vault: a password change brings a new master key

:passwd used to wrap the same master key under the new password, so an
old diary.db (a pre-* snapshot, an old revision on Proton Drive) and the
old password still opened every sealed file. It now makes a new master
key. The old password opens nothing from that moment; the old master
key is kept, sealed under the new one, in two new vault columns, only
until every sealed file has been re-sealed.

A background worker does that while the vault is open, without holding
it open. Each file gets a new id with its file key wrapped under the new
master key; its records are copied as they are. The move goes through
the same repointing as :encrypt, so the old id is put on backup_retired
and the mirror purges it from Drive. Which files are left is read off
their headers, so a lock or a restart halfway only pauses the work until
the next unlock. Once none is left, the old key is dropped.

Readers take a Keyring that tries the current key, then the retired
one. A second :passwd is refused until the first has finished. :vault
shows the progress. Every sealed file is uploaded to Proton once more.

README.md

@@ -309,12 +309,17 @@ it back out. `:unlock` and `:lock` open and close it, `:passwd` changes the
 password. A sealed file carries a lock in the list, and the bar says `vault
 open` while it is.
 
-`:passwd` wraps the same key under the new password, so no file has to be
-rewritten — and so it does not take back what the old password opens. A copy
-of `diary.db` from before the change (a `diary.db.pre-*` snapshot, a backup in
-Proton Drive) still unwraps the key with the old password, and that key still
-opens every sealed file. Change the password because you want a new one, not
-to shut out someone who has the old one and an old copy.
+`:passwd` makes a new master key as well as a new password. The old password
+stops opening anything at once; every sealed file is then re-sealed under the
+new key in the background, under a new name, while the vault is open — `:vault`
+shows how far it has come, and locking halfway only pauses it until the next
+`:unlock`. The old copies are deleted from `uploads/` and, on the next mirror
+run, from Proton Drive for good. After that, a copy of `diary.db` from before
+the change (a `diary.db.pre-*` snapshot, an old revision in Proton Drive) and
+the old password open nothing that is still kept anywhere. What they cannot
+take back is a copy someone already made of the files themselves. Re-sealing
+rewrites only each file's header, but every sealed file is uploaded to Proton
+Drive once more. A second `:passwd` waits until the first has finished.
 
 `:encrypt` on a folder or space seals it for good, not just once: every file
 in it now, and every file that lands in it later. An upload, an import, an SFTP
@@ -340,7 +345,10 @@ master key, and only that sealed copy is stored. Each file gets a random key of
 its own, sealed under the master key in the file's header together with its
 id, and its bytes are AES-256-GCM in 64 KiB records, the last one marked as
 last — so a file that is swapped, cut short or tampered with refuses to open.
-Changing the password re-seals the master key and rewrites no file.
+Changing the password makes a new master key. Until every file is re-sealed,
+the old one is kept sealed under the new one, so either kind of file opens and
+an interrupted re-seal carries on where it stopped; re-sealing a file wraps its
+own key under the new master key and copies its records as they are.
 
 A sealed file is served with `Cache-Control: no-store`, so the browser keeps
 no copy of what it showed once the vault shuts. A sealed image in a document

migrations/0018_vault_rekey.sql

@@ -0,0 +1,7 @@
+-- A changed vault password brings a new master key. Until every sealed file
+-- has been re-sealed under it, the old master key is kept here, sealed under
+-- the new one, so either password-change survivor can still be read; once
+-- the last file is done both columns go back to NULL. The old password opens
+-- neither: it only ever opened the old `sealed`, which is gone.
+ALTER TABLE vault ADD COLUMN retired_nonce BLOB;
+ALTER TABLE vault ADD COLUMN retired_sealed BLOB;

src/main.rs

@@ -137,6 +137,7 @@ async fn main() -> Result<()> {
         epoch: Arc::new(std::sync::atomic::AtomicI64::new(epoch)),
         sessions,
     };
+    routes::seal::spawn_rekey(state.clone());
 
     if let Some(sftp_bind) = config.sftp.bind {
         let sftp_state = state.clone();

src/routes/export.rs

@@ -386,13 +386,11 @@ pub async fn export(_: Session, State(state): State<AppState>) -> AppResult<Resp
             let source: Box<dyn std::io::Read> = match (&key, sealed.contains(id)) {
                 // A sealed file that will not open is not a file to leave out
                 // quietly: the archive would claim to be complete and not be.
-                (Some(key), true) => {
-                    Box::new(crate::vault::Reader::open(key, id, &path).map_err(|e| {
-                        AppError::BadRequest(format!(
-                            "{entry} is sealed and would not open ({e}) — nothing was exported"
-                        ))
-                    })?)
-                }
+                (Some(key), true) => Box::new(key.reader(id, &path).map_err(|e| {
+                    AppError::BadRequest(format!(
+                        "{entry} is sealed and would not open ({e}) — nothing was exported"
+                    ))
+                })?),
                 // A row whose file has gone missing must not fail the whole
                 // export; there is nothing to put in its place either way.
                 _ => match std::fs::File::open(&path) {

src/routes/import.rs

@@ -542,7 +542,7 @@ async fn run(state: &AppState, into: Into, multipart: Multipart) -> AppResult<Im
             files_as_they_were(state, manifest, &mut uploads, &mut written).await?;
         }
         if let Some(key) = &key {
-            seal_in_place(state, key, &uploads).await?;
+            seal_in_place(state, key.current(), &uploads).await?;
         }
         if uploads.is_empty() {
             return Err(AppError::BadRequest(
@@ -1067,7 +1067,8 @@ mod tests {
         .unwrap();
         assert!(encrypted && sub_sealed);
         let mut back = String::new();
-        crate::vault::Reader::open(&key, "m1", &uploads_dir.join("m1"))
+        crate::vault::Keyring::new(key.clone())
+            .reader("m1", &uploads_dir.join("m1"))
             .unwrap()
             .read_to_string(&mut back)
             .unwrap();

src/routes/inspect.rs

@@ -35,7 +35,7 @@ use crate::{
     auth::Session,
     error::{AppError, AppResult},
     state::AppState,
-    vault::{self, Password},
+    vault::Password,
 };
 
