keyfork-shard: initial commit

Cargo.lock

@@ -17,6 +17,12 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe"
 
+[[package]]
+name = "ahash"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "739f4a8db6605981345c5654f3a85b056ce52f37a39d34da03f25bf2151ea16e"
+
 [[package]]
 name = "aho-corasick"
 version = "1.0.4"
@@ -741,6 +747,15 @@ dependencies = [
  "subtle",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
+dependencies = [
+ "ahash",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.14.1"
@@ -797,7 +812,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8adf3ddd720272c6ea8bf59463c04e0f93d0bbf7c5439b691bca2987e0270897"
 dependencies = [
  "equivalent",
- "hashbrown",
+ "hashbrown 0.14.1",
 ]
 
 [[package]]
@@ -948,6 +963,19 @@ dependencies = [
  "smex",
 ]
 
+[[package]]
+name = "keyfork-shard"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "bincode",
+ "keyfork-derive-openpgp",
+ "sequoia-openpgp",
+ "serde",
+ "sharks",
+ "smex",
+]
+
 [[package]]
 name = "keyfork-slip10-test-data"
 version = "0.1.0"
@@ -1376,11 +1404,22 @@ checksum = "6a6b1679d49b24bbfe0c803429aa1874472f50d9b363131f0e89fc356b544d03"
 dependencies = [
  "getrandom 0.1.16",
  "libc",
- "rand_chacha",
+ "rand_chacha 0.2.2",
  "rand_core 0.5.1",
  "rand_hc",
 ]
 
+[[package]]
+name = "rand"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+dependencies = [
+ "libc",
+ "rand_chacha 0.3.1",
+ "rand_core 0.6.4",
+]
+
 [[package]]
 name = "rand_chacha"
 version = "0.2.2"
@@ -1391,6 +1430,16 @@ dependencies = [
  "rand_core 0.5.1",
 ]
 
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core 0.6.4",
+]
+
 [[package]]
 name = "rand_core"
 version = "0.3.1"
@@ -1697,6 +1746,17 @@ dependencies = [
  "lazy_static",
 ]
 
+[[package]]
+name = "sharks"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "902b1e955f8a2e429fb1bad49f83fb952e6195d3c360ac547ff00fb826388753"
+dependencies = [
+ "hashbrown 0.9.1",
+ "rand 0.8.5",
+ "zeroize",
+]
+
 [[package]]
 name = "shlex"
 version = "1.2.0"
@@ -2332,3 +2392,17 @@ name = "zeroize"
 version = "1.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2a0956f1ba7c7909bfb66c2e9e4124ab6f6482560f6628b5aaeba39207c9aad9"
+dependencies = [
+ "zeroize_derive",
+]
+
+[[package]]
+name = "zeroize_derive"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce36e65b0d2999d2aafac989fb249189a141aee1f53c612c1f37d72631959f69"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.29",
+]

Cargo.toml

@@ -10,6 +10,7 @@ members = [
     "keyfork-frame",
     "keyfork-mnemonic-util",
     "keyfork-plumbing",
+    "keyfork-shard",
     "keyfork-slip10-test-data",
     "keyforkd",
     "keyforkd-client",

keyfork-shard/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "keyfork-shard"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1.0.75"
+bincode = "1.3.3"
+keyfork-derive-openpgp = { version = "0.1.0", path = "../keyfork-derive-openpgp" }
+sequoia-openpgp = "1.16.1"
+serde = "1.0.188"
+sharks = "0.5.0"
+smex = { version = "0.1.0", path = "../smex" }

