keyfork-shard: remove old code!

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

@@ -7,52 +7,33 @@ use std::{
     process::ExitCode,
 };
 
-use keyfork_shard::openpgp::{combine, discover_certs, openpgp::Cert, parse_messages};
+use keyfork_shard::{openpgp::OpenPGP, Format};
 
 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 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,
-    )?;
-
-    print!("{}", smex::encode(&bytes));
+    let openpgp = OpenPGP;
+    let bytes = openpgp.decrypt_all_shards_to_secret(key_discovery.as_deref(), messages_file)?;
+    print!("{}", smex::encode(bytes));
 
     Ok(())
 }

crates/keyfork-shard/src/bin/keyfork-shard-decrypt-openpgp.rs

@@ -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.as_deref(), messages_file)?;
 
     Ok(())
 }

crates/keyfork-shard/src/bin/keyfork-shard-remote.rs

@@ -20,7 +20,7 @@ fn run() -> Result<()> {
 
     let mut bytes = vec![];
     remote_decrypt(&mut bytes)?;
-    print!("{}", smex::encode(&bytes));
+    print!("{}", smex::encode(bytes));
 
     Ok(())
 }

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

@@ -2,14 +2,12 @@
 
 use std::{env, path::PathBuf, process::ExitCode, str::FromStr};
 
-use keyfork_shard::openpgp::{discover_certs, openpgp::Cert, split};
+use keyfork_shard::{Format, openpgp::OpenPGP};
 
 #[derive(Clone, Debug)]
 enum Error {
     Usage(String),
     Input,
-    Threshold(u8, u8),
-    InvalidCertCount(usize, u8),
 }
 
 impl std::fmt::Display for Error {
@@ -19,15 +17,6 @@ impl std::fmt::Display for Error {
                 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}")
-            }
         }
     }
 }
@@ -36,31 +25,20 @@ 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>)> {
+fn validate(threshold: &str, max: &str, key_discovery: &str) -> Result<(u8, u8, PathBuf)> {
     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))
+    Ok((threshold, max, key_discovery))
 }
 
 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() {
+    let (threshold, max, key_discovery) = match args.as_slice() {
         [threshold, max, key_discovery] => validate(threshold, max, key_discovery)?,
         _ => return Err(Error::Usage(program_name).into()),
     };
@@ -72,8 +50,9 @@ fn run() -> Result<()> {
         smex::decode(line?)?
     };
 
-    split(threshold, cert_list, &input, std::io::stdout())?;
+    let openpgp = OpenPGP;
 
+    openpgp.shard_and_encrypt(threshold, max, &input, key_discovery.as_path(), std::io::stdout())?;
     Ok(())
 }
 

crates/keyfork-shard/src/lib.rs

@@ -1,10 +1,10 @@
 #![doc = include_str!("../README.md")]
 
-use std::io::{stdin, stdout, Write};
+use std::io::{stdin, stdout, Read, Write};
 
