274 lines
10 KiB
Swift
274 lines
10 KiB
Swift
//
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// Copyright 2024 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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//
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import Foundation
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public import LibSignalClient
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public struct MessageBackupKeyMaterialImpl: MessageBackupKeyMaterial {
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private enum Constants {
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static let MessageBackupIdInfoString = "20231003_Signal_Backups_GenerateBackupId"
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static let MessageBackupIdLength = 16
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static let MessageBackupEncryptionInfoString = "20231003_Signal_Backups_EncryptMessageBackup"
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static let MessageBackupEncryptionDataLength = 64
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static let MessageBackupPrivateKeyInfoString = "20231003_Signal_Backups_GenerateBackupIdKeyPair"
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static let MessageBackupPrivateKeyDataLength = 32
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static let MessageBackupMediaIdInfoString = "20231003_Signal_Backups_Media_ID"
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static let MessageBackupMediaIdDataLength = 15
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static let MessageBackupMediaEncryptionInfoString = "20231003_Signal_Backups_EncryptMedia"
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static let MessageBackupMediaEncryptionDataLength = 80
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static let MessageBackupThumbnailEncryptionInfoString = "20240513_Signal_Backups_EncryptThumbnail"
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static let MessageBackupThumbnailEncryptionDataLength = 64
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}
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private let svr: SecureValueRecovery
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public init(svr: SecureValueRecovery) {
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self.svr = svr
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}
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public func backupAuthRequestContext(localAci: Aci, tx: DBReadTransaction) throws -> BackupAuthCredentialRequestContext {
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guard let backupKey = svr.data(for: .backupKey, transaction: tx) else {
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throw MessageBackupKeyMaterialError.missingMasterKey
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}
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return BackupAuthCredentialRequestContext.create(backupKey: backupKey.rawData, aci: localAci.rawUUID)
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}
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public func backupID(localAci: Aci, mode: MessageBackup.EncryptionMode, tx: DBReadTransaction) throws -> Data {
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let keyBytes = try buildBackupEncryptionMaterial(
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salt: localAci.serviceIdBinary,
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info: Constants.MessageBackupIdInfoString,
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length: Constants.MessageBackupIdLength,
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mode: mode,
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tx: tx
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)
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return Data(keyBytes)
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}
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public func backupPrivateKey(localAci: Aci, tx: DBReadTransaction) throws -> PrivateKey {
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let privateKeyBytes = try buildBackupEncryptionMaterial(
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salt: localAci.serviceIdBinary,
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info: Constants.MessageBackupPrivateKeyInfoString,
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length: Constants.MessageBackupPrivateKeyDataLength,
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mode: .remote,
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tx: tx
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)
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return try PrivateKey(privateKeyBytes)
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}
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public func messageBackupKey(localAci: Aci, mode: MessageBackup.EncryptionMode, tx: DBReadTransaction) throws -> MessageBackupKey {
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switch mode {
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case .remote:
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guard let masterKey = svr.masterKeyDataForKeysSyncMessage(tx: tx) else {
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throw MessageBackupKeyMaterialError.missingMasterKey
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}
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return try MessageBackupKey(masterKey: Array(masterKey), aci: localAci)
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case .linknsync:
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// TODO: [link'n'sync] once libsignal API is available, init a MessageBackupKey
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// from the ephemeral backup key and the backupId derived from it + aci.
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throw OWSAssertionError("Unsupported")
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}
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}
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public func createEncryptingStreamTransform(
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localAci: Aci,
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mode: MessageBackup.EncryptionMode,
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tx: DBReadTransaction
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) throws -> EncryptingStreamTransform {
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let (encryptionKey, _) = try buildEncryptionMaterial(localAci: localAci, mode: mode, tx: tx)
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return try EncryptingStreamTransform(iv: Randomness.generateRandomBytes(16), encryptionKey: encryptionKey)
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}
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public func createDecryptingStreamTransform(
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localAci: Aci,
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mode: MessageBackup.EncryptionMode,
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tx: DBReadTransaction
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) throws -> DecryptingStreamTransform {
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let (encryptionKey, _) = try buildEncryptionMaterial(localAci: localAci, mode: mode, tx: tx)
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return try DecryptingStreamTransform(encryptionKey: encryptionKey)
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}
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public func createHmacGeneratingStreamTransform(
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localAci: Aci,
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mode: MessageBackup.EncryptionMode,
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tx: DBReadTransaction
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) throws -> HmacStreamTransform {
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let (_, hmacKey) = try buildEncryptionMaterial(localAci: localAci, mode: mode, tx: tx)
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return try HmacStreamTransform(hmacKey: hmacKey, operation: .generate)
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}
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public func createHmacValidatingStreamTransform(
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localAci: Aci,
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mode: MessageBackup.EncryptionMode,
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tx: DBReadTransaction
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) throws -> HmacStreamTransform {
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let (_, hmacKey) = try buildEncryptionMaterial(localAci: localAci, mode: mode, tx: tx)
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return try HmacStreamTransform(hmacKey: hmacKey, operation: .validate)
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}
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public func mediaEncryptionMetadata(
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mediaName: String,
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type: MediaTierEncryptionType,
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tx: any DBReadTransaction
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) throws -> MediaTierEncryptionMetadata {
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guard let backupKey = svr.data(for: .backupKey, transaction: tx) else {
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throw MessageBackupKeyMaterialError.missingMasterKey
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}
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let (info, length) = {
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switch type {
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case .attachment:
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(Constants.MessageBackupMediaEncryptionInfoString, Constants.MessageBackupMediaEncryptionDataLength)
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case .thumbnail:
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(Constants.MessageBackupThumbnailEncryptionInfoString, Constants.MessageBackupThumbnailEncryptionDataLength)
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}
