chatmail-core/src/securejoin.rs

//! Verified contact protocol implementation as [specified by countermitm project](https://countermitm.readthedocs.io/en/stable/new.html#setup-contact-protocol)

use std::time::{Duration, Instant};

use anyhow::{bail, Error};
use percent_encoding::{utf8_percent_encode, AsciiSet, NON_ALPHANUMERIC};

use crate::aheader::EncryptPreference;
use crate::chat::{self, Chat, ChatId};
use crate::config::*;
use crate::constants::*;
use crate::contact::*;
use crate::context::Context;
use crate::e2ee::*;
use crate::events::EventType;
use crate::headerdef::HeaderDef;
use crate::key::{DcKey, Fingerprint, SignedPublicKey};
use crate::lot::{Lot, LotState};
use crate::message::Message;
use crate::mimeparser::*;
use crate::param::*;
use crate::peerstate::*;
use crate::qr::check_qr;
use crate::sql;
use crate::stock::StockMessage;
use crate::token;

pub const NON_ALPHANUMERIC_WITHOUT_DOT: &AsciiSet = &NON_ALPHANUMERIC.remove(b'.');

macro_rules! joiner_progress {
    ($context:tt, $contact_id:expr, $progress:expr) => {
        assert!(
            $progress >= 0 && $progress <= 1000,
            "value in range 0..1000 expected with: 0=error, 1..999=progress, 1000=success"
        );
        $context.emit_event($crate::events::EventType::SecurejoinJoinerProgress {
            contact_id: $contact_id,
            progress: $progress,
        });
    };
}

macro_rules! inviter_progress {
    ($context:tt, $contact_id:expr, $progress:expr) => {
        assert!(
            $progress >= 0 && $progress <= 1000,
            "value in range 0..1000 expected with: 0=error, 1..999=progress, 1000=success"
        );
        $context.emit_event($crate::events::EventType::SecurejoinInviterProgress {
            contact_id: $contact_id,
            progress: $progress,
        });
    };
}

macro_rules! get_qr_attr {
    ($context:tt, $attr:ident) => {
        $context
            .bob
            .read()
            .await
            .qr_scan
            .as_ref()
            .unwrap()
            .$attr
            .as_ref()
            .unwrap()
    };
}

/// State for setup-contact/secure-join protocol joiner's side.
///
/// The setup-contact protocol needs to carry state for both the inviter (Alice) and the
/// joiner/invitee (Bob).  For Alice this state is minimal and in the `tokens` table in the
/// database.  For Bob this state is only carried live on the [Context] in this struct.
#[derive(Debug, Default)]
pub(crate) struct Bob {
    /// The next message expected by the protocol.
    expects: SecureJoinStep,
    /// The QR-scanned information of the currently running protocol.
    pub qr_scan: Option<Lot>,
}

/// The next message expected by [Bob] in the setup-contact/secure-join protocol.
#[derive(Debug, PartialEq)]
enum SecureJoinStep {
    /// No setup-contact protocol running.
    NotActive,
    /// Expecting the auth-required message.
    ///
    /// This corresponds to the `vc-auth-required` or `vg-auth-required` message of step 3d.
    AuthRequired,
    /// Expecting the contact-confirm message.
    ///
    /// This corresponds to the `vc-contact-confirm` or `vg-member-added` message of step
    /// 6b.
    ContactConfirm,
}

impl Default for SecureJoinStep {
    fn default() -> Self {
        Self::NotActive
    }
}

pub async fn dc_get_securejoin_qr(context: &Context, group_chat_id: ChatId) -> Option<String> {
    /*=======================================================
    ====             Alice - the inviter side            ====
    ====   Step 1 in "Setup verified contact" protocol   ====
    =======================================================*/

    ensure_secret_key_exists(context).await.ok();

    // invitenumber will be used to allow starting the handshake,
    // auth will be used to verify the fingerprint
    let invitenumber =
        token::lookup_or_new(context, token::Namespace::InviteNumber, group_chat_id).await;
    let auth = token::lookup_or_new(context, token::Namespace::Auth, group_chat_id).await;
    let self_addr = match context.get_config(Config::ConfiguredAddr).await {
        Some(addr) => addr,
        None => {
            error!(context, "Not configured, cannot generate QR code.",);
            return None;
        }
    };

    let self_name = context
        .get_config(Config::Displayname)
        .await
        .unwrap_or_default();

    let fingerprint: Fingerprint = match get_self_fingerprint(context).await {
        Some(fp) => fp,
        None => {
            return None;
        }
    };

    let self_addr_urlencoded =
        utf8_percent_encode(&self_addr, NON_ALPHANUMERIC_WITHOUT_DOT).to_string();
    let self_name_urlencoded =
        utf8_percent_encode(&self_name, NON_ALPHANUMERIC_WITHOUT_DOT).to_string();

    let qr = if !group_chat_id.is_unset() {
        // parameters used: a=g=x=i=s=
        if let Ok(chat) = Chat::load_from_db(context, group_chat_id).await {
            let group_name = chat.get_name();
            let group_name_urlencoded =
                utf8_percent_encode(&group_name, NON_ALPHANUMERIC).to_string();

            Some(format!(
                "OPENPGP4FPR:{}#a={}&g={}&x={}&i={}&s={}",
                fingerprint.hex(),
                self_addr_urlencoded,
                &group_name_urlencoded,
                &chat.grpid,
                &invitenumber,
                &auth,
            ))
        } else {
            error!(context, "Cannot get QR-code for chat-id {}", group_chat_id,);
            return None;
        }
    } else {
        // parameters used: a=n=i=s=
        Some(format!(
            "OPENPGP4FPR:{}#a={}&n={}&i={}&s={}",
            fingerprint.hex(),
            self_addr_urlencoded,
            self_name_urlencoded,
            &invitenumber,
            &auth,
        ))
    };

    info!(context, "Generated QR code: {}", qr.as_ref().unwrap());

    qr
}

async fn get_self_fingerprint(context: &Context) -> Option<Fingerprint> {
    match SignedPublicKey::load_self(context).await {
        Ok(key) => Some(key.fingerprint()),
        Err(_) => {
            warn!(context, "get_self_fingerprint(): failed to load key");
            None
        }
    }
}

async fn cleanup(context: &Context, ongoing_allocated: bool) {
    let mut bob = context.bob.write().await;
    bob.expects = SecureJoinStep::NotActive;
    bob.qr_scan = None;
    if ongoing_allocated {
        context.free_ongoing().await;
    }
}

