NSData+AES256.h

//
//  NSMutableData+AES256.h
//  Passcode
//
//  Created by Alan Quatermain
//	From: http://iphonedevelopment.blogspot.com/2009/02/strong-encryption-for-cocoa-cocoa-touch.html
//	&	http://pastie.org/426530


#import <CommonCrypto/CommonCryptor.h>

@implementation NSData (AES256)

- (NSData *)AES256EncryptWithKey:(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];
	
	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); //free the buffer;
	return nil;
}

- (NSData *)AES256DecryptWithKey:(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];
	
	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); //free the buffer;
	return nil;
}

@end