keyfork-shard/src/bin/keyfork-shard-combine-openpgp.rs

@@ -0,0 +1,98 @@
+use std::{
+    collections::VecDeque,
+    env,
+    io::{stdin, stdout},
+    path::PathBuf,
+    process::ExitCode,
+    str::FromStr,
+};
+
+use keyfork_shard::{combine, discover_certs, openpgp::Cert, EncryptedMessage};
+use openpgp::{
+    packet::Packet,
+    parse::Parse,
+    PacketPile,
+};
+use sequoia_openpgp as openpgp;
+
+#[derive(Clone, Debug)]
+enum Error {
+    Usage(String),
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Error::Usage(program_name) => {
+                write!(f, "Usage: {program_name} threshold key_discovery")
+            }
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+
+type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
+
+fn validate(threshold: &str, key_discovery: &str) -> Result<(u8, Vec<Cert>)> {
+    let threshold = u8::from_str(threshold)?;
+    let key_discovery = PathBuf::from(key_discovery);
+
+    // Verify path exists
+    std::fs::metadata(&key_discovery)?;
+
+    // Load certs from path
+    let certs = discover_certs(key_discovery)?;
+
+    Ok((threshold, certs))
+}
+
+fn run() -> Result<()> {
+    let mut args = env::args();
+    let program_name = args.next().expect("program name");
+    let args = args.collect::<Vec<_>>();
+    let (threshold, cert_list) = match args.as_slice() {
+        [threshold, key_discovery] => validate(threshold, key_discovery)?,
+        _ => return Err(Error::Usage(program_name).into()),
+    };
+
+    let stdin = stdin();
+
+    let mut pkesks = Vec::new();
+    let mut encrypted_messages = VecDeque::new();
+
+    for packet in PacketPile::from_reader(stdin)?.into_children() {
+        match packet {
+            Packet::PKESK(p) => pkesks.push(p),
+            Packet::SEIP(s) => {
+                encrypted_messages.push_back(EncryptedMessage::with_swap(&mut pkesks, s));
+            }
+            s => {
+                panic!("Invalid variant found: {}", s.tag());
+            }
+        }
+    }
+
+    let encrypted_metadata = encrypted_messages
+        .pop_front()
+        .expect("any pgp encrypted message");
+
+    combine(
+        threshold,
+        cert_list,
+        encrypted_metadata,
+        encrypted_messages.into(),
+        stdout(),
+    )?;
+
+    Ok(())
+}
+
+fn main() -> ExitCode {
+    let result = run();
+    if let Err(e) = result {
+        eprintln!("Error: {e}");
+        return ExitCode::FAILURE;
+    }
+    ExitCode::SUCCESS
+}

keyfork-shard/src/bin/keyfork-shard-split-openpgp.rs

@@ -0,0 +1,85 @@
+use std::{env, path::PathBuf, process::ExitCode, str::FromStr};
+
+use keyfork_shard::{discover_certs, openpgp::Cert, split};
+
+#[derive(Clone, Debug)]
+enum Error {
+    Usage(String),
+    Input,
+    Threshold(u8, u8),
+    InvalidCertCount(usize, u8),
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Error::Usage(program_name) => {
+                write!(f, "Usage: {program_name} threshold max key_discovery")
+            }
+            Error::Input => f.write_str("Expected hex encoded input"),
+            Error::Threshold(threshold, max) => {
+                write!(
+                    f,
+                    "Invalid threshold: 0 < threshold {threshold} <= max {max} < 256"
+                )
+            }
+            Error::InvalidCertCount(count, max) => {
+                write!(f, "Invalid cert count: count {count} != max {max}")
+            }
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+
+type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
+
+fn validate(threshold: &str, max: &str, key_discovery: &str) -> Result<(u8, Vec<Cert>)> {
+    let threshold = u8::from_str(threshold)?;
+    let max = u8::from_str(max)?;
+    let key_discovery = PathBuf::from(key_discovery);
+    if threshold > max {
+        return Err(Error::Threshold(threshold, max).into());
+    }
+
+    // Verify path exists
+    std::fs::metadata(&key_discovery)?;
+
+    // Load certs from path
+    let certs = discover_certs(key_discovery)?;
+    if certs.len() != max.into() {
+        return Err(Error::InvalidCertCount(certs.len(), max).into());
+    }
+
+    Ok((threshold, certs))
+}
+
+fn run() -> Result<()> {
+    let mut args = env::args();
+    let program_name = args.next().expect("program name");
+    let args = args.collect::<Vec<_>>();
+    let (threshold, cert_list) = match args.as_slice() {
+        [threshold, max, key_discovery] => validate(threshold, max, key_discovery)?,
+        _ => return Err(Error::Usage(program_name).into()),
+    };
+    let input = {
+        use std::io::stdin;
+        let Some(line) = stdin().lines().next() else {
+            return Err(Error::Input.into());
+        };
+        smex::decode(&line?)?
+    };
+
+    split(threshold, cert_list, &input, std::io::stdout())?;
+
+    Ok(())
+}
+
+fn main() -> ExitCode {
+    let result = run();
+    if let Err(e) = result {
+        eprintln!("Error: {e}");
+        return ExitCode::FAILURE;
+    }
+    ExitCode::SUCCESS
+}

