Add SSL pinning

8 files changed, 137 insertions, 3 deletions

diff --git a/ios/Assets/new_le_root_cert.cer b/ios/Assets/new_le_root_cert.cer
new file mode 100644
index 0000000000..9d2132e7f1
--- /dev/null
+++ b/ios/Assets/new_le_root_cert.cer
diff --git a/ios/Assets/old_le_root_cert.cer b/ios/Assets/old_le_root_cert.cer
new file mode 100644
index 0000000000..95500f6bd1
--- /dev/null
+++ b/ios/Assets/old_le_root_cert.cer
diff --git a/ios/BuildInstructions.md b/ios/BuildInstructions.md
index 13f84867ce..4c73601ee3 100644
--- a/ios/BuildInstructions.md
+++ b/ios/BuildInstructions.md
@@ -173,3 +173,12 @@ where `<KEYCHAIN>` is the name of the target Keychain where the signing credenti
 This guide does not use a separate Keychain store, so use `login.keychain-db` then.
 
 Reference: https://docs.travis-ci.com/user/common-build-problems/#mac-macos-sierra-1012-code-signing-errors
+
+# SSL pinning
+
+The iOS app utilizes SSL pinning. Root certificates can be updated by using the source certificates shipped along with `mullvad-rpc`:
+
+```
+openssl x509 -in ../mullvad-rpc/new_le_root_cert.pem -outform der -out Assets/new_le_root_cert.cer
+openssl x509 -in ../mullvad-rpc/old_le_root_cert.pem -outform der -out Assets/old_le_root_cert.cer
+```
diff --git a/ios/CHANGELOG.md b/ios/CHANGELOG.md
index 5c089e7252..f27785e79f 100644
--- a/ios/CHANGELOG.md
+++ b/ios/CHANGELOG.md
@@ -29,6 +29,7 @@ Line wrap the file at 100 chars.                                              Th
 - Add interactive map.
 - Reduce network traffic consumption by leveraging HTTP caching via ETag HTTP header to avoid 
   re-downloading the relay list if it hasn't changed.
+- Pin root SSL certificates.
 
