keyfork-shard: traitify functionality

This commit is contained in:
Ryan Heywood 2024-01-20 01:20:04 -05:00
parent 278e5c84fd
commit 8ddebfc3bb
Signed by: ryan
GPG Key ID: 8E401478A3FBEF72
4 changed files with 573 additions and 53 deletions

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@ -7,50 +7,33 @@ use std::{
process::ExitCode,
};
use keyfork_shard::openpgp::{combine, discover_certs, openpgp::Cert, parse_messages};
use keyfork_shard::{Format, openpgp::OpenPGP};
type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
fn validate(
shard: impl AsRef<Path>,
key_discovery: Option<&str>,
) -> Result<(File, Vec<Cert>)> {
) -> Result<(File, Option<PathBuf>)> {
let key_discovery = key_discovery.map(PathBuf::from);
key_discovery.as_ref().map(std::fs::metadata).transpose()?;
// Load certs from path
let certs = key_discovery
.map(discover_certs)
.transpose()?
.unwrap_or(vec![]);
Ok((File::open(shard)?, certs))
Ok((File::open(shard)?, key_discovery))
}
fn run() -> Result<()> {
let mut args = env::args();
let program_name = args.next().expect("program name");
let args = args.collect::<Vec<_>>();
let (messages_file, cert_list) = match args.as_slice() {
let (messages_file, key_discovery) = match args.as_slice() {
[shard, key_discovery] => validate(shard, Some(key_discovery))?,
[shard] => validate(shard, None)?,
_ => panic!("Usage: {program_name} <shard> [key_discovery]"),
};
let mut encrypted_messages = parse_messages(messages_file)?;
let openpgp = OpenPGP;
let encrypted_metadata = encrypted_messages
.pop_front()
.expect("any pgp encrypted message");
let mut bytes = vec![];
combine(
cert_list,
&encrypted_metadata,
encrypted_messages.into(),
&mut bytes,
)?;
let bytes = openpgp.decrypt_all_shards_to_secret(key_discovery, messages_file)?;
print!("{}", smex::encode(&bytes));

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@ -7,47 +7,33 @@ use std::{
process::ExitCode,
};
use keyfork_shard::openpgp::{decrypt, discover_certs, openpgp::Cert, parse_messages};
use keyfork_shard::{Format, openpgp::OpenPGP};
type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
fn validate<'a>(
messages_file: impl AsRef<Path>,
key_discovery: impl Into<Option<&'a str>>,
) -> Result<(File, Vec<Cert>)> {
let key_discovery = key_discovery.into().map(PathBuf::from);
fn validate(
shard: impl AsRef<Path>,
key_discovery: Option<&str>,
) -> Result<(File, Option<PathBuf>)> {
let key_discovery = key_discovery.map(PathBuf::from);
key_discovery.as_ref().map(std::fs::metadata).transpose()?;
// Load certs from path
let certs = key_discovery
.map(discover_certs)
.transpose()?
.unwrap_or(vec![]);
Ok((File::open(messages_file)?, certs))
Ok((File::open(shard)?, key_discovery))
}
fn run() -> Result<()> {
let mut args = env::args();
let program_name = args.next().expect("program name");
let args = args.collect::<Vec<_>>();
let (messages_file, cert_list) = match args.as_slice() {
[messages_file, key_discovery] => validate(messages_file, key_discovery.as_str())?,
[messages_file] => validate(messages_file, None)?,
_ => panic!("Usage: {program_name} messages_file [key_discovery]"),
let (messages_file, key_discovery) = match args.as_slice() {
[shard, key_discovery] => validate(shard, Some(key_discovery))?,
[shard] => validate(shard, None)?,
_ => panic!("Usage: {program_name} <shard> [key_discovery]"),
};
let mut encrypted_messages = parse_messages(messages_file)?;
let openpgp = OpenPGP;
let encrypted_metadata = encrypted_messages
.pop_front()
.expect("any pgp encrypted message");
decrypt(
&cert_list,
&encrypted_metadata,
encrypted_messages.make_contiguous(),
)?;
openpgp.decrypt_one_shard_for_transport(key_discovery, messages_file)?;
Ok(())
}

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@ -1,10 +1,13 @@
#![doc = include_str!("../README.md")]
use std::io::{stdin, stdout, Write};
use std::{
io::{stdin, stdout, Read, Write},
path::Path,
};
use aes_gcm::{
aead::{Aead, AeadCore, OsRng},
Aes256Gcm, KeyInit,
aead::{consts::U12, Aead, AeadCore, OsRng},
Aes256Gcm, KeyInit, Nonce,
};
use hkdf::Hkdf;
use keyfork_mnemonic_util::{Mnemonic, Wordlist};
@ -16,9 +19,279 @@ use sha2::Sha256;
use sharks::{Share, Sharks};
use x25519_dalek::{EphemeralSecret, PublicKey};
// 256 bit share encrypted is 49 bytes, couple more bytes before we reach max size
const ENC_LEN: u8 = 4 * 16;
#[cfg(feature = "openpgp")]
pub mod openpgp;
/// A format to use for splitting and combining secrets.