keyfork-shard/src/keyring.rs

@@ -0,0 +1,118 @@
+use crate::openpgp::{
+    self,
+    cert::Cert,
+    packet::{PKESK, SKESK},
+    parse::stream::{DecryptionHelper, VerificationHelper, MessageStructure},
+    KeyHandle, KeyID,
+};
+
+#[derive(Clone, Debug)]
+pub enum KeyringFailure {
+    SecretKeyNotFound,
+    #[allow(dead_code)]
+    SmartcardDecrypt,
+}
+
+impl std::fmt::Display for KeyringFailure {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            KeyringFailure::SecretKeyNotFound => f.write_str("Secret key was not found"),
+            KeyringFailure::SmartcardDecrypt => {
+                f.write_str("Smartcard could not decrypt any PKESKs")
+            }
+        }
+    }
+}
+
+impl std::error::Error for KeyringFailure {}
+
+#[derive(Clone, Debug)]
+pub struct Keyring {
+    full_certs: Vec<Cert>,
+    root: Option<Cert>,
+}
+
+impl Keyring {
+    pub fn new(certs: impl AsRef<[Cert]>) -> Self {
+        Self {
+            full_certs: certs.as_ref().to_vec(),
+            root: Default::default(),
+        }
+    }
+
+    // Sets the root cert, returning the old cert
+    pub fn set_root_cert(&mut self, cert: impl Into<Option<Cert>>) -> Option<Cert> {
+        let mut cert = cert.into();
+        std::mem::swap(&mut self.root, &mut cert);
+        cert
+    }
+
+    pub fn get_cert_for_primary_keyid<'a>(&'a self, keyid: &KeyID) -> Option<&'a Cert> {
+        self
+            .full_certs
+            .iter()
+            .find(|cert| &cert.keyid() == keyid)
+    }
+
+    // NOTE: This can't return an iterator because iterators are all different types
+    // and returning different types is naughty
+    fn get_certs_for_pkesk<'a>(&'a self, pkesk: &'a PKESK) -> impl Iterator<Item = &Cert> + 'a {
+        self.full_certs.iter().filter(move |cert| {
+            pkesk.recipient().is_wildcard()
+                || cert.keys().any(|k| {
+                    &k.keyid() == pkesk.recipient()
+                })
+        })
+    }
+}
+
+impl VerificationHelper for &mut Keyring {
+    fn get_certs(&mut self, _ids: &[KeyHandle]) -> openpgp::Result<Vec<Cert>> {
+        // TODO: no verification logic until we mark a cert as "root"
+        // this is the first cert in the metadata list
+        Ok(Vec::new())
+    }
+    fn check(&mut self, _structure: MessageStructure) -> openpgp::Result<()> {
+        // TODO: ensure that we have a "root" cert and assign it
+        Ok(())
+    }
+}
+
+impl DecryptionHelper for &mut Keyring {
+    fn decrypt<D>(
+        &mut self,
+        pkesks: &[PKESK],
+        _skesks: &[SKESK],
+        sym_algo: Option<openpgp::types::SymmetricAlgorithm>,
+        mut decrypt: D,
+    ) -> openpgp::Result<Option<openpgp::Fingerprint>>
+    where
+        D: FnMut(
+            openpgp::types::SymmetricAlgorithm,
+            &openpgp::crypto::SessionKey,
+        ) -> bool,
+    {
+        // optimized route: use all locally stored certs
+        for pkesk in pkesks {
+            for cert in self.get_certs_for_pkesk(pkesk) {
+                for key in cert.keys().secret() {
+                    let secret_key = key.key().clone();
+                    // NOTE: Returns an error if using an encrypted secret key.
+                    // TODO: support skipping or validating encrypted secret keys.
+                    let mut keypair = secret_key.into_keypair()?;
+                    if pkesk
+                        .decrypt(&mut keypair, sym_algo)
+                        .map(|(algo, sk)| decrypt(algo, &sk))
+                        .unwrap_or(false)
+                    {
+                        return Ok(Some(key.fingerprint()));
+                    }
+                }
+            }
+        }
+
+        // smartcard route: plug in smartcard, attempt decrypt, fail and bail
+
+        Err(KeyringFailure::SecretKeyNotFound.into())
+    }
+}

