user124461: Bitcoin is secure when 51% of the miners are honest.
We also need every node to have at least one honest peer to avoid eclipse attacks.
Are these the only assumptions based on which Bitcoin is secure? Is there a complete list of assumptions and a formal analysis of the threat model somewhere?

user-1: 
Bitcoin is secure when 51% of the miners are honest. We also need every node to have at least one honest peer to avoid eclipse attacks. Are these the only assumptions based on which Bitcoin is secure?

I don't consider them as assumptions instead they are different types of attacks.
51% attack is the most over-rated. You can find lot of Q&As related to 51% attack: https://bitcoin.stackexchange.com/search?q=%2251%25+attack%22
TL;DR: https://bitcoin.stackexchange.com/a/101560/
Eclipse attacks are possible in any peer to peer network and not something new in Bitcoin. However, security is improved on different levels by Bitcoin Core contributors regularly making them very difficult. Example: https://github.com/bitcoin/bitcoin/pull/12626
Things that affect security in Bitcoin IMO:

DNS seeds: How does the bitcoin core protect against initial DNS seed changes?
assumevalid: Does assumevalid lower the security of Bitcoin?
BGP hijacking: Was bitcoin peer to peer network affected because of the recent BGP hijack incident?
Vulnerabilities in layer 2 projects that may affect Bitcoin in some cases.
Zero day vulnerability in any full node implementations
Internet Shutdown in lot of places at the same time. Although there are few solutions: Mesh Networks, Satellite Communication and Text messages.


124461: <p>Bitcoin is secure when 51% of the miners are honest.
We also need every node to have at least one honest peer to avoid eclipse attacks.</p>
<p>Are these the only assumptions based on which Bitcoin is secure? Is there a complete list of assumptions and a formal analysis of the threat model somewhere?</p>
 -1: <blockquote>
<p>Bitcoin is secure when 51% of the miners are honest. We also need every node to have at least one honest peer to avoid eclipse attacks. Are these the only assumptions based on which Bitcoin is secure?</p>
</blockquote>
<p>I don't consider them as assumptions instead they are different types of attacks.</p>
<p>51% attack is the most over-rated. You can find lot of Q&amp;As related to 51% attack: <a href="https://bitcoin.stackexchange.com/search?q=%2251%25+attack%22">https://bitcoin.stackexchange.com/search?q=%2251%25+attack%22</a></p>
<p>TL;DR: <a href="https://bitcoin.stackexchange.com/a/101560/">https://bitcoin.stackexchange.com/a/101560/</a></p>
<p>Eclipse attacks are possible in any peer to peer network and not something new in Bitcoin. However, security is improved on different levels by Bitcoin Core contributors regularly making them very difficult. Example: <a href="https://github.com/bitcoin/bitcoin/pull/12626" rel="nofollow noreferrer">https://github.com/bitcoin/bitcoin/pull/12626</a></p>
<p>Things that affect security in Bitcoin IMO:</p>
<ol>
<li>DNS seeds: <a href="https://bitcoin.stackexchange.com/questions/104916/how-does-the-bitcoin-core-protect-against-initial-dns-seed-changes/">How does the bitcoin core protect against initial DNS seed changes?</a></li>
<li><code>assumevalid</code>: <a href="https://bitcoin.stackexchange.com/questions/88652/does-assumevalid-lower-the-security-of-bitcoin">Does assumevalid lower the security of Bitcoin?</a></li>
<li>BGP hijacking: <a href="https://bitcoin.stackexchange.com/questions/99266/was-bitcoin-peer-to-peer-network-affected-because-of-the-recent-bgp-hijack-incid">Was bitcoin peer to peer network affected because of the recent BGP hijack incident?</a></li>
<li>Vulnerabilities in layer 2 projects that may affect Bitcoin in some cases.</li>
<li>Zero day vulnerability in any full node implementations</li>
<li>Internet Shutdown in lot of places at the same time. Although there are few solutions: Mesh Networks, Satellite Communication and Text messages.</li>
</ol>