 /// Certificates and keys are kilobytes. Anything past this is not one, and is
@@ -137,7 +137,7 @@ pub async fn inspect(
         let mut bytes = Zeroizing::new(Vec::new());
         match key {
             Some(key) => {
-                vault::Reader::open(&key, &media_id, &path)?
+                key.reader(&media_id, &path)?
                     .take(MAX_INSPECT)
                     .read_to_end(&mut bytes)?;
             }

src/routes/media.rs

@@ -297,7 +297,14 @@ pub async fn upload_into(
         let mime = mime_of(&filename, field.content_type());
 
         let id = Uuid::new_v4().to_string();
-        let size = store_field(&state, &mut field, &id, &mut budget, key.as_deref()).await?;
+        let size = store_field(
+            &state,
+            &mut field,
+            &id,
+            &mut budget,
+            key.as_deref().map(vault::Keyring::current),
+        )
+        .await?;
         if size == 0 {
             continue;
         }
@@ -598,7 +605,7 @@ pub async fn stream_media(
 /// does break off, as a read over the mount does.
 async fn open_stream(
     mut file: tokio::fs::File,
-    key: &vault::Key,
+    key: &vault::Keyring,
     vault: Arc<vault::Vault>,
     id: &str,
     start: u64,
@@ -609,7 +616,7 @@ async fn open_stream(
     let len = file.metadata().await?.len();
     let mut header = [0u8; vault::HEADER];
     file.read_exact(&mut header).await?;
-    let mut opener = vault::Opener::new(key, id, &header, len)?;
+    let mut opener = key.opener(id, &header, len)?;
     let first = start / vault::CHUNK as u64;
     if first > 0 {
         opener.skip_to(first)?;

src/routes/seal.rs

@@ -17,6 +17,11 @@
 //! file, and the old id is put on `backup_retired`, which the mirror takes off
 //! Drive for good whatever `WORKSPACE_BACKUP_PRUNE` says. Documents that embed
 //! the file have their links moved to the new id in the same transaction.
+//!
+//! A vault password change re-writes every sealed file the same way, under a
+//! new id with its file key sealed under the new master key — see
+//! [`spawn_rekey`]. Once the old ids are off Drive, an old copy of the
+//! database and the old password open nothing that is still kept anywhere.
 
 use axum::{
     extract::{Path, State},
@@ -229,8 +234,12 @@ async fn reseal(state: &AppState, id: i64, seal: bool) -> AppResult<Resealed> {
             unchanged += 1;
             continue;
         }
-        match rewrite(state, &key, target, seal).await {
-            Ok(()) => files += 1,
+        let how = if seal { Rewrite::Seal } else { Rewrite::Open };
+        match rewrite(state, &key, &target.media_id, how).await {
+            Ok(new) => {
+                tracing::info!(node = target.node_id, to = %new, sealed = seal, "file re-written");
+                files += 1
+            }
             Err(e) => {
                 tracing::warn!(node = target.node_id, "could not re-write a file: {e:?}");
                 failed.push(e);
@@ -266,32 +275,52 @@ async fn reseal(state: &AppState, id: i64, seal: bool) -> AppResult<Resealed> {
     })
 }
 
-/// Re-write one file sealed or opened under a new id, then point everything
-/// at the new id and retire the old one.
-async fn rewrite(state: &AppState, key: &vault::Key, target: &Target, seal: bool) -> AppResult<()> {
+#[derive(Clone, Copy)]
+enum Rewrite {
+    /// A plain file into the vault.
+    Seal,
+    /// A sealed file out of it.
+    Open,
+    /// A sealed file under the current master key, from whichever it is under.
+    Rekey,
+}
+
+/// Re-write one file under a new id, then point everything at the new id and
+/// retire the old one. Returns the new id.
+async fn rewrite(
+    state: &AppState,
+    keys: &std::sync::Arc<vault::Keyring>,
+    media_id: &str,
+    how: Rewrite,
+) -> AppResult<String> {
     let uploads = state.config.uploads_dir();
-    let old = target.media_id.clone();
+    let old = media_id.to_string();
     let new = Uuid::new_v4().to_string();
+    let seal = !matches!(how, Rewrite::Open);
     let source = uploads.join(&old);
     let partial = uploads.join(format!("{new}.part"));
 
     let written = {
-        let (key, old, new, source, partial) = (
-            key.clone(),
+        let (keys, old, new, source, partial) = (
+            keys.clone(),
             old.clone(),
             new.clone(),
             source.clone(),
             partial.clone(),
         );
         tokio::task::spawn_blocking(move || -> anyhow::Result<()> {
-            if seal {
-                let mut plain = std::fs::File::open(&source)?;
-                vault::seal_file(&key, &new, &mut plain, &partial)?;
-            } else {
-                let mut opened = vault::Reader::open(&key, &old, &source)?;
-                let mut out = std::fs::File::create(&partial)?;
-                std::io::copy(&mut opened, &mut out)?;
-                out.sync_all()?;
+            match how {
+                Rewrite::Seal => {
+                    let mut plain = std::fs::File::open(&source)?;
+                    vault::seal_file(keys.current(), &new, &mut plain, &partial)?;
+                }
+                Rewrite::Open => {
+                    let mut opened = keys.reader(&old, &source)?;
+                    let mut out = std::fs::File::create(&partial)?;
+                    std::io::copy(&mut opened, &mut out)?;
+                    out.sync_all()?;
+                }
+                Rewrite::Rekey => vault::rewrap_file(&keys, &old, &new, &source, &partial)?,
             }
             Ok(())
         })
@@ -386,13 +415,87 @@ async fn rewrite(state: &AppState, key: &vault::Key, target: &Target, seal: bool
 
     // The database no longer knows the old bytes; they go from the disk too.
     let _ = tokio::fs::remove_file(&source).await;
-    tracing::info!(node = target.node_id, from = %old, to = %new, sealed = seal, "file re-written");
+    Ok(new)
+}
+
+/// Re-seal, in the background, every file still under the master key from
+/// before the last password change. It works only while the vault is open,
+/// and never holds it open: locked halfway, it waits for the next unlock and
+/// carries on from there — which file is done is read off each file's own
+/// header. Once none is left, the old master key is forgotten.
+pub fn spawn_rekey(state: AppState) {
+    state.vault.want_rekey();
+    tokio::spawn(async move {
+        loop {
+            state.vault.rekey_wanted().await;
+            if let Err(e) = rekey(&state).await {
+                tracing::error!("re-sealing after a vault password change stopped: {e:#}");
+            }
+        }
+    });
+}
+
+async fn rekey(state: &AppState) -> anyhow::Result<()> {
+    let Some(keys) = state.vault.peek_key().filter(|keys| keys.rekeying()) else {
+        return Ok(());
+    };
+    let sealed: Vec<String> =
+        sqlx::query_scalar("SELECT id FROM media WHERE encrypted ORDER BY created_at, id")
+            .fetch_all(&state.db)
+            .await?;
+    let left = {
+        let (keys, uploads) = (keys.clone(), state.config.uploads_dir());
+        tokio::task::spawn_blocking(move || {
+            sealed
+                .into_iter()
+                // One that will not even be read is no file to re-seal; the
+                // count of failures below is for those that should have been.
+                .filter(|id| {
+                    !vault::sealed_under(keys.current(), id, &uploads.join(id)).unwrap_or(true)
+                })
+                .collect::<Vec<_>>()
+        })
+        .await?
+    };
+
+    let total = left.len() as u64;
+    let mut progress = vault::Rekey { done: 0, total };
+    state.vault.set_progress(Some(progress));
+    tracing::info!("re-sealing {total} file(s) under the new vault key");
+    let mut failed = 0;
+    for id in &left {
+        // Locked meanwhile: the rest waits for the next unlock.
+        let Some(open) = state.vault.peek_key() else {
+            return Ok(());
+        };
+        if !std::sync::Arc::ptr_eq(&open, &keys) {
+            return Ok(());
+        }
+        match rewrite(state, &keys, id, Rewrite::Rekey).await {
+            Ok(_) => state.backup.signal(),
+            // Decrypted, deleted or re-written some other way meanwhile.
+            Err(AppError::NotFound) => {}
+            Err(e) => {
+                tracing::warn!(media = %id, "could not re-seal a file: {e:?}");
+                failed += 1;
+            }
+        }
+        progress.done += 1;
+        state.vault.set_progress(Some(progress));
+    }
+    if failed > 0 {
+        anyhow::bail!("{failed} file(s) would not re-seal; the old key is kept for them");
+    }
+    state.vault.finish_rekey(&keys).await?;
+    tracing::info!("every sealed file is under the new vault key");
     Ok(())
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::io::Read;
+
     use zeroize::Zeroizing;
 