 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::{English, Mnemonic};
@@ -16,9 +16,338 @@ 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 trait to specify where keys can be discovered from, such as a Rust-native type or a path on
+/// the filesystem that keys may be read from.
+pub trait KeyDiscovery<F: Format + ?Sized> {
+    /// Discover public keys for the associated format.
+    ///
+    /// # Errors
+    /// The method may return an error if public keys could not be loaded from the given discovery
+    /// mechanism. A discovery mechanism _must_ be able to detect public keys.
+    fn discover_public_keys(&self) -> Result<Vec<F::PublicKey>, F::Error>;
+
+    /// Discover private keys for the associated format.
+    ///
+    /// # Errors
+    /// The method may return an error if private keys could not be loaded from the given
+    /// discovery mechanism. Keys may exist off-system (such as with smartcards), in which case the
+    /// PrivateKeyData type of the asssociated format should be either `()` (if the keys may never
+    /// exist on-system) or an empty container (such as an empty Vec); in either case, this method
+    /// _must not_ return an error if keys are accessible but can't be transferred into memory.
+    fn discover_private_keys(&self) -> Result<F::PrivateKeyData, F::Error>;
+}
+
+/// 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 a single public key recipient.
+    type PublicKey;
+
+    /// A type encapsulating the private key recipients of shards.
+    type PrivateKeyData;
+
+    /// A type representing a Signer derived from the secret.
+    type SigningKey;
+
+    /// A type representing the parsed, but encrypted, Shard data.
+    type EncryptedData;
+
+    /// Derive a signer
+    fn derive_signing_key(&self, seed: &[u8]) -> Self::SigningKey;
+
+    /// Format a header containing necessary metadata. Such metadata contains a version byte, a
+    /// threshold byte, a public version of the [`Format::SigningKey`], and the public keys used to
+    /// encrypt shards. The public keys must be kept _in order_ to the encrypted shards. Keyfork
+    /// will use the same key_data for both, ensuring an iteration of this method will match with
+    /// iterations in methods called later.
+    ///
+    /// # Errors
+    /// The method may return an error if encryption to any of the public keys fails.
+    fn format_encrypted_header(
+        &self,
+        signing_key: &Self::SigningKey,
+        key_data: &[Self::PublicKey],
+        threshold: u8,
+    ) -> Result<Self::EncryptedData, Self::Error>;
+
+    /// Format a shard encrypted to the given public key, signing with the private key.
+    ///
+    /// # Errors
+    /// The method may return an error if the public key used to encrypt the shard is unsuitable
+    /// for encryption, or if an error occurs while encrypting.
+    fn encrypt_shard(
+        &self,
+        shard: &[u8],
+        public_key: &Self::PublicKey,
+        signing_key: &mut Self::SigningKey,
+    ) -> Result<Self::EncryptedData, 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<Vec<Self::EncryptedData>, 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,
+        encrypted_data: &[Self::EncryptedData],
+        shard_file: impl Write + Send + Sync,
+    ) -> Result<(), 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>,
+        encrypted_messages: &[Self::EncryptedData],
+    ) -> 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>,
+        encrypted_data: &[Self::EncryptedData],
+    ) -> 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_discovery: Option<impl KeyDiscovery<Self>>,
+        reader: impl Read + Send + Sync,
+    ) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
+        let private_keys = private_key_discovery
+            .map(|p| p.discover_private_keys())
+            .transpose()?;
+        let encrypted_messages = self.parse_shard_file(reader)?;
+        let (shares, threshold) = self.decrypt_all_shards(private_keys, &encrypted_messages)?;
+
+        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_discovery: Option<impl KeyDiscovery<Self>>,
+        reader: impl Read + Send + Sync,
+    ) -> Result<(), Box<dyn std::error::Error>> {
+        let mut pm = Terminal::new(stdin(), stdout())?;
+
+        // parse input
+        let private_keys = private_key_discovery
+            .map(|p| p.discover_private_keys())
+            .transpose()?;
+        let encrypted_messages = 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(QRCODE_PROMPT.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(QRCODE_ERROR.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::<English, _>(
+                        QRCODE_COULDNT_READ,
+                        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_bytes(PublicKey::from(&our_key).as_bytes())?;
+        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, &encrypted_messages)?;
+        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_bytes(&out_bytes) };
+
+        #[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::Highest) {
+                pm.prompt_message(PromptMessage::Text(
+                    concat!(
+                        "A QR code will be displayed after this prompt. ",
+                        "Send the QR code back to the operator combining the shards. ",
+                        "Nobody else should scan this QR code."
+                    )
+                    .to_string(),
+                ))?;
+                pm.prompt_message(PromptMessage::Data(qrcode))?;
+            }
+        }
+
+        pm.prompt_message(PromptMessage::Text(format!(
+            "Upon request, these words should be sent: {our_pubkey_mnemonic} {payload_mnemonic}"
+        )))?;
+
+        Ok(())
+    }
+
+    /// Split a secret into a shard for every shard in keys, with the given Shamir's Secret Sharing
+    /// threshold.
+    ///
+    /// # Errors
+    /// The method may return an error if the shares can't be encrypted.
+    fn shard_and_encrypt(
+        &self,
+        threshold: u8,
+        max: u8,
+        secret: &[u8],
+        public_key_discovery: impl KeyDiscovery<Self>,
+        writer: impl Write + Send + Sync,
+    ) -> Result<(), Box<dyn std::error::Error>> {
+        let mut signing_key = self.derive_signing_key(secret);
+
+        let sharks = Sharks(threshold);
+        let dealer = sharks.dealer(secret);
+
+        let public_keys = public_key_discovery.discover_public_keys()?;
+        assert!(
+            public_keys.len() < u8::MAX as usize,
+            "must have less than u8::MAX public keys"
+        );
+        assert_eq!(
+            max,
+            public_keys.len() as u8,
+            "max must be equal to amount of public keys"
+        );
+        let max = public_keys.len() as u8;
+        assert!(max >= threshold, "threshold must not exceed max keys");
+
+        let header = self.format_encrypted_header(&signing_key, &public_keys, threshold)?;
+        let mut messages = vec![header];
+        for (pk, share) in public_keys.iter().zip(dealer) {
+            let shard = Vec::from(&share);
+            messages.push(self.encrypt_shard(&shard, pk, &mut signing_key)?);
+        }
+
+        self.format_shard_file(&messages, writer)?;
+
+        Ok(())
+    }
+}
+
 /// Errors encountered while creating or combining shares using Shamir's Secret Sharing.
 #[derive(thiserror::Error, Debug)]
 pub enum SharksError {

crates/keyfork-shard/src/openpgp.rs

@@ -1,27 +1,16 @@
 //! OpenPGP Shard functionality.
 
 use std::{
-    collections::{HashMap, VecDeque},
-    io::{stdin, stdout, Read, Write},
+    collections::HashMap,
+    io::{Read, Write},
     path::Path,
     str::FromStr,
 };
 
-use aes_gcm::{
-    aead::{consts::U12, Aead},
-    aes::cipher::InvalidLength,
-    Aes256Gcm, Error as AesError, KeyInit, Nonce,
-};
-use hkdf::{Hkdf, InvalidLength as HkdfInvalidLength};
 use keyfork_derive_openpgp::{
-    derive_util::{DerivationPath, PathError, VariableLengthSeed},
+    derive_util::{DerivationPath, VariableLengthSeed},
     XPrv,
 };
-use keyfork_mnemonic_util::{English, Mnemonic, MnemonicFromStrError, MnemonicGenerationError};
-use keyfork_prompt::{
-    validators::{mnemonic::MnemonicSetValidator, Validator},
-    Error as PromptError, Message as PromptMessage, PromptHandler, Terminal,
-};
 use openpgp::{
     armor::{Kind, Writer},
     cert::{Cert, CertParser, ValidCert},
@@ -36,12 +25,10 @@ use openpgp::{
         Marshal,
     },
     types::KeyFlags,
-    Fingerprint, KeyID, PacketPile,
+    KeyID, PacketPile,
 };
 pub use sequoia_openpgp as openpgp;
-use sha2::Sha256;
-use sharks::{Share, Sharks};
-use x25519_dalek::{EphemeralSecret, PublicKey};
+use sharks::Share;
 
 mod keyring;
 use keyring::Keyring;
@@ -56,13 +43,7 @@ use smartcard::SmartcardManager;
 const SHARD_METADATA_VERSION: u8 = 1;
 const SHARD_METADATA_OFFSET: usize = 2;
 
