diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f3e82e..e44b0cf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased][]
 
 - Add `ManageExtension`: Factory reset the entire device or the state of a given client ([#11][])
+- `ChunkedExtension`: Add `AppendFile` and `PartialReadFile` syscalls.
 
 [#11]: https://github.com/trussed-dev/trussed-staging/pull/11
 
diff --git a/src/streaming/mod.rs b/src/streaming/mod.rs
index d368b7d..f8277e7 100644
--- a/src/streaming/mod.rs
+++ b/src/streaming/mod.rs
@@ -4,6 +4,7 @@
 mod store;
 use store::OpenSeekFrom;
 
+#[cfg(feature = "encrypted-chunked")]
 pub mod utils;
 
 #[cfg(feature = "encrypted-chunked")]
@@ -85,6 +86,8 @@ pub enum ChunkedRequest {
     ReadChunk(request::ReadChunk),
     WriteChunk(request::WriteChunk),
     AbortChunkedWrite(request::AbortChunkedWrite),
+    PartialReadFile(request::PartialReadFile),
+    AppendFile(request::AppendFile),
 }
 
 #[derive(Debug, Deserialize, Serialize)]
@@ -99,6 +102,8 @@ pub enum ChunkedReply {
     StartEncryptedChunkedRead(reply::StartEncryptedChunkedRead),
     WriteChunk(reply::WriteChunk),
     AbortChunkedWrite(reply::AbortChunkedWrite),
+    PartialReadFile(reply::PartialReadFile),
+    AppendFile(reply::AppendFile),
 }
 
 mod request {
@@ -265,6 +270,53 @@ mod request {
             Self::AbortChunkedWrite(request)
         }
     }
+
+    #[derive(Debug, PartialEq, Eq, Deserialize, Serialize)]
+    pub struct PartialReadFile {
+        pub location: Location,
+        pub path: PathBuf,
+        pub offset: usize,
+        pub length: usize,
+    }
+
+    impl TryFrom<ChunkedRequest> for PartialReadFile {
+        type Error = Error;
+        fn try_from(request: ChunkedRequest) -> Result<Self, Self::Error> {
+            match request {
+                ChunkedRequest::PartialReadFile(request) => Ok(request),
+                _ => Err(Error::InternalError),
+            }
+        }
+    }
+
+    impl From<PartialReadFile> for ChunkedRequest {
+        fn from(request: PartialReadFile) -> Self {
+            Self::PartialReadFile(request)
+        }
+    }
+
+    #[derive(Debug, PartialEq, Eq, Deserialize, Serialize)]
+    pub struct AppendFile {
+        pub location: Location,
+        pub path: PathBuf,
+        pub data: Message,
+    }
+
+    impl TryFrom<ChunkedRequest> for AppendFile {
+        type Error = Error;
+        fn try_from(request: ChunkedRequest) -> Result<Self, Self::Error> {
+            match request {
+                ChunkedRequest::AppendFile(request) => Ok(request),
+                _ => Err(Error::InternalError),
+            }
+        }
+    }
+
+    impl From<AppendFile> for ChunkedRequest {
+        fn from(request: AppendFile) -> Self {
+            Self::AppendFile(request)
+        }
+    }
 }
 
 mod reply {
@@ -419,6 +471,49 @@ mod reply {
             Self::AbortChunkedWrite(reply)
         }
     }
+
+    #[derive(Debug, PartialEq, Eq, Deserialize, Serialize)]
+    pub struct PartialReadFile {
+        pub data: Message,
+        pub file_length: usize,
+    }
+
+    impl TryFrom<ChunkedReply> for PartialReadFile {
+        type Error = Error;
+        fn try_from(reply: ChunkedReply) -> Result<Self, Self::Error> {
+            match reply {
+                ChunkedReply::PartialReadFile(reply) => Ok(reply),
+                _ => Err(Error::InternalError),
+            }
+        }
+    }
+
+    impl From<PartialReadFile> for ChunkedReply {
+        fn from(reply: PartialReadFile) -> Self {
+            Self::PartialReadFile(reply)
+        }
+    }
+
+    #[derive(Debug, PartialEq, Eq, Deserialize, Serialize)]
+    pub struct AppendFile {
+        pub file_length: usize,
+    }
+
+    impl TryFrom<ChunkedReply> for AppendFile {
+        type Error = Error;
+        fn try_from(reply: ChunkedReply) -> Result<Self, Self::Error> {
+            match reply {
+                ChunkedReply::AppendFile(reply) => Ok(reply),
+                _ => Err(Error::InternalError),
+            }
+        }
+    }
+
+    impl From<AppendFile> for ChunkedReply {
+        fn from(reply: AppendFile) -> Self {
+            Self::AppendFile(reply)
+        }
+    }
 }
 