 ### Fixed
 - Fix bug which caused the tunnel manager to become unresponsive in the rare event of failure to
diff --git a/ios/MullvadVPN.xcodeproj/project.pbxproj b/ios/MullvadVPN.xcodeproj/project.pbxproj
index 91ba67a7ff..4ec0dcc42a 100644
--- a/ios/MullvadVPN.xcodeproj/project.pbxproj
+++ b/ios/MullvadVPN.xcodeproj/project.pbxproj
@@ -73,6 +73,14 @@
 		584592612639B4A200EF967F /* ConsentContentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 584592602639B4A200EF967F /* ConsentContentView.swift */; };
 		5845F842236CBACD00B2D93C /* PacketTunnelIpc.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5845F841236CBACD00B2D93C /* PacketTunnelIpc.swift */; };
 		5845F843236CBDAB00B2D93C /* PacketTunnelIpc.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5845F841236CBACD00B2D93C /* PacketTunnelIpc.swift */; };
+		584789B8264D4A2A000E45FB /* old_le_root_cert.cer in Resources */ = {isa = PBXBuildFile; fileRef = 584789B4264D4A2A000E45FB /* old_le_root_cert.cer */; };
+		584789B9264D4A2A000E45FB /* old_le_root_cert.cer in Resources */ = {isa = PBXBuildFile; fileRef = 584789B4264D4A2A000E45FB /* old_le_root_cert.cer */; };
+		584789BE264D4A2A000E45FB /* new_le_root_cert.cer in Resources */ = {isa = PBXBuildFile; fileRef = 584789B7264D4A2A000E45FB /* new_le_root_cert.cer */; };
+		584789BF264D4A2A000E45FB /* new_le_root_cert.cer in Resources */ = {isa = PBXBuildFile; fileRef = 584789B7264D4A2A000E45FB /* new_le_root_cert.cer */; };
+		584789E026529D72000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 584789DF26529D72000E45FB /* SSLPinningURLSessionDelegate.swift */; };
+		584789E126529D72000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 584789DF26529D72000E45FB /* SSLPinningURLSessionDelegate.swift */; };
+		584789E626529DEF000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 584789DF26529D72000E45FB /* SSLPinningURLSessionDelegate.swift */; };
+		584789EC2652A1A2000E45FB /* Logging in Frameworks */ = {isa = PBXBuildFile; productRef = 584789EB2652A1A2000E45FB /* Logging */; };
 		584E96BC240FD4DA00D3334F /* Location.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58A1AA8623F43901009F7EA6 /* Location.swift */; };
 		584E96BD240FD4DA00D3334F /* Location.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58A1AA8623F43901009F7EA6 /* Location.swift */; };
 		584E96BE240FD4DB00D3334F /* Location.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58A1AA8623F43901009F7EA6 /* Location.swift */; };
@@ -318,6 +326,9 @@
 		5840250322B11AB700E4CFEC /* MullvadEndpoint.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MullvadEndpoint.swift; sourceTree = "<group>"; };
 		584592602639B4A200EF967F /* ConsentContentView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ConsentContentView.swift; sourceTree = "<group>"; };
 		5845F841236CBACD00B2D93C /* PacketTunnelIpc.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PacketTunnelIpc.swift; sourceTree = "<group>"; };
+		584789B4264D4A2A000E45FB /* old_le_root_cert.cer */ = {isa = PBXFileReference; lastKnownFileType = file; path = old_le_root_cert.cer; sourceTree = "<group>"; };
+		584789B7264D4A2A000E45FB /* new_le_root_cert.cer */ = {isa = PBXFileReference; lastKnownFileType = file; path = new_le_root_cert.cer; sourceTree = "<group>"; };
+		584789DF26529D72000E45FB /* SSLPinningURLSessionDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SSLPinningURLSessionDelegate.swift; sourceTree = "<group>"; };
 		584B26F3237434D00073B10E /* RelaySelectorTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelaySelectorTests.swift; sourceTree = "<group>"; };
 		5850366725A47AC700A43E93 /* IPAddressRange+Codable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "IPAddressRange+Codable.swift"; sourceTree = "<group>"; };