-use super::{
-    InvalidData, SharksError, HUNK_VERSION, QRCODE_COULDNT_READ, QRCODE_ERROR, QRCODE_PROMPT,
-    QRCODE_TIMEOUT,
-};
-
-// 256 bit share is 49 bytes + some amount of hunk bytes, gives us reasonable padding
-const ENC_LEN: u8 = 4 * 16;
+use super::{Format, KeyDiscovery, SharksError};
 
 /// Errors encountered while performing operations using OpenPGP.
 #[derive(Debug, thiserror::Error)]
@@ -71,22 +52,6 @@ pub enum Error {
     #[error("{0}")]
     Sharks(#[from] SharksError),
 
-    /// Unable to decrypt a share.
-    #[error("Error decrypting share: {0}")]
-    SymDecryptShare(#[from] AesError),
-
-    /// The generated AES key is of an invalid length.
-    #[error("Invalid length of AES key: {0}")]
-    AesLength(#[from] InvalidLength),
-
-    /// The HKDF function was given an input of an invalid length.
-    #[error("Invalid KDF length: {0}")]
-    HkdfLength(#[from] HkdfInvalidLength),
-
-    /// The secret did not match the previously-known secret fingerprint.
-    #[error("Derived secret hash {0} != expected {1}")]
-    InvalidSecret(Fingerprint, Fingerprint),
-
     /// An error occurred while performing an OpenPGP operation.
     #[error("OpenPGP error: {0}")]
     Sequoia(#[source] anyhow::Error),
@@ -103,45 +68,9 @@ pub enum Error {
     #[error("Smartcard error: {0}")]
     Smartcard(#[from] smartcard::Error),
 
-    /// An error occurred while displaying a prompt.
-    #[error("Prompt error: {0}")]
-    Prompt(#[from] PromptError),
-
-    /// An error occurred while generating a mnemonic.
-    #[error("Mnemonic generation error: {0}")]
-    MnemonicGeneration(#[from] MnemonicGenerationError),
-
-    /// An error occurred while parsing a mnemonic.
-    #[error("Mnemonic parse error: {0}")]
-    MnemonicFromStr(#[from] MnemonicFromStrError),
-
-    /// An error occurred while converting mnemonic data.
-    #[error("{0}")]
-    InvalidMnemonicData(#[from] InvalidData),
-
     /// An IO error occurred.
     #[error("IO error: {0}")]
     Io(#[source] std::io::Error),
-
-    /// An error occurred while deriving data.
-    #[error("Derivation: {0}")]
-    Derivation(#[from] keyfork_derive_openpgp::derive_util::extended_key::private_key::Error),
-
-    /// An error occurred while parsing a derivation path.
-    #[error("Derivation path: {0}")]
-    DerivationPath(#[from] PathError),
-
-    /// An error occurred while requesting derivation.
-    #[error("Derivation request: {0}")]
-    DerivationRequest(#[from] keyfork_derive_openpgp::derive_util::request::DerivationError),
-
-    /// An error occurred while decoding hex.
-    #[error("Unable to decode hex: {0}")]
-    HexDecode(#[from] smex::DecodeError),
-
-    /// An error occurred while creating an OpenPGP cert.
-    #[error("Keyfork OpenPGP: {0}")]
-    KeyforkOpenPGP(#[from] keyfork_derive_openpgp::Error),
 }
 
 #[allow(missing_docs)]
@@ -163,6 +92,61 @@ impl EncryptedMessage {
         }
     }
 
+    /// Parse OpenPGP packets for encrypted messages.
+    ///
+    /// # Errors
+    /// The function may return an error if Sequoia is unable to parse packets.
+    ///
+    /// # Panics
+    /// The function may panic if an unexpected packet is encountered.
+    pub fn from_reader(input: impl Read + Send + Sync) -> openpgp::Result<Vec<Self>> {
+        let mut pkesks = Vec::new();
+        let mut encrypted_messages = vec![];
+
+        for packet in PacketPile::from_reader(input)
+            .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)
+    }
+
+    /// Serialize all contents of the message to a writer.
+    ///
+    /// # Errors
+    /// The function may error for any condition in Sequoia's Serialize trait.
+    fn serialize(&self, mut o: impl std::io::Write + Send + Sync) -> openpgp::Result<()> {
+        for pkesk in &self.pkesks {
+            let mut packet = vec![];
+            pkesk.serialize(&mut packet).map_err(Error::Sequoia)?;
+            let message = Message::new(&mut o);
+            let mut message = ArbitraryWriter::new(message, Tag::PKESK).map_err(Error::Sequoia)?;
+            message.write_all(&packet).map_err(Error::SequoiaIo)?;
+            message.finalize().map_err(Error::Sequoia)?;
+        }
+        let mut packet = vec![];
+        self.message
+            .serialize(&mut packet)
+            .map_err(Error::Sequoia)?;
+
+        let message = Message::new(&mut o);
+        let mut message = ArbitraryWriter::new(message, Tag::SEIP).map_err(Error::Sequoia)?;
+        message.write_all(&packet).map_err(Error::SequoiaIo)?;
+        message.finalize().map_err(Error::Sequoia)?;
+
+        Ok(())
+    }
+
     /// Decrypt the message with a Sequoia policy and decryptor.
     ///
     /// This method creates a container containing the packets and passes the serialized container
@@ -176,23 +160,7 @@ impl EncryptedMessage {
         H: VerificationHelper + DecryptionHelper,
     {
         let mut packets = vec![];
-
-        for pkesk in &self.pkesks {
-            let mut packet = vec![];
-            pkesk.serialize(&mut packet).map_err(Error::Sequoia)?;
-            let message = Message::new(&mut packets);
-            let mut message = ArbitraryWriter::new(message, Tag::PKESK).map_err(Error::Sequoia)?;
-            message.write_all(&packet).map_err(Error::SequoiaIo)?;
-            message.finalize().map_err(Error::Sequoia)?;
-        }
-        let mut packet = vec![];
-        self.message
-            .serialize(&mut packet)
-            .map_err(Error::Sequoia)?;
-        let message = Message::new(&mut packets);
-        let mut message = ArbitraryWriter::new(message, Tag::SEIP).map_err(Error::Sequoia)?;
-        message.write_all(&packet).map_err(Error::SequoiaIo)?;
-        message.finalize().map_err(Error::Sequoia)?;
+        self.serialize(&mut packets).map_err(Error::Sequoia)?;
 