pub trait Format {
/// The error type returned from any failed operations.
type Error: std::error::Error + 'static;
/// A type encapsulating the public key recipients of shards.
type PublicKeyData;
/// A type encapsulating the private key recipients of shards.
type PrivateKeyData;
/// A type representing the parsed, but encrypted, Shard data.
type ShardData;
/// A type representing a Signer derived from the secret.
type Signer;
/// Parse the public key data from a readable type.
///
/// # Errors
/// The method may return an error if private key data could not be properly parsed from the
/// path.
/// occurred while parsing the public key data.
fn parse_public_key_data(
&self,
key_data_path: impl AsRef<Path>,
) -> Result<Self::PublicKeyData, Self::Error>;
/// Parse the private key data from a readable type. The private key may not be accessible (it
/// may be hardware only, such as a smartcard), for which this method may return None.
///
/// # Errors
/// The method may return an error if private key data could not be properly parsed from the
/// path.
fn parse_private_key_data(
&self,
key_data_path: impl AsRef<Path>,
) -> Result<Self::PrivateKeyData, Self::Error>;
/// Parse the Shard file into a processable type.
///
/// # Errors
/// The method may return an error if the Shard file could not be read from or if the Shard
/// file could not be properly parsed.
fn parse_shard_file(
&self,
shard_file: impl Read + Send + Sync,
) -> Result<Self::ShardData, Self::Error>;
/// Write the Shard data to a Shard file.
///
/// # Errors
/// The method may return an error if the Shard data could not be properly serialized or if the
/// Shard file could not be written to.
fn format_shard_file(
&self,
shard_data: Self::ShardData,
shard_file: impl Write,
) -> Result<(), Self::Error>;
/// Derive a Signer from the secret.
///
/// # Errors
/// This function may return an error if a Signer could not be properly created.
fn derive_signer(&self, secret: &[u8]) -> Result<Self::Signer, Self::Error>;
/// Encrypt multiple shares to public keys.
///
/// # Errors
/// The method may return an error if the share could not be encrypted to a public key or if
/// the ShardData could not be created.
fn generate_shard_data(
&self,
shares: &[Share],
signer: &Self::Signer,
public_keys: Self::PublicKeyData,
) -> Result<Self::ShardData, Self::Error>;
/// Decrypt shares and associated metadata from a readable input. For the current version of
/// Keyfork, the only associated metadata is a u8 representing the threshold to combine
/// secrets.
///
/// # Errors
/// The method may return an error if the shardfile couldn't be read from, if all shards
/// could not be decrypted, or if a shard could not be parsed from the decrypted data.
fn decrypt_all_shards(
&self,
private_keys: Option<Self::PrivateKeyData>,
shard_data: Self::ShardData,
) -> Result<(Vec<Share>, u8), Self::Error>;
/// Decrypt a single share and associated metadata from a reaable input. For the current
/// version of Keyfork, the only associated metadata is a u8 representing the threshold to
/// combine secrets.
///
/// # Errors
/// The method may return an error if the shardfile couldn't be read from, if a shard could not
/// be decrypted, or if a shard could not be parsed from the decrypted data.
fn decrypt_one_shard(
&self,
private_keys: Option<Self::PrivateKeyData>,
shard_data: Self::ShardData,
) -> Result<(Share, u8), Self::Error>;
/// Decrypt multiple shares and combine them to recreate a secret.
