pico-hsm/doc/extra_command.md

# Extra command

Pico HSM supports a customized extra command to use with different options. Since the drivers in the market do not support the following features, a raw APDU command shall be sent. 

To send a raw APDU command, `opensc-tool -s <APDU>` can be used. The `APDU` parameter is a string of hexadecimal numbers and it takes the following form:
```
8064XX00YYZZZZRR
```

It composed by the following fields:
- `80` to indicate that it is a custom vendor type command.
- `64` is the `INS` custom command.
- `XX` is the command to execute. It varies depending on the targeted command.
- `00` is the parameter of the command. At this moment, no commands support parameters.
- `YY` is the length of the data. If no data is provided, this field is absent.
- `ZZZZ` is the data to be sent. Optional. The length is variable.
- `RR` is the length of the expected response. If no response is expected, this field is absent.

## Real time clock and datetime
Pico HSM has an internal real time clock (RTC) which can track precisely the date and the time. However, when it is reset or powered down, the Pico HSM is reset to the initial datetime: 2020 January 1, 00:00:00.

### Getting the datetime
To obtain the current datetime (referenced to 00:00:00 2020/01/01), the `XX` parameter must be set to `0A`. There is no data and, thus, `YY` and `ZZZZ` are absent. The expected response is 8 bytes length.

For example, to obtain the current datetime:

```
$ opensc-tool -s 80640A0008
Using reader with a card: Free Software Initiative of Japan Gnuk
Sending: 80 64 0A 00 08 
Received (SW1=0x90, SW2=0x00):
07 E6 04 06 03 13 29 1E ......).
```

The response is composed by 8 bytes:
- The first two bytes are the current year, MSB first. Hence, `07E6h` equals to `2022`.
- 1 byte for the current month, `01h` is January and `0Ch` is December.
- 1 byte for the current day, from `01h` (1) to `1Fh` (31).
- 1 byte for the day of the week, `00h` is Sunday, `01h` is Monday, etc.
- 1 byte for the hours, from `00h` (0) to `17h` (23).
- 1 byte for the minutes, from `00h` (0) to `3Bh` (59).
- 1 byte for the seconds, from `00h` (0) to `3Bh` (59).

If the command is correctly received, `SW1=0x90` and `SW2=0x00`. Other values mean that an error has ocurred.

### Setting the datetime
To set the reference datetime, a datetime string must be provided. For example:

```
$ opensc-tool -s 80640A000807E6040603132917
Using reader with a card: Free Software Initiative of Japan Gnuk
Sending: 80 64 0A 00 08 07 E6 04 06 03 13 29 17 
Received (SW1=0x90, SW2=0x00)
```

will set the reference datetime to `Wednesday, 2022 April 6th, 19:41:23`.

## Dynamic options
Pico HSM support initialize options, such as setting Transport PIN or reset retry counter options. However, once it is initialized, these options cannot be modified anymore, without a new initialization (loosing all stored keys). Pico HSM offers the chance to define a set of dynamic options that can be enabled/disabled dynamically without initializing the device at every moment.

To specify a set of options, the `XX` parameter shall be set to `06`. The data parameter shall be 1 byte, where the options are combined with the or operand `|`. The length `YY` shall be set to `01`.

### Press-to-confirm button
Press-to-confirm button offers an extra security layer by requiring the user confirmation everytime that a private/secret key is loaded. This avoids ghost applications thay may perform hidden opperations without noticing the user, such as signing or decrypting. Pico HSM will inform the user that is awaiting for a confirmation by making almost a fixed Led blink.

This feature is disabled by default but can be enabled rapidly by setting the LSB bit to 1:

```
$ opensc-tool -s 806406000101
Using reader with a card: Free Software Initiative of Japan Gnuk
Sending: 80 64 06 00 01 01 
Received (SW1=0x90, SW2=0x00)
```

At this moment, when a private/secret key is loaded, the Pico HSM will wait for the pressed BOOTSEL button to confirm the operation.

To disable, the LSB bit must be set to 0:

```
$ opensc-tool -s 806406000100
Using reader with a card: Free Software Initiative of Japan Gnuk
Sending: 80 64 06 00 01 00
Received (SW1=0x90, SW2=0x00)
```