keyfork-shard/src/lib.rs

@@ -0,0 +1,337 @@
+use std::{
+    collections::HashMap,
+    io::{Read, Write},
+    path::Path,
+    str::FromStr,
+};
+
+use keyfork_derive_openpgp::derive_util::{
+    request::{DerivationAlgorithm, DerivationRequest},
+    DerivationPath,
+};
+use openpgp::{
+    armor::{Kind, Writer},
+    cert::{Cert, CertParser, ValidCert},
+    packet::{Tag, UserID, PKESK, SEIP},
+    parse::{stream::DecryptorBuilder, Parse},
+    policy::{NullPolicy, Policy, StandardPolicy},
+    serialize::{
+        stream::{ArbitraryWriter, Encryptor, LiteralWriter, Message, Recipient, Signer},
+        Marshal,
+    },
+    types::KeyFlags,
+    KeyID,
+};
+pub use sequoia_openpgp as openpgp;
+use sharks::{Share, Sharks};
+
+mod keyring;
+use keyring::Keyring;
+
+// TODO: better error handling
+
+#[derive(Debug, Clone)]
+pub struct WrappedError(String);
+
+impl std::fmt::Display for WrappedError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.0)
+    }
+}
+
+impl std::error::Error for WrappedError {}
+
+pub type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
+
+#[derive(Debug, Clone)]
+pub struct EncryptedMessage {
+    pkesks: Vec<PKESK>,
+    message: SEIP,
+}
+
+impl EncryptedMessage {
+    pub fn with_swap(pkesks: &mut Vec<PKESK>, seip: SEIP) -> Self {
+        Self {
+            pkesks: std::mem::take(pkesks),
+            message: seip,
+        }
+    }
+
+    pub fn decrypt_with(&self, policy: &'_ dyn Policy, keyring: &mut Keyring) -> Result<Vec<u8>> {
+        let mut packets = vec![];
+
+        for pkesk in &self.pkesks {
+            let mut packet = vec![];
+            pkesk.serialize(&mut packet)?;
+            let message = Message::new(&mut packets);
+            let mut message = ArbitraryWriter::new(message, Tag::PKESK)?;
+            message.write_all(&packet)?;
+            message.finalize()?;
+        }
+        let mut packet = vec![];
+        self.message.serialize(&mut packet)?;
+        let message = Message::new(&mut packets);
+        let mut message = ArbitraryWriter::new(message, Tag::SEIP)?;
+        message.write_all(&packet)?;
+        message.finalize()?;
+
+        /*
+        // TODO: only serialize the message and use provided PKESK vec
+        let mut pkesks = vec![];
+        let ppr = PacketParser::from_reader(&packets[..])?;
+        while let PacketParserResult::Some(mut pp) = ppr {
+            match pp.packet {
+                openpgp::Packet::PKESK(pkesk) => pkesks.push(pkesk),
+                openpgp::Packet::SEIP(_) => {
+                    keyring.decrypt(&pkesks, &[], None, |algo, sk| {
+                        // pushes packet to stack
+                        pp.decrypt(algo, sk).is_ok()
+                    });
+                },
+                p => panic!("Unexpected packet type: {}", p.tag()),
+            }
+        }
+        */
+
+        let mut decryptor =
+            DecryptorBuilder::from_bytes(&packets)?.with_policy(policy, None, keyring)?;
+
+        let mut content = vec![];
+        decryptor.read_to_end(&mut content)?;
+        Ok(content)
+    }
+}
+
+pub fn discover_certs(path: impl AsRef<Path>) -> Result<Vec<Cert>> {
+    let path = path.as_ref();
+
+    if path.is_file() {
+        let mut vec = vec![];
+        for cert in CertParser::from_file(path)? {
+            vec.push(cert?);
+        }
+        Ok(vec)
+    } else {
+        let mut vec = vec![];
+        for entry in path
+            .read_dir()?
+            .filter_map(Result::ok)
+            .filter(|p| p.path().is_file())
+        {
+            vec.push(Cert::from_file(entry.path())?);
+        }
+        Ok(vec)