     use crate::{error::AppError, routes::media};
@@ -594,4 +697,196 @@ mod tests {
         assert!(!sealed(&w.state, inner).await.unwrap());
         plain_file(&w.state, inner, "e.txt").await.unwrap();
     }
+
+    fn password(text: &str) -> vault::Password {
+        Zeroizing::new(text.to_string())
+    }
+
+    async fn row_retired(w: &World) -> bool {
+        sqlx::query_scalar::<_, Option<Vec<u8>>>("SELECT retired_sealed FROM vault")
+            .fetch_one(&w.state.db)
+            .await
+            .unwrap()
+            .is_some()
+    }
+
+    async fn sealed_ids(state: &AppState) -> Vec<String> {
+        sqlx::query_scalar("SELECT id FROM media WHERE encrypted ORDER BY id")
+            .fetch_all(&state.db)
+            .await
+            .unwrap()
+    }
+
+    #[tokio::test]
+    async fn a_password_change_re_seals_every_file_under_a_new_key() {
+        let w = world().await;
+        w.state.vault.lock();
+        assert!(w
+            .state
+            .vault
+            .setup(password("first password"))
+            .await
+            .unwrap());
+        for name in ["a.txt", "b.txt", "c.txt"] {
+            plain_file(&w.state, w.folder, name).await.unwrap();
+        }
+        seal_node(&w.state, w.folder).await.unwrap();
+        let old_master = w.state.vault.peek_key().unwrap().current().clone();
+        let before = sealed_ids(&w.state).await;
+        assert_eq!(before.len(), 3);
+
+        let changed = w
+            .state
+            .vault
+            .change_password(password("first password"), password("second password"))
+            .await
+            .unwrap();
+        assert!(matches!(changed, vault::Unlock::Opened));
+        assert!(w.state.vault.status().await.unwrap().rekey.is_some());
+
+        // Locked before any file was re-sealed, as a restart would leave it.
+        w.state.vault.lock();
+        let old = w
+            .state
+            .vault
+            .unlock(password("first password"))
+            .await
+            .unwrap();
+        assert!(matches!(old, vault::Unlock::WrongPassword));
+        let new = w
+            .state
+            .vault
+            .unlock(password("second password"))
+            .await
+            .unwrap();
+        assert!(matches!(new, vault::Unlock::Opened));
+
+        // Every file still reads, under whichever key it is.
+        let keys = w.state.vault.peek_key().unwrap();
+        assert!(keys.rekeying());
+        let uploads = w.state.config.uploads_dir();
+        for id in &before {
+            let mut out = Vec::new();
+            keys.reader(id, &uploads.join(id))
+                .unwrap()
+                .read_to_end(&mut out)
+                .unwrap();
+            assert_eq!(out, b"secret bytes");
+        }
+
+        // A second change waits for the first to finish.
+        let again = w
+            .state
+            .vault
+            .change_password(password("second password"), password("third password"))
+            .await
+            .unwrap();
+        assert!(matches!(again, vault::Unlock::Rekeying));
+
+        rekey(&w.state).await.unwrap();
+        assert!(!row_retired(&w).await);
+        assert!(w.state.vault.status().await.unwrap().rekey.is_none());
+        assert!(!w.state.vault.peek_key().unwrap().rekeying());
+
+        let after = sealed_ids(&w.state).await;
+        assert_eq!(after.len(), 3);
+        let current = w.state.vault.peek_key().unwrap();
+        for id in &after {
+            assert!(!before.contains(id), "re-sealed under a new id");
+            let path = uploads.join(id);
+            assert!(vault::sealed_under(current.current(), id, &path).unwrap());
+            assert!(!vault::sealed_under(&old_master, id, &path).unwrap());
+            let mut out = Vec::new();
+            current
+                .reader(id, &path)
+                .unwrap()
+                .read_to_end(&mut out)
+                .unwrap();
+            assert_eq!(out, b"secret bytes");
+        }
+        // The old copies are gone from the disk and on their way off Drive.
+        for id in &before {
+            assert!(!uploads.join(id).exists());
+            let retired: i64 = sqlx::query_scalar(
+                "SELECT COUNT(*) FROM backup_retired WHERE path = 'uploads/' || ?1",
+            )
+            .bind(id)
+            .fetch_one(&w.state.db)
+            .await
+            .unwrap();
+            assert_eq!(retired, 1);
+        }
+
+        // And the next change goes ahead.
+        let third = w
+            .state
+            .vault
+            .change_password(password("second password"), password("third password"))
+            .await
+            .unwrap();
+        assert!(matches!(third, vault::Unlock::Opened));
+    }
+
+    #[tokio::test]
+    async fn a_vault_locked_halfway_carries_on_after_the_next_unlock() {
+        let w = world().await;
+        w.state.vault.lock();
+        assert!(w
+            .state
+            .vault
+            .setup(password("first password"))
+            .await
+            .unwrap());
+        for name in ["a.txt", "b.txt"] {
+            plain_file(&w.state, w.folder, name).await.unwrap();
+        }
+        seal_node(&w.state, w.folder).await.unwrap();
+        w.state
+            .vault
+            .change_password(password("first password"), password("second password"))
+            .await
+            .unwrap();
+
+        // One file by hand, then the lock: what is left is half and half.
+        let keys = w.state.vault.peek_key().unwrap();
+        let first = sealed_ids(&w.state).await.remove(0);
+        rewrite(&w.state, &keys, &first, Rewrite::Rekey)
+            .await
+            .unwrap();
+        w.state.vault.lock();
+        rekey(&w.state).await.unwrap();
+        assert!(row_retired(&w).await, "nothing happens while it is locked");
+
+        w.state
+            .vault
+            .unlock(password("second password"))
+            .await
+            .unwrap();
+        rekey(&w.state).await.unwrap();
+        assert!(!row_retired(&w).await);
+        let current = w.state.vault.peek_key().unwrap();
+        for id in sealed_ids(&w.state).await {
+            let path = w.state.config.uploads_dir().join(&id);
+            assert!(vault::sealed_under(current.current(), &id, &path).unwrap());
+        }
+    }
+
+    #[tokio::test]
+    async fn with_nothing_sealed_a_change_needs_no_re_sealing() {
+        let w = world().await;
+        w.state.vault.lock();
+        assert!(w
+            .state
+            .vault
+            .setup(password("first password"))
+            .await
+            .unwrap());
+        w.state
+            .vault
+            .change_password(password("first password"), password("second password"))
+            .await
+            .unwrap();
+        assert!(!row_retired(&w).await);
+        assert!(w.state.vault.status().await.unwrap().rekey.is_none());
+    }
 }