#[derive(Debug, thiserror::Error)]
pub enum JoinError {
    #[error("Unknown QR-code")]
    QrCode,
    #[error("Aborted by user")]
    Aborted,
    #[error("Failed to send handshake message")]
    SendMessage(#[from] SendMsgError),
    // Note that this can currently only occur if there is a bug in the QR/Lot code as this
    // is supposed to create a contact for us.
    #[error("Unknown contact (this is a bug)")]
    UnknownContact,
    // Note that this can only occur if we failed to create the chat correctly.
    #[error("No Chat found for group (this is a bug)")]
    MissingChat(#[source] sql::Error),
}

/// Take a scanned QR-code and do the setup-contact/join-group/invite handshake.
///
/// This is the start of the process for the joiner.  See the module and ffi documentation
/// for more details.
///
/// When joining a group this will start an "ongoing" process and will block until the
/// process is completed, the [ChatId] for the new group is not known any sooner.  When
/// verifying a contact this returns immediately.
pub async fn dc_join_securejoin(context: &Context, qr: &str) -> Result<ChatId, JoinError> {
    if context.alloc_ongoing().await.is_err() {
        cleanup(&context, false).await;
        return Err(JoinError::Aborted);
    }

    securejoin(context, qr).await
}

async fn securejoin(context: &Context, qr: &str) -> Result<ChatId, JoinError> {
    /*========================================================
    ====             Bob - the joiner's side             =====
    ====   Step 2 in "Setup verified contact" protocol   =====
    ========================================================*/

    info!(context, "Requesting secure-join ...",);
    ensure_secret_key_exists(context).await.ok();
    let qr_scan = check_qr(context, &qr).await;
    if qr_scan.state != LotState::QrAskVerifyContact && qr_scan.state != LotState::QrAskVerifyGroup
    {
        error!(context, "Unknown QR code.",);
        cleanup(&context, true).await;
        return Err(JoinError::QrCode);
    }
    let contact_chat_id = match chat::create_by_contact_id(context, qr_scan.id).await {
        Ok(chat_id) => chat_id,
        Err(_) => {
            error!(context, "Unknown contact.");
            cleanup(&context, true).await;
            return Err(JoinError::UnknownContact);
        }
    };
    if context.shall_stop_ongoing().await {
        cleanup(&context, true).await;
        return Err(JoinError::Aborted);
    }
    let join_vg = qr_scan.get_state() == LotState::QrAskVerifyGroup;
    {
        let mut bob = context.bob.write().await;
        bob.qr_scan = Some(qr_scan);
    }
    if fingerprint_equals_sender(
        context,
        context
            .bob
            .read()
            .await
            .qr_scan
            .as_ref()
            .unwrap()
            .fingerprint
            .as_ref()
            .unwrap(),
        contact_chat_id,
    )
    .await
    {
        // the scanned fingerprint matches Alice's key,
        // we can proceed to step 4b) directly and save two mails
        info!(context, "Taking protocol shortcut.");
        context.bob.write().await.expects = SecureJoinStep::ContactConfirm;
        joiner_progress!(
            context,
            chat_id_2_contact_id(context, contact_chat_id).await,
            400
        );
        let own_fingerprint = get_self_fingerprint(context).await;

        // Bob -> Alice
        if let Err(err) = send_handshake_msg(
            context,
            contact_chat_id,
            if join_vg {
                "vg-request-with-auth"
            } else {
                "vc-request-with-auth"
            },
            get_qr_attr!(context, auth).to_string(),
            own_fingerprint,
            if join_vg {
                get_qr_attr!(context, text2).to_string()
            } else {
                "".to_string()
            },
        )
        .await
        {
            error!(context, "failed to send handshake message: {}", err);
            cleanup(&context, true).await;
            return Err(JoinError::SendMessage(err));
        }
    } else {
        context.bob.write().await.expects = SecureJoinStep::AuthRequired;

        // Bob -> Alice
        if let Err(err) = send_handshake_msg(
            context,
            contact_chat_id,
            if join_vg { "vg-request" } else { "vc-request" },
            get_qr_attr!(context, invitenumber),
            None,
            "",
        )
        .await
        {
            error!(context, "failed to send handshake message: {}", err);
            cleanup(&context, true).await;
            return Err(JoinError::SendMessage(err));
        }
    }

    if join_vg {
        // for a group-join, wait until the secure-join is done and the group is created
        while !context.shall_stop_ongoing().await {
            async_std::task::sleep(Duration::from_millis(50)).await;
        }

        // handle_securejoin_handshake() calls Context::stop_ongoing before the group chat
        // is created (it is created after handle_securejoin_handshake() returns by
        // dc_receive_imf()).  As a hack we just wait a bit for it to appear.
        let start = Instant::now();
        let chatid = loop {
            {
                let bob = context.bob.read().await;
                let grpid = bob.qr_scan.as_ref().unwrap().text2.as_ref().unwrap();
                match chat::get_chat_id_by_grpid(context, grpid).await {
                    Ok((chatid, _is_protected, _blocked)) => break chatid,
                    Err(err) => {
                        if start.elapsed() > Duration::from_secs(7) {
                            return Err(JoinError::MissingChat(err));
                        }
                    }
                }
            }
            async_std::task::sleep(Duration::from_millis(50)).await;
        };

        cleanup(&context, true).await;
        Ok(chatid)
    } else {
        // for a one-to-one-chat, the chat is already known, return the chat-id,
        // the verification runs in background
        context.free_ongoing().await;
        Ok(contact_chat_id)
    }
}

