keyfork-shard: add keyfork-shard-remote-openpgp

keyfork-shard/Cargo.toml

@@ -28,4 +28,4 @@ thiserror = "1.0.50"
 keyfork-prompt = { version = "0.1.0", path = "../keyfork-prompt", optional = true }
 x25519-dalek = { version = "2.0.0", features = ["getrandom"] }
 keyfork-mnemonic-util = { version = "0.1.0", path = "../keyfork-mnemonic-util" }
-aes-gcm = "0.10.3"
+aes-gcm = { version = "0.10.3", features = ["std"] }

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

@@ -0,0 +1,65 @@
+use std::{
+    env,
+    fs::File,
+    path::{Path, PathBuf},
+    process::ExitCode,
+};
+
+use keyfork_shard::openpgp::{remote_decrypt, discover_certs, openpgp::Cert, parse_messages};
+
+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);
+    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))
+}
+
+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 mut encrypted_messages = parse_messages(messages_file)?;
+
+    let encrypted_metadata = encrypted_messages
+        .pop_front()
+        .expect("any pgp encrypted message");
+
+    remote_decrypt(
+        &cert_list,
+        encrypted_metadata,
+        encrypted_messages.make_contiguous(),
+    )?;
+
+    Ok(())
+}
+
+fn main() -> ExitCode {
+    let result = run();
+    if let Err(e) = result {
+        eprintln!("Error: {e}");
+        let mut source = e.source();
+        while let Some(new_error) = source.take() {
+            eprintln!("Source: {new_error}");
+            source = new_error.source();
+        }
+        return ExitCode::FAILURE;
+    }
+    ExitCode::SUCCESS
+}

keyfork-shard/src/openpgp.rs

@@ -6,8 +6,8 @@ use std::{
 };
 
 use aes_gcm::{
-    aead::{consts::U12, Aead},
+    aead::{consts::U12, Aead, AeadCore, OsRng},
-    Aes256Gcm, KeyInit, Nonce,
+    Aes256Gcm, KeyInit, Nonce, Error as AesError
 };
 use keyfork_derive_openpgp::derive_util::{
     request::{DerivationAlgorithm, DerivationRequest},
@@ -48,11 +48,16 @@ use x25519_dalek::{EphemeralSecret, PublicKey};
 const SHARD_METADATA_VERSION: u8 = 1;
 const SHARD_METADATA_OFFSET: usize = 2;
 
+const ENC_LEN: u8 = 24 * 4;
+
 #[derive(Debug, thiserror::Error)]
 pub enum Error {
     #[error("Error with creating Share: {0}")]
     Share(String),
 
+    #[error("Error decrypting share: {0}")]
+    SymDecryptShare(#[from] AesError),
+
     #[error("Error combining shares: {0}")]
     CombineShares(String),
 
@@ -343,7 +348,7 @@ fn decrypt_one(
     messages: Vec<EncryptedMessage>,
     certs: &[Cert],
     metadata: EncryptedMessage,
-) -> Result<Vec<u8>> {
+) -> Result<(Vec<u8>, u8, Cert)> {
     let policy = NullPolicy::new();
 
     let mut keyring = Keyring::new(certs)?;
@@ -351,10 +356,10 @@ fn decrypt_one(
 
     let content = decrypt_metadata(&metadata, &policy, &mut keyring, &mut manager)?;
 
-    let (_threshold, root_cert, certs) = decode_metadata_v1(&content)?;
+    let (threshold, root_cert, certs) = decode_metadata_v1(&content)?;
 
     keyring.set_root_cert(root_cert.clone());
-    manager.set_root_cert(root_cert);
+    manager.set_root_cert(root_cert.clone());
 
     let mut messages: HashMap<KeyID, EncryptedMessage> =
         HashMap::from_iter(certs.iter().map(|c| c.keyid()).zip(messages));
@@ -362,13 +367,13 @@ fn decrypt_one(
     let decrypted_messages = decrypt_with_keyring(&mut messages, &certs, &policy, &mut keyring)?;
 
     if let Some(message) = decrypted_messages.into_values().next() {
-        return Ok(message);
+        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);
+        return Ok((message, threshold, root_cert));
     }
 
     unreachable!("smartcard manager should always decrypt")
@@ -413,7 +418,7 @@ pub fn decrypt(
         .diffie_hellman(&PublicKey::from(their_key))
         .to_bytes();
 
-    let share = decrypt_one(encrypted_messages.to_vec(), &certs, metadata)?;
+    let (share, ..) = decrypt_one(encrypted_messages.to_vec(), &certs, metadata)?;
     assert!(share.len() <= 65, "invalid share length (too long)");
     const LEN: u8 = 24 * 3;
     let mut encrypted_payload = [(LEN - share.len() as u8); LEN as usize];
@@ -421,16 +426,27 @@ pub fn decrypt(
 
     let shared_key =
         Aes256Gcm::new_from_slice(&shared_secret).expect("Invalid length of constant key size");
-    let bytes = shared_key.encrypt(their_nonce, share.as_slice()).unwrap();
+    let bytes = shared_key.encrypt(their_nonce, share.as_slice())?;
+    shared_key.decrypt(their_nonce, &bytes[..])?;
 
