNDL</string>
+	<string>$(PRODUCT_BUNDLE_PACKAGE_TYPE)</string>
 	<key>CFBundleShortVersionString</key>
 	<string>1.0</string>
 	<key>CFBundleVersion</key>

readium-lcp-swiftTests/readium-lcp-swiftTests-Bridging-Header.h

@@ -0,0 +1,4 @@
+//
+//  Use this file to import your target's public headers that you would like to expose to Swift.
+//
+