Here is some code I found in iphonedevelopment.blogspot.com on how to extend NSMutableData to encrypt and decrypt using AES 256 encryption standard, very useful.


#import <CommonCrypto/CommonCryptor.h>



@implementation NSMutableData (AES256)
- (BOOL) encryptWithKey: (NSString *) key {
// 'key' should be 32 bytes for AES256, will be null-padded otherwise
char * keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
bzero( keyPtr, sizeof(keyPtr) ); // fill with zeroes (for padding)

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

// encrypts in-place, since this is a mutable data object
size_t numBytesEncrypted = 0;
CCCryptorStatus result = CCCrypt( kCCEncrypt, , kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self mutableBytes], [self length], /* input */
[self mutableBytes], [self length], /* output */
&numBytesEncrypted );

return ( result == kCCSuccess );
}



- (BOOL) decryptWithKey: (NSString *) key {
// ‘key’ should be 32 bytes for AES256, will be null-padded otherwise
char * keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
bzero( keyPtr, sizeof(keyPtr) ); // fill with zeroes (for padding)

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

// encrypts in-place, since this is a mutable data object
size_t numBytesEncrypted = 0;
CCCryptorStatus result = CCCrypt( kCCDecrypt, , kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self mutableBytes], [self length], /* input */
[self mutableBytes], [self length], /* output */
&numBytesEncrypted );

return ( result == kCCSuccess );
}
@end