Ask HN: What are best practices for encrypting sensitive user data on a server?

https://news.ycombinator.com/item?id=9574657

by teapot01 • 11 years ago

6 9 11 years ago

news.ycombinator.com

teapot013• 11 years ago

What I'm interested in is how should I encrypt and store sensitive user data on a server such that it is retrievable but secure.

sumodirjo• 11 years ago

Do you plan to fully encrypt data as doing full harddisk encryption?

bigiain3• 11 years ago

Which doesn't help one bit when some script kiddie xss-es their way into your admin backend or SQLis your entire DB out through your un-updated ad server or contact form plugin...

It does help if a thief walks out with your server, or if some extremely uneducated and unprofessional law enforcement power down your server as they serve their warrant on your datacenter - but neither of those scenarios are anywhere near the top of the "reasons your sensitive data got compromised and showed up on pastebin" lists.

DanBC• 11 years ago

Secure from what?

Secure from remote but unskilled attackers using auto tools poorly?

Secure from remote but skilled users targetting your system?

Local and skilled users targetting your system?

Law enforcement smashing the door down?

Well formed legal documents?

Well funded government agencies?

Malicious employees?

teapot013• 11 years ago

Ultimately I think the main danger is a skilled attacker targeting the system. That said I would like to secure data from a local attacker as well. Ultimately I understand that it will be difficult to secure fully against someone with hardware access but any risk mitigation practices I could use?

dutchbrit• 11 years ago

Define sensitive user data and how do you want to store it? In a file or in a database? AES-256 is pretty good for encryption but you also need to handle decryption somehow - and you don't really want to store passphrases on a server. Passphrases can be encrypted using pgp if you want multiple users to have access to the passphrase. When it comes to password hashing (not encryption), then go with bcrypt or scrypt.

But please define sensitive data more in detail. Are we talking about passwords, messages or photos of passports etc?

teapot013• 11 years ago

Some clarification. Sensitive data will be things like full names addresses passport photos credit card details etc

Encryption. I'm thinking public key might work, but if I want to decrypt on the server how do I keep private keys private?

bigiain3• 11 years ago

You can't. Not against even a marginally skilled attacker. If the server contains what it needs to decrypt the data, any attacker who p0wns your server can extract that.

If you only need protection against skript kiddies running automated attacks - look at how Apache/OpenSSL deal with passphrase protected private keys. They go to some length to ensure the decrypted private key only ever exists in-memory, and doesn't get written to disk, but someone who's escalated to local root can (I'm pretty sure) grab the key out of ram (core dumping the whole process, if need be).

If you _have_ to have sensitive data stored and available to the server - consider storing the sensitive/encrypted data on a separate system with a much smaller attack surface than a publicly available web server (assuming that's what we're talking about here), with a extremely tightly specified API that's small and well defined enough to make it practical to come much closer to fully auditing the code - and where it's practical to monitor the API for intrusion or unexpected requests and shut it down pre-emptively before you lose your whole database.

Mostly though, I advise working out a way to not have to do that.

(Note that "storing credit card details" immediately confers the whole responsibility of PCI compliance on you. It is, in my experience, almost _never_ worthwhile doing that - leave that headache to Stripe/Square/Paypal/whoever, and re think your business process to suit.)

bigiain3• 11 years ago

The timeworn advice is: "TLS for data on the fly, GPG for data at rest". With suitably updated TLS/SSL libraries and configurations, and good GPG keys, this is still sound advice.

The big question in my mind is always "Does the server need to be able to decrypt that data?" If the server has the decryption keys, the attacker can probably steal them along with the encrypted data. I store GPG encrypted data on servers where they only have the public key - retrieving the data involves grabbing the encrypted data from the server and decrypting it somewhere else that has the private key available. (This is a handy trick for web forms that collect sensitive data - serialise it and GPG encrypt it immediately, then you can happily send the encrypted blob via non-100%-reliable email,and have the local encrypted blob available if the email copy fails to arrive.)

Ask HN: What are best practices for encrypting sensitive user data on a server?

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