Lantean

Not long ago, i had to extend an app to support iPhone 5. Yes… iOS has autolayout functionality, that should aid the development of UIView’s.

But how about assets?. How do you load assets specially crafted for 568px height screens?. Furthermore.. how do you patch classes that inherit from UITableViewCell, to return dynamic height, according to the device?.

Simple!. By means of a super short UIScreen extension. The header should look like this…:

[cc lang=”objc”]
@interface UIScreen (Lantean)
+(BOOL)isH568;
@end
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Write the following snippet in the .m file:

[cc lang=”objc”]
@implementation UIScreen (Lantean)
+(BOOL)isH568
{
static BOOL isH568 = NO;
static dispatch_once_t _once;

dispatch_once(&_once, ^
{
isH568 = ([UIScreen mainScreen].bounds.size.height == 568);
});
return isH568;
}
@end
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Fair enough. By checking [UIScreen isH568], you should be able to proceed as required… if the current device has the new 4 inches screen!.

Suppose that you need to calculate a NSData’s MD5 signature.. for whatever reason. Say… you need to check the backend’s signature.

Well… simply add a NSData extension, with the following method:

[cc lang=”objc”]
– (NSString*)md5
{
unsigned char result[16];
CC_MD5( self.bytes, self.length, result ); // This is the md5 call
return [NSString stringWithFormat:@”%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x”,
result[0], result[1], result[2], result[3],
result[4], result[5], result[6], result[7],
result[8], result[9], result[10], result[11],
result[12], result[13], result[14], result[15]
];
}
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Again, please, don’t you forget the imports!

[cc lang=”objc”]
#import
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Today we’re gonna encrypt information, stored in a NSData object, using AES-256 algorithm. As you may already know, AES-256 is a symmetric encryption schema. Which means that you need to share, somehow, the key you’re gonna use (in order to decrypt the data).

I’ve encapsulated a couple helper methods, as a NSData extension, for the sake of simplicity. I’ve based myself on this. Let’s see…

[cc lang=”objc”]
– (NSData*)aes256EncryptWithKey:(NSString*)key
{
// ‘key’ should be 32 bytes for AES256, will be null-padded otherwise
char keyPtr[kCCKeySizeAES256 + 1];
bzero( keyPtr, sizeof( keyPtr ) );

// fetch key data
[key getCString:keyPtr maxLength:sizeof( keyPtr ) encoding:NSUTF8StringEncoding];

NSUInteger dataLength = [self length];

// See the doc: For block ciphers, the output size will always be less than or equal to the input size plus the size of one block.
// That’s why we need to add the size of one block here
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc( bufferSize );

size_t numBytesEncrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt( kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesEncrypted );
if( cryptStatus == kCCSuccess )
{
// The returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}

free( buffer );
return nil;
}
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And now… the decrypt routine…

[cc lang=”objc”]
– (NSData*)aes256DecryptWithKey:(NSString*)key
{
// ‘key’ should be 32 bytes for AES256, will be null-padded otherwise
char keyPtr[kCCKeySizeAES256+1];
bzero( keyPtr, sizeof( keyPtr ) );

// fetch key data
[key getCString:keyPtr maxLength:sizeof( keyPtr ) encoding:NSUTF8StringEncoding];

NSUInteger dataLength = [self length];

// See the doc: For block ciphers, the output size will always be less than or equal to the input size plus the size of one block.
// That’s why we need to add the size of one block here
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc( bufferSize );

size_t numBytesDecrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt( kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesDecrypted );

if( cryptStatus == kCCSuccess )
{
// The returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
}

free( buffer );
return nil;
}
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Ahhhh… don’t you forget about the imports!

[cc lang=”objc”]
#import
#import
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