feat: encrypt notification tokens

src/push.rs

@@ -1,10 +1,16 @@
 use std::sync::atomic::Ordering;
 use std::sync::Arc;
 
-use anyhow::Result;
+use anyhow::{Context as _, Result};
+use base64::Engine as _;
+use pgp::crypto::aead::AeadAlgorithm;
+use pgp::crypto::sym::SymmetricKeyAlgorithm;
+use pgp::ser::Serialize;
+use rand::thread_rng;
 use tokio::sync::RwLock;
 
 use crate::context::Context;
+use crate::key::DcKey;
 
 /// Manages subscription to Apple Push Notification services.
 ///
@@ -24,20 +30,85 @@ pub struct PushSubscriber {
     inner: Arc<RwLock<PushSubscriberState>>,
 }
 
+/// The key was generated with
+/// `rsop generate-key --profile rfc9580`
+/// and public key was extracted with `rsop extract-cert`.
+const NOTIFIERS_PUBLIC_KEY: &str = "-----BEGIN PGP PUBLIC KEY BLOCK-----
+
+xioGZ03cdhsAAAAg6PasQQylEuWAp9N5PXN93rqjZdqOqN3s9RJEU/K8FZzCsAYf
+GwoAAABBBQJnTdx2AhsDAh4JCAsJCAcKDQwLBRUKCQgLAhYCIiEGiJJktnCmEtXa
+qsSIGRJtupMnxycz/yT0xZK9ez+YkmIAAAAAUfgg/sg0sR2mytzADFBpNAaY0Hyu
+aru8ics3eUkeNn2ziL4ZsIMx+4mcM5POvD0PG9LtH8Rz/y9iItD0c2aoRBab7iri
+/gDm6aQuj3xXgtAiXdaN9s+QPxR9gY/zG1t9iXgBzioGZ03cdhkAAAAgwJ0wQFsk
+MGH4jklfK1fFhYoQZMjEFCRBIk+r1S+WaSDClQYYGwgAAAAsBQJnTdx2AhsMIiEG
+iJJktnCmEtXaqsSIGRJtupMnxycz/yT0xZK9ez+YkmIAAAAKCRCIkmS2cKYS1WdP
+EFerccH2BoIPNbrxi6hwvxxy7G1mHg//ofD90fqmeY9xTfKMYl16bqQh4R1PiYd5
+LMc5VqgXHgioqTYKbltlOtWC+HDt/PrymQsN4q/aEmsM
+=5jvt
+-----END PGP PUBLIC KEY BLOCK-----";
+
+/// Pads the token with spaces.
+///
+/// This makes it impossible to tell
+/// if the user is an Apple user with shorter tokens
+/// or FCM user with longer tokens by the length of ciphertext.
+fn pad_device_token(s: &str) -> String {
+    // 512 is larger than any token, tokens seen so far have not been larger than 200 bytes.
+    let expected_len: usize = 512;
+    let payload_len = s.len();
+    let padding_len = expected_len.saturating_sub(payload_len);
+    let padding = " ".repeat(padding_len);
+    let res = format!("{s}{padding}");
+    debug_assert_eq!(res.len(), expected_len);
+    res
+}
+
+/// Encrypts device token with OpenPGP.
+///
+/// The result is base64-encoded and not ASCII armored to avoid dealing with newlines.
+pub(crate) fn encrypt_device_token(device_token: &str) -> Result<String> {
+    let public_key = pgp::composed::SignedPublicKey::from_asc(NOTIFIERS_PUBLIC_KEY)?.0;
+    let encryption_subkey = public_key
+        .public_subkeys
+        .first()
+        .context("No encryption subkey found")?;
+    let padded_device_token = pad_device_token(device_token);
+    let literal_message = pgp::composed::Message::new_literal("", &padded_device_token);
+    let mut rng = thread_rng();
+    let chunk_size = 8;
+
+    let encrypted_message = literal_message.encrypt_to_keys_seipdv2(
+        &mut rng,
+        SymmetricKeyAlgorithm::AES128,
+        AeadAlgorithm::Ocb,
+        chunk_size,
+        &[&encryption_subkey],
+    )?;
+    let encoded_message = encrypted_message.to_bytes()?;
+    Ok(format!(
+        "openpgp:{}",
+        base64::engine::general_purpose::STANDARD.encode(encoded_message)
+    ))
+}
+
 impl PushSubscriber {
     /// Creates new push notification subscriber.
     pub(crate) fn new() -> Self {
         Default::default()
     }
 
-    /// Sets device token for Apple Push Notification service.
+    /// Sets device token for Apple Push Notification service
+    /// or Firebase Cloud Messaging.
     pub(crate) async fn set_device_token(&self, token: &str) {
         self.inner.write().await.device_token = Some(token.to_string());
     }
 
     /// Retrieves device token.
     ///
+    /// The token is encrypted with OpenPGP.
+    ///
     /// Token may be not available if application is not running on Apple platform,
+    /// does not have Google Play services,
     /// failed to register for remote notifications or is in the process of registering.
     ///
     /// IMAP loop should periodically check if device token is available
@@ -121,3 +192,37 @@ impl Context {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_set_device_token() {
+        let push_subscriber = PushSubscriber::new();
+        assert_eq!(push_subscriber.device_token().await, None);
+
+        push_subscriber.set_device_token("some-token").await;
+        let device_token = push_subscriber.device_token().await.unwrap();
+        assert_eq!(device_token, "some-token");
+    }
+
+    #[test]
+    fn test_pad_device_token() {
+        let apple_token = "0155b93b7eb867a0d8b7328b978bb15bf22f70867e39e168d03f199af9496894";
+        assert_eq!(pad_device_token(apple_token).trim(), apple_token);
+    }
+
+    #[test]
+    fn test_encrypt_device_token() {
+        let fcm_token = encrypt_device_token("fcm-chat.delta:c67DVcpVQN2rJHiSszKNDW:APA91bErcJV2b8qG0IT4aiuCqw6Al0_SbydSuz3V0CHBR1X7Fp8YzyvlpxNZIOGYVDFKejZGE1YiGSaqxmkr9ds0DuALmZNDwqIhuZWGKKrs3r7DTSkQ9MQ").unwrap();
+        let fcm_beta_token = encrypt_device_token("fcm-chat.delta.beta:chu-GhZCTLyzq1XseJp3na:APA91bFlsfDawdszWTyOLbxBy7KeRCrYM-SBFqutebF5ix0EZKMuCFUT_Y7R7Ex_eTQG_LbOu3Ky_z5UlTMJtI7ufpIp5wEvsFmVzQcOo3YhrUpbiSVGIlk").unwrap();
+        let apple_token = encrypt_device_token(
+            "0155b93b7eb867a0d8b7328b978bb15bf22f70867e39e168d03f199af9496894",
+        )
+        .unwrap();
+
+        assert_eq!(fcm_token.len(), fcm_beta_token.len());
+        assert_eq!(apple_token.len(), fcm_token.len());
+    }
+}