What are the reasons to use Signal over Telegram

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Nice try FBI.

Well, if my pin is four numbers, that'll make it so hard to crack. /s

If you can't show hard evidence that everything is offline locally, no keys stored in the cloud, then it's just not secure.

BTW, "keys" when talking about encryption is the keys used to encrypt and decrypt, it wouldn't be very interesting to encrypt them, because now you have another set of keys you have to deal with.

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The sender ('s unique device) can with 100% accuracy be appended to the message by the server after it's received.

How?

If I share an IP with 100 million other Signal users and I send a sealed sender message, how does Signal distinguish between me and the other 100 million users? My sender certificate is encrypted and only able to be decrypted by the recipient.

If I’m the only user with my IP address, then sure, Signal could identify me. I can use a VPN or similar technology if I’m concerned about this, of course. Signal doesn’t consider obscuring IPs to be in scope for their mission - there was a recent Cloudflare vulnerability that impacted Signal where they mentioned this. From https://www.404media.co/cloudflare-issue-can-leak-chat-app-users-broad-location/

404 Media asked daniel to demonstrate the issue by learning the location of multiple Signal users with their consent. In one case, daniel sent a user an image. Soon after, daniel sent a link to a Google Maps page showing the city the user was likely in.

…

404 Media first asked Signal for comment in early December. The organization did not provide a statement in time for publication, but daniel shared their response to his bug report.

“What you're describing (observing cache hits and misses) is a generic property of how Content Distribution Networks function. Signal's use of CDNs is neither unique nor alarming, and also doesn't impact Signal's end-to-end encryption. CDNs are utilized by every popular application and website on the internet, and they are essential for high-performance and reliability while serving a global audience,” Signal’s security team wrote.

“There is already a large body of existing work that explores this topic in detail, but if someone needs to completely obscure their network location (especially at a level as coarse and imprecise as the example that appears in your video) a VPN is absolutely necessary. That functionality falls outside of Signal's scope. Signal protects the privacy of your messages and calls, but it has never attempted to fully replicate the set of network-layer anonymity features that projects like Wireguard, Tor, and other open-source VPN software can provide,” it added.

I saw a post about this recently on Lemmy (and Reddit), so there’s probably more discussion there.

since the sender is identified at the start of every conversation.

What do you mean when you say “conversation” here? Do you mean when you first access a user’s profile key, which is required to send a sealed sender message to them if they haven’t enabled “Allow From Anyone” in their settings? If so, then yes, the sender’s identity when requesting the contact would necessarily be exposed. If the recipient has that option enabled, that’s not necessarily true, but I don’t know for sure.

Even if we trust Signal, with Sealed Sender, without any sort of random delay in message delivery, a nation-state level adversary could observe inbound and outbound network activity and derive high confidence information about who’s contacting whom.

All of that said, my understanding is that contact discovery is a bigger vulnerability than Sealed Sender if we don’t trust Signal’s servers. Here’s the blog post from 2017 where Moxie describe their approach. (See also this blog post where they talk about improvements to “Oblivious RAM,” though it doesn’t have more information on SGX.) He basically said “This solution isn’t great if you don’t trust that the servers are running verified code.”

This method of contact discovery isn’t ideal because of these shortcomings, but at the very least the Signal service’s design does not depend on knowledge of a user’s social graph in order to function. This has meant that if you trust the Signal service to be running the published server source code, then the Signal service has no durable knowledge of a user’s social graph if it is hacked or subpoenaed.

He then continued on to describe their use of SGX and remote attestation over a network, which was touched on in the Sealed Sender post. Specifically:

Modern Intel chips support a feature called Software Guard Extensions (SGX). SGX allows applications to provision a “secure enclave” that is isolated from the host operating system and kernel, similar to technologies like ARM’s TrustZone. SGX enclaves also support a feature called remote attestation. Remote attestation provides a cryptographic guarantee of the code that is running in a remote enclave over a network.

