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# Contributing
Thanks for taking the time to contribute to this project!
All changes need to:
- pass basic checks, including tests, formatting and lints,
- be signed-off.
## Basic checks
We are using standard Rust ecosystem tools including `rustfmt` and `clippy` with one minor difference.
Due to a couple of `rustfmt` features being available only in nightly (see the `.rustfmt.toml` file) nightly `rustfmt` is necessary.
All of these details are captured in a `.justfile` and can be checked by running [`just`'](https://just.systems/).
To run all checks locally before sending them to CI you can set your git hooks directory:
```sh
git config core.hooksPath scripts/hooks/
```
## Developer Certificate of Origin
The sign-off is a simple line at the end of the git commit message, which certifies that you wrote it or otherwise have the right to pass it on as a open-source patch.
The rules are pretty simple: if you can [certify the below][DCO]:
```
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.
```
then you just add a line saying
Signed-off-by: Random J Developer <random@developer.example.org>
using your name.
If you set your `user.name` and `user.email`, you can sign your commit automatically with [`git commit --signoff`][GSO].
To sign-off your last commit:
git commit --amend --signoff
[DCO]: https://developercertificate.org
[GSO]: https://git-scm.com/docs/git-commit#git-commit---signoff
If you want to fix multiple commits use:
git rebase --signoff main
To check if your commits are correctly signed-off locally use `just check-commits`.

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[package]
name = "age-plugin-openpgp-card"
description = "Age plugin for using ed25519 on OpenPGP Card devices (Yubikeys, Nitrokeys)"
version = "0.1.0"
edition = "2021"
license = "Apache-2.0 OR MIT"
keywords = ["age", "cli", "encryption", "openpgp", "yubikey"]
categories = ["command-line-utilities", "cryptography"]
authors = ["Wiktor Kwapisiewicz <wiktor@metacode.biz>"]
repository = "https://github.com/wiktor-k/age-plugin-openpgp-card"
[dependencies]
age-core = "0.10.0"
age-plugin = "0.5.0"
base64 = "0.22.0"
bech32 = "0.9"
card-backend-pcsc = "0.5.0"
clap = { version = "4.5.4", features = ["derive"] }
openpgp-card = "0.4.2"
subtle = "2.5.0"
thiserror = "1.0.58"
x25519-dalek = "2.0.1"
zeroize = "1.7.0"

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FROM rust
RUN apt-get update && apt-get install -y --no-install-recommends \
vsmartcard-vpcd libpcsclite-dev pcscd opensc git libclang-dev nettle-dev \
&& rm -rf /var/lib/apt/lists/*
RUN cargo install --features="vpicc" --git https://github.com/Nitrokey/opcard-rs#v1.3.0 --example vpicc opcard
RUN cargo install openpgp-card-tools rage
COPY Cargo.toml Cargo.lock README.md /app/
COPY src /app/src
WORKDIR /app/
RUN cargo install --path .
COPY scripts /app/scripts
RUN ./scripts/encrypt-decrypt.sh