src/routes/vault.rs

@@ -74,6 +74,15 @@ fn answer(attempt: Attempt<'_>, outcome: Unlock) -> AppResult<()> {
         Unlock::NotConfigured => Err(AppError::BadRequest(
             "there is no vault yet — :vault sets one up".into(),
         )),
+        // The password was right; the vault is open, re-sealing goes on.
+        Unlock::Rekeying => {
+            attempt.succeeded();
+            Err(AppError::Conflict(
+                "files are still being re-sealed after the last password change — \
+                 leave the vault open until :vault says it is done"
+                    .into(),
+            ))
+        }
     }
 }
 
@@ -106,7 +115,13 @@ pub async fn change_password(
             .change_password(input.current, input.password)
             .await?,
     )?;
-    tracing::info!("vault password changed");
+    let status = state.vault.status().await?;
+    match status.rekey {
+        Some(_) => {
+            tracing::info!("vault password changed; re-sealing every file under the new key")
+        }
+        None => tracing::info!("vault password changed"),
+    }
     state.backup.signal();
-    Ok(Json(state.vault.status().await?))
+    Ok(Json(status))
 }

src/sftp/fs.rs

@@ -387,7 +387,7 @@ impl SpaceFs {
         &self,
         parent: i64,
         over_sealed: bool,
-    ) -> SftpResult<Option<Arc<vault::Key>>> {
+    ) -> SftpResult<Option<Arc<vault::Keyring>>> {
         let sealed: bool = sqlx::query_scalar("SELECT sealed FROM nodes WHERE id = ?1")
             .bind(parent)
             .fetch_optional(&self.db)
@@ -402,7 +402,7 @@ impl SpaceFs {
 
     /// The vault's key, while it is open; a refusal while it is shut. Taken
     /// without counting as a use, so a mount never holds the vault open.
-    fn vault_key(&self) -> SftpResult<Arc<vault::Key>> {
+    fn vault_key(&self) -> SftpResult<Arc<vault::Keyring>> {
         self.state
             .as_ref()
             .and_then(|state| state.vault.peek_key())
@@ -850,7 +850,7 @@ impl SpaceFs {
                     let (key, id, part) =
                         (key.clone(), old.media_id.clone(), partial.to_path_buf());
                     tokio::task::spawn_blocking(move || -> anyhow::Result<u64> {
-                        let mut plain = vault::Reader::open(&key, &id, &source)?;
+                        let mut plain = key.reader(&id, &source)?;
                         Ok(std::io::copy(
                             &mut plain,
                             &mut std::fs::File::create(&part)?,
@@ -916,7 +916,12 @@ impl SpaceFs {
                     let (key, id, plain, sealed) =
                         (key.clone(), media_id.clone(), partial.to_path_buf(), target);
                     tokio::task::spawn_blocking(move || -> anyhow::Result<()> {
-                        vault::seal_file(&key, &id, &mut std::fs::File::open(&plain)?, &sealed)?;
+                        vault::seal_file(
+                            key.current(),
+                            &id,
+                            &mut std::fs::File::open(&plain)?,
+                            &sealed,
+                        )?;
                         std::fs::remove_file(&plain)?;
                         Ok(())
                     })
@@ -1383,11 +1388,10 @@ impl russh_sftp::server::Handler for SpaceFs {
                                 .read_exact(&mut header)
                                 .await
                                 .map_err(|_| StatusCode::Failure)?;
-                            let opener = vault::Opener::new(&key, &file.media_id, &header, len)
-                                .map_err(|e| {
-                                    tracing::warn!("sftp: could not open {leaf}: {e:?}");
-                                    StatusCode::Failure
-                                })?;
+                            let opener = key.opener(&file.media_id, &header, len).map_err(|e| {
+                                tracing::warn!("sftp: could not open {leaf}: {e:?}");
+                                StatusCode::Failure
+                            })?;
                             OpenHandle::ReadSealed(Box::new(SealedRead {
                                 file: opened,
                                 opener,

src/vault.rs

@@ -8,10 +8,10 @@
 //!
 //! Keys:
 //!
-//! - a random 256-bit **master key**, made once at setup and never stored in
-//!   the clear: the `vault` row holds it sealed under a key derived from the
-//!   password with Argon2id. Changing the password re-seals the master key and
-//!   touches no file;
+//! - a random 256-bit **master key**, never stored in the clear: the `vault`
+//!   row holds it sealed under a key derived from the password with Argon2id.
+//!   Changing the password makes a new master key, and every sealed file is
+//!   then re-sealed under it in the background — see [`Keyring`];
 //! - a random 256-bit **file key** per file, sealed under the master key in
 //!   the file's own header, so no two files share a key and nonces never need
 //!   counting across files.
@@ -65,6 +65,9 @@ pub const HEADER: usize = MAGIC.len() + WRAP_NONCE + 32 + TAG + STREAM_NONCE;
 
 /// What the master key is sealed with, besides the password-derived key.
 const MASTER_AAD: &[u8] = b"narl-vault-master-key";
+/// What the master key before a password change is sealed with, besides the
+/// master key after it.
+const RETIRED_AAD: &[u8] = b"narl-vault-retired-key";
 
 /// The shortest password the vault takes. It guards everything in it, and
 /// unlike the login it cannot be reset by editing a config file.
@@ -73,7 +76,11 @@ pub const MIN_PASSWORD: usize = 10;
 /// Argon2id costs for new vaults: 64 MiB, three passes, one lane. A fraction
 /// of a second on a small server, which is the budget for an unlock. Kept per
 /// vault, so raising them later does not lock anybody out.
+#[cfg(not(test))]
 const M_COST: u32 = 64 * 1024;
+/// Tests set up and change real vaults; at full cost each would take seconds.
+#[cfg(test)]
+const M_COST: u32 = 256;
 const T_COST: u32 = 3;
 const P_COST: u32 = 1;
 