 impl ExtensionImpl<ChunkedExtension> for super::StagingBackend {
@@ -502,6 +597,27 @@ impl ExtensionImpl<ChunkedExtension> for super::StagingBackend {
                 store::start_chunked_write(store, client_id, &request.path, request.location, &[])?;
                 Ok(reply::StartChunkedWrite {}.into())
             }
+            ChunkedRequest::PartialReadFile(request) => {
+                let (data, file_length) = store::partial_read_file(
+                    store,
+                    client_id,
+                    &request.path,
+                    request.location,
+                    request.offset,
+                    request.length,
+                )?;
+                Ok(reply::PartialReadFile { data, file_length }.into())
+            }
+            ChunkedRequest::AppendFile(request) => {
+                let file_length = store::append_file(
+                    store,
+                    client_id,
+                    &request.path,
+                    request.location,
+                    &request.data,
+                )?;
+                Ok(reply::AppendFile { file_length }.into())
+            }
             #[cfg(feature = "encrypted-chunked")]
             ChunkedRequest::StartEncryptedChunkedWrite(request) => {
                 clear_chunked_state(store, client_id, backend_ctx)?;
@@ -834,6 +950,40 @@ pub trait ChunkedClient: ExtensionClient<ChunkedExtension> + FilesystemClient {
     fn read_file_chunk(&mut self) -> ChunkedResult<'_, reply::ReadChunk, Self> {
         self.extension(request::ReadChunk {})
     }
+
+    /// Partially read a file from a given offset, returning a chunk of the given length and the
+    /// total file size.
+    ///
+    /// If the length is greater than [`trussed::config::MAX_MESSAGE_LENGTH`][] or if the offset is
+    /// greater than the file size, an error is returned.
+    fn partial_read_file(
+        &mut self,
+        location: Location,
+        path: PathBuf,
+        offset: usize,
+        length: usize,
+    ) -> ChunkedResult<'_, reply::PartialReadFile, Self> {
+        self.extension(request::PartialReadFile {
+            location,
+            path,
+            offset,
+            length,
+        })
+    }
+
+    /// Append data to an existing file and return the size of the file after the write.
+    fn append_file(
+        &mut self,
+        location: Location,
+        path: PathBuf,
+        data: Message,
+    ) -> ChunkedResult<'_, reply::AppendFile, Self> {
+        self.extension(request::AppendFile {
+            location,
+            path,
+            data,
+        })
+    }
 }
 
 impl<C: ExtensionClient<ChunkedExtension> + FilesystemClient> ChunkedClient for C {}
diff --git a/src/streaming/store.rs b/src/streaming/store.rs
index 38d101b..3d57c2b 100644
--- a/src/streaming/store.rs
+++ b/src/streaming/store.rs
@@ -2,11 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 or MIT
 
 use littlefs2::driver::Storage as LfsStorage;
-use littlefs2::fs::{File, Filesystem};
+use littlefs2::fs::{File, Filesystem, OpenOptions};
 use littlefs2::io::{SeekFrom, Write};
 
 use trussed::store::{create_directories, Store};
-use trussed::types::{Bytes, Location, Path, PathBuf};
+use trussed::types::{Bytes, Location, Message, Path, PathBuf};
 use trussed::Error;
 
 use serde::{Deserialize, Serialize};
@@ -33,9 +33,13 @@ pub fn fs_read_chunk<Storage: LfsStorage, const N: usize>(
     fs: &Filesystem<Storage>,
     path: &Path,
     pos: OpenSeekFrom,
+    length: usize,
 ) -> Result<(Bytes<N>, usize), Error> {
     let mut contents = Bytes::default();
-    contents.resize_default(contents.capacity()).unwrap();
+    if length > contents.capacity() {
+        return Err(Error::FilesystemReadFailure);
+    }
+    contents.resize_default(length).unwrap();
     let file_len = File::open_and_then(fs, path, |file| {
         file.seek(pos.into())?;
         let read_n = file.read(&mut contents)?;
@@ -45,6 +49,7 @@ pub fn fs_read_chunk<Storage: LfsStorage, const N: usize>(
     .map_err(|_| Error::FilesystemReadFailure)?;
     Ok((contents, file_len))
 }
+
 /// Reads contents from path in location of store.
 #[inline(never)]
 pub fn read_chunk<const N: usize>(
@@ -55,9 +60,9 @@ pub fn read_chunk<const N: usize>(
 ) -> Result<(Bytes<N>, usize), Error> {
     debug_now!("reading chunk {},{:?}", &path, pos);
     match location {
-        Location::Internal => fs_read_chunk(store.ifs(), path, pos),
-        Location::External => fs_read_chunk(store.efs(), path, pos),
-        Location::Volatile => fs_read_chunk(store.vfs(), path, pos),
+        Location::Internal => fs_read_chunk(store.ifs(), path, pos, N),
+        Location::External => fs_read_chunk(store.efs(), path, pos, N),
+        Location::Volatile => fs_read_chunk(store.vfs(), path, pos, N),
     }
 }
 
@@ -290,3 +295,51 @@ pub fn flush_chunks(
         &client_path,
     )
 }
+
+pub fn partial_read_file(
+    store: impl Store,
+    client_id: &Path,
+    path: &PathBuf,
+    location: Location,
+    offset: usize,
+    length: usize,
+) -> Result<(Message, usize), Error> {
+    let path = actual_path(client_id, path)?;
+    let offset = u32::try_from(offset).map_err(|_| Error::FilesystemReadFailure)?;
+    let pos = OpenSeekFrom::Start(offset);
+    match location {
+        Location::Internal => fs_read_chunk(store.ifs(), &path, pos, length),
+        Location::External => fs_read_chunk(store.efs(), &path, pos, length),
+        Location::Volatile => fs_read_chunk(store.vfs(), &path, pos, length),
+    }
+}
+
+fn fs_append_file<Storage: LfsStorage>(
+    fs: &Filesystem<Storage>,
+    path: &Path,
+    data: &[u8],
+) -> Result<usize, Error> {
+    OpenOptions::new()
+        .write(true)
+        .append(true)
+        .open_and_then(fs, path, |file| {
+            file.write_all(data)?;
+            file.len()
+        })
+        .map_err(|_| Error::FilesystemWriteFailure)
+}
+
+pub fn append_file(
+    store: impl Store,
+    client_id: &Path,
+    path: &PathBuf,
+    location: Location,
+    data: &[u8],
+) -> Result<usize, Error> {
+    let path = actual_path(client_id, path)?;
+    match location {
+        Location::Internal => fs_append_file(store.ifs(), &path, data),
+        Location::External => fs_append_file(store.efs(), &path, data),
+        Location::Volatile => fs_append_file(store.vfs(), &path, data),
+    }
+}