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84
README.md
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# age-plugin-openpgp-card # Age Plugin: OpenPGP Card
From: https://github.com/wiktor-k/age-plugin-openpgp-card [![CI](https://github.com/wiktor-k/age-plugin-openpgp-card/actions/workflows/rust.yml/badge.svg)](https://github.com/wiktor-k/age-plugin-openpgp-card/actions/workflows/rust.yml)
[![Crates.io](https://img.shields.io/crates/v/age-plugin-openpgp-card)](https://crates.io/crates/age-plugin-openpgp-card)
This age plugin lets you reuse your OpenPGP Card devices (such as [Yubikeys](https://www.yubico.com/products/yubikey-5-overview/) or [Nitrokeys](https://www.nitrokey.com/products/nitrokeys)) for [age decryption](https://age-encryption.org/).
Why? [OpenPGP Card](https://en.wikipedia.org/wiki/OpenPGP_card), contrary to its name, is just a generic cryptographic device standard.
Most importantly the specification and the real-world devices (e.g. [Yubikeys](https://docs.yubico.com/hardware/yubikey/yk-tech-manual/yk5-apps.html#elliptic-curve-cryptographic-ecc-algorithms) and [Nitrokeys](https://docs.nitrokey.com/nitrokey3/faq#which-algorithms-and-maximum-key-length-are-supported)) support [curve25519](https://en.wikipedia.org/wiki/Curve25519).
This application is a no-moving-parts solution which requires only [`pcsc-lite`](https://github.com/LudovicRousseau/PCSC) on Linux and reuses built-in smartcard services on Windows and macOS. No GnuPG needed, no other OpenPGP software is used or accessed.
If you don't need curve25519 and are using Yubikeys then the [`age-plugin-yubikey`](https://github.com/str4d/age-plugin-yubikey) provides a more polished experience.
This plugin assumes that you have already provisioned the card.
[`oct admin generate`](https://codeberg.org/openpgp-card/openpgp-card-tools/#generate-keys-on-the-card) may be used to provision the card with a new curve25519 key.
(This is actually how end-to-end tests are implemented. See `scripts/encrypt-and-decrypt.sh`).
## Installation
At this moment the installation from `crates.io` is the only supported method:
```sh
cargo install --locked age-plugin-openpgp-card
```
## Usage
Running the tool directly outputs the public keys and the identity stubs for all connected cards:
```sh
$ age-plugin-openpgp-card | tee identity.txt
# Card ident 0006:15422467
# age1dkfzfyk58yvkf07n32nygkyuqxtnq2am427sy79gjkh6krf96frsucn0me
AGE-PLUGIN-OPENPGP-CARD-1XQCRQD36XY6NGV3JXSMRWAN88PC
```
Note that the public key looks like a regular age ed25519 key.
The stub encodes the card identifier and is mostly irrelevant.
If the stub is lost it may be regenerated - if the key on the card is the same the decryption will succeed.
Any age-compatible tool can be used for encryption:
```sh
$ echo I like strawberries | age -r age1dkfzfyk58yvkf07n32nygkyuqxtnq2am427sy79gjkh6krf96frsucn0me -a > encrypted.age
```
And the identity stubs are required for decryption:
```sh
$ age -d -i identity.txt < encrypted.age
I like strawberries
```
The plugin will ask you for the PIN using built-in plugin protocol (e.g. [`rage`](https://github.com/str4d/rage) would show a pin-entry prompt).
## Tests
This repository contains end-to-end integration tests which run a [virtual Nitrokey card](https://github.com/Nitrokey/opcard-rs), provision it with a new key and then encrypt and decrypt data using `rage`.
## Thanks
The plugin is basically glue code for already existing, awesome libraries and tools:
- [`openpgp-card`](https://crates.io/crates/openpgp-card) which interacts with the smartcards,
- [`age-plugin`](https://crates.io/crates/age-plugin) which provides easy to use framework for writing age plugins,
And, last but not least, [`opcard`](https://github.com/Nitrokey/opcard-rs) which provides us with a virtual card to test that all of this really works!
Thank you very much for all contributors to these projects 🙇‍♂️
## License
This project is licensed under either of:
- [Apache License, Version 2.0](https://www.apache.org/licenses/LICENSE-2.0),
- [MIT license](https://opensource.org/licenses/MIT).
at your option.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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# Security policy
If you have discovered a security vulnerability in this project, please report it privately.
Do not disclose it as a public issue.
This gives us time to work with you to fix the issue before public exposure, reducing the chance that the exploit will be used before a patch is released.
This project is maintained by a team of volunteers on a reasonable-effort basis.
As such, please give us at least 90 days to work on a fix before public exposure.
We will contact you back within 2 business days after reporting the issue.
Thanks for helping make the project safe for everyone!
## Reporting a vulnerability
Please, report the vulnerability either through [new security advisory form][ADV] or by directly contacting our security contacts.
[ADV]: https://github.com/wiktor-k/age-plugin-openpgp-card/security/advisories/new
Security contacts:
- [Wiktor Kwapisiewicz][WK], preferably encrypted with the following OpenPGP certificate: [`6539 09A2 F0E3 7C10 6F5F AF54 6C88 57E0 D8E8 F074`][KEY].
[WK]: https://github.com/wiktor-k
[KEY]: https://keys.openpgp.org/vks/v1/by-fingerprint/653909A2F0E37C106F5FAF546C8857E0D8E8F074
## Supported Versions
Security updates are applied only to the most recent release.