         let mut decryptor = DecryptorBuilder::from_bytes(&packets)
             .map_err(Error::Sequoia)?
@@ -207,13 +175,17 @@ impl EncryptedMessage {
     }
 }
 
-/// 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>> {
+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() {
@@ -234,37 +206,317 @@ pub fn discover_certs(path: impl AsRef<Path>) -> Result<Vec<Cert>> {
             }
             Ok(vec)
         }
+    }
 }
 
-/// Parse messages from a type implementing [`Read`] and store them as [`EncryptedMessage`].
-///
-/// # Errors
-/// The function may return an error if the reader has run out of data or if the data is not
-/// properly formatted OpenPGP messages.
-///
-/// # 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.
-pub fn parse_messages(reader: impl Read + Send + Sync) -> Result<VecDeque<EncryptedMessage>> {
-    let mut pkesks = Vec::new();
-    let mut encrypted_messages = VecDeque::new();
+impl Format for OpenPGP {
+    type Error = Error;
+    type PublicKey = Cert;
+    type PrivateKeyData = Vec<Cert>;
+    type SigningKey = Cert;
+    type EncryptedData = EncryptedMessage;
 
-    for packet in PacketPile::from_reader(reader)
+    /// Derive an OpenPGP Shard certificate from the given seed.
+    fn derive_signing_key(&self, seed: &[u8]) -> Self::SigningKey {
+        let seed = VariableLengthSeed::new(seed);
+        // build cert to sign encrypted shares
+        let userid = UserID::from("keyfork-sss");
+        let path = DerivationPath::from_str("m/7366512'/0'").expect("valid derivation path");
+        let xprv = XPrv::new(seed)
+            .derive_path(&path)
+            .expect("valid derivation");
+        keyfork_derive_openpgp::derive(
+            xprv,
+            &[KeyFlags::empty().set_certification().set_signing()],
+            &userid,
+        )
+        .expect("valid cert creation")
+    }
+
+    fn format_encrypted_header(
+        &self,
+        signing_key: &Self::SigningKey,
+        key_data: &[Self::PublicKey],
+        threshold: u8,
+    ) -> Result<Self::EncryptedData, Self::Error> {
+        let policy = StandardPolicy::new();
+        let mut pp = vec![SHARD_METADATA_VERSION, threshold];
+        // Note: Sequoia does not export private keys on a Cert, only on a TSK
+        signing_key
+            .serialize(&mut pp)
+            .expect("serialize cert into bytes");
+        for cert in key_data {
+            cert.serialize(&mut pp)
+                .expect("serialize pubkey into bytes");
+        }
+
+        // verify packet pile
+        let mut iter = openpgp::cert::CertParser::from_bytes(&pp[SHARD_METADATA_OFFSET..])
+            .expect("should have certs");
+        let first_cert = iter.next().transpose().ok().flatten().expect("first cert");
+        assert_eq!(signing_key, &first_cert);
+
+        for (packet_cert, cert) in iter.zip(key_data) {
+            assert_eq!(
+                &packet_cert.expect("parsed packet cert"),
+                cert,
+                "packet pile could not recreate cert: {}",
+                cert.fingerprint(),
+            );
+        }
+
+        let valid_certs = key_data
+            .iter()
+            .map(|c| c.with_policy(&policy, None))
+            .collect::<openpgp::Result<Vec<_>>>()
+            .map_err(Error::Sequoia)?;
+        let recipients = valid_certs.iter().flat_map(|vc| {
+            get_encryption_keys(vc).map(|key| Recipient::new(KeyID::wildcard(), key.key()))
+        });
+
+        // Process is as follows:
+        // * Any OpenPGP message
+        // * An encrypted message
+        // * A literal message
+        // * The packet pile
+        //
+        // When decrypting, OpenPGP will see:
+        // * A message, and parse it
+        // * An encrypted message, and decrypt it
+        // * A literal message, and extract it
+        // * The packet pile
+        let mut output = vec![];
+        let message = Message::new(&mut output);
+        let encrypted_message = Encryptor2::for_recipients(message, recipients)
+            .build()
+            .map_err(Error::Sequoia)?;
+        let mut literal_message = LiteralWriter::new(encrypted_message)
+            .build()
+            .map_err(Error::Sequoia)?;
+        literal_message.write_all(&pp).map_err(Error::SequoiaIo)?;
+        literal_message.finalize().map_err(Error::Sequoia)?;
+
+        // Parse it into an EncryptedMessage. Yes, this takes a serialized message
+        // and deserializes it. Don't think about it too hard. It's easier this way.
+
+        let mut pkesks = vec![];
+        for packet in PacketPile::from_reader(output.as_slice())
             .map_err(Error::Sequoia)?
             .into_children()
         {
             match packet {
                 Packet::PKESK(p) => pkesks.push(p),
-            Packet::SEIP(s) => {
-                encrypted_messages.push_back(EncryptedMessage::new(&mut pkesks, s));
-            }
-            s => {
-                panic!("Invalid variant found: {}", s.tag());
-            }
+                Packet::SEIP(s) => return Ok(EncryptedMessage::new(&mut pkesks, s)),
+                s => panic!("Invalid variant found: {}", s.tag()),
             }
         }
 
