Encryption & Decryption in iPhone sdk

#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






Links: http://stackoverflow.com/questions/2840374/iphone-encryption-not-working

http://pastie.org/966473

http://pastie.org/426530