///
/// # Errors
/// The method may return an error if the shares can't be decrypted or if the shares can't
/// be combined into a secret.
fn decrypt_all_shards_to_secret(
&self,
private_key_data_path: Option<impl AsRef<Path>>,
reader: impl Read + Send + Sync,
) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
let private_keys = private_key_data_path
.map(|p| self.parse_private_key_data(p))
.transpose()?;
let shard_data = self.parse_shard_file(reader)?;
let (shares, threshold) = self.decrypt_all_shards(private_keys, shard_data)?;
let secret = Sharks(threshold)
.recover(&shares)
.map_err(|e| SharksError::CombineShare(e.to_string()))?;
Ok(secret)
}
/// Establish an AES-256-GCM transport key using ECDH, decrypt a single shard, and encrypt the
/// shard to the AES key.
///
/// # Errors
/// The method may return an error if a share can't be decrypted. The method will not return an
/// error if the camera is inaccessible or if a hardware error is encountered while scanning a
/// QR code; instead, a mnemonic prompt will be used.
fn decrypt_one_shard_for_transport(
&self,
private_key_data_path: Option<impl AsRef<Path>>,
reader: impl Read + Send + Sync,
) -> Result<(), Box<dyn std::error::Error>> {
let mut pm = Terminal::new(stdin(), stdout())?;
let wordlist = Wordlist::default();
// parse input
let private_keys = private_key_data_path
.map(|p| self.parse_private_key_data(p))
.transpose()?;
let shard_data = self.parse_shard_file(reader)?;
// establish AES-256-GCM key via ECDH
let mut nonce_data: Option<[u8; 12]> = None;
let mut pubkey_data: Option<[u8; 32]> = None;
// receive remote data via scanning QR code from camera
#[cfg(feature = "qrcode")]
{
pm.prompt_message(PromptMessage::Text(
"Press enter, then present QR code to camera".to_string(),
))?;
if let Ok(Some(hex)) =
keyfork_qrcode::scan_camera(std::time::Duration::from_secs(30), 0)
{
let decoded_data = smex::decode(&hex)?;
nonce_data = Some(decoded_data[..12].try_into().map_err(|_| InvalidData)?);
pubkey_data = Some(decoded_data[12..].try_into().map_err(|_| InvalidData)?)
} else {
pm.prompt_message(PromptMessage::Text(
"Unable to detect QR code, falling back to text".to_string(),
))?;
};
}
// if QR code scanning failed or was unavailable, read from a set of mnemonics
let (nonce, their_pubkey) = match (nonce_data, pubkey_data) {
(Some(nonce), Some(pubkey)) => (nonce, pubkey),
_ => {
let validator = MnemonicSetValidator {
word_lengths: [9, 24],
};
let [nonce_mnemonic, pubkey_mnemonic] =
pm.prompt_validated_wordlist("Their words: ", &wordlist, 3, validator.to_fn())?;
let nonce = nonce_mnemonic
.as_bytes()
.try_into()
.map_err(|_| InvalidData)?;
let pubkey = pubkey_mnemonic
.as_bytes()
.try_into()
.map_err(|_| InvalidData)?;
(nonce, pubkey)
}
};
// create our shared key
let our_key = EphemeralSecret::random();
let our_pubkey_mnemonic =
Mnemonic::from_entropy(PublicKey::from(&our_key).as_bytes(), Default::default())?;
let shared_secret = our_key
.diffie_hellman(&PublicKey::from(their_pubkey))
.to_bytes();
let hkdf = Hkdf::<Sha256>::new(None, &shared_secret);
let mut hkdf_output = [0u8; 256 / 8];
hkdf.expand(&[], &mut hkdf_output)?;
let shared_key = Aes256Gcm::new_from_slice(&hkdf_output)?;
// decrypt a single shard and create the payload
let (share, threshold) = self.decrypt_one_shard(private_keys, shard_data)?;
let mut payload = Vec::from(&share);
payload.insert(0, HUNK_VERSION);
payload.insert(1, threshold);
assert!(
payload.len() <= ENC_LEN as usize,
"invalid share length (too long, max {ENC_LEN} bytes)"
);
// encrypt data
let nonce = Nonce::<U12>::from_slice(&nonce);
let payload_bytes = shared_key.encrypt(nonce, payload.as_slice())?;
// convert data to a static-size payload
// NOTE: Padding length is less than u8::MAX because ENC_LEN < u8::MAX
#[allow(clippy::assertions_on_constants)]
{
assert!(ENC_LEN < u8::MAX, "padding byte can be u8");
}
#[allow(clippy::cast_possible_truncation)]
let mut out_bytes = [payload_bytes.len() as u8; ENC_LEN as usize];
assert!(
payload_bytes.len() < out_bytes.len(),
"encrypted payload larger than acceptable limit"
);
out_bytes[..payload_bytes.len()].clone_from_slice(&payload_bytes);
// NOTE: This previously used a single repeated value as the padding byte, but resulted in
// difficulty when entering in prompts manually, as one's place could be lost due to
// repeated keywords. This is resolved below by having sequentially increasing numbers up to
// but not including the last byte.
