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|
//! Demonstrates how to reply to an encrypted message without having
//! everyone's certs.
//!
//! This example demonstrates how to fall back to the original
//! message's session key in order to encrypt a reply.
//!
//! Replying to an encrypted message usually requires the encryption
//! (sub)keys for every recipient. If even one key is not available,
//! it is not possible to encrypt the new session key. Rather than
//! falling back to replying unencrypted, one can reuse the original
//! message's session key that was encrypted for every recipient and
//! reuse the original PKESKs.
//!
//! Decrypts an asymmetrically-encrypted OpenPGP message using the
//! openpgp crate, Sequoia's low-level API, remembering the session
//! key and PKESK packets. It then encrypts a new message reusing
//! both the session key and PKESK packets.
//!
//! # Examples
//!
//! First, we generate two keys. Second, we encrypt a message for
//! both certs. We then decrypt the original message using Alice's
//! key and this example program, composing an encrypted reply reusing
//! the session key and PKESK packets. Finally, we decrypt the reply
//! using Bob's key.
//!
//! ```sh
//! $ sqop generate-key alice@example.org > alice.pgp
//! $ sqop generate-key bob@example.org > bob.pgp
//! $ echo Original message | sqop encrypt alice.pgp bob.pgp > original.pgp
//! $ echo Reply | cargo run -p sequoia-openpgp --example reply-encrypted -- \
//! original.pgp alice.pgp > reply.pgp
//! $ sqop decrypt --session-key-out original.sk bob.pgp < reply.pgp
//! Encrypted using AES with 256-bit key
//! - Original message:
//! Original message
//! - Reusing (AES with 256-bit key, 62F3EADC...) with 2 PKESK packets
//! Reply
//! $ cat original.sk
//! 9:62F3EADC98E1D3D34495E79264B5959391B4FABB2B2A2B7E03861F92D0B03161
//! ```
use std::collections::HashMap;
use std::env;
use std::io;
use anyhow::Context;
use sequoia_openpgp as openpgp;
use openpgp::{KeyID, Fingerprint};
use openpgp::cert::prelude::*;
use openpgp::packet::prelude::*;
use openpgp::crypto::{KeyPair, SessionKey};
use openpgp::types::SymmetricAlgorithm;
use openpgp::parse::{Parse, stream::*};
use openpgp::serialize::{Serialize, stream::*};
use openpgp::policy::Policy;
use openpgp::policy::StandardPolicy as P;
pub fn main() -> openpgp::Result<()> {
let p = &P::new();
let args: Vec<String> = env::args().collect();
if args.len() < 3 {
return Err(anyhow::anyhow!("Reply-to-all without having all certs.\n\n\
Usage: {} <encrypted-msg> <keyfile> [<keyfile>...] \
<plaintext >ciphertext\n", args[0]));
}
let encrypted_message = &args[1];
// Read the transferable secret keys from the given files.
let certs =
args[2..].iter().map(|f| {
openpgp::Cert::from_file(f)
}).collect::<openpgp::Result<Vec<_>>>()
.context("Failed to read key")?;
// Now, create a decryptor with a helper using the given Certs.
let mut decryptor =
DecryptorBuilder::from_file(encrypted_message)?
.with_policy(p, None, Helper::new(p, certs))?;
// Finally, stream the decrypted data to stderr.
eprintln!("- Original message:");
io::copy(&mut decryptor, &mut io::stderr())
.context("Decryption failed")?;
let (algo, sk, pkesks) = decryptor.into_helper().recycling_bin.unwrap();
eprintln!("- Reusing ({}, {}) with {} PKESK packets",
algo, openpgp::fmt::hex::encode(&sk), pkesks.len());
// Compose a writer stack corresponding to the output format and
// packet structure we want.
let mut sink = io::stdout();
// Stream an OpenPGP message.
let message = Message::new(&mut sink);
let mut message = Armorer::new(message).build()?;
// Emit the stashed PKESK packets.
for p in pkesks {
openpgp::Packet::from(p).serialize(&mut message)?;
}
// We want to encrypt a literal data packet.
let message = Encryptor2::with_session_key(message, algo, sk)?
.build().context("Failed to create encryptor")?;
let mut message = LiteralWriter::new(message).build()
.context("Failed to create literal writer")?;
// Copy stdin to our writer stack to encrypt the data.
io::copy(&mut io::stdin(), &mut message)
.context("Failed to encrypt")?;
// Finally, finalize the OpenPGP message by tearing down the
// writer stack.
message.finalize()?;
Ok(())
}
/// This helper provides secrets for the decryption, fetches public
/// keys for the signature verification and implements the
/// verification policy.
struct Helper {
keys: HashMap<KeyID, (Fingerprint, KeyPair)>,
recycling_bin: Option<(SymmetricAlgorithm, SessionKey, Vec<PKESK>)>,
}
impl Helper {
/// Creates a Helper for the given Certs with appropriate secrets.
fn new(p: &dyn Policy, certs: Vec<openpgp::Cert>) -> Self {
// Map (sub)KeyIDs to primary fingerprints and secrets.
let mut keys = HashMap::new();
for cert in certs {
for ka in cert.keys().unencrypted_secret().with_policy(p, None)
.supported()
.for_storage_encryption().for_transport_encryption()
{
keys.insert(ka.key().keyid(),
(cert.fingerprint(),
ka.key().clone().into_keypair().unwrap()));
}
}
Helper {
keys,
recycling_bin: None,
}
}
}
impl DecryptionHelper for Helper {
fn decrypt<D>(&mut self,
pkesks: &[openpgp::packet::PKESK],
_skesks: &[openpgp::packet::SKESK],
sym_algo: Option<SymmetricAlgorithm>,
mut decrypt: D)
-> openpgp::Result<Option<openpgp::Fingerprint>>
where D: FnMut(SymmetricAlgorithm, &SessionKey) -> bool
{
// Try each PKESK until we succeed.
let mut recipient = None;
let mut encryption_context = None;
for pkesk in pkesks {
if let Some((fp, pair)) = self.keys.get_mut(pkesk.recipient()) {
if pkesk.decrypt(pair, sym_algo)
.map(|(algo, session_key)| {
let success = decrypt(algo, &session_key);
if success {
// Keep a copy the algorithm, session key,
// and all PKESK packets for the reply.
encryption_context =
Some((
algo,
session_key.clone(),
pkesks.iter().cloned().collect(),
));
}
success
})
.unwrap_or(false)
{
recipient = Some(fp.clone());
break;
}
}
}
// Store for later use.
self.recycling_bin = encryption_context;
Ok(recipient)
}
}
impl VerificationHelper for Helper {
fn get_certs(&mut self, _ids: &[openpgp::KeyHandle])
-> openpgp::Result<Vec<openpgp::Cert>> {
Ok(Vec::new()) // Feed the Certs to the verifier here.
}
fn check(&mut self, structure: MessageStructure)
-> openpgp::Result<()> {
for layer in structure.iter() {
match layer {
MessageLayer::Compression { algo } =>
eprintln!("Compressed using {}", algo),
MessageLayer::Encryption { sym_algo, aead_algo } =>
if let Some(aead_algo) = aead_algo {
eprintln!("Encrypted and protected using {}/{}",
sym_algo, aead_algo);
} else {
eprintln!("Encrypted using {}", sym_algo);
},
MessageLayer::SignatureGroup { ref results } =>
for result in results {
match result {
Ok(GoodChecksum { ka, .. }) => {
eprintln!("Good signature from {}", ka.cert());
},
|