+    }
+}
+
+fn get_encryption_keys<'a>(
+    cert: &'a ValidCert,
+) -> openpgp::cert::prelude::ValidKeyAmalgamationIter<
+    'a,
+    openpgp::packet::key::PublicParts,
+    openpgp::packet::key::UnspecifiedRole,
+> {
+    cert.keys()
+        .alive()
+        .revoked(false)
+        .supported()
+        .for_storage_encryption()
+}
+
+fn get_decryption_keys<'a>(
+    cert: &'a ValidCert,
+) -> openpgp::cert::prelude::ValidKeyAmalgamationIter<
+    'a,
+    openpgp::packet::key::SecretParts,
+    openpgp::packet::key::UnspecifiedRole,
+> {
+    cert.keys()
+        /*
+        .alive()
+        .revoked(false)
+        .supported()
+        */
+        .for_storage_encryption()
+        .secret()
+}
+
+pub fn combine(
+    threshold: u8,
+    certs: Vec<Cert>,
+    metadata: EncryptedMessage,
+    messages: Vec<EncryptedMessage>,
+    mut output: impl Write,
+) -> Result<()> {
+    // Be as liberal as possible when decrypting.
+    // We don't want to invalidate someone's keys just because the old sig expired.
+    let policy = NullPolicy::new();
+
+    let mut keyring = Keyring::new(certs);
+    let content = metadata.decrypt_with(&policy, &mut keyring)?;
+
+    let mut cert_parser = CertParser::from_bytes(&content)?;
+    let root_cert = match cert_parser.next() {
+        Some(Ok(c)) => c,
+        Some(Err(e)) => panic!("Could not find root (first) certificate: {e}"),
+        None => panic!("No certs found in cert parser"),
+    };
+    let certs = cert_parser.collect::<openpgp::Result<Vec<_>>>()?;
+    keyring.set_root_cert(root_cert);
+    let mut messages: HashMap<KeyID, EncryptedMessage> =
+        HashMap::from_iter(certs.iter().map(|c| c.keyid()).zip(messages));
+    let mut decrypted_messages: HashMap<KeyID, Vec<u8>> = HashMap::new();
+
+    // NOTE: This is ONLY stable because we control the generation of PKESK packets and
+    // encode the policy to ourselves.
+    for valid_cert in certs.iter().map(|cert| cert.with_policy(&policy, None)) {
+        let valid_cert = valid_cert?;
+        // get keys from keyring for cert
+        let Some(secret_cert) = keyring.get_cert_for_primary_keyid(&valid_cert.keyid()) else {
+            continue;
+        };
+        let secret_cert = secret_cert.with_policy(&policy, None)?;
+        let keys = get_decryption_keys(&secret_cert).collect::<Vec<_>>();
+        if !keys.is_empty() {
+            if let Some(message) = messages.get_mut(&valid_cert.keyid()) {
+                for (pkesk, key) in message.pkesks.iter_mut().zip(keys) {
+                    pkesk.set_recipient(key.keyid());
+                }
+                // we have a pkesk, decrypt via keyring
+                let result = message.decrypt_with(&policy, &mut keyring);
+                match result {
+                    Ok(message) => {
+                        decrypted_messages.insert(valid_cert.keyid(), message);
+                    }
+                    Err(e) => {
+                        eprintln!(
+                            "Could not decrypt with fingerprint {}: {}",
+                            valid_cert.keyid(),
+                            e
+                        );
+                        // do nothing, key will be retained
+                    }
+                }
+            }
+        }
+    }
+
+    // clean decrypted messages from encrypted messages
+    messages.retain(|k, _v| !decrypted_messages.contains_key(k));
+
+    let left_from_threshold = threshold as usize - decrypted_messages.len();
+    if left_from_threshold > 0 {
+        eprintln!("remaining keys: {left_from_threshold}, prompting yubikeys");
+    }
