[Haskell-cafe] Encrypting streamed data

Ivan Lazar Miljenovic ivan.miljenovic at gmail.com
Thu Jul 6 22:29:01 UTC 2017

On 7 July 2017 at 01:44, Viktor Dukhovni <ietf-dane at dukhovni.org> wrote:
>> On Jul 6, 2017, at 12:58 AM, Ivan Lazar Miljenovic <ivan.miljenovic at gmail.com> 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 at gmail.com

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