16进制字符串转换为NSData，然后转换为NSString---用于安全支付环境

+(NSData *)hexToByteToNSData:(NSString *)str
{
    int j=0;
    Byte bytes[[str length]/2];
    for(int i=0;i<[str length];i++)
    {
        int int_ch;  ///两位16进制数转化后的10进制数
        unichar hex_char1 = [str characterAtIndex:i]; ////两位16进制数中的第一位(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 = [str characterAtIndex:i]; ///两位16进制数中的第二位(低位)
        int int_ch2;
        if(hex_char2 >= '0' && hex_char2 <='9')
            int_ch2 = (hex_char2-48); //// 0 的Ascll - 48
        else if(hex_char2 >= 'A' && hex_char2 <='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;
        bytes[j] = int_ch;  ///将转化后的数放入Byte数组里
        //        if (j==[str length]/2-2) {
        //            int k=2;
        //            int_ch=bytes[0]^bytes[1];
        //            while (k
        //                int_ch=int_ch^bytes[k];
        //                k++;
        //            }
        //            bytes[j] = int_ch;
        //        }
        j++;
    }
    NSData *newData = [[NSData alloc] initWithBytes:bytes length:[str length]/2 ];
    NSLog(@"%@",newData);
    return newData;
}