firebase-ios-sdk/FirebaseInstallations/Source/Library/IIDMigration/FIRInstallationsIIDStore.m

/*
 * Copyright 2019 Google
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#import "FirebaseInstallations/Source/Library/IIDMigration/FIRInstallationsIIDStore.h"

#if __has_include(<FBLPromises/FBLPromises.h>)
#import <FBLPromises/FBLPromises.h>
#else
#import "FBLPromises.h"
#endif

#import <CommonCrypto/CommonDigest.h>
#import "FirebaseInstallations/Source/Library/Errors/FIRInstallationsErrorUtil.h"

static NSString *const kFIRInstallationsIIDKeyPairPublicTagPrefix =
    @"com.google.iid.keypair.public-";
static NSString *const kFIRInstallationsIIDKeyPairPrivateTagPrefix =
    @"com.google.iid.keypair.private-";
static NSString *const kFIRInstallationsIIDCreationTimePlistKey = @"|S|cre";

@implementation FIRInstallationsIIDStore

- (FBLPromise<NSString *> *)existingIID {
  return [FBLPromise onQueue:dispatch_get_global_queue(QOS_CLASS_UTILITY, 0)
                          do:^id _Nullable {
                            if (![self hasPlistIIDFlag]) {
                              return nil;
                            }

                            NSData *IIDPublicKeyData = [self IIDPublicKeyData];
                            return [self IIDWithPublicKeyData:IIDPublicKeyData];
                          }]
      .validate(^BOOL(NSString *_Nullable IID) {
        return IID.length > 0;
      });
}

- (FBLPromise<NSNull *> *)deleteExistingIID {
  return [FBLPromise onQueue:dispatch_get_global_queue(QOS_CLASS_UTILITY, 0)
                          do:^id _Nullable {
                            NSError *error;
                            if (![self deleteIIDFlagFromPlist:&error]) {
                              return error;
                            }

                            if (![self deleteIID:&error]) {
                              return error;
                            }

                            return [NSNull null];
                          }];
}

#pragma mark - IID decoding

- (NSString *)IIDWithPublicKeyData:(NSData *)publicKeyData {
  NSData *publicKeySHA1 = [self sha1WithData:publicKeyData];

  const uint8_t *bytes = publicKeySHA1.bytes;
  NSMutableData *identityData = [NSMutableData dataWithData:publicKeySHA1];

  uint8_t b0 = bytes[0];
  // Take the first byte and make the initial four 7 by initially making the initial 4 bits 0
  // and then adding 0x70 to it.
  b0 = 0x70 + (0xF & b0);
  // failsafe should give you back b0 itself
  b0 = (b0 & 0xFF);
  [identityData replaceBytesInRange:NSMakeRange(0, 1) withBytes:&b0];
  NSData *data = [identityData subdataWithRange:NSMakeRange(0, 8 * sizeof(Byte))];
  return [self base64URLEncodedStringWithData:data];
}

/** FirebaseInstallations SDK uses the SHA1 hash for backwards compatibility with the legacy
 * FirebaseInstanceID SDK. The SHA1 hash is used to access Instance IDs stored on the device and not
 * for any security-relevant process. This is a one-time step that allows migration of old client
 * identifiers. Cryptographic security is not needed here, so potential hash collisions are not a
 * problem.
 */
- (NSData *)sha1WithData:(NSData *)data {
  unsigned char output[CC_SHA1_DIGEST_LENGTH];
  unsigned int length = (unsigned int)[data length];

  CC_SHA1(data.bytes, length, output);
  return [NSData dataWithBytes:output length:CC_SHA1_DIGEST_LENGTH];
}

- (NSString *)base64URLEncodedStringWithData:(NSData *)data {
  NSString *string = [data base64EncodedStringWithOptions:0];
  string = [string stringByReplacingOccurrencesOfString:@"/" withString:@"_"];
  string = [string stringByReplacingOccurrencesOfString:@"+" withString:@"-"];
  string = [string stringByReplacingOccurrencesOfString:@"=" withString:@""];
  return string;
}

#pragma mark - Keychain

- (NSData *)IIDPublicKeyData {
  NSString *tag = [self keychainKeyTagWithPrefix:kFIRInstallationsIIDKeyPairPublicTagPrefix];
  NSDictionary *query = [self keyPairQueryWithTag:tag returnData:YES];