/// Error for [send_handshake_msg].
///
/// Wrapping the [anyhow::Error] means we can "impl From" more easily on errors from this
/// function.
#[derive(Debug, thiserror::Error)]
#[error("Failed sending handshake message")]
pub struct SendMsgError(#[from] anyhow::Error);

async fn send_handshake_msg(
    context: &Context,
    contact_chat_id: ChatId,
    step: &str,
    param2: impl AsRef<str>,
    fingerprint: Option<Fingerprint>,
    grpid: impl AsRef<str>,
) -> Result<(), SendMsgError> {
    let mut msg = Message::default();
    msg.viewtype = Viewtype::Text;
    msg.text = Some(format!("Secure-Join: {}", step));
    msg.hidden = true;
    msg.param.set_cmd(SystemMessage::SecurejoinMessage);
    if step.is_empty() {
        msg.param.remove(Param::Arg);
    } else {
        msg.param.set(Param::Arg, step);
    }
    if !param2.as_ref().is_empty() {
        msg.param.set(Param::Arg2, param2);
    }
    if let Some(fp) = fingerprint {
        msg.param.set(Param::Arg3, fp.hex());
    }
    if !grpid.as_ref().is_empty() {
        msg.param.set(Param::Arg4, grpid.as_ref());
    }
    if step == "vg-request" || step == "vc-request" {
        msg.param.set_int(Param::ForcePlaintext, 1);
    } else {
        msg.param.set_int(Param::GuaranteeE2ee, 1);
    }

    chat::send_msg(context, contact_chat_id, &mut msg).await?;
    Ok(())
}

async fn chat_id_2_contact_id(context: &Context, contact_chat_id: ChatId) -> u32 {
    if let [contact_id] = chat::get_chat_contacts(context, contact_chat_id).await[..] {
        contact_id
    } else {
        0
    }
}

async fn fingerprint_equals_sender(
    context: &Context,
    fingerprint: &Fingerprint,
    contact_chat_id: ChatId,
) -> bool {
    if let [contact_id] = chat::get_chat_contacts(context, contact_chat_id).await[..] {
        if let Ok(contact) = Contact::load_from_db(context, contact_id).await {
            let peerstate = match Peerstate::from_addr(context, contact.get_addr()).await {
                Ok(peerstate) => peerstate,
                Err(err) => {
                    warn!(
                        context,
                        "Failed to sender peerstate for {}: {}",
                        contact.get_addr(),
                        err
                    );
                    return false;
                }
            };

            if let Some(peerstate) = peerstate {
                if peerstate.public_key_fingerprint.is_some()
                    && fingerprint == peerstate.public_key_fingerprint.as_ref().unwrap()
                {
                    return true;
                }
            }
        }
    }
    false
}
#[derive(Debug, thiserror::Error)]
pub(crate) enum HandshakeError {
    #[error("Can not be called with special contact ID")]
    SpecialContactId,
    #[error("Not a Secure-Join message")]
    NotSecureJoinMsg,
    #[error("Failed to look up or create chat for contact #{contact_id}")]
    NoChat {
        contact_id: u32,
        #[source]
        cause: Error,
    },
    #[error("Chat for group {group} not found")]
    ChatNotFound { group: String },
    #[error("No configured self address found")]
    NoSelfAddr,
    #[error("Failed to send message")]
    MsgSendFailed(#[from] SendMsgError),
    #[error("Failed to parse fingerprint")]
    BadFingerprint(#[from] crate::key::FingerprintError),
}

/// What to do with a Secure-Join handshake message after it was handled.
pub(crate) enum HandshakeMessage {
    /// The message has been fully handled and should be removed/delete.
    Done,
    /// The message should be ignored/hidden, but not removed/deleted.
    Ignore,
    /// The message should be further processed by incoming message handling.
    Propagate,
}

/// Handle incoming secure-join handshake.
///
/// This function will update the securejoin state in [Context::bob]
/// and also terminate the ongoing process using
/// [Context::stop_ongoing] as required by the protocol.
///
/// A message which results in [Err] will be hidden from the user but
/// not deleted, it may be a valid message for something else we are
/// not aware off.  E.g. it could be part of a handshake performed by
/// another DC app on the same account.
///
/// When handle_securejoin_handshake() is called,
/// the message is not yet filed in the database;
/// this is done by receive_imf() later on as needed.
#[allow(clippy::indexing_slicing)]
pub(crate) async fn handle_securejoin_handshake(
    context: &Context,
    mime_message: &MimeMessage,
    contact_id: u32,
) -> Result<HandshakeMessage, HandshakeError> {
    if contact_id <= DC_CONTACT_ID_LAST_SPECIAL {
        return Err(HandshakeError::SpecialContactId);
    }
    let step = mime_message
        .get(HeaderDef::SecureJoin)
        .ok_or(HandshakeError::NotSecureJoinMsg)?;

    info!(
        context,
        ">>>>>>>>>>>>>>>>>>>>>>>>> secure-join message \'{}\' received", step,
    );

    let contact_chat_id =
        match chat::create_or_lookup_by_contact_id(context, contact_id, Blocked::Not).await {
            Ok((chat_id, blocked)) => {
                if blocked != Blocked::Not {
                    chat_id.unblock(context).await;
                }
                chat_id
            }
            Err(err) => {
                return Err(HandshakeError::NoChat {
                    contact_id,
                    cause: err,
                });
            }
        };

    let join_vg = step.starts_with("vg-");

    match step.as_str() {
        "vg-request" | "vc-request" => {
            /*=======================================================
            ====             Alice - the inviter side            ====
            ====   Step 3 in "Setup verified contact" protocol   ====
            =======================================================*/

