Add S3 encryption

crates/pile-value/src/source/s3.rs

@@ -23,6 +23,7 @@ pub struct S3DataSource {
 	pub prefix: Option<SmartString<LazyCompact>>,
 	pub client: Arc<aws_sdk_s3::Client>,
 	pub pattern: GroupPattern,
+	pub encryption_key: Option<[u8; 32]>,
 	pub index: OnceLock<HashMap<SmartString<LazyCompact>, Item>>,
 }
 
@@ -35,6 +36,7 @@ impl S3DataSource {
 		region: String,
 		credentials: &S3Credentials,
 		pattern: GroupPattern,
+		encryption_key: Option<[u8; 32]>,
 	) -> Result<Arc<Self>, std::io::Error> {
 		let client = {
 			let creds = Credentials::new(
@@ -63,6 +65,7 @@ impl S3DataSource {
 			prefix: prefix.map(|x| x.into()),
 			client: Arc::new(client),
 			pattern,
+			encryption_key,
 			index: OnceLock::new(),
 		});
 
@@ -94,8 +97,15 @@ impl S3DataSource {
 
 			for obj in resp.contents() {
 				let Some(full_key) = obj.key() else { continue };
-				let key = strip_prefix(full_key, source.prefix.as_deref());
-				all_keys.insert(key.into());
+				let raw_key = strip_prefix(full_key, source.prefix.as_deref());
+				let key = match &source.encryption_key {
+					None => raw_key.into(),
+					Some(enc_key) => match decrypt_path(enc_key, raw_key) {
+						Some(decrypted) => decrypted.into(),
+						None => continue,
+					},
+				};
+				all_keys.insert(key);
 			}
 
 			if !is_truncated {
@@ -219,6 +229,50 @@ impl DataSource for Arc<S3DataSource> {
 	}
 }
 
+/// Derive an encryption key from a password
+pub fn string_to_key(password: &str) -> [u8; 32] {
+	blake3::derive_key("pile s3 encryption", password.as_bytes())
+}
+
+/// Encrypt a logical path to a base64 S3 key using a deterministic nonce.
+pub fn encrypt_path(enc_key: &[u8; 32], path: &str) -> String {
+	use base64::Engine;
+	use chacha20poly1305::{KeyInit, XChaCha20Poly1305, XNonce, aead::Aead};
+
+	let hash = blake3::keyed_hash(enc_key, path.as_bytes());
+	let nonce_bytes = &hash.as_bytes()[..24];
+	let nonce = XNonce::from_slice(nonce_bytes);
+	let key = chacha20poly1305::Key::from_slice(enc_key);
+	let cipher = XChaCha20Poly1305::new(key);
+	#[expect(clippy::expect_used)]
+	let ciphertext = cipher
+		.encrypt(nonce, path.as_bytes())
+		.expect("path encryption should not fail");
+
+	let mut result = nonce_bytes.to_vec();
+	result.extend_from_slice(&ciphertext);
+	base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(result)
+}
+
+/// Decrypt a base64 S3 key back to its logical path.
+fn decrypt_path(enc_key: &[u8; 32], encrypted: &str) -> Option<String> {
+	use base64::Engine;
+	use chacha20poly1305::{KeyInit, XChaCha20Poly1305, XNonce, aead::Aead};
+
+	let bytes = base64::engine::general_purpose::URL_SAFE_NO_PAD
+		.decode(encrypted)
+		.ok()?;
+	if bytes.len() < 24 + 16 {
+		return None;
+	}
+	let (nonce_bytes, ciphertext) = bytes.split_at(24);
+	let nonce = XNonce::from_slice(nonce_bytes);
+	let key = chacha20poly1305::Key::from_slice(enc_key);
+	let cipher = XChaCha20Poly1305::new(key);
+	let plaintext = cipher.decrypt(nonce, ciphertext).ok()?;
+	String::from_utf8(plaintext).ok()
+}
+
 fn strip_prefix<'a>(key: &'a str, prefix: Option<&str>) -> &'a str {
 	match prefix {
 		None => key,