-    Ok(encrypted_messages)
+        panic!("Unable to build EncryptedMessage from PacketPile");
+    }
+
+    fn encrypt_shard(
+        &self,
+        shard: &[u8],
+        public_key: &Cert,
+        signing_key: &mut Self::SigningKey,
+    ) -> Result<EncryptedMessage> {
+        let policy = StandardPolicy::new();
+        let valid_cert = public_key
+            .with_policy(&policy, None)
+            .map_err(Error::Sequoia)?;
+        let encryption_keys = get_encryption_keys(&valid_cert).collect::<Vec<_>>();
+
+        let signing_key = signing_key
+            .primary_key()
+            .parts_into_secret()
+            .map_err(Error::Sequoia)?
+            .key()
+            .clone()
+            .into_keypair()
+            .map_err(Error::Sequoia)?;
+
+        // Process is as follows:
+        // * Any OpenPGP message
+        // * An encrypted message
+        // * A signed message
+        // * A literal message
+        // * The shard itself
+        //
+        // When decrypting, OpenPGP will see:
+        // * A message, and parse it
+        // * An encrypted message, and decrypt it
+        // * A signed message, and verify it
+        // * A literal message, and extract it
+        // * The shard itself
+        let mut message_output = vec![];
+        let message = Message::new(&mut message_output);
+        let encrypted_message = Encryptor2::for_recipients(
+            message,
+            encryption_keys
+                .iter()
+                .map(|k| Recipient::new(KeyID::wildcard(), k.key())),
+        )
+        .build()
+        .map_err(Error::Sequoia)?;
+        let signed_message = Signer::new(encrypted_message, signing_key)
+            .build()
+            .map_err(Error::Sequoia)?;
+        let mut message = LiteralWriter::new(signed_message)
+            .build()
+            .map_err(Error::Sequoia)?;
+        message.write_all(shard).map_err(Error::SequoiaIo)?;
+        message.finalize().map_err(Error::Sequoia)?;
+
+        let message = EncryptedMessage::from_reader(message_output.as_slice())
+            .map_err(Error::Sequoia)?
+            .into_iter()
+            .next()
+            .expect("serialized message should be parseable");
+
+        Ok(message)
+    }
+
+    fn parse_shard_file(
+        &self,
+        shard_file: impl Read + Send + Sync,
+    ) -> Result<Vec<Self::EncryptedData>, Self::Error> {
+        EncryptedMessage::from_reader(shard_file).map_err(Error::Sequoia)
+    }
+
+    fn format_shard_file(
+        &self,
+        encrypted_data: &[Self::EncryptedData],
+        shard_file: impl Write + Send + Sync,
+    ) -> Result<(), Self::Error> {
+        let mut writer = Writer::new(shard_file, Kind::Message).map_err(Error::SequoiaIo)?;
+        for message in encrypted_data {
+            message.serialize(&mut writer).map_err(Error::Sequoia)?;
+        }
+        writer.finalize().map_err(Error::SequoiaIo)?;
+        Ok(())
+    }
+
+    fn decrypt_all_shards(
+        &self,
+        private_keys: Option<Self::PrivateKeyData>,
+        encrypted_data: &[Self::EncryptedData],
+    ) -> 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 mut encrypted_messages = encrypted_data.iter();
+
+        let metadata = encrypted_messages.next().expect("metdata");
+        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(encrypted_messages.cloned())
+            .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>,
+        encrypted_data: &[Self::EncryptedData],
+    ) -> 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 mut encrypted_messages = encrypted_data.iter();
+
+        let metadata = encrypted_messages.next().expect("metadata");
+        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(encrypted_messages.cloned())
+            .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");
+    }
+}
+
+impl KeyDiscovery<OpenPGP> for &Path {
+    fn discover_public_keys(&self) -> Result<Vec<<OpenPGP as Format>::PublicKey>> {
+        OpenPGP::discover_certs(self)
+    }
+
+    fn discover_private_keys(&self) -> Result<<OpenPGP as Format>::PrivateKeyData> {
+        todo!()
+    }
+}
+
+impl KeyDiscovery<OpenPGP> for &[Cert] {
+    fn discover_public_keys(&self) -> Result<Vec<<OpenPGP as Format>::PublicKey>> {
+        Ok(self.to_vec())
+    }
+
+    fn discover_private_keys(&self) -> Result<<OpenPGP as Format>::PrivateKeyData> {
+        Ok(self.to_vec())
+    }
 }
 