            // this message may be unencrypted (Bob, the joiner and the sender, might not have Alice's key yet)
            // it just ensures, we have Bobs key now. If we do _not_ have the key because eg. MitM has removed it,
            // send_message() will fail with the error "End-to-end-encryption unavailable unexpectedly.", so, there is no additional check needed here.
            // verify that the `Secure-Join-Invitenumber:`-header matches invitenumber written to the QR code
            let invitenumber = match mime_message.get(HeaderDef::SecureJoinInvitenumber) {
                Some(n) => n,
                None => {
                    warn!(context, "Secure-join denied (invitenumber missing)");
                    return Ok(HandshakeMessage::Ignore);
                }
            };
            if !token::exists(context, token::Namespace::InviteNumber, &invitenumber).await {
                warn!(context, "Secure-join denied (bad invitenumber).");
                return Ok(HandshakeMessage::Ignore);
            }
            info!(context, "Secure-join requested.",);

            inviter_progress!(context, contact_id, 300);

            // Alice -> Bob
            send_handshake_msg(
                context,
                contact_chat_id,
                &format!("{}-auth-required", &step[..2]),
                "",
                None,
                "",
            )
            .await?;
            Ok(HandshakeMessage::Done)
        }
        "vg-auth-required" | "vc-auth-required" => {
            /*========================================================
            ====             Bob - the joiner's side             =====
            ====   Step 4 in "Setup verified contact" protocol   =====
            ========================================================*/

            // verify that Alice's Autocrypt key and fingerprint matches the QR-code
            let cond = {
                let bob = context.bob.read().await;
                let scan = bob.qr_scan.as_ref();
                scan.is_none()
                    || bob.expects != SecureJoinStep::AuthRequired
                    || join_vg && scan.unwrap().state != LotState::QrAskVerifyGroup
            };

            if cond {
                warn!(context, "auth-required message out of sync.");
                // no error, just aborted somehow or a mail from another handshake
                return Ok(HandshakeMessage::Ignore);
            }
            let scanned_fingerprint_of_alice: Fingerprint =
                get_qr_attr!(context, fingerprint).clone();
            let auth = get_qr_attr!(context, auth).to_string();

            if !encrypted_and_signed(context, mime_message, Some(&scanned_fingerprint_of_alice)) {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    if mime_message.was_encrypted() {
                        "No valid signature."
                    } else {
                        "Not encrypted."
                    },
                )
                .await;
                context.stop_ongoing().await;
                return Ok(HandshakeMessage::Ignore);
            }
            if !fingerprint_equals_sender(context, &scanned_fingerprint_of_alice, contact_chat_id)
                .await
            {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Fingerprint mismatch on joiner-side.",
                )
                .await;
                context.stop_ongoing().await;
                return Ok(HandshakeMessage::Ignore);
            }
            info!(context, "Fingerprint verified.",);
            let own_fingerprint = get_self_fingerprint(context).await.unwrap();
            joiner_progress!(context, contact_id, 400);
            context.bob.write().await.expects = SecureJoinStep::ContactConfirm;

            // Bob -> Alice
            send_handshake_msg(
                context,
                contact_chat_id,
                &format!("{}-request-with-auth", &step[..2]),
                auth,
                Some(own_fingerprint),
                if join_vg {
                    get_qr_attr!(context, text2).to_string()
                } else {
                    "".to_string()
                },
            )
            .await?;
            Ok(HandshakeMessage::Done)
        }
        "vg-request-with-auth" | "vc-request-with-auth" => {
            /*==========================================================
            ====              Alice - the inviter side              ====
            ====   Steps 5+6 in "Setup verified contact" protocol   ====
            ====  Step 6 in "Out-of-band verified groups" protocol  ====
            ==========================================================*/

            // verify that Secure-Join-Fingerprint:-header matches the fingerprint of Bob
            let fingerprint: Fingerprint = match mime_message.get(HeaderDef::SecureJoinFingerprint)
            {
                Some(fp) => fp.parse()?,
                None => {
                    could_not_establish_secure_connection(
                        context,
                        contact_chat_id,
                        "Fingerprint not provided.",
                    )
                    .await;
                    return Ok(HandshakeMessage::Ignore);
                }
            };
            if !encrypted_and_signed(context, mime_message, Some(&fingerprint)) {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Auth not encrypted.",
                )
                .await;
                return Ok(HandshakeMessage::Ignore);
            }
            if !fingerprint_equals_sender(context, &fingerprint, contact_chat_id).await {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Fingerprint mismatch on inviter-side.",
                )
                .await;
                return Ok(HandshakeMessage::Ignore);
            }
            info!(context, "Fingerprint verified.",);
            // verify that the `Secure-Join-Auth:`-header matches the secret written to the QR code
            let auth_0 = match mime_message.get(HeaderDef::SecureJoinAuth) {
                Some(auth) => auth,
                None => {
                    could_not_establish_secure_connection(
                        context,
                        contact_chat_id,
                        "Auth not provided.",
                    )
                    .await;
                    return Ok(HandshakeMessage::Ignore);
                }
            };
            if !token::exists(context, token::Namespace::Auth, &auth_0).await {
                could_not_establish_secure_connection(context, contact_chat_id, "Auth invalid.")
                    .await;
                return Ok(HandshakeMessage::Ignore);
            }
            if mark_peer_as_verified(context, &fingerprint).await.is_err() {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Fingerprint mismatch on inviter-side.",
                )
                .await;
                return Ok(HandshakeMessage::Ignore);
            }
            Contact::scaleup_origin_by_id(context, contact_id, Origin::SecurejoinInvited).await;
            info!(context, "Auth verified.",);
            secure_connection_established(context, contact_chat_id).await;
            emit_event!(context, EventType::ContactsChanged(Some(contact_id)));
            inviter_progress!(context, contact_id, 600);
            if join_vg {
                // the vg-member-added message is special:
                // this is a normal Chat-Group-Member-Added message
                // with an additional Secure-Join header
                let field_grpid = match mime_message.get(HeaderDef::SecureJoinGroup) {
                    Some(s) => s.as_str(),
                    None => {
                        warn!(context, "Missing Secure-Join-Group header");
                        return Ok(HandshakeMessage::Ignore);
                    }
                };
                match chat::get_chat_id_by_grpid(context, field_grpid).await {
                    Ok((group_chat_id, _, _)) => {
                        if let Err(err) =
                            chat::add_contact_to_chat_ex(context, group_chat_id, contact_id, true)
                                .await
                        {
                            error!(context, "failed to add contact: {}", err);
                        }
                    }
                    Err(err) => {
                        error!(context, "Chat {} not found: {}", &field_grpid, err);
                        return Err(HandshakeError::ChatNotFound {
                            group: field_grpid.to_string(),
                        });
                    }
                }
            } else {
                // Alice -> Bob
                send_handshake_msg(
                    context,
                    contact_chat_id,
                    "vc-contact-confirm",
                    "",
                    Some(fingerprint),
                    "",
                )
                .await?;

