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As I understand it if someone is able to hack my DNS server and edit my TXT DNS record on a FQDN (fully qualified domain name) they could alter the Monero address that the associated with my OpenAlias and redirect future payments to an address controlled by the attacker.

Is this understanding correct?

Assume that my DNS service is completely separate from the server hosting my Monero daemon and wallet associated with my OpenAlias address. Am I correct that funds received prior to the DNS server hack will remain completely secure?

Are there any other important OpenAlias related security concerns that I should be aware of over and above the normal security precautions associated with running a daemon and receiving Monero payments?

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    Both are correct. – user36303 Jul 21 '16 at 16:00
  • @user36303 Thank you. I modified my question to inquire about any additional OpenAlias security concerns I should have – Julio Jul 21 '16 at 16:09
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Yes. Anyone who gains control of the TXT records would be able to change the address they reference. To answer your second question, you are correct that this would not affect any Monero received prior to the TXT record change, so your received funds would remain safe. This is why it is best to think of it as an alias to your address and not as the address itself.

One other security consideration with OpenAlias is that DNS lookups can leak information. Each time your computer does a DNS lookup, it is possible that the lookup is leaked and collected by a third party. The OpenAlias website recommends that you use DNSCrypt for lookups (https://dnscrypt.org/), and also suggests that is is ready to work with alternative DNS systems such as namecoin.

From their website (https://openalias.org/#implement):

In order to ensure that lookups do not betray the user's privacy it is best to implement DNSCrypt from OpenDNS, and force resolution via a DNSCrypt-compatible resolver. Dependent on your use-case, you may choose to bake DNSCrypt into your software, or bundle dnscrypt-proxy along with your application.

At some point the Monero simplewallet may be updated to use DNSCrypt lookups, but right now it doesn't seem to. Until then, using OpenAlias would potentially leak information that your IP address intends to interact with that Monero address.

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As I understand it if someone is able to hack my DNS server and edit my TXT DNS record on a FQDN (fully qualified domain name) they could alter the Monero address that the associated with my OpenAlias and redirect future payments to an address controlled by the attacker.

Is this understanding correct?

Literally at the top of the OpenAlias site it says: "By leveraging DNSSEC we are able to prevent MITM-style attacks on an alias. As with HTTPS, users are able to choose to operate in a less secure fashion if they are willing to accept the risks."

Additionally, in the application workflow it asks developers to "check if we have a valid DNSSEC trust chain (RRSIG, DNSKEY, NSEC3), if not then alert the user that it is potentially untrusted, continue if the user agrees".

The way DNSSEC works, you start with the root key (i.e. for .) and then follow the DNSSEC verification process all the way down. So for fluffypony.gets.paid.co.za you'd validate ., then .za, then .co.za, then paid.co.za, and so on. DNSSEC also prevents a resolver from lying and saying "this record doesn't exist", when it does.

If a Monero client / resolver doesn't implement DNSSEC that's their own fault, and they take user security for granted.

As to other risks, I'm happy with the answer that Ryan gave regarding ISP metadata leakage.

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  • How does this protect against the DNS record being modified ? How would the DNS server disintinguish between a change made by the authorised owner and a change made by someone who compromised the owner's computer ? – user36303 Jul 22 '16 at 20:49
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    @user36303 if the domain owner made the change then it's a legitimate change. If you don't own the domain then it's like not owning your private keys, and getting all angry that the person that owns your private keys stole your funds. – fluffyponyza Jul 22 '16 at 21:29
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    @user36303 Using OpenAlias provides the "Human Meaningful" part of Zooko's Triangle (en.wikipedia.org/wiki/Zooko%27s_triangle) to the Monero addressing. Because it isn't directly attached to the Monero address cryptographically, it could be seen as a "Secure + Human Meaningful" naming system (properties provided by OpenAlias through DNS/DNSSEC) which is a layer on top of a Monero address ("Secure + Decentralized"). There is no cryptographic tie between the two, so each part is secured separately. – Ryan Jul 22 '16 at 22:03
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    The question was "if someone is able to hack my DNS server and edit my TXT DNS record on a FQDN", so it's not another DNS server poisoning the cache, but an actual bone fide change, and thus probably undetectable by any chain of trust, so DNSSC wouldn't help there AFAICT (but I don't know that, and wanted to ask :)) – user36303 Jul 23 '16 at 7:52
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    @user36303 DNSSEC would help, because any changes you make also require signing with your KSK (Key Signing Key). An attacker can change the KSK, but to do so they would need to change the DS record with your registrar, which requires your ZSK (Zone Signing Key). As long as you don't keep your KSK / ZSK accessible there's no way an attacker can compromise your DNS records without invalidating the DNSSEC trust. – fluffyponyza Jul 24 '16 at 11:14

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