 		58561C98239A5D1500BD6B5E /* IPEndpoint.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = IPEndpoint.swift; sourceTree = "<group>"; };
@@ -432,6 +443,7 @@
 			isa = PBXFrameworksBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				584789EC2652A1A2000E45FB /* Logging in Frameworks */,
 				58871D1E25D535A3002297FA /* WireGuardKit in Frameworks */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -665,6 +677,7 @@
 				58B993B02608A34500BA7811 /* LoginContentView.swift */,
 				58FEEB57260B662E00A621A8 /* AutomaticKeyboardResponder.swift */,
 				5868BD32261DCD2600E6027F /* CustomSplitViewController.swift */,
+				584789DF26529D72000E45FB /* SSLPinningURLSessionDelegate.swift */,
 			);
 			path = MullvadVPN;
 			sourceTree = "<group>";
@@ -703,6 +716,8 @@
 		58F3C0A824A50C0E003E76BE /* Assets */ = {
 			isa = PBXGroup;
 			children = (
+				584789B7264D4A2A000E45FB /* new_le_root_cert.cer */,
+				584789B4264D4A2A000E45FB /* old_le_root_cert.cer */,
 				58F3C0A524A50155003E76BE /* relays.json */,
 			);
 			path = Assets;
@@ -744,6 +759,7 @@
 			name = MullvadVPNTests;
 			packageProductDependencies = (
 				58871D1D25D535A3002297FA /* WireGuardKit */,
+				584789EB2652A1A2000E45FB /* Logging */,
 			);
 			productName = MullvadVPNTests;
 			productReference = 58B0A2A0238EE67E00BC001D /* MullvadVPNTests.xctest */;
@@ -897,6 +913,8 @@
 				586ADD4723FC13F400CE9E87 /* countries.geo.json in Resources */,
 				58CE5E6E224146210008646E /* LaunchScreen.storyboard in Resources */,
 				58CE5E6B224146210008646E /* Assets.xcassets in Resources */,
+				584789B8264D4A2A000E45FB /* old_le_root_cert.cer in Resources */,
+				584789BE264D4A2A000E45FB /* new_le_root_cert.cer in Resources */,
 				58CE5E69224146200008646E /* Main.storyboard in Resources */,
 				58E5BC2624FEB6DB00A53A76 /* AccountViewController.xib in Resources */,
 				58B9814E24FEA70D00C0D59E /* WireguardKeysViewController.xib in Resources */,
@@ -907,7 +925,9 @@
 			isa = PBXResourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				584789B9264D4A2A000E45FB /* old_le_root_cert.cer in Resources */,
 				58F3C0A724A50C02003E76BE /* relays.json in Resources */,
+				584789BF264D4A2A000E45FB /* new_le_root_cert.cer in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -937,6 +957,7 @@
 				5807E2C3243203E700F5FF30 /* String+Split.swift in Sources */,
 				5896AE82246ACE84005B36CB /* KeychainReturn.swift in Sources */,
 				58B0A2A8238EE68200BC001D /* RelaySelectorTests.swift in Sources */,
+				584789E626529DEF000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */,
 				584E96BE240FD4DB00D3334F /* Location.swift in Sources */,
 				5857F23F24C844AD00CF6F47 /* Locking.swift in Sources */,
 				5857F23424C8443700CF6F47 /* AsyncOperation.swift in Sources */,
@@ -985,6 +1006,7 @@
 				580EE21524B3231200F9D8A1 /* OperationBlockObserver.swift in Sources */,
 				58BFA5C622A7C97F00A6173D /* RelayCache.swift in Sources */,
 				582BB1B1229569620055B6EF /* CustomNavigationBar.swift in Sources */,
+				584789E026529D72000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */,
 				588D2FE3248AC27F00E313F7 /* AsyncOperation.swift in Sources */,
 				5877153023981F7B001F8237 /* WireguardKeysViewController.swift in Sources */,
 				5850367F25A481D800A43E93 /* IPAddressRange+Codable.swift in Sources */,
@@ -1092,6 +1114,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				58CB0EE124B86751001EF0D8 /* MullvadRest.swift in Sources */,
+				584789E126529D72000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */,
 				580EE21F24B3237F00F9D8A1 /* OutputOperation.swift in Sources */,
 				5850366825A47AC700A43E93 /* IPAddressRange+Codable.swift in Sources */,
 				58F7D310250FA12E0097BE4E /* AnyIPEndpoint.swift in Sources */,
@@ -1618,6 +1641,11 @@
 /* End XCRemoteSwiftPackageReference section */
 