                inviter_progress!(context, contact_id, 1000);
            }
            Ok(HandshakeMessage::Ignore) // "Done" would delete the message and break multi-device (the key from Autocrypt-header is needed)
        }
        "vg-member-added" | "vc-contact-confirm" => {
            /*=======================================================
            ====             Bob - the joiner's side             ====
            ====   Step 7 in "Setup verified contact" protocol   ====
            =======================================================*/
            let abort_retval = if join_vg {
                HandshakeMessage::Propagate
            } else {
                HandshakeMessage::Ignore
            };

            if context.bob.read().await.expects != SecureJoinStep::ContactConfirm {
                info!(context, "Message belongs to a different handshake.",);
                return Ok(abort_retval);
            }
            let cond = {
                let bob = context.bob.read().await;
                let scan = bob.qr_scan.as_ref();
                scan.is_none() || (join_vg && scan.unwrap().state != LotState::QrAskVerifyGroup)
            };
            if cond {
                warn!(
                    context,
                    "Message out of sync or belongs to a different handshake.",
                );
                return Ok(abort_retval);
            }
            let scanned_fingerprint_of_alice: Fingerprint =
                get_qr_attr!(context, fingerprint).clone();

            let vg_expect_encrypted = if join_vg {
                let group_id = get_qr_attr!(context, text2).to_string();
                // This is buggy, is_protected_group will always be
                // false since the group is created by receive_imf by
                // the very handshake message we're handling now.  But
                // only after we have returned.  It does not impact
                // the security invariants of secure-join however.
                let (_, is_protected_group, _) = chat::get_chat_id_by_grpid(context, &group_id)
                    .await
                    .unwrap_or((ChatId::new(0), false, Blocked::Not));
                // when joining a non-verified group
                // the vg-member-added message may be unencrypted
                // when not all group members have keys or prefer encryption.
                // So only expect encryption if this is a verified group
                is_protected_group
            } else {
                // setup contact is always encrypted
                true
            };
            if vg_expect_encrypted
                && !encrypted_and_signed(context, mime_message, Some(&scanned_fingerprint_of_alice))
            {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Contact confirm message not encrypted.",
                )
                .await;
                return Ok(abort_retval);
            }

            if mark_peer_as_verified(context, &scanned_fingerprint_of_alice)
                .await
                .is_err()
            {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Fingerprint mismatch on joiner-side.",
                )
                .await;
                return Ok(abort_retval);
            }
            Contact::scaleup_origin_by_id(context, contact_id, Origin::SecurejoinJoined).await;
            emit_event!(context, EventType::ContactsChanged(None));
            let cg_member_added = mime_message
                .get(HeaderDef::ChatGroupMemberAdded)
                .map(|s| s.as_str())
                .unwrap_or_else(|| "");
            if join_vg
                && !context
                    .is_self_addr(cg_member_added)
                    .await
                    .map_err(|_| HandshakeError::NoSelfAddr)?
            {
                info!(context, "Message belongs to a different handshake (scaled up contact anyway to allow creation of group).");
                return Ok(abort_retval);
            }
            secure_connection_established(context, contact_chat_id).await;
            context.bob.write().await.expects = SecureJoinStep::NotActive;

            // Bob -> Alice
            send_handshake_msg(
                context,
                contact_chat_id,
                if join_vg {
                    "vg-member-added-received"
                } else {
                    "vc-contact-confirm-received" // only for observe_securejoin_on_other_device()
                },
                "",
                Some(scanned_fingerprint_of_alice),
                "",
            )
            .await?;

            context.stop_ongoing().await;
            Ok(if join_vg {
                HandshakeMessage::Propagate
            } else {
                HandshakeMessage::Ignore // "Done" deletes the message and breaks multi-device
            })
        }
        "vg-member-added-received" | "vc-contact-confirm-received" => {
            /*==========================================================
            ====              Alice - the inviter side              ====
            ====  Step 8 in "Out-of-band verified groups" protocol  ====
            ==========================================================*/

            if let Ok(contact) = Contact::get_by_id(context, contact_id).await {
                if contact.is_verified(context).await == VerifiedStatus::Unverified {
                    warn!(context, "{} invalid.", step);
                    return Ok(HandshakeMessage::Ignore);
                }
                if join_vg {
                    // Responsible for showing "$Bob securely joined $group" message
                    inviter_progress!(context, contact_id, 800);
                    inviter_progress!(context, contact_id, 1000);
                    let field_grpid = mime_message
                        .get(HeaderDef::SecureJoinGroup)
                        .map(|s| s.as_str())
                        .unwrap_or_else(|| "");
                    if let Err(err) = chat::get_chat_id_by_grpid(context, &field_grpid).await {
                        warn!(context, "Failed to lookup chat_id from grpid: {}", err);
                        return Err(HandshakeError::ChatNotFound {
                            group: field_grpid.to_string(),
                        });
                    }
                }
                Ok(HandshakeMessage::Ignore) // "Done" deletes the message and breaks multi-device
            } else {
                warn!(context, "{} invalid.", step);
                Ok(HandshakeMessage::Ignore)
            }
        }
        _ => {
            warn!(context, "invalid step: {}", step);
            Ok(HandshakeMessage::Ignore)
        }
    }
}

