在OFB模式下用AES-128解密一些代码？

Question

我使用那个很棒的代码https://github.com/Gurpartap/AESCrypt-ObjC试图解密一些在OFB模式下用AES-128加密的数据。 加密文本在base64中，iv和密钥是十六进制！

所以我使用了以下功能：

    + (NSString *)decrypt:(NSString *)base64EncodedString password:(NSData *)password andIV:(NSData *)iv{
             NSData *encryptedData = [NSData base64DataFromString:base64EncodedString];
             NSData *decryptedData = [encryptedData decryptedAES256DataUsingKey:password andIV:iv error:nil];
             return [[NSString alloc] initWithData:decryptedData encoding:NSUTF8StringEncoding];
     }

    - (NSData *) decryptedAES256DataUsingKey: (id) key andIV:iv error: (NSError **) error
        {
              CCCryptorStatus status = kCCSuccess;
               NSData * result = [self decryptedDataUsingAlgorithm: kCCAlgorithmAES128
                                              key: key
                                            initializationVector:iv
                                          options: kCCModeOFB
                                            error: &status];

              if ( result != nil )
              return ( result );

              if ( error != NULL )
              *error = [NSError errorWithCCCryptorStatus: status];

              return ( nil );
        }


     - (NSData *) decryptedDataUsingAlgorithm: (CCAlgorithm) algorithm
                                 key: (id) key      // data or string
                initializationVector: (id) iv       // data or string
                             options: (CCOptions) options
                               error: (CCCryptorStatus *) error
    {

             CCCryptorRef cryptor = NULL;
         CCCryptorStatus status = kCCSuccess;

         NSParameterAssert([key isKindOfClass: [NSData class]] || [key isKindOfClass: [NSString class]]);
         NSParameterAssert(iv == nil || [iv isKindOfClass: [NSData class]] || [iv isKindOfClass: [NSString class]]);

        NSMutableData * keyData, * ivData;
       if ( [key isKindOfClass: [NSData class]] )
          keyData = (NSMutableData *) [key mutableCopy];
       else
          keyData = [[key dataUsingEncoding: NSUTF8StringEncoding] mutableCopy];

       if ( [iv isKindOfClass: [NSString class]] )
          ivData = [[iv dataUsingEncoding: NSUTF8StringEncoding] mutableCopy];
       else
          ivData = (NSMutableData *) [iv mutableCopy];  // data or nil

           #if !__has_feature(objc_arc)
                  [keyData autorelease];
                  [ivData autorelease];
           #endif

      // ensure correct lengths for key and iv data, based on algorithms
       FixKeyLengths( algorithm, keyData, ivData );

       status = CCCryptorCreate( kCCDecrypt, algorithm, options,
                       [keyData bytes], [keyData length], [ivData bytes],
                       &cryptor );

       if ( status != kCCSuccess )
       {
         if ( error != NULL )
            *error = status;
             return ( nil );
       }

       NSData * result = [self _runCryptor: cryptor result: &status];
       if ( (result == nil) && (error != NULL) )
         *error = status;

       CCCryptorRelease( cryptor );

       return ( result );
      }

我称之为：

    // Do any additional setup after loading the view, typically from a nib.
NSString *hexString = @"d00f41f5495e9468fabdfe55d0bbf031";
NSData *keyData = [self dataFromHexString:hexString];

NSString *hexiv = @"921f3eb904e6b48e5ae26128ead7e434";
NSData *ivData = [self dataFromHexString:hexString];

NSString *encryptedData = [AESCrypt decrypt:@"vuFSz1QqLtj4akw=" password:keyData andIV:ivData];
NSLog(@"EncryptedData = %@",encryptedData);

其中vuFSz1QqLtj4akw =加密的“Hello World”，将hexString转换为nsdata的方法如下：

   - (NSData *)dataFromHexString:(NSString *)string
  {
       NSMutableData *stringData = [[NSMutableData alloc] init] ;
       unsigned char whole_byte;
       char byte_chars[3] = {'\0','\0','\0'};
       int i;
       for (i=0; i < [string length] / 2; i++) {
          byte_chars[0] = [string characterAtIndex:i*2];
          byte_chars[1] = [string characterAtIndex:i*2+1];
          whole_byte = strtol(byte_chars, NULL, 16);
          [stringData appendBytes:&whole_byte length:1];
       }
       return stringData;
    }

但所有这些都给我NULL加密数据！任何帮助将不胜感激