-(NSData *)convertHexStrToData:(NSString *)str
{
if (!str || [str length] == 0) {
return nil;
}

NSMutableData *hexData = [[NSMutableData alloc] initWithCapacity:20];
NSRange range;
if ([str length] % 2 == 0) {
    range = NSMakeRange(0, 2);
} else {
    range = NSMakeRange(0, 1);
}
for (NSInteger i = range.location; i < [str length]; i += 2) {
    unsigned int anInt;
    NSString *hexCharStr = [str substringWithRange:range];
    NSScanner *scanner = [[NSScanner alloc] initWithString:hexCharStr];
    
    [scanner scanHexInt:&anInt];
    NSData *entity = [[NSData alloc] initWithBytes:&anInt length:1];
    [hexData appendData:entity];
    
    range.location += range.length;
    range.length = 2;
}
return hexData;

}｝

• (NSString *)convertDataToHexStr:(NSData *)data {
  if (!data || [data length] == 0) {
  return @"";
  }
  NSMutableString *string = [[NSMutableString alloc] initWithCapacity:[data length]];

  [data enumerateByteRangesUsingBlock:^(const void *bytes, NSRange byteRange, BOOL *stop) {
  unsigned char dataBytes = (unsigned char)bytes;
  for (NSInteger i = 0; i < byteRange.length; i++) {
  NSString *hexStr = [NSString stringWithFormat:@"%x", (dataBytes[i]) & 0xff];
  if ([hexStr length] == 2) {
  [string appendString:hexStr];
  } else {
  [string appendFormat:@"0%@", hexStr];
  }
  }
  }];

  return string;
  }