iTunes에서 백업을 암호화하지 않았는데 비밀번호를 물어볼 경우...
아래 도움이 될만한 문서를 간단하게 번역해봤습니다.
1) 현재 사용중인 iTunes Store 비밀번호를 먼저 입력해본다.
2) 장비 액세스하기 전에 입력하는 (보통 4자리 숫자) 암호를 입력해본다.
3) 0000을 비밀번호로 입력해본다.
4) 지금 사용중이지 않은 오래된 iTunes 비밀번호를 입력해본다.
5) Mac이용자라면... 키체인접근 방식을 사용해볼수있다.
키체인접근을 실행한다.
Applications > Utilities > Keychain Access.app
(응용프로그램 > 유틸리티 > 키체인접근) 또는 Spotlight 검색에서 키체인접근을 치면됩니다.
키체인접근 스크린에서 우측 윗쪽 부분에 보이는 검색칸에 iPhone Backup을 검색한다.
iPhone Backup 중 가장 최근 기록을 더블클릭 한다.
밑에 보이는 Show Password(암호보기)를 클릭한후 관리자 암호를 입력해본다.
그럼 iTunes 백업 비밀번호가 뜬다.
6) Windows이용자라면... iTunes계정 비밀번호를 바꾼 후 iTunes Store를 접근해보는수 밖에 없다.
백업 암호를 입력하라고 뜨면, 바꾸기 전에 사용하던 비밀번호와 새로운 비밀번호를 둘다 입력해본다.
7) Windows 관리자 암호를 입력해본다 또는 처음 PC/iPhone 설치할때 설정한 관리자 암호를 입력해본다.
8) 1-7번까지 방법을 다 시도해보았지만 실패하셨다면, 하드리셋 (모든 데이터를 지우고 새 장비로 설정)해보시는 수 밖에 없다고 합니다.
하드리셋하는 방법 http://support.apple.com/kb/HT4137?viewlocale=ko_KR&locale=ko_KR
iTunes Asks for a Password to Unlock a Backup that You Never Set
If you are trying to update your iPhone or other iDevice, you may try to restore from a backup so that you do not have to recover your data. However, iTunes may ask for a password, one that you do not remember setting because you never checked the option for an encrypted backup. There are several passwords you can try to change the password, given that you can remember your iTunes Store password, etc.
Step 1) Try your iTunes Store password first. This is most commonly the password to restore your backup.
Step 2) Try your 4 digit unlock code for your device. If you have a more complex unlock code involving characters and such, try that too.
Step 3) Try 0000 as the password, sometimes the default password is in fact, 0000.
Step 4) Sometimes, the password can be a really old iTunes password that you set a long time ago but have since changed it. The original password is sometimes your backup password. This may be a bug in iTunes but try it and see if it works.
Step 5) If you are using a Mac, you can try using the Keychain method. First, open Applications > Utilities > Keychain Access.app. Second, in the search dialog, search for "iPhone Backup." Third, double click on the most recent entry for "iPhone Backup." Fourth, at the bottom of the dialogue box, click "Show password" and type in the administrative password for the computer. This will reveal your iTunes backup password!
Step 6) If you are using Windows, the only thing left to try will be to change your iTunes password on your actual account to access the iTunes Store. Then on the backup password dialogue, try the old password and the newly set password.
Step 7) Try your Windows Administrator password. This is a common solution. Also, even more common is to try the Windows administrator password that you used when you first set up your computer or when you first set up your iPhone.
Step 8) If you have managed to attempt all the steps and nothing has worked, it seems like you will have to restore and set up the phone as a new one.