66 lines
1.9 KiB
Swift
66 lines
1.9 KiB
Swift
//
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// Copyright 2025 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 enum MediaTierEncryptionType: CaseIterable {
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case outerLayerFullsizeOrThumbnail
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case transitTierThumbnail
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}
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public struct MediaTierEncryptionMetadata: Equatable {
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let type: MediaTierEncryptionType
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let mediaId: Data
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let hmacKey: Data
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let aesKey: Data
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func attachmentKey() throws -> AttachmentKey {
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return try AttachmentKey(combinedKey: aesKey + hmacKey)
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}
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}
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public struct MediaRootBackupKey: BackupKeyMaterial {
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public var credentialType: BackupAuthCredentialType { .media }
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public var backupKey: BackupKey
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public init(backupKey: BackupKey) {
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self.backupKey = backupKey
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}
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public func deriveMediaId(_ mediaName: String) throws(BackupKeyMaterialError) -> Data {
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do {
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return try backupKey.deriveMediaId(mediaName)
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} catch {
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throw BackupKeyMaterialError.derivationError(error)
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}
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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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) throws(BackupKeyMaterialError) -> MediaTierEncryptionMetadata {
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let mediaId = try self.deriveMediaId(mediaName)
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let keyBytes: Data
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do {
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switch type {
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case .outerLayerFullsizeOrThumbnail:
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keyBytes = try backupKey.deriveMediaEncryptionKey(mediaId)
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case .transitTierThumbnail:
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keyBytes = try backupKey.deriveThumbnailTransitEncryptionKey(mediaId)
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}
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} catch {
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throw BackupKeyMaterialError.derivationError(error)
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}
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owsPrecondition(keyBytes.count >= 64)
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return MediaTierEncryptionMetadata(
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type: type,
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mediaId: mediaId,
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hmacKey: keyBytes.prefix(32),
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aesKey: keyBytes.dropFirst(32).prefix(32),
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)
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}
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}
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