119 lines
4.8 KiB
Markdown
119 lines
4.8 KiB
Markdown
# SmartPGP applet
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SmartPGP is a free and open source implementation of the [OpenPGP card
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3.4 specification](https://gnupg.org/ftp/specs/OpenPGP-smart-card-application-3.4.pdf) in JavaCard.
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## Features
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The following features are implemented at the applet level, but some
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of them depend on underlying hardware support and available
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(non-)volatile memory resources:
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- RSA (>= 2048 bits modulus, 17 bits exponent) for signature, encryption and authentication
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- On-board key generation and external private key import
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- PIN codes (user, admin and resetting code) up to 127 characters each
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- Certificate up to 1 kB (DER encoded) for each key
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- Login, URL, and private DOs up to 256 bytes
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- Command and response chaining
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- AES 128/256 bits deciphering primitive
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## Default values
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The SmartPGP applet is configured with the following default values:
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- Admin PIN is 12345678
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- User PIN is 123456
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- No PUK (a.k.a. resetting code) is defined
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- RSA 2048 bits for PGP keys
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These values can be changed by modifying the [Constants](src/dev/c0de/smartpgp/Constants.java) class.
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After the applet has been installed, the [smartpgp-cli](bin/smartpgp-cli) utility
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will be able to change the above values.
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_Note: These settings are restored if you factory reset the applet._
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__Note: If you change algorithm attributes, the key and corresponding certificate will be erased.__
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## Build and Install instructions
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### Prerequisites
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- A Java compiler (No higher than OpenJDK 11 or equivalent)
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- A device compliant with JavaCard 3.0.1 (or above) with enough available resources
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- Applet: ~23 KiB of non-volatile (eeprom/flash) memory
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- Persistant Data: ~10 KiB of non-volatile (eeprom/flash) memory
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- Transient Data: ~2 KiB of volatile (RAM) memory
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<!-- - The [pyscard](https://pypi.org/project/pyscard/) and [pyasn1](https://pypi.org/project/pyasn1/)
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Python libraries for `smartcard-cli`. -->
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### Importing RSA keys above 2048 bits
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The internal buffer that stores keys is configured with a default value that is only large enough for RSA 2048 bit keys.
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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.
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This can be accomplished by modifying `Constants.INTERNAL_BUFFER_MAX_LENGTH` in [Constants.java](src/dev/c0de/smartpgp/Constants.java)
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#### RSA 2048 bit keys
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When produced by OpenPGP, these keys are 949 Bytes in length.
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`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x3b6` (decimal: 950)
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#### RSA 3072 bit keys
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When produced by OpenPGP, these keys are 1294 Bytes in length.
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`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x50f` (decimal: 1295)
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#### RSA 4096 bit keys
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When produced by OpenPGP, these keys are 1644 Bytes in length.
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`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x66d` (decimal: 1645)
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### Reducing flash and/or RAM consumption
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When the applet is installed, all data structures will be allocated
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to their maximum size. This is a standard practice for JavaCard applets
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to ensure that there will not be a memory allocation failure at runtime.
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A consequence of this is that, if you configure a large rsa key and
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use a small key, that extra space can not be used for anything else.
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If your device does not have enough flash memory and/or RAM, or you plan
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to not use some features (eg. on-device certificates), you can modify
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the following variables in [Constants.java](src/dev/c0de/smartpgp/Constants.java)
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- `Constants.INTERNAL_BUFFER_MAX_LENGTH`: the size in bytes of the
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internal RAM buffer used for input/output chaining. Chaining is
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especially used in case of long commands and responses such as those
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involved in private key import and certificate import/export;
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- `Constants.EXTENDED_CAPABILITIES`, bytes 5 and 6: the maximum size
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in bytes of a certificate associated to a key. The default is 1152 Bytes.
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A certificate can be stored for each of the three keys.
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### Building the CAP file
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- (Optional) Edit the `build.xml` file and replace the `APPLET_AID`
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with your a unique value. Alternatively, set the
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right AID instance bytes during applet installation.
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Generate the AID using [this tool](https://c0de.dev/c0de/SmartPGP-AID-Generator)
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- Execute `ant` to build `SmartPGPApplet.cap`
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### Installing the CAP file
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The CAP file installation depends on your device, so you have to refer
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to the instructions given by your device manufacturer. Most open cards
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relying on Global Platform with default keys are supported by
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[GlobalPlatformPro](https://github.com/martinpaljak/GlobalPlatformPro).
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You must use a valid, unique AID that matches the OpenPGP card specification (see section 4.2.1)
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for each card (`-create <AID>` with GlobalPlatformPro)
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Example Installation commands:
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- `gp --install SmartPGPApplet.cap --default`
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- `gp --install SmartPGPApplet.cap --create <AID>`
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