/// observe_securejoin_on_other_device() must be called when a self-sent securejoin message is seen.
///
/// in a multi-device-setup, there may be other devices that "see" the handshake messages.
/// if the seen messages seen are self-sent messages encrypted+signed correctly with our key,
/// we can make some conclusions of it:
///
/// - if we see the self-sent-message vg-member-added/vc-contact-confirm,
///   we know that we're an inviter-observer.
///   the inviting device has marked a peer as verified on vg-request-with-auth/vc-request-with-auth
///   before sending vg-member-added/vc-contact-confirm - so, if we observe vg-member-added/vc-contact-confirm,
///   we can mark the peer as verified as well.
///
/// - if we see the self-sent-message vg-member-added-received
///   we know that we're an joiner-observer.
///   the joining device has marked the peer as verified on vg-member-added/vc-contact-confirm
///   before sending vg-member-added-received - so, if we observe vg-member-added-received,
///   we can mark the peer as verified as well.
pub(crate) async fn observe_securejoin_on_other_device(
    context: &Context,
    mime_message: &MimeMessage,
    contact_id: u32,
) -> Result<HandshakeMessage, HandshakeError> {
    if contact_id <= DC_CONTACT_ID_LAST_SPECIAL {
        return Err(HandshakeError::SpecialContactId);
    }
    let step = mime_message
        .get(HeaderDef::SecureJoin)
        .ok_or(HandshakeError::NotSecureJoinMsg)?;
    info!(context, "observing secure-join message \'{}\'", step);

    let contact_chat_id =
        match chat::create_or_lookup_by_contact_id(context, contact_id, Blocked::Not).await {
            Ok((chat_id, blocked)) => {
                if blocked != Blocked::Not {
                    chat_id.unblock(context).await;
                }
                chat_id
            }
            Err(err) => {
                return Err(HandshakeError::NoChat {
                    contact_id,
                    cause: err,
                });
            }
        };

    match step.as_str() {
        "vg-member-added"
        | "vc-contact-confirm"
        | "vg-member-added-received"
        | "vc-contact-confirm-received" => {
            if !encrypted_and_signed(
                context,
                mime_message,
                get_self_fingerprint(context).await.as_ref(),
            ) {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    "Message not encrypted correctly.",
                )
                .await;
                return Ok(HandshakeMessage::Ignore);
            }
            let fingerprint: Fingerprint = match mime_message.get(HeaderDef::SecureJoinFingerprint)
            {
                Some(fp) => fp.parse()?,
                None => {
                    could_not_establish_secure_connection(
                        context,
                        contact_chat_id,
                        "Fingerprint not provided, please update Delta Chat on all your devices.",
                    )
                    .await;
                    return Ok(HandshakeMessage::Ignore);
                }
            };
            if mark_peer_as_verified(context, &fingerprint).await.is_err() {
                could_not_establish_secure_connection(
                    context,
                    contact_chat_id,
                    format!("Fingerprint mismatch on observing {}.", step).as_ref(),
                )
                .await;
                return Ok(HandshakeMessage::Ignore);
            }
            Ok(if step.as_str() == "vg-member-added" {
                HandshakeMessage::Propagate
            } else {
                HandshakeMessage::Ignore
            })
        }
        _ => Ok(HandshakeMessage::Ignore),
    }
}

async fn secure_connection_established(context: &Context, contact_chat_id: ChatId) {
    let contact_id: u32 = chat_id_2_contact_id(context, contact_chat_id).await;
    let contact = Contact::get_by_id(context, contact_id).await;

    let addr = if let Ok(ref contact) = contact {
        contact.get_addr()
    } else {
        "?"
    };
    let msg = context
        .stock_string_repl_str(StockMessage::ContactVerified, addr)
        .await;
    chat::add_info_msg(context, contact_chat_id, msg).await;
    emit_event!(context, EventType::ChatModified(contact_chat_id));
}

async fn could_not_establish_secure_connection(
    context: &Context,
    contact_chat_id: ChatId,
    details: &str,
) {
    let contact_id = chat_id_2_contact_id(context, contact_chat_id).await;
    let contact = Contact::get_by_id(context, contact_id).await;
    let msg = context
        .stock_string_repl_str(
            StockMessage::ContactNotVerified,
            if let Ok(ref contact) = contact {
                contact.get_addr()
            } else {
                "?"
            },
        )
        .await;

    chat::add_info_msg(context, contact_chat_id, &msg).await;
    error!(context, "{} ({})", &msg, details);
}

async fn mark_peer_as_verified(context: &Context, fingerprint: &Fingerprint) -> Result<(), Error> {
    if let Some(ref mut peerstate) =
        Peerstate::from_fingerprint(context, &context.sql, fingerprint).await?
    {
        if peerstate.set_verified(
            PeerstateKeyType::PublicKey,
            fingerprint,
            PeerstateVerifiedStatus::BidirectVerified,
        ) {
            peerstate.prefer_encrypt = EncryptPreference::Mutual;
            peerstate.to_save = Some(ToSave::All);
            peerstate
                .save_to_db(&context.sql, false)
                .await
                .unwrap_or_default();
            return Ok(());
        }
    }
    bail!(
        "could not mark peer as verified for fingerprint {}",
        fingerprint.hex()
    );
}

