Encryption password. How many characters?

There is no restriction or limit on the number or type of characters. If you are like most people it is a passcode you have used in the past. To speed up guessing uncheck Encrypt Backup and you will be prompted immediately. Here's a list of successful guesses gleaned from the forum:

• First iTunes account password (40 different users)
• Old iTunes account password, but not the oldest one
• Password used for almost all accounts (3 different users)
• All digit Password created a long time ago
• Computer/laptop login password (4 users)
• Laptop password (2 users)
• Computer password (4 users)
• Email password (3 users)
• iTunes with no capital letters
• Password not used anywhere else
• All numeric used in the past
• Password for old gaming site
• PC password (5 users)
• “iphonelogin”
• work computer password
• Current app store password (2 users)
• Paypal account password
• iPad unlock passcode
• Strongest variation of the base password I have ever used
• Old password
• Old work password
• Macbook password (2 users)
• Restriction passcode
• Gmail password (2 users)
• Current Apple ID password (2 users)
• Apple MobileMe password
• Apple ID password, but all lower case (8 users)
• Apple ID password, first one ever used, but all lower case (2 users)
• iPhone passcode when corporate profile was installed
• Passcode for a website
• iPhone screen unlock passcode (9 users)
• iPhone unlock passcode at the time the first backup was made (3 users)
• First password for work computer
• Old password used over 2 years ago (2 users)
• Previous owner’s iTunes password
• Current laptop password
• Wireless network password
• Electric bill and Skype password
• icloud password, all lower case
• Windows login for very old laptop
• iMac password (3 users)
• First iPhone 4 digit passcode
• iTunes password from last year
• 4 year old password
• iTunes password (current) (3 users)
• Old PC password
• Password for “Good” application
• Password used for everything+1234
• 1234 (4 users)
• 12345 (2 users)
• 0000
• Password I use for everything else (2 users)
• One of my husband’s passwords
• Some old non-Apple product password
• Screen passcode of the first iPhone that was backed up (2 users)
• Old password with different case on first letter
• “password” (2 users)
• Windows Administrator password (2 users)
• Original Windows Administrator password
• Mackbook administrator password
• “iphone”+4 digit unlock code
• Voicemail password
• asd
• “herpderp”
• “darwin” (first name from credit card account)
• First name, all lower case
• Ms Exchange account password
• Facebook password
• Browser password
• Network admin password

That's a lot of possibilities, 😉. Great work.