Programming iOS 8: Dive Deep into Views, View Controllers, and Frameworks
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NOOK Book. Create, arrange, draw, layer, and animate views that respond to touch Use view controllers to manage multiple screens of interface Master interface classes for scroll views, table views, text, popovers, split views, web views, and controls Dive into frameworks for sound, video, maps, and sensors Access user libraries: music, photos, contacts, and calendar Explore additional topics, including files, networking, and threads Stay up-to-date on iOS 12 innovations, such as User Notification framework improvements, as well as changes in Xcode 10 and Swift 4.
All example code is available on GitHub for you to download, study, and run. Want to brush up on the basics? He has been programming computers since He makes a living writing books, articles, and software documentation, as well as by programming, consulting, and training. Customer Reviews Average Review. See All Customer Reviews. Shop Books.
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What really sets the iPhone apart from laptops and PCs is its use of onboard What really sets the iPhone apart from laptops and PCs is its use of onboard sensors, including those that are location-enabled. This exposure is probably an acceptable risk for metadata, but storing it in an encrypted SQLite store might be better, especially when storing full message contents.
A forensic attacker could then retrieve that completion database.
As such, developers have to consider the all too common trade-off between user experience and security. For some applications, no amount of unencrypted data stored to disk is acceptable. Other applications handle sensitive data, but they involve so much text entry that disabling autocorrection would be extremely burdensome. Fields that take smaller amounts of sensitive data, though, are a no-brainer. Consider answers to security questions, for example. This is also applicable and a good idea for UISearchBar objects because having search contents leak to disk is usually undesirable.
Check out Listing for an example of how you might try to disable this attribute.
Around iOS 5. There are currently two ways around this, ranging from very silly to utterly ridiculous. It does, however, prevent text from getting written to the disk.
Just switch keylogging on and then turn it off. The classes are implemented such that they forget to turn keylogging back on if you simply wiggle it on and off again. Listing shows how to do this. Figure shows an exampledynamic-text. Note that the database may not actually get updated until you hitthe Home button. Figure Contents of dynamic-text. In iOS 8 and later, additional information is stored in the Keyboardcache. This data is used to help with the QuickType word prediction sys-tem, but it also leaks more information about conversations and peoplewho have communicated with the device owner.
Because QuickType adapts based on therecipient, the tags. Many applica- tions in the wild store user credentials this way, and many have been called out for it. To protect users, let the server enforce such decisions as often as possible instead.
For example, if someone happens to answer a call in the middle of entering sensitive information into an application, that screen state will be written to disk and remain there until overwritten with another Once these snapshots are written to disk, a physical attacker can easilyretrieve them with common forensics tools.
Figure A snapshot of a user searchingfor embarrassing material on Wikipedia,saved to local storage Just suspend your application and open UIApplicationAutomaticSnapshotDefault-Portrait. There are, however, a couple ofother ways you can prevent this data from leaking. Screen Sanitization StrategiesFirst, you can alter the screen state before the screenshot actually occurs. The former is invoked when the applica- tion temporarily loses focus for example, when interrupted by an incoming phone call overlay and the latter when the application is forcibly killed or has opted out of background operation.
The simplest and most reliable method of obscuring screen contents, and the one that I primarily recommend, is simply placing a splash screen with some logo art on top of all the current views. You can implement this as shown in Listing Alternatively, you could set the hidden attribute of the relevant con-tainer objects—for example, UITextFields, whose contents might be sensitive.
You can use this same approach to hide the entire UIView. This is less visuallyappealing but easily does the job in a pinch. A slightly fancier option is to perform some of your own animation,13 asin Listing This just does a fade-out before removing the content fromthe view. For example, to remove the splash imageplaced over the screen in Listing , you could add something like List-ing to the applicationWillEnterForeground method. Check that the PNG images saved there have all parts of the win- dow obscured by the splash image. The com.
On top of the layer is an instance of the UIWindow class, which manages one or more views, instances of the UIView class. By default, windows have a windowLevel property of 0. The most obvious scenario is that of an alert, and in that case,UIAlertView creates a new window on top of all others except the status bar bydefault.
The window currently receiving user events is referred to as the keywindow, and it can be referenced via the keyWindow method in UIApplication. While the code will look likeit works much of the time, it still leaves any subviews of the root visible. Because several methods of hiding content are error prone, I almostalways recommend that developers use the splash screen approach.
Programming iOS Dive Deep into Views, View Controllers, and Frameworks - PDF Free Download
There is,however, an even easier, foolproof approach for some use cases: preventingsuspension entirely. Adding that item will cause the application to jump to the applicationWill-Terminate event rather than stopping at the applicationDidEnterBackgroundevent, which normally immediately precedes the taking of the screenshot. Then, the decodeRestorableStateWithCoder method is called on relaunch of the application. When you are examining a new codebase, you can quickly determine whether any state preservation is happening by grepping the codebase for restorationIdentifier, rather than clicking your way through all the Story- board UI elements.