 fn get_encryption_keys<'a>(
@@ -415,378 +667,3 @@ fn decrypt_metadata(
         message.decrypt_with(policy, keyring)?
     })
 }
-
-fn decrypt_one(
-    messages: Vec<EncryptedMessage>,
-    certs: &[Cert],
-    metadata: &EncryptedMessage,
-) -> Result<(Vec<u8>, u8, Cert)> {
-    let policy = NullPolicy::new();
-
-    let mut keyring = Keyring::new(certs)?;
-    let mut manager = SmartcardManager::new()?;
-
-    let content = decrypt_metadata(metadata, &policy, &mut keyring, &mut manager)?;
-
-    let (threshold, root_cert, certs) = decode_metadata_v1(&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(messages).collect();
-
-    let decrypted_messages = decrypt_with_keyring(&mut messages, &certs, &policy, &mut keyring)?;
-
-    if let Some(message) = decrypted_messages.into_values().next() {
-        return Ok((message, threshold, root_cert));
-    }
-
-    let decrypted_messages = decrypt_with_manager(1, &mut messages, &certs, &policy, &mut manager)?;
-
-    if let Some(message) = decrypted_messages.into_values().next() {
-        return Ok((message, threshold, root_cert));
-    }
-
-    unreachable!("smartcard manager should always decrypt")
-}
-
-/// Decrypt a single shard, encrypt to a remote operator, and present the transport shard as a QR
-/// code and mnemonic to be sent to the remote operator.
-///
-/// # Errors
-///
-/// The function may error if an error occurs while displaying a prompt or while decrypting the
-/// shard. An error will not be returned if the camera has a hardware error while scanning a QR
-/// code; instead, a mnemonic prompt will be used.
-///
-/// # Panics
-///
-/// 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`].
-pub fn decrypt(
-    certs: &[Cert],
-    metadata: &EncryptedMessage,
-    encrypted_messages: &[EncryptedMessage],
-) -> Result<()> {
-    let mut pm = Terminal::new(stdin(), stdout())?;
-
-    let mut nonce_data: Option<[u8; 12]> = None;
-    let mut pubkey_data: Option<[u8; 32]> = None;
-
-    #[cfg(feature = "qrcode")]
-    {
-        pm.prompt_message(PromptMessage::Text(QRCODE_PROMPT.to_string()))?;
-        if let Ok(Some(hex)) =
-            keyfork_qrcode::scan_camera(std::time::Duration::from_secs(QRCODE_TIMEOUT), 0)
-        {
-            let decoded_data = smex::decode(&hex)?;
-            let _ = nonce_data.insert(decoded_data[..12].try_into().map_err(|_| InvalidData)?);
-            let _ = pubkey_data.insert(decoded_data[12..].try_into().map_err(|_| InvalidData)?);
-        } else {
-            pm.prompt_message(PromptMessage::Text(QRCODE_ERROR.to_string()))?;
-        };
-    }
-
-    let (nonce, 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::<English, _>(
-                QRCODE_COULDNT_READ,
-                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)
-        }
-    };
-
-    let nonce = Nonce::<U12>::from_slice(&nonce);
-
-    let our_key = EphemeralSecret::random();
-    let our_pubkey_mnemonic = Mnemonic::from_bytes(PublicKey::from(&our_key).as_bytes())?;
-
-    let shared_secret = our_key.diffie_hellman(&PublicKey::from(pubkey)).to_bytes();
-
-    let (mut share, threshold, ..) = decrypt_one(encrypted_messages.to_vec(), certs, metadata)?;
-    share.insert(0, HUNK_VERSION);
-    share.insert(1, threshold);
-    assert!(
-        share.len() <= ENC_LEN as usize,
-        "invalid share length (too long, max {ENC_LEN} 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)?;
-
-    let bytes = shared_key.encrypt(nonce, share.as_slice())?;
-    shared_key.decrypt(nonce, &bytes[..])?;
-
-    // NOTE: Padding length is less than u8::MAX because ENC_LEN < u8::MAX
-    // NOTE: This previously used a single 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 done below by having sequentially increasing numbers up to but not
-    // including the last byte.
-    #[allow(clippy::assertions_on_constants)]
-    {
-        assert!(ENC_LEN < u8::MAX, "padding byte can be u8");
-    }
-    #[allow(clippy::cast_possible_truncation)]
-    let mut out_bytes = [bytes.len() as u8; ENC_LEN as usize];
-    assert!(
-        bytes.len() < out_bytes.len(),
-        "encrypted payload larger than acceptable limit"
-    );
-    out_bytes[..bytes.len()].clone_from_slice(&bytes);
-    #[allow(clippy::cast_possible_truncation)]
-    for (i, byte) in (out_bytes[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_bytes(&out_bytes) };
-
-    #[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::Highest) {
-            pm.prompt_message(PromptMessage::Text(
-                concat!(
-                    "A QR code will be displayed after this prompt. ",
-                    "Send the QR code back to the operator combining the shards. ",
-                    "Nobody else should scan this QR code."
-                )
-                .to_string(),
-            ))?;
-            pm.prompt_message(PromptMessage::Data(qrcode))?;
-        }
-    }
-
-    pm.prompt_message(PromptMessage::Text(format!(
-        "Upon request, these words should be sent: {our_pubkey_mnemonic} {payload_mnemonic}"
-    )))?;
-
-    Ok(())
-}
-
-/// Combine mulitple shards into a secret.
-///
-/// # Errors
-/// The function may return an error if an error occurs while decrypting shards, parsing shards, or
-/// combining the shards into a secret.
-pub fn combine(
-    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 mut manager = SmartcardManager::new()?;
-    let content = decrypt_metadata(metadata, &policy, &mut keyring, &mut manager)?;
-
-    let (threshold, root_cert, certs) = decode_metadata_v1(&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.
-
-    let mut messages: HashMap<KeyID, EncryptedMessage> =
-        certs.iter().map(Cert::keyid).zip(messages).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()))?;
-    let secret = Sharks(threshold)
-        .recover(&shares)
-        .map_err(|e| SharksError::CombineShare(e.to_string()))?;
-
-    // TODO: extract as function
-    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,
-    )?;
-
-    // NOTE: Signatures on certs will be different. Compare fingerprints instead.
-    let derived_fp = derived_cert.fingerprint();
-    let expected_fp = root_cert.fingerprint();
-    if derived_fp != expected_fp {
-        return Err(Error::InvalidSecret(derived_fp, expected_fp));
-    }
-
-    output.write_all(&secret).map_err(Error::Io)?;
-
-    Ok(())
-}
-
-/// Split a secret into an OpenPGP formatted Shard file.
-///
-/// # Errors
-///
-/// The function may return an error if the shards can't be encrypted to the provided OpenPGP
-/// certs or if an error happens while writing the Shard file.
-///
-/// # Panics
-///
-/// The function may panic if the metadata can't properly store the certificates used to generate
-/// the encrypted shares.
-pub fn split(threshold: u8, certs: Vec<Cert>, secret: &[u8], output: impl Write) -> Result<()> {
-    let seed = VariableLengthSeed::new(secret);
-    // build cert to sign encrypted shares
-    let userid = UserID::from("keyfork-sss");
-    let path = DerivationPath::from_str("m/7366512'/0'")?;
-    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)?;
-
-    let sharks = Sharks(threshold);
-    let dealer = sharks.dealer(secret);
-    let generated_shares = dealer.map(|s| Vec::from(&s)).collect::<Vec<_>>();
-    let policy = StandardPolicy::new();
-    let mut writer = Writer::new(output, Kind::Message).map_err(Error::SequoiaIo)?;
-
-    let mut total_recipients = vec![];
-    let mut messages = vec![];
-
-    for (share, cert) in generated_shares.iter().zip(certs) {
-        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, signing_key.clone())
-            .build()
-            .map_err(Error::Sequoia)?;
-        let mut message = LiteralWriter::new(message)
-            .build()
-            .map_err(Error::Sequoia)?;
-        message.write_all(share).map_err(Error::SequoiaIo)?;
-        message.finalize().map_err(Error::Sequoia)?;
-
-        messages.push(message_output);
-    }
-
-    let mut pp = vec![SHARD_METADATA_VERSION, threshold];
-    // store derived cert to verify provided shares
-    derived_cert.serialize(&mut pp).map_err(Error::Sequoia)?;
-    for recipient in &total_recipients {
-        recipient.serialize(&mut pp).map_err(Error::Sequoia)?;
-    }
-
-    // verify packet pile
-    for (packet_cert, cert) in openpgp::cert::CertParser::from_bytes(&pp[2..])
-        .map_err(Error::Sequoia)?
-        .skip(1)
-        .zip(total_recipients.iter())
-    {
-        assert_eq!(
-            &packet_cert.map_err(Error::Sequoia)?,
-            cert,
-            "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<_>>>()
-        .map_err(Error::Sequoia)?;
-
-    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 = Encryptor2::for_recipients(message, total_recipients)
-        .build()
-        .map_err(Error::Sequoia)?;
-    let mut message = LiteralWriter::new(message)
-        .build()
-        .map_err(Error::Sequoia)?;
-    message.write_all(&pp).map_err(Error::SequoiaIo)?;
-    message.finalize().map_err(Error::Sequoia)?;
-    writer
-        .write_all(&message_output)
-        .map_err(Error::SequoiaIo)?;
-
-    for message in messages {
-        writer.write_all(&message).map_err(Error::SequoiaIo)?;
-    }
-
-    writer.finalize().map_err(Error::SequoiaIo)?;
-
-    Ok(())
-}