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[advisories]
version = 2
yanked = "deny"
ignore = [
]
[bans]
deny = [
]
multiple-versions = "allow"
[licenses]
version = 2
allow = [
"Apache-2.0",
"MIT",
"ISC",
"Unicode-DFS-2016",
"BSD-3-Clause",
]

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#!/bin/bash
set -euxo pipefail
/etc/init.d/pcscd start
# start a virtual smartcard
vpicc &
sleep 2
export PINENTRY_PROGRAM=/app/scripts/fake-pinentry.sh
echo 12345678 > admin-pin
echo 123456 > user-pin
oct admin --card 0000:00000000 --admin-pin admin-pin generate --user-pin user-pin --output /tmp/no-need-for-this cv25519
age-plugin-openpgp-card | tee identity.txt
grep -oh "age1.*" identity.txt > recipients.txt
echo I like strawberries | rage -R recipients.txt -a | tee encrypted.age
rage -d -i identity.txt < encrypted.age

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#!/bin/sh
# Use this for your test suites when a POSIX shell is available.
#
# The encrypted keys in your test suite that you expect to work must
# be locked with a passphrase of "passphrase"
#
# Author: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
#
# License: Creative Commons Zero ("Public Domain Dedication") --
# Anyone may reuse it, modify it, redistribute it for any purpose.
echo "OK This is only for test suites, and should never be used in production"
while read cmd rest; do
cmd=$(printf "%s" "$cmd" | tr 'A-Z' 'a-z')
if [ -z "$cmd" ]; then
continue;
fi
case "$cmd" in
\#*)
;;
getpin)
echo "D 123456"
echo "OK"
;;
bye)
echo "OK"
exit 0
;;
*)
echo "OK"
;;
esac
done

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scripts/hooks/pre-commit Symbolic link
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../../.justfile

5
scripts/hooks/pre-push Executable file
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#!/usr/bin/env sh
set -euo pipefail
just check-commits

