From 0d20ebc62b925dde999ce7ca3f5915140793596a Mon Sep 17 00:00:00 2001
From: Matthew Chen <matthew@signal.org>
Date: Fri, 14 Dec 2018 09:23:56 -0500
Subject: [PATCH] Add encryption to DeviceNames.

---
 SignalServiceKit/src/Util/DeviceNames.swift | 87 +++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 SignalServiceKit/src/Util/DeviceNames.swift

diff --git a/SignalServiceKit/src/Util/DeviceNames.swift b/SignalServiceKit/src/Util/DeviceNames.swift
new file mode 100644
index 000000000..31530ede8
--- /dev/null
+++ b/SignalServiceKit/src/Util/DeviceNames.swift
@@ -0,0 +1,87 @@
+//
+//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//
+
+import Foundation
+import Curve25519Kit
+
+@objc
+public enum DeviceNameError: Int, Error {
+    case assertionFailure
+}
+
+@objc
+public class DeviceNames: NSObject {
+    // Never instantiate this class.
+    private override init() {}
+
+    @objc
+    public class func encryptDeviceName(plaintext: String,
+                                        identityKeyPair: ECKeyPair) throws -> Data {
+
+        guard let plaintextData = plaintext.data(using: .utf8) else {
+            owsFail("Could not convert text to UTF-8.")
+        }
+
+        let ephemeralKeyPair = Curve25519.generateKeyPair()
+
+        // master_secret = ECDH(ephemeral_private, identity_public).
+        let masterSecret: Data
+        do {
+            masterSecret = try Curve25519.generateSharedSecret(fromPublicKey: identityKeyPair.publicKey,
+                                                                     privateKey: ephemeralKeyPair.privateKey)
+        } catch {
+            Logger.error("Could not generate shared secret: \(error)")
+            throw error
+        }
+
+        // synthetic_iv = HmacSHA256(key=HmacSHA256(key=master_secret, input=“auth”), input=plaintext)[0:16]
+        guard let syntheticIVInput = "auth".data(using: .utf8) else {
+            owsFail("Could not convert text to UTF-8.")
+        }
+        guard let syntheticIVKey = Cryptography.computeSHA256HMAC(syntheticIVInput, withHMACKey: masterSecret) else {
+            owsFailDebug("Could not compute synthetic IV key.")
+            throw DeviceNameError.assertionFailure
+        }
+        let ivLength: UInt = 16
+        guard let syntheticIV = Cryptography.truncatedSHA256HMAC(plaintextData, withHMACKey: syntheticIVKey, truncation: ivLength) else {
+            owsFailDebug("Could not compute synthetic IV.")
+            throw DeviceNameError.assertionFailure
+        }
+
+        // cipher_key = HmacSHA256(key=HmacSHA256(key=master_secret, “cipher”), input=synthetic_iv)
+        guard let cipherKeyInput = "cipher".data(using: .utf8) else {
+            owsFail("Could not convert text to UTF-8.")
+        }
+        guard let cipherKeyKey = Cryptography.computeSHA256HMAC(cipherKeyInput, withHMACKey: masterSecret) else {
+            owsFailDebug("Could not compute cipher key key.")
+            throw DeviceNameError.assertionFailure
+        }
+        guard let cipherKey = Cryptography.computeSHA256HMAC(syntheticIV, withHMACKey: cipherKeyKey) else {
+            owsFailDebug("Could not compute cipher key.")
+            throw DeviceNameError.assertionFailure
+        }
+
+        // cipher_text = AES-CTR(key=cipher_key, input=plaintext, counter=0)
+        //
+        // TODO: Is this right?
+        let cipherTextIV = Data(count: Int(kAES256CTR_IVLength))
+        guard let cipherTextKey = OWSAES256Key(data: cipherKey) else {
+            owsFailDebug("Invalid cipher key.")
+            throw DeviceNameError.assertionFailure
+        }
+        guard let cipherText: AES256CTREncryptionResult = Cryptography.encryptAESCTR(plaintextData: plaintextData, initializationVector: cipherTextIV, key: cipherTextKey) else {
+            owsFailDebug("Could not compute cipher text.")
+            throw DeviceNameError.assertionFailure
+        }
+
+        let protoBuilder = SignalIOSProtoDeviceName.builder(ephemeralPublic: ephemeralKeyPair.publicKey,
+                                                            syntheticIv: syntheticIV,
+                                                            ciphertext: cipherText.ciphertext)
+        let protoData = try protoBuilder.buildSerializedData()
+
+        let protoDataBase64 = protoData.base64EncodedData()
+
+        return protoDataBase64
+    }
+}