+    for _ in 0..left_from_threshold {
+        todo!("prompt for Yubikeys")
+    }
+
+    let shares = decrypted_messages
+        .values()
+        .map(|message| Share::try_from(message.as_slice()))
+        .collect::<Result<Vec<_>, &str>>()
+        .map_err(|e| WrappedError(e.to_string()))?;
+    let secret = Sharks(threshold).recover(&shares)?;
+
+    output.write_all(smex::encode(&secret).as_bytes())?;
+
+    Ok(())
+}
+
+pub fn split(threshold: u8, certs: Vec<Cert>, secret: &[u8], output: impl Write) -> Result<()> {
+    // build cert to sign encrypted shares
+    let userid = UserID::from("keyfork-sss");
+    let kdr = DerivationRequest::new(
+        DerivationAlgorithm::Ed25519,
+        &DerivationPath::from_str("m/7366512'/0'")?,
+    )
+    .derive_with_master_seed(secret.to_vec())?;
+    let derived_cert = keyfork_derive_openpgp::derive(
+        kdr,
+        &[KeyFlags::empty().set_certification().set_signing()],
+        userid,
+    )?;
+    let signing_key = derived_cert
+        .primary_key()
+        .parts_into_secret()?
+        .key()
+        .clone()
+        .into_keypair()?;
+
+    let sharks = Sharks(threshold);
+    let dealer = sharks.dealer(secret);
+    let shares = dealer.map(|s| Vec::from(&s)).collect::<Vec<_>>();
+    let policy = StandardPolicy::new();
+    let mut writer = Writer::new(output, Kind::Message)?;
+
+    let mut total_recipients = vec![];
+    let mut messages = vec![];
+
+    for (share, cert) in shares.iter().zip(certs) {
+        total_recipients.push(cert.clone());
+        let valid_cert = cert.with_policy(&policy, None)?;
+        let encryption_keys = get_encryption_keys(&valid_cert).collect::<Vec<_>>();
+
+        let mut message_output = vec![];
+        let message = Message::new(&mut message_output);
+        let message = Encryptor::for_recipients(
+            message,
+            encryption_keys
+                .iter()
+                .map(|k| Recipient::new(KeyID::wildcard(), k.key())),
+        )
+        .build()?;
+        let message = Signer::new(message, signing_key.clone()).build()?;
+        let mut message = LiteralWriter::new(message).build()?;
+        message.write_all(share)?;
+        message.finalize()?;
+
+        messages.push(message_output);
+    }
+
+    let mut pp = vec![];
+    // store derived cert to verify provided shares
+    derived_cert.serialize(&mut pp)?;
+    for recipient in &total_recipients {
+        recipient.serialize(&mut pp)?;
+    }
+
+    // verify packet pile
+    for (packet_cert, cert) in openpgp::cert::CertParser::from_bytes(&pp)?
+        .skip(1)
+        .zip(total_recipients.iter())
+    {
+        if packet_cert? != *cert {
+            panic!(
+                "packet pile could not recreate cert: {}",
+                cert.fingerprint()
+            );
+        }
+    }
+
+    let valid_certs = total_recipients
+        .iter()
+        .map(|c| c.with_policy(&policy, None))
+        .collect::<openpgp::Result<Vec<_>>>()?;
+
+    let total_recipients = valid_certs.iter().flat_map(|vc| {
+        get_encryption_keys(vc).map(|key| Recipient::new(KeyID::wildcard(), key.key()))
+    });
+
+    // metadata
+    let mut message_output = vec![];
+    let message = Message::new(&mut message_output);
+    let message = Encryptor::for_recipients(message, total_recipients).build()?;
+    let mut message = LiteralWriter::new(message).build()?;
+    message.write_all(&pp)?;
+    message.finalize()?;
+    writer.write_all(&message_output)?;
+
+    for message in messages {
+        writer.write_all(&message)?;
+    }
+
+    writer.finalize()?;
+
+    Ok(())
+}