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}()
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let mediaId = try self.mediaId(mediaName: mediaName, type: type, backupKey: backupKey)
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let keyBytes = try buildBackupEncryptionMaterial(
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salt: mediaId,
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info: info,
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length: length,
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backupKey: backupKey.rawData
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)
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guard keyBytes.count == length else {
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throw MessageBackupKeyMaterialError.invalidEncryptionKey
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}
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switch type {
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case .attachment:
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return MediaTierEncryptionMetadata(
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type: type,
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mediaId: mediaId,
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hmacKey: Data(Array(keyBytes[0..<32])),
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aesKey: Data(Array(keyBytes[32..<64])),
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iv: Data(Array(keyBytes[64..<80]))
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)
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case .thumbnail:
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return MediaTierEncryptionMetadata(
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type: type,
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mediaId: mediaId,
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hmacKey: Data(Array(keyBytes[32..<64])),
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aesKey: Data(Array(keyBytes[0..<32])),
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iv: Randomness.generateRandomBytes(16)
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)
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}
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}
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public func mediaId(
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mediaName: String,
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type: MediaTierEncryptionType,
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backupKey: SVR.DerivedKeyData
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) throws -> Data {
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guard let mediaNameData = mediaName.data(using: .utf8) else {
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owsFailDebug("Failed to encode data")
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throw MessageBackupKeyMaterialError.invalidKeyInfo
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}
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let info = {
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switch type {
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case .attachment:
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Constants.MessageBackupMediaEncryptionInfoString
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case .thumbnail:
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Constants.MessageBackupThumbnailEncryptionInfoString
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}
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}()
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let mediaId = Data(try buildBackupEncryptionMaterial(
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salt: mediaNameData,
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info: Constants.MessageBackupMediaIdInfoString,
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length: Constants.MessageBackupMediaIdDataLength,
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backupKey: backupKey.rawData
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))
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return mediaId
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}
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private func buildEncryptionMaterial(
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localAci: Aci,
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mode: MessageBackup.EncryptionMode,
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tx: DBReadTransaction
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) throws -> (encryptionKey: Data, hmacKey: Data) {
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let keyBytes = try buildBackupEncryptionMaterial(
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salt: try backupID(localAci: localAci, mode: mode, tx: tx),
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info: Constants.MessageBackupEncryptionInfoString,
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length: Constants.MessageBackupEncryptionDataLength,
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mode: mode,
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tx: tx
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)
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guard keyBytes.count == Constants.MessageBackupEncryptionDataLength else {
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throw MessageBackupKeyMaterialError.invalidEncryptionKey
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}
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return (encryptionKey: Data(Array(keyBytes[32..<64])), hmacKey: Data(Array(keyBytes[0..<32])))
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}
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private func buildBackupEncryptionMaterial(
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salt: ContiguousBytes,
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info: String,
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length: Int,
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mode: MessageBackup.EncryptionMode,
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tx: DBReadTransaction
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) throws -> [UInt8] {
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return try buildBackupEncryptionMaterial(
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salt: salt,
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info: info,
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length: length,
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backupKey: try backupKey(mode: mode, tx: tx)
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)
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}
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private func buildBackupEncryptionMaterial(
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salt: ContiguousBytes,
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info: String,
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length: Int,
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backupKey: Data
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) throws -> [UInt8] {
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guard let infoData = info.data(using: .utf8) else {
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owsFailDebug("Failed to encode data")
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throw MessageBackupKeyMaterialError.invalidKeyInfo
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}
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let keyBytes = try hkdf(
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outputLength: length,
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inputKeyMaterial: backupKey,
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salt: salt,
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info: infoData
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)
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guard keyBytes.count == length else {
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throw MessageBackupKeyMaterialError.invalidEncryptionKey
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}
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return keyBytes
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}
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/// Get the root backup key used by the encryption mode. The key may be derived
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/// differently depending on the mode, but derivations downstream of it work the same.
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private func backupKey(mode: MessageBackup.EncryptionMode, tx: DBReadTransaction) throws -> Data {
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switch mode {
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case .remote:
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guard let backupKey = svr.data(for: .backupKey, transaction: tx) else {
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throw MessageBackupKeyMaterialError.missingMasterKey
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}
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guard backupKey.type == .backupKey else {
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throw OWSAssertionError("Wrong key provided")
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}
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return backupKey.rawData
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case .linknsync(let ephemeralBackupKey):
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let rawKey = ephemeralBackupKey.data
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guard rawKey.byteLength == SVR.DerivedKey.backupKeyLength else {
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throw MessageBackupKeyMaterialError.invalidEncryptionKey
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}
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return rawKey
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}
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}
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}
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