OpenPGP encoder/decoder for Kotlin

Implements OpenPGP packet encoding and decoding as defined in RFC 9580.

This is a library, not an application. It provides the building blocks for parsing, inspecting, and generating OpenPGP messages and keys on the JVM: algorithms, fingerprints, packet model, and signature verification.

Modules

Module	Description
common	OpenPGP primitives: hash / symmetric / public-key / AEAD / compression algorithms, fingerprints, MPI and OID utilities, CRC-24, exceptions
packet	Core packet model. PacketDecoder / PacketEncoder are the entry points; one subpackage per packet type (public key, secret key, signature, PKESK, SKESK, SEIPD, ...)
signature-ext	Signature verification layered on :packet. Uses BouncyCastle (bcprov-jdk18on) for Ed25519 / Ed448 signature verification
sample	Runnable demo (Main.kt) that decodes a .gpg file and verifies signatures

Dependency direction: common <- packet <- signature-ext / sample.

Supported packet versions

Packet	Versions
Public Key / Public Subkey, Secret Key	v4, v6
Signature	v4, v6
One-Pass Signature	v3, v6
PKESK / SKESK (session key packets)	v4, v6
Symmetrically Encrypted and Integrity Protected Data	v1, v2
User ID, User Attribute, Compressed Data, Literal Data, Marker, Padding, Trust	—

Requirements

• JDK 17+ (CI runs on Temurin JDK 21)
• Gradle 8.5 (via the included wrapper)
• Kotlin 2.3.20, JUnit 5.11 for tests

Getting started

Always use the wrapper (./gradlew). CI runs detekt first, then assemble and test — keep that order locally too.

./gradlew detekt                              # lint (zero-tolerance)
./gradlew assemble                            # build all modules
./gradlew test                                # run all tests
./gradlew :packet:test                        # run tests for a single module

Usage

Decode a .gpg file into packets:

import dev.keiji.openpgp.packet.PacketDecoder
import java.io.File
import java.io.FileInputStream

val bytes = FileInputStream(File("message.gpg")).use { it.readAllBytes() }
val packetList = PacketDecoder.decode(bytes)

packetList.forEach { println(it) }

See sample/src/main/java/dev/keiji/openpgp/sample/Main.kt for a complete example, including signature verification.

License

Copyright 2023-2026 ARIYAMA Keiji

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.