#[allow(clippy::cast_possible_truncation)]
for (i, byte) in (out_bytes[payload_bytes.len()..(ENC_LEN as usize - 1)])
.iter_mut()
.enumerate()
{
*byte = (i % u8::MAX as usize) as u8;
}
// safety: size of out_bytes is constant and always % 4 == 0
let payload_mnemonic =
unsafe { Mnemonic::from_raw_entropy(&out_bytes, Default::default()) };
#[cfg(feature = "qrcode")]
{
use keyfork_qrcode::{qrencode, ErrorCorrection};
let mut qrcode_data = our_pubkey_mnemonic.to_bytes();
qrcode_data.extend(payload_mnemonic.as_bytes());
if let Ok(qrcode) = qrencode(&smex::encode(&qrcode_data), ErrorCorrection::Lowest) {
pm.prompt_message(PromptMessage::Data(qrcode))?;
}
}
pm.prompt_message(PromptMessage::Text(format!(
"Our words: {our_pubkey_mnemonic} {payload_mnemonic}"
)))?;
Ok(())
}
}
/// Errors encountered while creating or combining shares using Shamir's Secret Sharing.
#[derive(thiserror::Error, Debug)]
pub enum SharksError {

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@ -59,6 +59,7 @@ const SHARD_METADATA_OFFSET: usize = 2;
use super::{
InvalidData, SharksError, HUNK_VERSION, QRCODE_COULDNT_READ, QRCODE_ERROR, QRCODE_PROMPT,
QRCODE_TIMEOUT,
Format,
};
// 256 bit share is 49 bytes + some amount of hunk bytes, gives us reasonable padding
@ -163,6 +164,18 @@ impl EncryptedMessage {
}
}
/// Serialize all contents of the message to a writer.
///
/// # Errors
/// The function may error for any condition in Sequoia's Serialize trait.
pub fn serialize(&self, o: &mut dyn std::io::Write) -> openpgp::Result<()> {
for pkesk in &self.pkesks {
pkesk.serialize(o)?;
}
self.message.serialize(o)?;
Ok(())
}
/// Decrypt the message with a Sequoia policy and decryptor.
///
/// This method creates a container containing the packets and passes the serialized container
@ -207,12 +220,273 @@ impl EncryptedMessage {
}
}
///
pub struct OpenPGP;
impl OpenPGP {
/// Read all OpenPGP certificates in a path and return a [`Vec`] of them. Certificates are read
/// from a file, or from files one level deep in a directory.
///
/// # Errors
/// The function may return an error if it is unable to read the directory or if Sequoia is unable
/// to load certificates from the file.
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).map_err(Error::Sequoia)? {
vec.push(cert.map_err(Error::Sequoia)?);
}
Ok(vec)
} else {
let mut vec = vec![];
for entry in path
.read_dir()
.map_err(Error::Io)?