  CFTypeRef keyRef = NULL;
  OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)query, (CFTypeRef *)&keyRef);

  if (status != noErr) {
    if (keyRef) {
      CFRelease(keyRef);
    }
    return nil;
  }

  return (__bridge NSData *)keyRef;
}

- (BOOL)deleteIID:(NSError **)outError {
  if (![self deleteKeychainKeyWithTagPrefix:kFIRInstallationsIIDKeyPairPublicTagPrefix
                                      error:outError]) {
    return NO;
  }

  if (![self deleteKeychainKeyWithTagPrefix:kFIRInstallationsIIDKeyPairPrivateTagPrefix
                                      error:outError]) {
    return NO;
  }

  return YES;
}

- (BOOL)deleteKeychainKeyWithTagPrefix:(NSString *)tagPrefix error:(NSError **)outError {
  NSString *keyTag = [self keychainKeyTagWithPrefix:kFIRInstallationsIIDKeyPairPublicTagPrefix];
  NSDictionary *keyQuery = [self keyPairQueryWithTag:keyTag returnData:NO];

  OSStatus status = SecItemDelete((__bridge CFDictionaryRef)keyQuery);

  // When item is not found, it should NOT be considered as an error. The operation should
  // continue.
  if (status != noErr && status != errSecItemNotFound) {
    FIRInstallationsItemSetErrorToPointer(
        [FIRInstallationsErrorUtil keychainErrorWithFunction:@"SecItemDelete" status:status],
        outError);
    return NO;
  }

  return YES;
}

- (NSDictionary *)keyPairQueryWithTag:(NSString *)tag returnData:(BOOL)shouldReturnData {
  NSMutableDictionary *query = [NSMutableDictionary dictionary];
  NSData *tagData = [tag dataUsingEncoding:NSUTF8StringEncoding];

  query[(__bridge id)kSecClass] = (__bridge id)kSecClassKey;
  query[(__bridge id)kSecAttrApplicationTag] = tagData;
  query[(__bridge id)kSecAttrKeyType] = (__bridge id)kSecAttrKeyTypeRSA;
  if (shouldReturnData) {
    query[(__bridge id)kSecReturnData] = @(YES);
  }

#if TARGET_OS_OSX
  if (self.keychainRef) {
    query[(__bridge NSString *)kSecMatchSearchList] = @[ (__bridge id)(self.keychainRef) ];
  }
#endif  // TARGET_OSX

  return query;
}

- (NSString *)keychainKeyTagWithPrefix:(NSString *)prefix {
  NSString *mainAppBundleID = [[NSBundle mainBundle] bundleIdentifier];
  if (mainAppBundleID.length == 0) {
    return nil;
  }
  return [NSString stringWithFormat:@"%@%@", prefix, mainAppBundleID];
}

- (NSString *)mainbundleIdentifier {
  NSString *bundleIdentifier = [[NSBundle mainBundle] bundleIdentifier];
  if (!bundleIdentifier.length) {
    return nil;
  }
  return bundleIdentifier;
}

#pragma mark - Plist

- (BOOL)deleteIIDFlagFromPlist:(NSError **)outError {
  NSString *path = [self plistPath];
  if (![[NSFileManager defaultManager] fileExistsAtPath:path]) {
    return YES;
  }

  NSMutableDictionary *plistContent = [[NSMutableDictionary alloc] initWithContentsOfFile:path];
  plistContent[kFIRInstallationsIIDCreationTimePlistKey] = nil;

  if (@available(macOS 10.13, iOS 11.0, tvOS 11.0, *)) {
    return [plistContent writeToURL:[NSURL fileURLWithPath:path] error:outError];
  }

  return [plistContent writeToFile:path atomically:YES];
}

- (BOOL)hasPlistIIDFlag {
  NSString *path = [self plistPath];
  if (![[NSFileManager defaultManager] fileExistsAtPath:path]) {
    return NO;
  }

  NSDictionary *plistContent = [[NSDictionary alloc] initWithContentsOfFile:path];
  return plistContent[kFIRInstallationsIIDCreationTimePlistKey] != nil;
}

- (NSString *)plistPath {
  NSString *plistNameWithExtension = @"com.google.iid-keypair.plist";
  NSString *_subDirectoryName = @"Google/FirebaseInstanceID";

  NSArray *directoryPaths =
      NSSearchPathForDirectoriesInDomains([self supportedDirectory], NSUserDomainMask, YES);
  NSArray *components = @[ directoryPaths.lastObject, _subDirectoryName, plistNameWithExtension ];

  return [NSString pathWithComponents:components];
}

- (NSSearchPathDirectory)supportedDirectory {
#if TARGET_OS_TV
  return NSCachesDirectory;
#else
  return NSApplicationSupportDirectory;
#endif
}

@end