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src/main.rs Normal file
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#![doc = include_str!("../README.md")]
use std::collections::HashMap;
use std::io;
use age_core::{
format::FILE_KEY_BYTES,
primitives::{aead_decrypt, hkdf},
secrecy::ExposeSecret,
};
use age_core::{
format::{FileKey, Stanza},
secrecy::Zeroize as _,
};
use age_plugin::{
identity::{self, IdentityPluginV1},
recipient::{self, RecipientPluginV1},
run_state_machine, Callbacks,
};
use bech32::{ToBase32, Variant};
use card_backend_pcsc::PcscBackend;
use clap::Parser;
use openpgp_card::{crypto_data::PublicKeyMaterial, Card};
use subtle::ConstantTimeEq;
use x25519_dalek::PublicKey;
// Use lower-case HRP to avoid https://github.com/rust-bitcoin/rust-bech32/issues/40
const IDENTITY_PREFIX: &str = "age-plugin-openpgp-card-";
const PUBLIC_KEY_PREFIX: &str = "age";
const PLUGIN_NAME: &str = "openpgp-card";
pub const X25519_RECIPIENT_TAG: &str = "X25519";
const X25519_RECIPIENT_KEY_LABEL: &[u8] = b"age-encryption.org/v1/X25519";
pub const EPK_LEN_BYTES: usize = 32;
pub const ENCRYPTED_FILE_KEY_BYTES: usize = FILE_KEY_BYTES + 16;
struct RecipientPlugin;
impl RecipientPluginV1 for RecipientPlugin {
fn add_recipient(
&mut self,
_index: usize,
_plugin_name: &str,
_bytes: &[u8],
) -> Result<(), recipient::Error> {
todo!()
}
fn add_identity(
&mut self,
_index: usize,
_plugin_name: &str,
_bytes: &[u8],
) -> Result<(), recipient::Error> {
todo!()
}
fn wrap_file_keys(
&mut self,
_file_keys: Vec<FileKey>,
_callbacks: impl Callbacks<recipient::Error>,
) -> io::Result<Result<Vec<Vec<Stanza>>, Vec<recipient::Error>>> {
todo!()
}
}
struct CardStub {
ident: String,
}
struct IdentityPlugin {
cards: Vec<CardStub>,
}
use base64::{prelude::BASE64_STANDARD_NO_PAD, Engine};
pub(crate) fn base64_arg<A: AsRef<[u8]>, const N: usize, const B: usize>(
arg: &A,
) -> Option<[u8; N]> {
if N > B {
return None;
}
let mut buf = [0; B];
match BASE64_STANDARD_NO_PAD.decode_slice(arg, buf.as_mut()) {
Ok(n) if n == N => Some(buf[..N].try_into().unwrap()),
_ => None,
}
}
#[derive(Debug, thiserror::Error)]
enum DecryptError {
#[error("Invalid header")]
InvalidHeader,
#[error("Card does not contain ECC key")]
NonEccCard,
}
impl IdentityPlugin {
fn get_card(ident: &str) -> Result<Option<Card>, Box<dyn std::error::Error>> {
for backend in PcscBackend::cards(None)? {
let mut card = Card::new(backend?)?;
let tx = card.transaction()?;
if ident == tx.application_identifier()?.ident() {
drop(tx);
return Ok(Some(card));
}
}
Ok(None)
}
fn unwrap_stanza(
&mut self,
stanza: &Stanza,
callbacks: &mut impl Callbacks<identity::Error>,
) -> Result<Option<FileKey>, Box<dyn std::error::Error>> {
if stanza.tag != X25519_RECIPIENT_TAG {
return Err(std::io::Error::other("bad stanza tag").into());
}
// Enforce valid and canonical stanza format.
// https://c2sp.org/age#x25519-recipient-stanza
let ephemeral_share = match &stanza.args[..] {
[arg] => match base64_arg::<_, EPK_LEN_BYTES, 33>(arg) {
Some(ephemeral_share) => ephemeral_share,
None => return Err(DecryptError::InvalidHeader.into()),
},
_ => return Err(DecryptError::InvalidHeader.into()),
};
if stanza.body.len() != ENCRYPTED_FILE_KEY_BYTES {
return Err(DecryptError::InvalidHeader.into());
}
let epk: PublicKey = ephemeral_share.into();
let encrypted_file_key: [u8; ENCRYPTED_FILE_KEY_BYTES] = stanza.body[..]
.try_into()
.expect("Length should have been checked above");
'cards: for card_stub in self.cards.iter() {
let mut card = loop {
let car = Self::get_card(&card_stub.ident)?;
