Installation on my 2012 MacBook Pro (Retina) took just under 35 minutes, and the process is simple. Double-click the Installer, enter your username and password, select your target destination — for most users this is the Macintosh HD — and the installer does the rest, even rebooting itself when needed.
After the installation, a setup assistant will prompt you to log into iCloud and set up iCloud Keychain. This brings us to our first new feature.
iCloud Keychain is what your keychain is for your keys — for passwords. iCloud Keychain is a single place to store your username and passwords for all types of applications, network shares, disk images and websites. This is nothing new to Keychain users — this technology has been included on every Mac dating back to 1999's Mac OS 8.6. What's new is the addition of iCloud support, which keeps all authorized computers (and, eventually, iOS devices) up to date with the latest password data, which is stored in a 256-bit AES encrypted file. When you're prompted for a username and password by a network share or Internet site, Keychain automatically fills in the information so you don't have to.
Security experts always advise users to create a unique password for every account, but few people do that. iCloud Keychain could help change those bad habits with a built-in password creator that can be used when setting up a new account. It generates a random series of numbers and letters, producing a password that would be tough to guess (and maybe tougher to remember). But Keychain remembers it for you, and passes that data to your other devices. So the next time you log into a site on any device you own — including a mobile device like an iPhone — the username and password is remembered by Keychain via iCloud and entered automatically.
Keychain also remembers credit card data — if you allow it to — so you don't have to keep pulling out your credit card and manually entering data when doing online purchases. (For security's sake, you're still required to fill in the 3-digit security code located on the back of the card.)
After you've installed Mavericks, you can decide whether to set up iCloud Keychain now or wait until later.
Knowing what iCloud Keychain is, you can make an informed decision during the initial setup about whether to use it. You can either activate it now or leave it for later. If you do use iCloud Keychain, it will require you to verify who you are. One way that's done is by sending notifications to your other devices, so you can confirm that you are, indeed, the owner of the Apple ID account you're signed in with; the alternative is to send an SMS message to the phone number listed in your Apple ID. (Once you get the SMS, you input the code into a dialog box in Mavericks.)
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