@@ -98,30 +105,37 @@ fn derive(password: &str, salt: &[u8], m: u32, t: u32, p: u32) -> Result<Key> {
 }
 
 fn seal_master(kek: &Key, master: &Key) -> Result<([u8; WRAP_NONCE], Vec<u8>)> {
+    wrap(kek, master, MASTER_AAD)
+}
+
+/// `None` is a wrong password: the tag does not verify.
+fn open_master(kek: &Key, nonce: &[u8], sealed: &[u8]) -> Option<Key> {
+    unwrap(kek, nonce, sealed, MASTER_AAD)
+}
+
+/// Seal one 32-byte key under another.
+fn wrap(kek: &Key, key: &Key, aad: &[u8]) -> Result<([u8; WRAP_NONCE], Vec<u8>)> {
     let nonce = random::<WRAP_NONCE>();
     let sealed = Aes256Gcm::new(kek.as_ref().into())
         .encrypt(
             Nonce::from_slice(&nonce),
             Payload {
-                msg: master.as_ref(),
-                aad: MASTER_AAD,
+                msg: key.as_ref(),
+                aad,
             },
         )
-        .map_err(|_| anyhow!("could not seal the master key"))?;
+        .map_err(|_| anyhow!("could not seal a key"))?;
     Ok((nonce, sealed))
 }
 
-/// `None` is a wrong password: the tag does not verify.
-fn open_master(kek: &Key, nonce: &[u8], sealed: &[u8]) -> Option<Key> {
+/// `None` when `kek` is not the key it was sealed under.
+fn unwrap(kek: &Key, nonce: &[u8], sealed: &[u8], aad: &[u8]) -> Option<Key> {
+    if nonce.len() != WRAP_NONCE {
+        return None;
+    }
     let plain = Zeroizing::new(
         Aes256Gcm::new(kek.as_ref().into())
-            .decrypt(
-                Nonce::from_slice(nonce),
-                Payload {
-                    msg: sealed,
-                    aad: MASTER_AAD,
-                },
-            )
+            .decrypt(Nonce::from_slice(nonce), Payload { msg: sealed, aad })
             .ok()?,
     );
     let mut key = Zeroizing::new([0u8; 32]);
@@ -202,6 +216,13 @@ impl Sealer {
     }
 }
 
+/// A header's wrap nonce, sealed file key and stream nonce.
+fn split_header(header: &[u8]) -> (&[u8], &[u8], &[u8]) {
+    let (wrap_nonce, rest) = header[MAGIC.len()..].split_at(WRAP_NONCE);
+    let (sealed_key, stream_nonce) = rest.split_at(32 + TAG);
+    (wrap_nonce, sealed_key, stream_nonce)
+}
+
 fn file_aad(media_id: &str) -> Vec<u8> {
     let mut aad = MAGIC.to_vec();
     aad.extend_from_slice(media_id.as_bytes());
@@ -239,21 +260,11 @@ impl Opener {
             return Err(anyhow!("sealed file is truncated"));
         }
 
-        let (wrap_nonce, rest) = header[MAGIC.len()..].split_at(WRAP_NONCE);
-        let (sealed_key, stream_nonce) = rest.split_at(32 + TAG);
-        let file_key = Zeroizing::new(
-            Aes256Gcm::new(master.as_ref().into())
-                .decrypt(
-                    Nonce::from_slice(wrap_nonce),
-                    Payload {
-                        msg: sealed_key,
-                        aad: &file_aad(media_id),
-                    },
-                )
-                .map_err(|_| {
-                    anyhow!("this file was not sealed under this vault, or not as {media_id}")
-                })?,
-        );
+        let (wrap_nonce, sealed_key, stream_nonce) = split_header(header);
+        let file_key =
+            unwrap(master, wrap_nonce, sealed_key, &file_aad(media_id)).ok_or_else(|| {
+                anyhow!("this file was not sealed under this vault, or not as {media_id}")
+            })?;
         let stream = StreamBE32::from_aead(
             Aes256Gcm::new(file_key.as_slice().into()),
             stream_nonce.into(),
@@ -304,7 +315,7 @@ impl Opener {
 }
 
 /// A sealed file read as its plaintext, for code that wants `std::io::Read`:
-/// the export's zip writer, re-sealing.
+/// the export's zip writer, re-sealing. Made by [`Keyring::reader`].
 pub struct Reader<R> {
     inner: R,
     opener: Opener,
@@ -312,24 +323,6 @@ pub struct Reader<R> {
     at: usize,
 }
 
-impl Reader<std::fs::File> {
-    pub fn open(master: &Key, media_id: &str, path: &std::path::Path) -> Result<Self> {
-        let mut file = std::fs::File::open(path)
-            .with_context(|| format!("could not read {}", path.display()))?;
-        let len = file.metadata()?.len();
-        let mut header = [0u8; HEADER];
-        file.read_exact(&mut header)
-            .context("sealed file is truncated")?;
-        let opener = Opener::new(master, media_id, &header, len)?;
-        Ok(Self {
-            inner: file,
-            opener,
-            buffer: Vec::new(),
-            at: 0,
-        })
-    }
-}
-
 impl<R: Read> Read for Reader<R> {
     fn read(&mut self, out: &mut [u8]) -> std::io::Result<usize> {
         while self.at == self.buffer.len() {
@@ -376,6 +369,116 @@ pub fn seal_file(
     Ok(size)
 }
 
