[Haskell-cafe] Encrypting streamed data

Rein Henrichs rein.henrichs at gmail.com
Thu Jul 6 22:56:29 UTC 2017

If you are not a security expert, I would strongly recommend against
rolling your own encryption scheme. If you are a security expert, you would
probably not be asking us for advice on how to roll your own encryption
scheme. I would suggest that you find something off the rack that might
meet your needs (whether it's written in Haskell or not) and make sure you
understand how it works and what your threat model is well enough to decide
whether it does, in fact, meet your needs.

On Thu, Jul 6, 2017 at 3:29 PM Ivan Lazar Miljenovic <
ivan.miljenovic at gmail.com> wrote:

> 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
> http://IvanMiljenovic.wordpress.com
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