把16進位制字串轉換成NSData：

-(NSData *)hexString:(NSString *)hexString {
    int j=0;
    Byte bytes[20];
    ///3ds key的Byte 陣列， 128位
    for(int i=0; i<[hexString length]; i++)
    {
        int int_ch;  /// 兩位16進位制數轉化後的10進位制數
        
        unichar hex_char1 = [hexString characterAtIndex:i]; ////兩位16進位制數中的第一位(高位*16)
        int int_ch1;
        if(hex_char1 >= '0' && hex_char1 <='9')
            int_ch1 = (hex_char1-48)*16;   //// 0 的Ascll - 48
        else if(hex_char1 >= 'A' && hex_char1 <='F')
            int_ch1 = (hex_char1-55)*16; //// A 的Ascll - 65
        else
            int_ch1 = (hex_char1-87)*16; //// a 的Ascll - 97
        i++;
        
        unichar hex_char2 = [hexString characterAtIndex:i]; ///兩位16進位制數中的第二位(低位)
        int int_ch2;
        if(hex_char2 >= '0' && hex_char2 <='9')
            int_ch2 = (hex_char2-48); //// 0 的Ascll - 48
        else if(hex_char1 >= 'A' && hex_char1 <='F')
            int_ch2 = hex_char2-55; //// A 的Ascll - 65
        else
            int_ch2 = hex_char2-87; //// a 的Ascll - 97
        
        int_ch = int_ch1+int_ch2;
        NSLog(@"int_ch=%d",int_ch);
        bytes[j] = int_ch;  ///將轉化後的數放入Byte數組裡
        j++;
    }
    
    NSData *newData = [[NSData alloc] initWithBytes:bytes length:20];
    
    return newData;
}
 

    Byte byte[] = {1, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    NSData *sData=[NSData dataWithBytes:byte length:10];