 /* Begin XCSwiftPackageProductDependency section */
+		584789EB2652A1A2000E45FB /* Logging */ = {
+			isa = XCSwiftPackageProductDependency;
+			package = 585834F624D2BC1F00A8AF56 /* XCRemoteSwiftPackageReference "swift-log" */;
+			productName = Logging;
+		};
 		585834F724D2BC1F00A8AF56 /* Logging */ = {
 			isa = XCSwiftPackageProductDependency;
 			package = 585834F624D2BC1F00A8AF56 /* XCRemoteSwiftPackageReference "swift-log" */;
diff --git a/ios/MullvadVPN/MullvadRest.swift b/ios/MullvadVPN/MullvadRest.swift
index ae002dab75..4d6b6da45d 100644
--- a/ios/MullvadVPN/MullvadRest.swift
+++ b/ios/MullvadVPN/MullvadRest.swift
@@ -8,6 +8,7 @@
 
 import Foundation
 import Network
+import Security
 import WireGuardKit
 
 /// REST API v1 base URL
@@ -415,8 +416,26 @@ struct RestSessionEndpoint<Input, Response> where Input: RestPayload {
 
 // MARK: - REST interface
 
-struct MullvadRest {
-    let session = URLSession(configuration: .ephemeral)
+class MullvadRest {
+    let session: URLSession
+
+    private let sessionDelegate: SSLPinningURLSessionDelegate
+
+    /// Returns array of trusted root certificates
+    private static var trustedRootCertificates: [SecCertificate] {
+        let oldRootCertificate = Bundle.main.path(forResource: "old_le_root_cert", ofType: "cer")!
+        let newRootCertificate = Bundle.main.path(forResource: "new_le_root_cert", ofType: "cer")!
+
+        return [oldRootCertificate, newRootCertificate].map { (path) -> SecCertificate in
+            let data = FileManager.default.contents(atPath: path)!
+            return SecCertificateCreateWithData(nil, data as CFData)!
+        }
+    }
+
+    init() {
+        sessionDelegate = SSLPinningURLSessionDelegate(trustedRootCertificates: Self.trustedRootCertificates)
+        session = URLSession(configuration: .ephemeral, delegate: sessionDelegate, delegateQueue: nil)
+    }
 
     func createAccount() -> RestSessionEndpoint<EmptyPayload, AccountResponse> {
         return RestSessionEndpoint(session: session, endpoint: Self.createAccount())
diff --git a/ios/MullvadVPN/SSLPinningURLSessionDelegate.swift b/ios/MullvadVPN/SSLPinningURLSessionDelegate.swift
new file mode 100644
index 0000000000..73df25f55d
--- /dev/null
+++ b/ios/MullvadVPN/SSLPinningURLSessionDelegate.swift
@@ -0,0 +1,73 @@
+//
+//  SSLPinningURLSessionDelegate.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 17/05/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+import Logging
+
+class SSLPinningURLSessionDelegate: NSObject, URLSessionDelegate {
+
+    private let trustedRootCertificates: [SecCertificate]
+    private let logger = Logger(label: "SSLPinningURLSessionDelegate")
+
+    init(trustedRootCertificates: [SecCertificate]) {
+        self.trustedRootCertificates = trustedRootCertificates
+    }
+
+    // MARK: - URLSessionDelegate
+
+    func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
+        let evaluation: (disposition: URLSession.AuthChallengeDisposition, credential: URLCredential?)
+
+        if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust {
+            if let serverTrust = challenge.protectionSpace.serverTrust, self.verifyServerTrust(serverTrust) {
+                evaluation = (.useCredential, URLCredential(trust: serverTrust))
+            } else {
+                evaluation = (.cancelAuthenticationChallenge, nil)
+            }
+        } else {
+            evaluation = (.rejectProtectionSpace, nil)
+        }
+
+        completionHandler(evaluation.disposition, evaluation.credential)
+    }
+
+
+    // MARK: - Private
+
+    private func verifyServerTrust(_ serverTrust: SecTrust) -> Bool {
+        // Set trusted root certificates
+        var secResult = SecTrustSetAnchorCertificates(serverTrust, trustedRootCertificates as CFArray)
+        guard secResult == errSecSuccess else {
+            self.logger.error("SecTrustSetAnchorCertificates failure: \(self.formatErrorMessage(code: secResult))")
+            return false
+        }
+
+        // Tell security framework to only trust the provided root certificates
+        secResult = SecTrustSetAnchorCertificatesOnly(serverTrust, true)
+        guard secResult == errSecSuccess else {
+            self.logger.error("SecTrustSetAnchorCertificatesOnly failure: \(self.formatErrorMessage(code: secResult))")
+            return false
+        }
+
+        var error: CFError?
+        if SecTrustEvaluateWithError(serverTrust, &error) {
+            return true
+        } else {
+            self.logger.error("SecTrustEvaluateWithError failure: \(error?.localizedDescription ?? "<nil>")")
+            return false
+        }
+    }
+
+    private func formatErrorMessage(code: OSStatus) -> String {
+        let message = SecCopyErrorMessageString(code, nil) as String? ?? "<nil>"
+
+        return "\(message) (code: \(code))"
+    }
+
+
+}
diff --git a/ios/update-relays.sh b/ios/update-relays.sh
index efb0a8a65c..97fd3beafc 100755
--- a/ios/update-relays.sh
+++ b/ios/update-relays.sh
@@ -9,7 +9,11 @@ RELAYS_FILE="$PROJECT_DIR/Assets/relays.json"
 
 if [ $CONFIGURATION == "Release" ]; then
   echo "Remove relays file"
-  rm "$RELAYS_FILE" || true
+  if [ -f "$RELAYS_FILE" ]; then
+    rm "$RELAYS_FILE"
+  else
+    echo "Relays file does not exist"
+  fi
 fi
 
 if [ ! -f "$RELAYS_FILE" ]; then