crates/keyfork-shard/src/openpgp/keyring.rs

@@ -111,12 +111,10 @@ impl DecryptionHelper for &mut Keyring {
                 pkesk.recipient().is_wildcard()
                     || cert.keys().any(|k| &k.keyid() == pkesk.recipient())
             }) {
-                #[allow(deprecated, clippy::map_flatten)]
                 let name = cert
                     .userids()
                     .next()
-                    .map(|userid| userid.userid().name().transpose())
-                    .flatten()
+                    .and_then(|userid| userid.userid().name2().transpose())
                     .transpose()
                     .ok()
                     .flatten();

crates/keyfork/src/cli/recover.rs

@@ -3,10 +3,7 @@ use clap::{Parser, Subcommand};
 use std::path::PathBuf;
 
 use keyfork_mnemonic_util::{English, Mnemonic};
-use keyfork_shard::{
-    openpgp::{combine, discover_certs, parse_messages},
-    remote_decrypt,
-};
+use keyfork_shard::{remote_decrypt, Format};
 
 type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
 
@@ -37,15 +34,10 @@ impl RecoverSubcommands {
             } => {
                 let content = std::fs::read_to_string(shard_file)?;
                 if content.contains("BEGIN PGP MESSAGE") {
-                    let certs = key_discovery
-                        .as_ref()
-                        .map(discover_certs)
-                        .transpose()?
-                        .unwrap_or(vec![]);
-                    let mut messages = parse_messages(content.as_bytes())?;
-                    let metadata = messages.pop_front().expect("any pgp encrypted message");
-                    let mut seed = vec![];
-                    combine(certs, &metadata, messages.into(), &mut seed)?;
+                    let openpgp = keyfork_shard::openpgp::OpenPGP;
+                    // TODO: remove .clone() by making handle() consume self
+                    let seed = openpgp
+                        .decrypt_all_shards_to_secret(key_discovery.as_deref(), content.as_bytes())?;
                     Ok(seed)
                 } else {
                     panic!("unknown format of shard file");

crates/keyfork/src/cli/shard.rs

@@ -1,5 +1,6 @@
 use super::Keyfork;
 use clap::{builder::PossibleValue, Parser, Subcommand, ValueEnum};
+use keyfork_shard::Format as _;
 use std::{
     io::{stdin, stdout, Read, Write},
     path::{Path, PathBuf},
@@ -31,27 +32,23 @@ trait ShardExec {
         &self,
         threshold: u8,
         max: u8,
-        key_discovery: impl AsRef<Path>,
+        key_discovery: &Path,
         secret: &[u8],
+        output: &mut (impl Write + Send + Sync),
+    ) -> Result<(), Box<dyn std::error::Error>>;
+
+    fn combine(
+        &self,
+        key_discovery: Option<&Path>,
+        input: impl Read + Send + Sync,
         output: &mut impl Write,
     ) -> Result<(), Box<dyn std::error::Error>>;
 
