Inferencium - Blog - Losing Signal

0. Introduction

I was a fan, user, and promoter, of Signal for years. Signal created, and uses, the gold-standard of end-to-end encryption^[0], and has the greatest security in the aspects of confidentiality and integrity (but not availability). However, in 2022, a strong competitor arrived out of seemingly nowhere; SimpleX. SimpleX not only implements the best parts of Signal, including Signal's end-to-end encryption^[1], it also fixes the flaws of Signal.

In this article, I will take a look at the differences of the 2 highest-end security-and-privacy-focussed communication platforms.

1. Identity

Identity can be managed in 2 major ways. One of those ways is to have a non-repudible identity, often used in cases where the user's contact(s) already know the user, and/or the user wishes to use their real-life identity. The other way is to have a repudible identity, which is often the case for people wishing to engage in free-speech-based conversation, and/or remain anonymous.

In Signal's case, a phone number is required^[2], immediately binding the user to a non-repudible identity, regardless of whether Signal's Phone Number Privacy and Usernames features (which were, to say the least, a huge letdown) are used, as the phone number must be used at all times as the persistent identifier for Signal accounts. It is also difficult to create multiple Signal accounts on the same device, due to the requirement of multiple SIM cards being necessary.

In SimpleX's case, no account is required, at all. A profile (not an account) is generated on the application's first start, never leaves the device (other than to send to contacts and groups; all of which are sent to only with consent from the user by explicitly choosing to add/join them), and can be destroyed at any time. No phone number, no email address, not even a random string, is required to use SimpleX. In addition, multiple profiles can be created in the same database^[3], allowing for instantaneous switching of identities^[4]. Incognito profiles also exist, allowing usage of an existing profile without exposing it, by stripping the profile picture, and switching the profile name to a random 2-word name^[5]. Thanks to SimpleX's pairwise identifiers, it is impossible to know whether a contact is the same one someone else is talking to. Due to this design, all SimpleX profiles are repudible-by-default, the safest default for users; should a user want to make their profile non-repudible, they can simply meet contacts in person or via video call, or sign arbitary data via an OpenSSH-key or similar. This flexibility allows for both non-repudible and repudible identities to be created not only within the same database, but also on the same device.

2. Security

In the aspect of security, it seems that Signal and SimpleX are equal. However, taking a closer look reveals that this is not the case.

2.1. Availability

While the confidentiality and integrity aspects are equal, the availability aspect is pratically non-existent in Signal, yet properly implemented in SimpleX. Due to its centralised architecture, Signal has become unavailable on multiple occasions^[6][7][8]. This demonstrates how easy it is to take Signal down, whether maliciously, by hackers or authoritarian governments, or non-maliciously, by system failure or maintenance events. Signal president, Meredith Whittaker, has even claimed that there is no realistic alternative to Signal's centralised architecture^[9][10]; SimpleX has proven otherwise.

In contrast, SimpleX uses a decentralised architecture, allowing users to add any servers they wish to their application^[11], which can then be used to connect to other users. All data remains on the user's device, making it impossible for it to be made unavailable for any reason, other than loss of the device without a backup. Anyone can create a SimpleX server, for both messaging^[12] and files^[13]. The chance of not a single server being available on the planet is close-to-zero.

2.2. Groups

Signal groups have no practical security. Users who are made admins have full control of the group, and can perform any action. Signal has no concept of a moderator. This has led to group takeovers. Signal groups also do not support moderating messages by admins, causing all posted content to be permanent unless deleted by users on their own devices (not to be confused with message deletion, found later in the article). Moderation should be possible to keep posted content in line with group policy, and to provide evidence that illegal content was removed if the group is scrutinized by law enforcement.

SimpleX has a complete implementation of access-control lists for groups^[14]. This allows for fine-grained control of limiting the capabilities of staff members, reducing the chance of takeovers by rogue staff members, or accidental damage to the group by unauthorised personnel gaining access to staff members' devices. Moderation of messages is also possible, whether the messages are truly deleted from the participants' devices or not.

3. Privacy

3.1. Message Deletion

Signal does not allow disabling remote deletion of users' messages. Not only does this provide the ability for participants to delete messages which may be deemed important to the user, it provides a false sense of security as remote message deletion can never be guaranteed to work; particularly when the clients being used are open-source and may be modified^[17].

SimpleX allows disabling the ability for any participant to delete their own messages on the other party's device, both in direct messages and groups. This provides data sovereignty to all participants of a chat, and allows disabling the false sense of security remote message deletion provides. SimpleX could further improve its message-deletion feature... by removing it, entirely.

3.2. Member Exposure

Signal enforces end-to-end encryption for every group, including public groups which are known to the entire world. A major issue with this approach, particularly with groups used to post information in a news-like manner, is all members are exposed to each other. Such exposure is useful in private groups, but is unnecessary in public groups which are already known to the entire world. Signal has no concept of such a group.

SimpleX allows public groups focussing on news-like, informative postings to have no end-to-end encryption, instead providing complete anonymity of the members of the group. SimpleX names this concept "channels"^[15]. Within SimpleX channels, all members ("subscribers") are unknown to each other, and cannot be seen by anyone other than the channel owner(s). Subscribers can see the channel owner(s), only. In the case of such public channels, end-to-end encryption is not only useless in the security or privacy aspects, it adds unnecessary overhead to the connections; large groups with end-to-end encryption enabled do not scale well.

Losing Signal