.filter_map(Result::ok)
.filter(|p| p.path().is_file())
{
vec.push(Cert::from_file(entry.path()).map_err(Error::Sequoia)?);
}
Ok(vec)
}
}
}
impl Format for OpenPGP {
type Error = Error;
type PublicKeyData = Vec<Cert>;
type PrivateKeyData = Vec<Cert>;
type ShardData = Vec<EncryptedMessage>;
type Signer = openpgp::crypto::KeyPair;
fn parse_public_key_data(
&self,
key_data_path: impl AsRef<Path>,
) -> std::result::Result<Self::PublicKeyData, Self::Error> {
Self::discover_certs(key_data_path)
}
fn parse_private_key_data(
&self,
key_data_path: impl AsRef<Path>,
) -> std::result::Result<Self::PrivateKeyData, Self::Error> {
Self::discover_certs(key_data_path)
}
fn parse_shard_file(
&self,
shard_file: impl Read + Send + Sync,
) -> Result<Self::ShardData, Self::Error> {
let mut pkesks = Vec::new();
let mut encrypted_messages = vec![];
for packet in PacketPile::from_reader(shard_file)
.map_err(Error::Sequoia)?
.into_children()
{
match packet {
Packet::PKESK(p) => pkesks.push(p),
Packet::SEIP(s) => {
encrypted_messages.push(EncryptedMessage::new(&mut pkesks, s));
}
s => {
panic!("Invalid variant found: {}", s.tag());
}
}
}
Ok(encrypted_messages)
}
fn derive_signer(&self, secret: &[u8]) -> Result<Self::Signer, Self::Error> {
let userid = UserID::from("keyfork-sss");
let path = DerivationPath::from_str("m/7366512'/0'")?;
let seed = VariableLengthSeed::new(secret);
let xprv = XPrv::new(seed).derive_path(&path)?;
let derived_cert = keyfork_derive_openpgp::derive(
xprv,
&[KeyFlags::empty().set_certification().set_signing()],
&userid,
)?;
let signing_key = derived_cert
.primary_key()
.parts_into_secret()
.map_err(Error::Sequoia)?
.key()
.clone()
.into_keypair()
.map_err(Error::Sequoia)?;
Ok(signing_key)
}
fn format_shard_file(
&self,
shard_data: Self::ShardData,
shard_file: impl Write,
) -> Result<(), Self::Error> {
let mut writer = Writer::new(shard_file, Kind::Message).map_err(Error::SequoiaIo)?;
for message in shard_data {
message.serialize(&mut writer).map_err(Error::Sequoia)?;
}
writer.finalize().map_err(Error::SequoiaIo)?;
Ok(())
}
fn generate_shard_data(
&self,
shares: &[Share],
signer: &Self::Signer,
public_keys: Self::PublicKeyData,
) -> std::result::Result<Self::ShardData, Self::Error> {
let policy = StandardPolicy::new();
let mut total_recipients = vec![];
let mut messages = vec![];
for (share, cert) in shares.iter().zip(public_keys) {
total_recipients.push(cert.clone());
let valid_cert = cert.with_policy(&policy, None).map_err(Error::Sequoia)?;
let encryption_keys = get_encryption_keys(&valid_cert).collect::<Vec<_>>();
let mut message_output = vec![];
let message = Message::new(&mut message_output);
let message = Encryptor2::for_recipients(
message,
encryption_keys
.iter()
.map(|k| Recipient::new(KeyID::wildcard(), k.key())),
)
.build()
.map_err(Error::Sequoia)?;
let message = Signer::new(message, signer.clone())
.build()
.map_err(Error::Sequoia)?;
let mut message = LiteralWriter::new(message)
.build()
.map_err(Error::Sequoia)?;
// NOTE: This shouldn't be an alloc, but it's a minor alloc, so it's fine.
message
.write_all(&Vec::from(share))
.map_err(Error::SequoiaIo)?;
message.finalize().map_err(Error::Sequoia)?;
messages.push(message_output);
}
// A little bit of back and forth, we're going to parse the messages just to serialize them
// later.
let message = messages.into_iter().flatten().collect::<Vec<_>>();
let data = self.parse_shard_file(message.as_slice())?;
Ok(data)
}
fn decrypt_all_shards(
&self,
private_keys: Option<Self::PrivateKeyData>,
mut shard_data: Self::ShardData,
) -> std::result::Result<(Vec<Share>, u8), Self::Error> {
// 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(private_keys.unwrap_or_default())?;
let mut manager = SmartcardManager::new()?;
let metadata = shard_data.remove(0);
let metadata_content = decrypt_metadata(&metadata, &policy, &mut keyring, &mut manager)?;
let (threshold, root_cert, certs) = decode_metadata_v1(&metadata_content)?;
keyring.set_root_cert(root_cert.clone());
manager.set_root_cert(root_cert.clone());
// Generate a controlled binding from certificates to encrypted messages. This is stable
// because we control the order packets are encrypted and certificates are stored.
