How to encrypt the NSString value using DES in iPhone?

Question

I used following code to encrypt the NSString value with Key,

NSString *token = @"encryptValue";
NSString *key = @"encryptKey";

NSData * keyData = [key dataUsingEncoding: NSUTF8StringEncoding];
NSData * plainData = [token dataUsingEncoding: NSUTF8StringEncoding];
NSMutableData * encData = [NSMutableData dataWithLength: plainData.length + 256];
size_t bytesWritten = 0;
CCCryptorStatus ccStatus = CCCrypt (kCCEncrypt,
                    kCCAlgorithmDES,
                    kCCOptionPKCS7Padding,
                    [keyData bytes], 
                    kCCKeySizeDES,
                    NULL,
                    [plainData bytes],
                    [plainData length],
                    encData.mutableBytes,
                    encData.length,
                    &bytesWritten);
encData.length = bytesWritten;    
NSString *encrypted = [[NSString alloc]  initWithBytes:[encData bytes] length:[encData length] encoding: NSUTF8StringEncoding];  
NSLog(@"ENCRYPT : %@",encrypted); 

But I'm getting (null) is the result. Is anything wrong? How to encrypt the NSString value?

Answer 1

Here is a way for AES, probably for DES would be similar, take a look this works with me... Make a new category AES on NSData
For NSData+AES.h

#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonCryptor.h>

@interface NSData (AES)

- (NSData*) EncryptAES: (NSString *) key;
- (NSData *) DecryptAES: (NSString *) key;

@end

For NSData+AES.m

    #import "NSData+AES.h"
    @implementation NSData(AES)

    - (NSData*) EncryptAES: (NSString *) key
    {
        char keyPtr[kCCKeySizeAES256+1];
        bzero( keyPtr, sizeof(keyPtr) );

        [key getCString: keyPtr maxLength: sizeof(keyPtr) encoding: NSUTF16StringEncoding];
        size_t numBytesEncrypted = 0;

        NSUInteger dataLength = [self length];

        size_t bufferSize = dataLength + kCCBlockSizeAES128;
        void *buffer = malloc(bufferSize);

        CCCryptorStatus result = CCCrypt( kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                         keyPtr, kCCKeySizeAES256,
                                         NULL,
                                         [self bytes], [self length],
                                         buffer, bufferSize,
                                         &numBytesEncrypted );

        if( result == kCCSuccess )
            return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];

        return nil;
    }

    - (NSData *) DecryptAES: (NSString *) key
    {
        char  keyPtr[kCCKeySizeAES256+1];
        bzero( keyPtr, sizeof(keyPtr) );

        [key getCString: keyPtr maxLength: sizeof(keyPtr) encoding: NSUTF16StringEncoding];

        size_t numBytesEncrypted = 0;

        NSUInteger dataLength = [self length];

        size_t bufferSize = dataLength + kCCBlockSizeAES128;
        void *buffer_decrypt = malloc(bufferSize);    

        CCCryptorStatus result = CCCrypt( kCCDecrypt , kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                         keyPtr, kCCKeySizeAES256,
                                         NULL,
                                         [self bytes], [self length],
                                         buffer_decrypt, bufferSize,
                                         &numBytesEncrypted );

        if( result == kCCSuccess )
        return [NSData dataWithBytesNoCopy:buffer_decrypt length:numBytesEncrypted];

        return nil;
    }

    @end

Usage: Import NSData+AES.h

//Encryption
NSString *myString = @"This is the content";
NSString *key = @"my secret key";
NSData *data = [myString dataUsingEncoding:NSUTF8StringEncoding];
NSData *encryptedData = [data EncryptAES:key];

//Decryption
NSString *decryptedString = [[[NSString alloc] initWithData:[encryptedData DecryptAES:key] encoding:NSUTF8StringEncoding] autorelease]; // remove autorelease if using ARC