Later in that blog post, Moxie says “The enclave code builds reproducibly, so anyone can verify that the published source code corresponds to the MRENCLAVE value of the remote enclave.” But how do we actually perform this remote attestation? And is it as secure and reliable as Signal attests?

In the docs for the “auditee” application, the Examples page provides some additional information and describes how to use their tool to verify the MRENCLAVE value. Note that they also say that the tool is a work in progress and shouldn’t be trusted. The Intel SGX documentation likely has information as well, but most of the links that I found were dead, so I didn’t investigate further.

A blog post titled Enhancing trust for SGX enclaves raised some concerns with SGX’s current implementation, specifically mentioning Signal’s usage, and suggested (and implemented) some improvements.

I haven’t personally verified the MRENCLAVE values for any of Signal’s services and I’m not aware of anyone who has (successfully, at least), but I also haven’t seen any security experts stating that the technology is unsound or doesn’t actually do what’s claimed.

Finally, I recommend you check out https://community.signalusers.org/t/overview-of-third-party-security-audits/13243 - some of the issues noted there involve the social graph and at least one involves Sealed Sender specifically (though the link is dead; I didn’t check to see if the Internet Archive has a backup).

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I think whas this video https://www.youtube.com/watch?v=A8ZXDiQLH9I

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Its impossible to verify what code their server is running.

Signal has posted multiple times about their use of SGX Secure Enclaves and how you can use Remote Attestation techniques to verify a subset of the code that’s running on their server, which directly contradicts your claim. (It doesn’t contradict the claim that you cannot verify all the code their server is running, though.) Have you looked into that? What issues did you find with it?

I posted a comment here going into more detail about it, but I haven’t personally confirmed myself that it’s feasible.

[email protected]

Nice try FBI.

Wouldn’t “NSA” or “CIA” be more appropriate here?

Well, if my pin is four numbers, that'll make it so hard to crack. /s

If you’re using a 4 number PIN then that’s on you. The blog post I shared covers that explicitly: “However, there’s a limit to how slow things can get without affecting legitimate client performance, and some user-chosen passwords may be so weak that no feasible amount of “key-stretching” will prevent brute force attacks” and later, “However, it would allow an attacker with access to the service to run an “offline” brute force attack. Users with a BIP39 passphrase (as above) would be safe against such a brute force, but even with an expensive KDF like Argon2, users who prefer a more memorable passphrase might not be, depending on the amount of money the attacker wants to spend on the attack.”

If you can't show hard evidence that everything is offline locally, no keys stored in the cloud, then it's just not secure.

If you can’t share a reputable source backing up that claim, along with a definition of what “secure” means, then your claim that “it’s just not secure” isn’t worth the bits taken to store the text in your comment.

You haven’t even specified your threat model.

BTW, "keys" when talking about encryption is the keys used to encrypt and decrypt,

Are you being earnest here? First, even if we were just talking about encryption, the question of what’s being encrypted is relevant. Secondly, we weren’t just talking about encryption. Here’s your complete comment, for reference:

I have read that it is self hostable (but I haven’t digged into it) but as it’s not a federating service so not better than other alternative out there.

Also read that the keys are stored locally but also somehow stored in the cloud (??), which makes it all completely worthless if it is true.

That said, the three letter agencies can probably get in any android/apple phones if they want to, like I’m not forgetting the oh so convenient “bug” heartbleed…

Just so you know, “keys” are used for a number of purposes in Signal (and for software applications in general) and not all of those purposes involve encryption. Many keys are used for verification/authentication.

Assuming you were being earnest: I recommend that you take some courses on encryption and cybersecurity, because you have some clear misconceptions. Specifically, I recommend that you start with Cryptography I (by Stanford, hosted on Coursera. See also Stanford’s page for the course, which contains a link to the free textbook). Its follow-up, Crypto II, isn’t available on Coursera, but I believe that this 8 hour long Youtube video contains several of the lectures from it. Alternatively, Berkeley’s Zero Knowledge Proofs course would be a good follow-up, and basically everything (excepting the quizzes) appears to be freely available online.

it wouldn't be very interesting to encrypt them, because now you have another set of keys you have to deal with.