If the appli- cation delegate implements the encodeRestorableStateWithCoder method, it can specify an encodeObject method that preserves the. Secure State Preservation If a product needs the UX and convenience of state preservation but needs data to be stored securely while on disk, you can encrypt sensitive object con- tents before passing them to the encodeObject method. When the application is installed, generate an encryption key and store it in the Keychain with secItemAdd.
Then, in your encodeRestorableStateWithCoder methods, read the key out of the Keychain and use it as the key for an encryption operation. You can use the SecureNSCoder project16 to help implement that functionality. SecureNSCoder can automatically generate a key for your application, store it in the Keychain, and use it to encode and decode your program state.
Then, include SecureArchiverDelegate. Then implement the awakeFromNib method shown in Listing By default, only three of your application directories are safe from the clutches of iCloud. Closing Thoughts Data leakage on mobile devices is a broad and ever-changing area that makes up a large percentage of issues found in mobile applications when subjected to security audits.
Programming iOS 8
There are some mitigations inplace to prevent code execution attacks, as discussed in Chapter 1, butthese can be bypassed by more skilled attackers. In C, the most commonly used functions that accept format strings are in the printf family; there are a number of other functions, such as syslog, that accept them as well. It can, however, be leveraged to overwrite portions of memory.
If attackers can then view this output, they can collect 1. Of course, both of these vulnerabilities rely on a program not control-ling user input properly. Preventing Classic C Format String AttacksThe typical example of a format string vulnerability is when a programpasses a variable directly to printf, without manually specifying a formatstring.
When the code executes, you should see a string of hexadecimal outputwritten to your console. This output contains the hexadecimal values ofvariables stored on the stack. If an application has stored a password orencryption key as a value on the stack and parses some attacker-supplieddata, an attacker could cause this information to leak to somewhere they canthen read. But you can prevent attackers from hijacking strings pretty easily bycontrolling user input.
These examples, of course, are plain old C, but knowing how they work will help you explore format string attacks with an Objective-C twist. If that happens, you still have a format string issue, and the resulting string will contain values from the stack.
The basic memory layout of a process consists of the program code, any data the program needs to run, the stack, and the heap, as shown in Figure The heap is where the bulk of nonexecutable program data will reside, in memory dynamically allocated by the program. The stack is where local variables are stored, as well as addresses of functions and, importantly, a pointer to the address that contains the next instructions that the program is to execute. Legacy Issues and Baggage from C Under most cir-cumstances, this program should function normally and compare the user-supplied password to the stored password since usernames and passwordstend to be less than 32 characters.
However, when either value is suppliedwith an input that exceeds 32 characters, the additional characters startoverwriting the memory adjacent to the variable on the stack, as illustratedin Figure This means that an attacker can overwrite the return addressof the function, specifying that the next thing to be executed is a blob ofmalicious code the attacker has placed in the current input or elsewhere inmemory.
Thesecopy data into a destination buffer without checking whether the destinationcan actually handle that much data, which is why adding a size check was soimportant in the previous section. Butthis code never checks the size of the things buffer before attempting to copyit into buf.
The strl family is not avail- able on all platforms but is available on BSD-based systems, including iOS. As you likely know, there are two types of integers in C and therefore, in Objective-C : signed and unsigned. Signed integers can be positive or negative, and unsigned integers are always positive. An unsigned integer will wrap around past the maximum value of an integer, starting over at zero.
If the integer is signed, it will start at a negative number, the minimum value of an unsigned integer. When the number is incremented, the output on the con- sole should wrap around to a negative number, Todd C. This code creates an object of type Goat, as well as the ReadGoats function, which accepts a socket and the number of goats to read from that socket. With the right value of count, an attacker could make the malloc attempt to allocate zero bytes, or a very small number. There are also many other resources that can help you hone your C security skills.
Injection attacks are standard for web applications, but client-side injection attacks are less common and go largely unnoticed by developers and security engineers.
Client-side injection attacks happen when remotely supplied data is parsed by the program running on the device. One prominent app reported to have an XSS vulnerability was the Skype. In this case, the attack could steal sensitive data the contents of the Address Book from the device. Such attacks can also be used to, say, insert a fake login page that submits creden- tials to an attacker-controlled domain.
You can do this most effectively with a two-part approach, using both input sanitization and output encoding. Input Sanitization Input sanitization involves stripping potentially harmful characters from external inputs, using either a blacklist or whitelist approach.
Blacklisting Bad Input In a blacklist, you try to list every character that could cause a security prob- lem if accepted as input and give that list to your application.
Programming iOS 10: Dive Deep into Views, View Controllers, and Frameworks
Not only does this preclude most any malicious input, but it also keeps data clean in your database. Some programs and websites actually disallowlegitimate characters in some inputs most notably, user passwords. Youmay have run across an app or site that refuses to accept a password con-taining special characters such as! This is often an indicationthat the programmers are handling data on the backend in a remarkablyincompetent way.
For input sanitization to work correctly, it also needs to happen as closeas possible to the point before the data is processed or stored. For example,when an iOS application talks to a remote API, the application can certainlytry to strip out harmful characters or restrict input to a certain characterrange. The user can then modify data after itleaves the app but before it reaches the server and add the harmful charac-ters back.