if let Some(card) = car {
break card;
} else {
let res = callbacks.confirm(
&format!("Please insert card {}", card_stub.ident),
"OK",
None,
)??;
if !res {
continue 'cards;
};
}
};
let mut tx = card.transaction()?;
let pk: Vec<u8> = if let PublicKeyMaterial::E(ecc) =
tx.public_key(openpgp_card::KeyType::Decryption)?
{
ecc.data().into()
} else {
return Err(DecryptError::NonEccCard.into());
};
tx.verify_pw1_user(
callbacks
.request_secret(&format!("Unlock card {}", card_stub.ident))??
.expose_secret()
.as_bytes(),
)?;
if let Ok(Some(uif)) = tx.application_related_data()?.uif_pso_aut() {
if uif.touch_policy().touch_required() {
callbacks.message(&format!(
"Touch your card {} now to decrypt.",
card_stub.ident
))??;
}
};
let shared_secret = tx.decipher(openpgp_card::crypto_data::Cryptogram::ECDH(
&ephemeral_share,
))?;
if shared_secret
.iter()
.fold(0, |acc, b| acc | b)
.ct_eq(&0)
.into()
{
return Err(DecryptError::InvalidHeader.into());
}
let mut salt = [0; 64];
salt[..32].copy_from_slice(epk.as_bytes());
salt[32..].copy_from_slice(&pk[..]);
let enc_key = hkdf(&salt, X25519_RECIPIENT_KEY_LABEL, &shared_secret);
// A failure to decrypt is non-fatal (we try to decrypt the recipient
// stanza with other X25519 keys), because we cannot tell which key
// matches a particular stanza.
if let Some(result) = aead_decrypt(&enc_key, FILE_KEY_BYTES, &encrypted_file_key)
.ok()
.map(|mut pt| {
// It's ours!
let file_key: [u8; FILE_KEY_BYTES] = pt[..].try_into().unwrap();
pt.zeroize();
FileKey::from(file_key)
})
{
return Ok(Some(result));
}
}
Ok(None)
}
}
impl IdentityPluginV1 for IdentityPlugin {
fn add_identity(
&mut self,
index: usize,
plugin_name: &str,
bytes: &[u8],
) -> Result<(), identity::Error> {
if plugin_name == PLUGIN_NAME {
self.cards.push(CardStub {
ident: String::from_utf8_lossy(bytes).to_string(),
});
Ok(())
} else {
Err(identity::Error::Identity {
index,
message: "invalid recipient".into(),
})
}
}
fn unwrap_file_keys(
&mut self,
files: Vec<Vec<Stanza>>,
mut callbacks: impl Callbacks<identity::Error>,
) -> io::Result<HashMap<usize, Result<FileKey, Vec<identity::Error>>>> {
let mut file_keys = HashMap::with_capacity(files.len());
for (file_index, stanzas) in files.iter().enumerate() {
for (stanza_index, stanza) in stanzas.iter().enumerate() {
match self.unwrap_stanza(stanza, &mut callbacks).map_err(|e| {
vec![identity::Error::Stanza {
file_index,
stanza_index,
message: e.to_string(),
}]
}) {
Ok(Some(file_key)) => {
file_keys.entry(file_index).or_insert(Ok(file_key));
}
Err(error) => {
file_keys.entry(file_index).or_insert(Err(error));
}
_ => {}
}
}
}
Ok(file_keys)
}
}
#[derive(Debug, Parser)]
struct PluginOptions {
#[arg(help = "run the given age plugin state machine", long)]
age_plugin: Option<String>,
}
fn main() -> Result<(), Box<dyn std::error::Error>> {
let opts = PluginOptions::parse();
if let Some(state_machine) = opts.age_plugin {
return Ok(run_state_machine(
&state_machine,
Some(|| RecipientPlugin),
Some(|| IdentityPlugin { cards: vec![] }),
)?);
}
for backend in PcscBackend::cards(None)? {
let mut card = Card::new(backend?)?;
let mut tx = card.transaction()?;
if let PublicKeyMaterial::E(ecc) = tx.public_key(openpgp_card::KeyType::Decryption)? {
let ident = tx.application_identifier()?.ident();
println!("# Card ident {}", ident);
println!(
"# {}",
bech32::encode(PUBLIC_KEY_PREFIX, ecc.data().to_base32(), Variant::Bech32)?
);
println!(
"{}",
bech32::encode(IDENTITY_PREFIX, ident.to_base32(), Variant::Bech32,)?
.to_uppercase()
);
println!();
}
}
Ok(())
}