+/// The keys an open vault holds: the master key everything is sealed under
+/// from now on, and — while files sealed before the last password change
+/// are still being re-sealed — the master key before it, which only reads.
+pub struct Keyring {
+    current: Key,
+    retired: Option<Key>,
+}
+
+impl Keyring {
+    pub fn new(current: Key) -> Self {
+        Self {
+            current,
+            retired: None,
+        }
+    }
+
+    /// The key to seal with.
+    pub fn current(&self) -> &Key {
+        &self.current
+    }
+
+    /// Whether files sealed before the last password change may be left.
+    pub fn rekeying(&self) -> bool {
+        self.retired.is_some()
+    }
+
+    fn masters(&self) -> impl Iterator<Item = &Key> {
+        std::iter::once(&self.current).chain(self.retired.as_ref())
+    }
+
+    /// [`Opener::new`] under whichever key the file was sealed with.
+    pub fn opener(&self, media_id: &str, header: &[u8], len: u64) -> Result<Opener> {
+        let mut first = None;
+        for master in self.masters() {
+            match Opener::new(master, media_id, header, len) {
+                Ok(opener) => return Ok(opener),
+                Err(e) => {
+                    first.get_or_insert(e);
+                }
+            }
+        }
+        Err(first.expect("a keyring holds a key"))
+    }
+
+    /// [`Reader::open`] under whichever key the file was sealed with.
+    pub fn reader(&self, media_id: &str, path: &std::path::Path) -> Result<Reader<std::fs::File>> {
+        let mut file = std::fs::File::open(path)
+            .with_context(|| format!("could not read {}", path.display()))?;
+        let len = file.metadata()?.len();
+        let mut header = [0u8; HEADER];
+        file.read_exact(&mut header)
+            .context("sealed file is truncated")?;
+        let opener = self.opener(media_id, &header, len)?;
+        Ok(Reader {
+            inner: file,
+            opener,
+            buffer: Vec::new(),
+            at: 0,
+        })
+    }
+}
+
+/// Whether the file at `path` was sealed under `master` as `media_id`. Reads
+/// the header only.
+pub fn sealed_under(master: &Key, media_id: &str, path: &std::path::Path) -> Result<bool> {
+    let mut header = [0u8; HEADER];
+    std::fs::File::open(path)?.read_exact(&mut header)?;
+    if &header[..MAGIC.len()] != MAGIC {
+        return Err(anyhow!("not a sealed file"));
+    }
+    let (wrap_nonce, sealed_key, _) = split_header(&header);
+    Ok(unwrap(master, wrap_nonce, sealed_key, &file_aad(media_id)).is_some())
+}
+
+/// Copy the sealed file `old_id` at `source` to `target` as `new_id`, its
+/// file key sealed under the keyring's current master key. Only the header
+/// changes: the records, under the file's own key, are copied as they are.
+pub fn rewrap_file(
+    keys: &Keyring,
+    old_id: &str,
+    new_id: &str,
+    source: &std::path::Path,
+    target: &std::path::Path,
+) -> Result<()> {
+    use std::io::Write;
+    let mut source = std::fs::File::open(source)?;
+    let mut header = [0u8; HEADER];
+    source
+        .read_exact(&mut header)
+        .context("sealed file is truncated")?;
+    if &header[..MAGIC.len()] != MAGIC {
+        return Err(anyhow!("not a sealed file"));
+    }
+    let (wrap_nonce, sealed_key, stream_nonce) = split_header(&header);
+    let file_key = keys
+        .masters()
+        .find_map(|master| unwrap(master, wrap_nonce, sealed_key, &file_aad(old_id)))
+        .ok_or_else(|| anyhow!("{old_id} was not sealed under this vault"))?;
+    let (wrap_nonce, sealed_key) = wrap(&keys.current, &file_key, &file_aad(new_id))?;
+
+    let mut out = std::io::BufWriter::new(std::fs::File::create(target)?);
+    out.write_all(MAGIC)?;
+    out.write_all(&wrap_nonce)?;
+    out.write_all(&sealed_key)?;
+    out.write_all(stream_nonce)?;
+    std::io::copy(&mut source, &mut out)?;
+    out.into_inner().map_err(|e| e.into_error())?.sync_all()?;
+    Ok(())
+}
+
 /// A vault password on its way to Argon2, wiped from memory once it is done.
 pub type Password = Zeroizing<String>;
 
@@ -391,13 +494,24 @@ pub struct Vault {
     db: SqlitePool,
     idle: Duration,
     open: Mutex<Option<Unlocked>>,
+    /// Wakes whatever re-seals files after a password change.
+    rekey: tokio::sync::Notify,
+    /// How far that has come, while it runs.
+    progress: Mutex<Option<Rekey>>,
 }
 
 struct Unlocked {
-    key: Arc<Key>,
+    keys: Arc<Keyring>,
     touched: Instant,
 }
 
+/// Re-sealing after a password change: files done, out of how many.
+#[derive(serde::Serialize, Clone, Copy, Default)]
+pub struct Rekey {
+    pub done: u64,
+    pub total: u64,
+}
+
 #[derive(serde::Serialize)]
 pub struct Status {
     /// Whether a vault password has been set at all.
@@ -407,6 +521,9 @@ pub struct Status {
     pub locks_in: Option<u64>,
     /// How many files are sealed: what an export needs the vault open for.
     pub sealed: i64,
+    /// Present while files sealed before the last password change are left.
+    /// `total` is 0 until they have been counted, which needs the vault open.
+    pub rekey: Option<Rekey>,
 }
 
 /// What a password check came to.
@@ -414,6 +531,8 @@ pub enum Unlock {
     Opened,
     WrongPassword,
     NotConfigured,
+    /// The last password change is still re-sealing files.
+    Rekeying,
 }
 
 impl Vault {
@@ -422,21 +541,65 @@ impl Vault {
             db,
             idle,
             open: Mutex::new(None),
+            rekey: tokio::sync::Notify::new(),
+            progress: Mutex::new(None),
         })
     }
 
+    fn put(&self, keys: Keyring) {
+        let rekeying = keys.rekeying();
+        *self.slot() = Some(Unlocked {
+            keys: Arc::new(keys),
+            touched: Instant::now(),
+        });
+        if rekeying {
+            self.rekey.notify_one();
+        }
+    }
+
+    /// Wait until there may be files to re-seal.
+    pub async fn rekey_wanted(&self) {
+        self.rekey.notified().await;
+    }
+
+    /// Ask for a look at whether files are left to re-seal: at startup, when
+    /// the vault may have been changed while nothing was watching.
+    pub fn want_rekey(&self) {
+        self.rekey.notify_one();
+    }
+
+    pub fn set_progress(&self, progress: Option<Rekey>) {
+        *self.progress.lock().unwrap_or_else(|e| e.into_inner()) = progress;
+    }
+
+    /// Every file is under the current master key: forget the one before it,
+    /// on disk and in memory. `keys` is the keyring that did the work; a
+    /// vault that has since been locked, or changed again, is left alone.
+    pub async fn finish_rekey(&self, keys: &Arc<Keyring>) -> Result<()> {
+        sqlx::query("UPDATE vault SET retired_nonce = NULL, retired_sealed = NULL WHERE id = 1")
+            .execute(&self.db)
+            .await?;
+        let mut slot = self.slot();
+        if let Some(open) = slot.as_mut().filter(|open| Arc::ptr_eq(&open.keys, keys)) {
+            open.keys = Arc::new(Keyring::new(keys.current.clone()));
+        }
+        drop(slot);
+        self.set_progress(None);
+        Ok(())
+    }
+
     fn slot(&self) -> std::sync::MutexGuard<'_, Option<Unlocked>> {
         self.open.lock().unwrap_or_else(|e| e.into_inner())
     }
 