// TODO: remove alloc, convert EncryptedMessage to &EncryptedMessage
let mut messages: HashMap<KeyID, EncryptedMessage> = certs
.iter()
.map(Cert::keyid)
.zip(shard_data)
.collect();
let mut decrypted_messages =
decrypt_with_keyring(&mut messages, &certs, &policy, &mut keyring)?;
// 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 {
#[allow(clippy::cast_possible_truncation)]
let new_messages = decrypt_with_manager(
left_from_threshold as u8,
&mut messages,
&certs,
&policy,
&mut manager,
)?;
decrypted_messages.extend(new_messages);
}
let shares = decrypted_messages
.values()
.map(|message| Share::try_from(message.as_slice()))
.collect::<Result<Vec<_>, &str>>()
.map_err(|e| SharksError::Share(e.to_string()))?;
Ok((shares, threshold))
}
fn decrypt_one_shard(
&self,
private_keys: Option<Self::PrivateKeyData>,
mut shard_data: Self::ShardData,
) -> std::result::Result<(Share, u8), Self::Error> {
let policy = NullPolicy::new();
let mut keyring = Keyring::new(private_keys.unwrap_or_default())?;
let mut manager = SmartcardManager::new()?;
let metadata = shard_data.remove(0);
let metadata_content = decrypt_metadata(&metadata, &policy, &mut keyring, &mut manager)?;
let (threshold, root_cert, certs) = decode_metadata_v1(&metadata_content)?;
keyring.set_root_cert(root_cert.clone());
manager.set_root_cert(root_cert.clone());
let mut messages: HashMap<KeyID, EncryptedMessage> = certs
.iter()
.map(Cert::keyid)
.zip(shard_data)
.collect();
let decrypted_messages =
decrypt_with_keyring(&mut messages, &certs, &policy, &mut keyring)?;
if let Some(message) = decrypted_messages.into_values().next() {
let share = Share::try_from(message.as_slice()).map_err(|e| SharksError::Share(e.to_string()))?;
return Ok((share, threshold));
}
let decrypted_messages =
decrypt_with_manager(1, &mut messages, &certs, &policy, &mut manager)?;
if let Some(message) = decrypted_messages.into_values().next() {
let share = Share::try_from(message.as_slice()).map_err(|e| SharksError::Share(e.to_string()))?;
return Ok((share, threshold));
}
panic!("unable to decrypt shard");
}
}
/// Read all OpenPGP certificates in a path and return a [`Vec`] of them. Certificates are read
/// from a file, or from files one level deep in a directory.
///
/// # Errors
/// The function may return an error if it is unable to read the directory or if Sequoia is unable
/// to load certificates from the file.
#[deprecated]
pub fn discover_certs(path: impl AsRef<Path>) -> Result<Vec<Cert>> {
let path = path.as_ref();
@ -245,6 +519,7 @@ pub fn discover_certs(path: impl AsRef<Path>) -> Result<Vec<Cert>> {
/// # Panics
/// When given packets that are not a list of PKESK packets and SEIP packets, the function panics.
/// The `split` utility should never give packets that are not in this format.
#[deprecated]
pub fn parse_messages(reader: impl Read + Send + Sync) -> Result<VecDeque<EncryptedMessage>> {
let mut pkesks = Vec::new();
let mut encrypted_messages = VecDeque::new();
@ -416,6 +691,7 @@ fn decrypt_metadata(
})
}
#[deprecated]
fn decrypt_one(
messages: Vec<EncryptedMessage>,
certs: &[Cert],
@ -465,6 +741,8 @@ fn decrypt_one(
/// The function may panic if a share is decrypted but has a length larger than 256 bits. This is
/// atypical usage and should not be encountered in normal usage, unless something that is not a
/// Keyfork seed has been fed into [`split`].
#[deprecated]
#[allow(deprecated)]
pub fn decrypt(
certs: &[Cert],
metadata: &EncryptedMessage,