-    // NOTE: Padding length is less than u8::MAX because 24 * 4 < u8::MAX
+    // NOTE: Padding length is less than u8::MAX because ENC_LEN < u8::MAX
-    const ENC_LEN: u8 = 24 * 4;
+    // NOTE: This previously used a single value as the padding byte, but resulted in
-    let mut out_bytes = [(ENC_LEN - bytes.len() as u8); ENC_LEN as usize];
+    // 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.
+    assert!(ENC_LEN < u8::MAX, "padding byte can be u8");
+    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);
+    for (i, byte) in (&mut out_bytes[bytes.len()..(ENC_LEN as usize - 1)])
+        .into_iter()
+        .enumerate()
+    {
+        *byte = (i % u8::MAX as usize) as u8;
+    }
 
     // safety: size of out_bytes is constant and always % 4 == 0
     let mnemonic = unsafe { Mnemonic::from_raw_entropy(&out_bytes, Default::default()) };
@@ -440,6 +456,80 @@ pub fn decrypt(
     Ok(())
 }
 
+pub fn remote_decrypt(
+    certs: &[Cert],
+    metadata: EncryptedMessage,
+    encrypted_messages: &[EncryptedMessage],
+) -> Result<()> {
+    let mut pm = PromptManager::new(stdin(), stdout())?;
+    let wordlist = Wordlist::default();
+
+    // Get our cert so we know our metadata
+    let (share, threshold, root_cert) = decrypt_one(encrypted_messages.to_vec(), &certs, metadata)?;
+    let mut shares = Vec::with_capacity(threshold as usize);
+    shares.push(share);
+
+    for _ in 1..threshold {
+        let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
+        let nonce_mnemonic =
+            unsafe { Mnemonic::from_raw_entropy(nonce.as_slice(), Default::default()) };
+        let our_key = EphemeralSecret::random();
+        let key_mnemonic =
+            Mnemonic::from_entropy(PublicKey::from(&our_key).as_bytes(), Default::default())?;
+        pm.prompt_message(PromptMessage::Text(format!(
+            "Our words: {nonce_mnemonic} {key_mnemonic}"
+        )))?;
+
+        let pubkey_mnemonic = pm.prompt_wordlist("Their words: ", &wordlist)?;
+        let their_key = Mnemonic::from_str(&pubkey_mnemonic)?.entropy();
+        let their_key: [u8; 32] = their_key.try_into().expect("24 words");
+
+        let shared_secret = our_key
+            .diffie_hellman(&PublicKey::from(their_key))
+            .to_bytes();
+        let shared_key =
+            Aes256Gcm::new_from_slice(&shared_secret).expect("Invalid length of constant key size");
+
+        let payload_mnemonic = pm.prompt_wordlist("Their payload: ", &wordlist)?;
+        let payload = Mnemonic::from_str(&payload_mnemonic)?.entropy();
+
+        let decrypted_share = shared_key.decrypt(&nonce, &payload[..payload[payload.len() - 1] as usize])?;
+        shares.push(decrypted_share);
+    }
+
+    let shares = shares
+        .into_iter()
+        .map(|s| Share::try_from(s.as_slice()))
+        .collect::<Result<Vec<_>, &str>>()
+        .map_err(|e| Error::Share(e.to_string()))?;
+    let secret = Sharks(threshold)
+        .recover(&shares)
+        .map_err(|e| Error::CombineShares(e.to_string()))?;
+
+    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,
+    )?;
+
+    // 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));
+    }
+
+    print!("{}", smex::encode(&secret));
+
+    Ok(())
+}
+
 pub fn combine(
     certs: Vec<Cert>,
     metadata: EncryptedMessage,
@@ -457,7 +547,7 @@ pub fn combine(
     let (threshold, root_cert, certs) = decode_metadata_v1(&content)?;
 
     keyring.set_root_cert(root_cert.clone());
-    manager.set_root_cert(root_cert);
+    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.
@@ -492,6 +582,7 @@ pub fn combine(
         .recover(&shares)
         .map_err(|e| Error::CombineShares(e.to_string()))?;
 
+    // TODO: extract as function
     let userid = UserID::from("keyfork-sss");
     let kdr = DerivationRequest::new(
         DerivationAlgorithm::Ed25519,
@@ -506,10 +597,7 @@ pub fn combine(
 
     // NOTE: Signatures on certs will be different. Compare fingerprints instead.
     let derived_fp = derived_cert.fingerprint();
-    let expected_fp = keyring
+    let expected_fp = root_cert.fingerprint();
-        .root_cert()
-        .expect("cert was previously set")
-        .fingerprint();
     if derived_fp != expected_fp {
         return Err(Error::InvalidSecret(derived_fp, expected_fp));
     }