-    /// The master key, if the vault is open — and keep it open a while longer.
+    /// The keys, if the vault is open — and keep it open a while longer.
     /// A vault left alone past the idle time closes on the next look.
-    pub fn key(&self) -> Option<Arc<Key>> {
+    pub fn key(&self) -> Option<Arc<Keyring>> {
         let mut slot = self.slot();
         match slot.as_mut() {
             Some(open) if open.touched.elapsed() < self.idle => {
                 open.touched = Instant::now();
-                Some(open.key.clone())
+                Some(open.keys.clone())
             }
             Some(_) => {
                 *slot = None;
@@ -457,11 +620,11 @@ impl Vault {
     /// The key while the vault is open, without counting as a use: for what
     /// is not the owner at the browser — a mount — which may use the vault
     /// while it is open but must not keep it so.
-    pub fn peek_key(&self) -> Option<Arc<Key>> {
+    pub fn peek_key(&self) -> Option<Arc<Keyring>> {
         self.slot()
             .as_ref()
             .filter(|open| open.touched.elapsed() < self.idle)
-            .map(|open| open.key.clone())
+            .map(|open| open.keys.clone())
     }
 
     pub fn lock(&self) {
@@ -472,10 +635,7 @@ impl Vault {
     /// vault allows.
     #[cfg(test)]
     pub fn open_with(&self, key: Key) {
-        *self.slot() = Some(Unlocked {
-            key: Arc::new(key),
-            touched: Instant::now(),
-        });
+        self.put(Keyring::new(key));
     }
 
     /// Drop the key once it has gone unused past the idle time. Without this
@@ -508,7 +668,11 @@ impl Vault {
     }
 
     pub async fn status(&self) -> Result<Status> {
-        let configured = self.row().await?.is_some();
+        let row = self.row().await?;
+        let configured = row.is_some();
+        let rekeying =
+            row.is_some_and(|row| row.get::<Option<Vec<u8>>, _>("retired_sealed").is_some());
+        let progress = *self.progress.lock().unwrap_or_else(|e| e.into_inner());
         let sealed: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM media WHERE encrypted")
             .fetch_one(&self.db)
             .await?;
@@ -523,12 +687,14 @@ impl Vault {
             unlocked: remaining.is_some(),
             locks_in: remaining.map(|left| left.as_secs()),
             sealed,
+            rekey: rekeying.then(|| progress.unwrap_or_default()),
         })
     }
 
     async fn row(&self) -> Result<Option<sqlx::sqlite::SqliteRow>> {
         Ok(sqlx::query(
-            "SELECT salt, m_cost, t_cost, p_cost, nonce, sealed FROM vault WHERE id = 1",
+            "SELECT salt, m_cost, t_cost, p_cost, nonce, sealed, retired_nonce, retired_sealed
+             FROM vault WHERE id = 1",
         )
         .fetch_optional(&self.db)
         .await?)
@@ -567,15 +733,12 @@ impl Vault {
             return Ok(false);
         }
 
-        *self.slot() = Some(Unlocked {
-            key: Arc::new(master),
-            touched: Instant::now(),
-        });
+        self.put(Keyring::new(master));
         Ok(true)
     }
 
-    /// The master key the password stands for, if it is the right one.
-    async fn check(&self, password: Password) -> Result<Option<Option<Key>>> {
+    /// The keys the password stands for, if it is the right one.
+    async fn check(&self, password: Password) -> Result<Option<Option<Keyring>>> {
         let Some(row) = self.row().await? else {
             return Ok(None);
         };
@@ -583,45 +746,77 @@ impl Vault {
         let (m, t, p): (i64, i64, i64) = (row.get("m_cost"), row.get("t_cost"), row.get("p_cost"));
         let nonce: Vec<u8> = row.get("nonce");
         let sealed: Vec<u8> = row.get("sealed");
-        let key = tokio::task::spawn_blocking(move || -> Result<Option<Key>> {
+        let retired: Option<(Vec<u8>, Vec<u8>)> = row
+            .get::<Option<Vec<u8>>, _>("retired_nonce")
+            .zip(row.get::<Option<Vec<u8>>, _>("retired_sealed"));
+        let keys = tokio::task::spawn_blocking(move || -> Result<Option<Keyring>> {
             let kek = derive(&password, &salt, m as u32, t as u32, p as u32)?;
-            Ok(open_master(&kek, &nonce, &sealed))
+            let Some(current) = open_master(&kek, &nonce, &sealed) else {
+                return Ok(None);
+            };
+            let retired = match retired {
+                None => None,
+                Some((nonce, sealed)) => Some(
+                    unwrap(&current, &nonce, &sealed, RETIRED_AAD)
+                        .ok_or_else(|| anyhow!("the vault's previous key does not open"))?,
+                ),
+            };
+            Ok(Some(Keyring { current, retired }))
         })
         .await??;
-        Ok(Some(key))
+        Ok(Some(keys))
     }
 
     pub async fn unlock(&self, password: Password) -> Result<Unlock> {
         Ok(match self.check(password).await? {
             None => Unlock::NotConfigured,
             Some(None) => Unlock::WrongPassword,
-            Some(Some(key)) => {
-                *self.slot() = Some(Unlocked {
-                    key: Arc::new(key),
-                    touched: Instant::now(),
-                });
+            Some(Some(keys)) => {
+                self.put(keys);
                 Unlock::Opened
             }
         })
     }
 
-    /// Re-seal the master key under a new password. No file changes: they are
-    /// sealed under the master key, which stays what it was.
+    /// A new password, and a new master key with it. The old master key is
+    /// kept, sealed under the new one, only until every file has been
+    /// re-sealed; the old password opens nothing from the moment this
+    /// returns. Refused while the last change is still re-sealing, so there
+    /// are never more than two master keys to try.
     pub async fn change_password(&self, current: Password, new: Password) -> Result<Unlock> {
-        let master = match self.check(current).await? {
+        let old = match self.check(current).await? {
             None => return Ok(Unlock::NotConfigured),
             Some(None) => return Ok(Unlock::WrongPassword),
-            Some(Some(key)) => key,
+            Some(Some(keys)) if keys.rekeying() => {
+                self.put(keys);
+                return Ok(Unlock::Rekeying);
+            }
+            Some(Some(keys)) => keys.current,
         };
+        let sealed_files: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM media WHERE encrypted")
+            .fetch_one(&self.db)
+            .await?;
         let salt = random::<16>();
-        let (nonce, sealed, master) = tokio::task::spawn_blocking(move || -> Result<_> {
+        let (nonce, sealed, retired, keys) = tokio::task::spawn_blocking(move || -> Result<_> {
+            let master: Key = Zeroizing::new(random::<32>());
             let kek = derive(&new, &salt, M_COST, T_COST, P_COST)?;
             let (nonce, sealed) = seal_master(&kek, &master)?;
-            Ok((nonce, sealed, master))
+            // Nothing sealed, nothing to carry over.
+            let retired = match sealed_files {
+                0 => None,
+                _ => Some(wrap(&master, &old, RETIRED_AAD)?),
+            };
+            let keys = Keyring {
+                current: master,
+                retired: retired.is_some().then_some(old),
+            };
+            Ok((nonce, sealed, retired, keys))
         })
         .await??;
+        let (retired_nonce, retired_sealed) = retired.unzip();
         sqlx::query(
-            "UPDATE vault SET salt = ?1, m_cost = ?2, t_cost = ?3, p_cost = ?4, nonce = ?5, sealed = ?6
+            "UPDATE vault SET salt = ?1, m_cost = ?2, t_cost = ?3, p_cost = ?4, nonce = ?5, sealed = ?6,
+                              retired_nonce = ?7, retired_sealed = ?8
              WHERE id = 1",
         )
         .bind(salt.as_slice())
@@ -630,12 +825,12 @@ impl Vault {
         .bind(P_COST as i64)
         .bind(nonce.as_slice())
         .bind(sealed)
+        .bind(retired_nonce.as_ref().map(|nonce| nonce.as_slice()))
+        .bind(retired_sealed)
         .execute(&self.db)
         .await?;
-        *self.slot() = Some(Unlocked {
-            key: Arc::new(master),
-            touched: Instant::now(),
-        });
+        self.set_progress(None);
+        self.put(keys);
         Ok(Unlock::Opened)
     }
 }
@@ -646,7 +841,7 @@ mod tests {
 