-    fn combine<T>(
+    fn decrypt(
         &self,
-        key_discovery: Option<T>,
+        key_discovery: Option<&Path>,
         input: impl Read + Send + Sync,
-        output: &mut impl Write,
-    ) -> Result<(), Box<dyn std::error::Error>>
-    where
-        T: AsRef<Path>;
-
-    fn decrypt<T>(
-        &self,
-        key_discovery: Option<T>,
-        input: impl Read + Send + Sync,
-    ) -> Result<(), Box<dyn std::error::Error>>
-    where
-        T: AsRef<Path>;
+    ) -> Result<(), Box<dyn std::error::Error>>;
 }
 
 #[derive(Clone, Debug)]
@@ -62,77 +59,36 @@ impl ShardExec for OpenPGP {
         &self,
         threshold: u8,
         max: u8,
-        key_discovery: impl AsRef<Path>,
+        key_discovery: &Path,
         secret: &[u8],
-        output: &mut impl Write,
+        output: &mut (impl Write + Send + Sync),
     ) -> Result<(), Box<dyn std::error::Error>> {
-        // Get certs and input
-        let certs = keyfork_shard::openpgp::discover_certs(key_discovery.as_ref())?;
-        assert_eq!(
-            certs.len(),
-            max.into(),
-            "cert count {} != max {max}",
-            certs.len()
-        );
-        keyfork_shard::openpgp::split(threshold, certs, secret, output).map_err(Into::into)
+        let opgp = keyfork_shard::openpgp::OpenPGP;
+        opgp.shard_and_encrypt(threshold, max, secret, key_discovery, output)
     }
 
-    fn combine<T>(
+    fn combine(
         &self,
-        key_discovery: Option<T>,
+        key_discovery: Option<&Path>,
         input: impl Read + Send + Sync,
         output: &mut impl Write,
     ) -> Result<(), Box<dyn std::error::Error>>
-    where
-        T: AsRef<Path>,
     {
-        let certs = key_discovery
-            .map(|kd| keyfork_shard::openpgp::discover_certs(kd.as_ref()))
-            .transpose()?
-            .unwrap_or(vec![]);
-
-        let mut encrypted_messages = keyfork_shard::openpgp::parse_messages(input)?;
-        let encrypted_metadata = encrypted_messages
-            .pop_front()
-            .expect("any pgp encrypted message");
-
-        let mut bytes = vec![];
-
-        keyfork_shard::openpgp::combine(
-            certs,
-            &encrypted_metadata,
-            encrypted_messages.into(),
-            &mut bytes,
-        )?;
-
-        write!(output, "{}", smex::encode(&bytes))?;
+        let openpgp = keyfork_shard::openpgp::OpenPGP;
+        let bytes = openpgp.decrypt_all_shards_to_secret(key_discovery, input)?;
+        write!(output, "{}", smex::encode(bytes))?;
 
         Ok(())
     }
 
-    fn decrypt<T>(
+    fn decrypt(
         &self,
-        key_discovery: Option<T>,
+        key_discovery: Option<&Path>,
         input: impl Read + Send + Sync,
     ) -> Result<(), Box<dyn std::error::Error>>
-    where
-        T: AsRef<Path>,
     {
-        let certs = key_discovery
-            .map(|kd| keyfork_shard::openpgp::discover_certs(kd.as_ref()))
-            .transpose()?
-            .unwrap_or(vec![]);
-
-        let mut encrypted_messages = keyfork_shard::openpgp::parse_messages(input)?;
-        let encrypted_metadata = encrypted_messages
-            .pop_front()
-            .expect("any pgp encrypted message");
-
-        keyfork_shard::openpgp::decrypt(
-            &certs,
-            &encrypted_metadata,
-            encrypted_messages.make_contiguous(),
-        )?;
+        let openpgp = keyfork_shard::openpgp::OpenPGP;
+        openpgp.decrypt_one_shard_for_transport(key_discovery, input)?;
         Ok(())
     }
 }
@@ -225,7 +181,7 @@ impl ShardSubcommands {
 
                 match format {
                     Some(Format::OpenPGP(o)) => {
-                        o.decrypt(key_discovery.as_ref(), shard_content.as_bytes())
+                        o.decrypt(key_discovery.as_deref(), shard_content.as_bytes())
                     }
                     Some(Format::P256(_p)) => todo!(),
                     None => panic!("{COULD_NOT_DETERMINE_FORMAT}"),
@@ -242,7 +198,7 @@ impl ShardSubcommands {
 
                 match format {
                     Some(Format::OpenPGP(o)) => o.combine(
-                        key_discovery.as_ref(),
+                        key_discovery.as_deref(),
                         shard_content.as_bytes(),
                         &mut stdout,
                     ),

crates/keyfork/src/cli/wizard.rs

@@ -15,6 +15,8 @@ use keyfork_prompt::{
     Message, PromptHandler, Terminal,
 };
 
+use keyfork_shard::{Format, openpgp::OpenPGP};
+
 #[derive(thiserror::Error, Debug)]
 #[error("Invalid PIN length: {0}")]
 pub struct PinLength(usize);
@@ -163,11 +165,13 @@ fn generate_shard_secret(
         certs.push(cert);
     }
 
+    let opgp = OpenPGP;
+
     if let Some(output_file) = output_file {
         let output = File::create(output_file)?;
-        keyfork_shard::openpgp::split(threshold, certs, &seed, output)?;
+        opgp.shard_and_encrypt(threshold, certs.len() as u8, &seed, &certs[..], output)?;
     } else {
-        keyfork_shard::openpgp::split(threshold, certs, &seed, std::io::stdout())?;
+        opgp.shard_and_encrypt(threshold, certs.len() as u8, &seed, &certs[..], std::io::stdout())?;
     }
     Ok(())
 }