/* ******************************************************************************
 * Tools: Misc.
 ******************************************************************************/

fn encrypted_and_signed(
    context: &Context,
    mimeparser: &MimeMessage,
    expected_fingerprint: Option<&Fingerprint>,
) -> bool {
    if !mimeparser.was_encrypted() {
        warn!(context, "Message not encrypted.",);
        false
    } else if let Some(expected_fingerprint) = expected_fingerprint {
        if !mimeparser.signatures.contains(expected_fingerprint) {
            warn!(
                context,
                "Message does not match expected fingerprint {}.", expected_fingerprint,
            );
            false
        } else {
            true
        }
    } else {
        warn!(context, "Fingerprint for comparison missing.");
        false
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::chat;
    use crate::chat::ProtectionStatus;
    use crate::peerstate::Peerstate;
    use crate::test_utils::TestContext;

    #[async_std::test]
    async fn test_setup_contact() {
        let alice = TestContext::new_alice().await;
        let bob = TestContext::new_bob().await;

        // Generate QR-code, ChatId(0) indicates setup-contact
        let qr = dc_get_securejoin_qr(&alice.ctx, ChatId::new(0))
            .await
            .unwrap();

        // Bob scans QR-code, sends vc-request
        let bob_chatid = dc_join_securejoin(&bob.ctx, &qr).await.unwrap();

        let sent = bob.pop_sent_msg().await;
        assert_eq!(sent.id(), bob_chatid);
        assert_eq!(sent.recipient(), "alice@example.com".parse().unwrap());
        let msg = alice.parse_msg(&sent).await;
        assert!(!msg.was_encrypted());
        assert_eq!(msg.get(HeaderDef::SecureJoin).unwrap(), "vc-request");
        assert!(msg.get(HeaderDef::SecureJoinInvitenumber).is_some());

        // Alice receives vc-request, sends vc-auth-required
        alice.recv_msg(&sent).await;

        let sent = alice.pop_sent_msg().await;
        let msg = bob.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(msg.get(HeaderDef::SecureJoin).unwrap(), "vc-auth-required");

        // Bob receives vc-auth-required, sends vc-request-with-auth
        bob.recv_msg(&sent).await;

        let sent = bob.pop_sent_msg().await;
        let msg = alice.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vc-request-with-auth"
        );
        assert!(msg.get(HeaderDef::SecureJoinAuth).is_some());
        let bob_fp = SignedPublicKey::load_self(&bob.ctx)
            .await
            .unwrap()
            .fingerprint();
        assert_eq!(
            *msg.get(HeaderDef::SecureJoinFingerprint).unwrap(),
            bob_fp.hex()
        );

        // Alice should not yet have Bob verified
        let contact_bob_id =
            Contact::lookup_id_by_addr(&alice.ctx, "bob@example.net", Origin::Unknown).await;
        let contact_bob = Contact::load_from_db(&alice.ctx, contact_bob_id)
            .await
            .unwrap();
        assert_eq!(
            contact_bob.is_verified(&alice.ctx).await,
            VerifiedStatus::Unverified
        );

        // Alice receives vc-request-with-auth, sends vc-contact-confirm
        alice.recv_msg(&sent).await;
        assert_eq!(
            contact_bob.is_verified(&alice.ctx).await,
            VerifiedStatus::BidirectVerified
        );

        let sent = alice.pop_sent_msg().await;
        let msg = bob.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vc-contact-confirm"
        );

        // Bob should not yet have Alice verified
        let contact_alice_id =
            Contact::lookup_id_by_addr(&bob.ctx, "alice@example.com", Origin::Unknown).await;
        let contact_alice = Contact::load_from_db(&bob.ctx, contact_alice_id)
            .await
            .unwrap();
        assert_eq!(
            contact_bob.is_verified(&bob.ctx).await,
            VerifiedStatus::Unverified
        );

        // Bob receives vc-contact-confirm, sends vc-contact-confirm-received
        bob.recv_msg(&sent).await;
        assert_eq!(
            contact_alice.is_verified(&bob.ctx).await,
            VerifiedStatus::BidirectVerified
        );

        let sent = bob.pop_sent_msg().await;
        let msg = alice.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vc-contact-confirm-received"
        );
    }

    #[async_std::test]
    async fn test_setup_contact_bad_qr() {
        let bob = TestContext::new_bob().await;
        let ret = dc_join_securejoin(&bob.ctx, "not a qr code").await;
        assert!(matches!(ret, Err(JoinError::QrCode)));
    }

    #[async_std::test]
    async fn test_setup_contact_bob_knows_alice() {
        let alice = TestContext::new_alice().await;
        let bob = TestContext::new_bob().await;

        // Ensure Bob knows Alice_FP
        let alice_pubkey = SignedPublicKey::load_self(&alice.ctx).await.unwrap();
        let peerstate = Peerstate {
            context: &bob.ctx,
            addr: "alice@example.com".into(),
            last_seen: 10,
            last_seen_autocrypt: 10,
            prefer_encrypt: EncryptPreference::Mutual,
            public_key: Some(alice_pubkey.clone()),
            public_key_fingerprint: Some(alice_pubkey.fingerprint()),
            gossip_key: Some(alice_pubkey.clone()),
            gossip_timestamp: 10,
            gossip_key_fingerprint: Some(alice_pubkey.fingerprint()),
            verified_key: None,
            verified_key_fingerprint: None,
            to_save: Some(ToSave::All),
            fingerprint_changed: false,
        };
        peerstate.save_to_db(&bob.ctx.sql, true).await.unwrap();

        // Generate QR-code, ChatId(0) indicates setup-contact
        let qr = dc_get_securejoin_qr(&alice.ctx, ChatId::new(0))
            .await
            .unwrap();