The link I shared with you has 6 keys (stretched_key, auth_key, c1, c2, master_key, and application_key) in a single code block. By encrypting the master key (used to derive application keys such as the one that encrypts social graph information) with a user-derived, stretched key, Signal can offer an optional feature: the ability to recover that encrypted information if their device is lost, stolen, wiped, etc., though of course message history is out of scope.

Full disk encryption also uses multiple keys in a similar way. Take LUKS, for example. Your drive is encrypted with a master key. You derive the master key by decrypting one of the access keys using its corresponding pass phrase. (Source: section 4.3 in the LUKS1 On-Disk Format Specification (I don't believe this basic behavior was changed in LUKS2).)

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They have to know who the message needs to go to, granted. But they don’t have to know who the message comes from, hence why the sealed sender technique works. The recipient verifies the message via the keys that are exchanged if they have been communicating with that correspondent before or else it is a new message request.

So I don’t see how they can build social graphs if they don’t know who the sender if all messages are, they can only plot recipients which is not enough.

You need to identify yourself to receive your messages, and you send and receive messages from the same IP address, and there are typically not many if any other Signal users sharing the same IP address. So, the cryptography of "sealed sender" is just for show - the metadata privacy remains dependent on them keeping their promise not to correlate your receiving identity with the identities of the people you're sending to. If you assume that they'll keep that promise, then the sealed sender cryptography provides no benefit; if they don't keep the promise, sealed sender doesn't really help. They outsource the keeping of their promises to Amazon, btw (a major intelligence contractor).
Just in case sealed sender was actually making it inconvenient for the server to know who is talking to who... Signal silently falls back to "unsealed sender" messages if server returns 401 when trying to send "sealed sender" messages, which the server actually does sometimes. As the current lead dev of Signal-for-Android explains: "Sealed sender is not a guarantee, but rather a best-effort sort of thing" so "I don't think notifying the user of a unsealed send fallback is necessary".

Given the above, don't you think the fact that they've actually gone to the trouble of building sealed sender at all, which causes many people to espouse the belief you just did (that their cryptographic design renders them incapable of learning the social graph, not to mention learning which edges in the graph are most active, and when) puts them rather squarely in doth protest too much territory?

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If I share an IP with 100 million other Signal users and I send a sealed sender message, how does Signal distinguish between me and the other 100 million users?

If you shared an IP with 100 million other Signal users that would be pretty amazing, given that there are less than 50 million users total. And don't you think the majority of Signal users share an IP with zero other Signal users most of the time? And when they do share an IP, it is with a relatively small number of other users? Anyway, even if the point of sealed sender was only to provide sender anonymity within the anonymity set of people you share an IP with, that would still be providing useful metadata. But also: it can be silently disabled by the server. See my other comment here.

[email protected]

With Signal, the key to encrypt your messages are on your device, and is never sent to the company.

Signal, and anyone who hacks them, or governments that attack them, cannot read your messages. This has been proven in court.

With Telegram, the key to encrypt your messages are on their server.

Telegram, and anyone who hacks them, or governments that attack them, can read all of your messages. This has also been proven in court.

[email protected]

Just so you know, “keys” are used for a number of purposes in Signal (and for software applications in general) and not all of those purposes involve encryption. Many keys are used for verification/authentication.

And it's I who should take a course in encryption and cybersecurity.

ROFL

Good to see you have your study material at hand though, and yes cryptography is complicated but you'll get the hang of it eventually.

[email protected]

And it's I who should take a course in encryption and cybersecurity.

Yes. I was trying to be nice, but you’re clearly completely ignorant and misinformed when it comes to information security. Given that you self described as a “cryptography nerd,” it’s honestly embarrassing.

But since you’ve doubled down on being rude, just because I pointed out that you don’t know what you’re talking about, it’s unlikely you’ll ever learn enough about the topic to have a productive conversation, anyway.

Have fun protecting your ignorance.

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What are the reasons to use Signal over Telegram