     use zeroize::Zeroizing;
 
-    use super::{derive, open_master, seal_master, Opener, Reader, Sealer, CHUNK, HEADER, TAG};
+    use super::{derive, open_master, seal_master, Opener, Sealer, CHUNK, HEADER, TAG};
 
     fn key(byte: u8) -> super::Key {
         Zeroizing::new([byte; 32])
@@ -683,7 +878,7 @@ mod tests {
         let db = sqlx::SqlitePool::connect("sqlite::memory:").await.unwrap();
         let vault = super::Vault::new(db, std::time::Duration::from_millis(20));
         *vault.slot() = Some(super::Unlocked {
-            key: std::sync::Arc::new(key(1)),
+            keys: std::sync::Arc::new(super::Keyring::new(key(1))),
             touched: std::time::Instant::now(),
         });
         vault.expire();
@@ -701,7 +896,7 @@ mod tests {
         let vault = super::Vault::new(db, std::time::Duration::from_millis(40));
         let started = std::time::Instant::now();
         *vault.slot() = Some(super::Unlocked {
-            key: std::sync::Arc::new(key(1)),
+            keys: std::sync::Arc::new(super::Keyring::new(key(1))),
             touched: started,
         });
         assert!(vault.peek_key().is_some());
@@ -766,7 +961,8 @@ mod tests {
         let path = dir.path().join("x");
         std::fs::write(&path, seal(&master, "x", &plain, CHUNK)).expect("write");
         let mut out = Vec::new();
-        Reader::open(&master, "x", &path)
+        super::Keyring::new(master)
+            .reader("x", &path)
             .expect("reader")
             .read_to_end(&mut out)
             .expect("read");
@@ -811,4 +1007,37 @@ mod tests {
         let wrong = derive("correct horse!", b"saltsaltsaltsalt", 256, 1, 1).expect("derive");
         assert!(open_master(&wrong, &nonce, &sealed).is_none());
     }
+
+    #[test]
+    fn a_rewrapped_file_opens_under_the_new_key_only() {
+        let (old, new) = (key(1), key(2));
+        let plain: Vec<u8> = (0..(2 * CHUNK + 9)).map(|i| (i % 253) as u8).collect();
+        let dir = tempfile::tempdir().expect("tempdir");
+        let (source, target) = (dir.path().join("a"), dir.path().join("b"));
+        std::fs::write(&source, seal(&old, "a", &plain, CHUNK)).expect("write");
+
+        let keys = super::Keyring {
+            current: new.clone(),
+            retired: Some(old.clone()),
+        };
+        // Both are readable while the change is under way.
+        let mut out = Vec::new();
+        keys.reader("a", &source)
+            .unwrap()
+            .read_to_end(&mut out)
+            .unwrap();
+        assert_eq!(out, plain);
+
+        super::rewrap_file(&keys, "a", "b", &source, &target).unwrap();
+        assert!(super::sealed_under(&new, "b", &target).unwrap());
+        assert!(!super::sealed_under(&old, "b", &target).unwrap());
+        let mut out = Vec::new();
+        super::Keyring::new(new)
+            .reader("b", &target)
+            .unwrap()
+            .read_to_end(&mut out)
+            .unwrap();
+        assert_eq!(out, plain);
+        assert!(super::Keyring::new(old).reader("b", &target).is_err());
+    }
 }

web/src/lib/api.ts

@@ -199,6 +199,11 @@ export interface VaultStatus {
   locks_in: number | null
   /** How many files are sealed: what an export needs the vault open for. */
   sealed: number
+  /**
+   * Present while files sealed before the last password change are still
+   * being re-sealed under the new key; `total` is 0 until counted.
+   */
+  rekey: { done: number; total: number } | null
 }
 
 /** The Proton Drive mirror, as `/api/backup` reports it. */

web/src/lib/commands.ts

@@ -889,7 +889,14 @@ export const commands: CommandSpec[] = [
         const vault = workspace.vault
         if (vault?.configured) {
           const left = vault.locks_in ? ` · locks in ${Math.ceil(vault.locks_in / 60)}m unless used` : ''
-          return workspace.say(vault.unlocked ? `vault open${left} — :lock closes it` : 'vault locked — :unlock opens it')
+          const rekey = vault.rekey
+            ? vault.unlocked
+              ? ` · re-sealing after the password change, ${vault.rekey.total ? `${vault.rekey.done}/${vault.rekey.total}` : 'counting'}`
+              : ' · re-sealing after the password change waits for :unlock'
+            : ''
+          return workspace.say(
+            vault.unlocked ? `vault open${left}${rekey} — :lock closes it` : `vault locked${rekey} — :unlock opens it`,
+          )
         }
         const password = await workspace.askSecret('new vault password, 10+ characters — it cannot be recovered')
         if (password === null) return
@@ -925,7 +932,7 @@ export const commands: CommandSpec[] = [
   {
     name: 'passwd',
     group: 'vault',
-    help: "change the vault's password — no file is rewritten",
+    help: "change the vault's password — every sealed file is then re-sealed under a new key, while the vault is open",
     run: () =>
       workspace.guard(async () => {
         const current = await workspace.askSecret('current vault password')
@@ -936,7 +943,11 @@ export const commands: CommandSpec[] = [
         if (again === null) return
         if (again !== password) return workspace.say('the two passwords differ — nothing was changed', 'error')
         workspace.vault = await api.changeVaultPassword(current, password)
-        workspace.say('vault password changed')
+        workspace.say(
+          workspace.vault.rekey
+            ? `vault password changed — re-sealing ${workspace.vault.sealed} file(s) under the new key; leave the vault open, :vault shows how far`
+            : 'vault password changed',
+        )
       }),
   },
   {