SmartPGP/README.md

# SmartPGP applet

SmartPGP is a free and open source implementation of the [OpenPGP card
3.4 specification](https://gnupg.org/ftp/specs/OpenPGP-smart-card-application-3.4.pdf) in JavaCard.

## Features

The following features are implemented at the applet level, but some
of them depend on underlying hardware support and available
(non-)volatile memory resources:

- RSA (>= 2048 bits modulus, 17 bits exponent) for signature, encryption and authentication
- On-board key generation and external private key import
- PIN codes (user, admin and resetting code) up to 127 characters each
- Certificate up to 1 kB (DER encoded) for each key
- Login, URL, and private DOs up to 256 bytes
- Command and response chaining
- AES 128/256 bits deciphering primitive

## Default values

The SmartPGP applet is configured with the following default values:

- Admin PIN is 12345678
- User PIN is 123456
- No PUK (a.k.a. resetting code) is defined
- RSA 2048 bits for PGP keys

These values can be changed by modifying the [Constants](src/dev/c0de/smartpgp/Constants.java) class.

After the applet has been installed, the [smartpgp-cli](bin/smartpgp-cli) utility
will be able to change the above values.

_Note: These settings are restored if you factory reset the applet._

__Note: If you change algorithm attributes, the key and corresponding certificate will be erased.__

## Build and Install instructions

### Prerequisites

- A Java compiler (No higher than OpenJDK 11 or equivalent)
- A device compliant with JavaCard 3.0.1 (or above) with enough available resources
  - Applet: ~23 KiB of non-volatile (eeprom/flash) memory
  - Persistant Data: ~10 KiB of non-volatile (eeprom/flash) memory
  - Transient Data: ~2 KiB of volatile (RAM) memory

<!-- - The [pyscard](https://pypi.org/project/pyscard/) and [pyasn1](https://pypi.org/project/pyasn1/)
  Python libraries for `smartcard-cli`. -->

### Importing RSA keys above 2048 bits

The internal buffer that stores keys is configured with a default value that is only large enough for RSA 2048 bit keys.

If your card is able to handle larger RSA key bit-lengths (3072 or 4096), and you want to import those keys, you will need to increase the buffer size.

This can be accomplished by modifying `Constants.INTERNAL_BUFFER_MAX_LENGTH` in [Constants.java](src/dev/c0de/smartpgp/Constants.java)

#### RSA 2048 bit keys

When produced by OpenPGP, these keys are 949 Bytes in length.  
`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x3b6` (decimal: 950)

#### RSA 3072 bit keys

When produced by OpenPGP, these keys are 1294 Bytes in length.  
`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x50f` (decimal: 1295)

#### RSA 4096 bit keys

When produced by OpenPGP, these keys are 1644 Bytes in length.  
`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x66d` (decimal: 1645)

### Reducing flash and/or RAM consumption

When the applet is installed, all data structures will be allocated
to their maximum size. This is a standard practice for JavaCard applets
to ensure that there will not be a memory allocation failure at runtime.

A consequence of this is that, if you configure a large rsa key and
use a small key, that extra space can not be used for anything else.

If your device does not have enough flash memory and/or RAM, or you plan
to not use some features (eg. on-device certificates), you can modify
the following variables in [Constants.java](src/dev/c0de/smartpgp/Constants.java)

- `Constants.INTERNAL_BUFFER_MAX_LENGTH`: the size in bytes of the
  internal RAM buffer used for input/output chaining. Chaining is
  especially used in case of long commands and responses such as those
  involved in private key import and certificate import/export;
  
- `Constants.EXTENDED_CAPABILITIES`, bytes 5 and 6: the maximum size
  in bytes of a certificate associated to a key. The default is 1152 Bytes.
  A certificate can be stored for each of the three keys.

### Building the CAP file

- (Optional) Edit the `build.xml` file and replace the `APPLET_AID`
  with your a unique value. Alternatively, set the
  right AID instance bytes during applet installation.
  Generate the AID using [this tool](https://c0de.dev/c0de/SmartPGP-AID-Generator)

- Execute `ant` to build `SmartPGPApplet.cap`

### Installing the CAP file

The CAP file installation depends on your device, so you have to refer
to the instructions given by your device manufacturer. Most open cards
relying on Global Platform with default keys are supported by
[GlobalPlatformPro](https://github.com/martinpaljak/GlobalPlatformPro).

You must use a valid, unique AID that matches the OpenPGP card specification (see section 4.2.1)
for each card (`-create <AID>` with GlobalPlatformPro)

Example Installation commands:

- `gp --install SmartPGPApplet.cap --default`
- `gp --install SmartPGPApplet.cap --create <AID>`