        // Bob scans QR-code, sends vc-request-with-auth, skipping vc-request
        dc_join_securejoin(&bob.ctx, &qr).await.unwrap();

        let sent = bob.pop_sent_msg().await;
        let msg = alice.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vc-request-with-auth"
        );
        assert!(msg.get(HeaderDef::SecureJoinAuth).is_some());
        let bob_fp = SignedPublicKey::load_self(&bob.ctx)
            .await
            .unwrap()
            .fingerprint();
        assert_eq!(
            *msg.get(HeaderDef::SecureJoinFingerprint).unwrap(),
            bob_fp.hex()
        );

        // Alice should not yet have Bob verified
        let (contact_bob_id, _modified) = Contact::add_or_lookup(
            &alice.ctx,
            "Bob",
            "bob@example.net",
            Origin::ManuallyCreated,
        )
        .await
        .unwrap();
        let contact_bob = Contact::load_from_db(&alice.ctx, contact_bob_id)
            .await
            .unwrap();
        assert_eq!(
            contact_bob.is_verified(&alice.ctx).await,
            VerifiedStatus::Unverified
        );

        // Alice receives vc-request-with-auth, sends vc-contact-confirm
        alice.recv_msg(&sent).await;
        assert_eq!(
            contact_bob.is_verified(&alice.ctx).await,
            VerifiedStatus::BidirectVerified
        );

        let sent = alice.pop_sent_msg().await;
        let msg = bob.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vc-contact-confirm"
        );

        // Bob should not yet have Alice verified
        let contact_alice_id =
            Contact::lookup_id_by_addr(&bob.ctx, "alice@example.com", Origin::Unknown).await;
        let contact_alice = Contact::load_from_db(&bob.ctx, contact_alice_id)
            .await
            .unwrap();
        assert_eq!(
            contact_bob.is_verified(&bob.ctx).await,
            VerifiedStatus::Unverified
        );

        // Bob receives vc-contact-confirm, sends vc-contact-confirm-received
        bob.recv_msg(&sent).await;
        assert_eq!(
            contact_alice.is_verified(&bob.ctx).await,
            VerifiedStatus::BidirectVerified
        );

        let sent = bob.pop_sent_msg().await;
        let msg = alice.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vc-contact-confirm-received"
        );
    }

    #[async_std::test]
    async fn test_secure_join() {
        let alice = TestContext::new_alice().await;
        let bob = TestContext::new_bob().await;

        let chatid = chat::create_group_chat(&alice.ctx, ProtectionStatus::Protected, "the chat")
            .await
            .unwrap();

        // Generate QR-code, secure-join implied by chatid
        let qr = dc_get_securejoin_qr(&alice.ctx, chatid).await.unwrap();

        // Bob scans QR-code, sends vg-request; blocks on ongoing process
        let joiner = {
            let qr = qr.clone();
            let ctx = bob.ctx.clone();
            async_std::task::spawn(async move { dc_join_securejoin(&ctx, &qr).await.unwrap() })
        };

        let sent = bob.pop_sent_msg().await;
        assert_eq!(sent.recipient(), "alice@example.com".parse().unwrap());
        let msg = alice.parse_msg(&sent).await;
        assert!(!msg.was_encrypted());
        assert_eq!(msg.get(HeaderDef::SecureJoin).unwrap(), "vg-request");
        assert!(msg.get(HeaderDef::SecureJoinInvitenumber).is_some());

        // Alice receives vg-request, sends vg-auth-required
        alice.recv_msg(&sent).await;

        let sent = alice.pop_sent_msg().await;
        let msg = bob.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(msg.get(HeaderDef::SecureJoin).unwrap(), "vg-auth-required");

        // Bob receives vg-auth-required, sends vg-request-with-auth
        bob.recv_msg(&sent).await;
        let sent = bob.pop_sent_msg().await;
        let msg = alice.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vg-request-with-auth"
        );
        assert!(msg.get(HeaderDef::SecureJoinAuth).is_some());
        let bob_fp = SignedPublicKey::load_self(&bob.ctx)
            .await
            .unwrap()
            .fingerprint();
        assert_eq!(
            *msg.get(HeaderDef::SecureJoinFingerprint).unwrap(),
            bob_fp.hex()
        );

        // Alice should not yet have Bob verified
        let contact_bob_id =
            Contact::lookup_id_by_addr(&alice.ctx, "bob@example.net", Origin::Unknown).await;
        let contact_bob = Contact::load_from_db(&alice.ctx, contact_bob_id)
            .await
            .unwrap();
        assert_eq!(
            contact_bob.is_verified(&alice.ctx).await,
            VerifiedStatus::Unverified
        );

        // Alice receives vg-request-with-auth, sends vg-member-added
        alice.recv_msg(&sent).await;
        assert_eq!(
            contact_bob.is_verified(&alice.ctx).await,
            VerifiedStatus::BidirectVerified
        );

        let sent = alice.pop_sent_msg().await;
        let msg = bob.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(msg.get(HeaderDef::SecureJoin).unwrap(), "vg-member-added");

        // Bob should not yet have Alice verified
        let contact_alice_id =
            Contact::lookup_id_by_addr(&bob.ctx, "alice@example.com", Origin::Unknown).await;
        let contact_alice = Contact::load_from_db(&bob.ctx, contact_alice_id)
            .await
            .unwrap();
        assert_eq!(
            contact_bob.is_verified(&bob.ctx).await,
            VerifiedStatus::Unverified
        );

        // Bob receives vg-member-added, sends vg-member-added-received
        bob.recv_msg(&sent).await;
        assert_eq!(
            contact_alice.is_verified(&bob.ctx).await,
            VerifiedStatus::BidirectVerified
        );

        let sent = bob.pop_sent_msg().await;
        let msg = alice.parse_msg(&sent).await;
        assert!(msg.was_encrypted());
        assert_eq!(
            msg.get(HeaderDef::SecureJoin).unwrap(),
            "vg-member-added-received"
        );

        let bob_chatid = joiner.await;
        let bob_chat = Chat::load_from_db(&bob.ctx, bob_chatid).await.unwrap();
        assert!(bob_chat.is_protected());
    }
}