Re: [Haskell-cafe] Encrypting streamed data

On 7 July 2017 at 01:44, Viktor Dukhovni wrote:

...

On Jul 6, 2017, at 12:58 AM, Ivan Lazar Miljenovic wrote:

I have a use case for needing to use public key cryptography to encrypt a large amount of data in a streaming fashion (get it out of a DB, encrypt, put into an AWS S3 bucket).

What are the data-format requirements? Do you need (binary) CMS output? GPG-compatible output? Or just roll your own?

The intent is to be able to transfer data between two parties such that only the recipient is able to view it (hence the usage of public key cryptography). GPG/PGP compatability is preferable as it's common, but anything that is sufficiently standardised (as this will potentially be used by others that aren't me doing so with Haskell and thus can't just use a library to do so) will suffice. (The other advantage of GPG/PGP is that the security testing team is more familiar with it and thus likely to sign off on it.)

Integrity protection can be tricky with large data streams. Most data formats for enveloped data have a single MAC at the end, which means that the decoder has to consume all the data before it is known to be valid!

So if you're in a position to avoid a standard all-in-one format, it makes sense to "packetize" the stream, with integrity protection for each "packet", and packet sequence numbers to preserve overall stream integrity. With vast amounts of data, you'll want to be careful with the symmetric cipher modes, AEAD (AES-GCM, for example) protects only a limited amount of data before you need to rekey. It may be simplest to just generate a new symmetric key for every N megabytes of data.

With a careful design of the "packet" format, you can use in-memory crypto for each packet. Don't forget to include an "end-of-stream" packet to defeat truncation attacks.

This sounds good in theory, but in practice I'm not versed enough in security to want to try and roll my own if I could avoid it, and trying to document such a format for others to use could be problematic.allowed to post. -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com