[Cryptography] Encryption opinion

[Bear]

On Thu, 2014-08-14 at 15:38 -0400, Jorge Perdomo wrote:
> Hello cryptography experts,
> 
> 
> I am the co-founder of goTenna, a small startup in Brooklyn that is
> developing a product that is intended to allow resilient decentralized
> and encrypted communications for people using smartphones regardless
> of central connectivity.
> 
> 
> We launched publicly a few weeks ago with the plans of using 1024-bit
> RSA for our encryption, but have received a lot of complaints from
> people telling us that RSA wasn't safe and whatnot.  I'm not an
> expert, but through our research we felt like 1024RSA for a 160
> character text message was plenty strong, but we could be wrong.

NIST has been recommending against the use of 1024 bit RSA 
since 2010.  People are right to be worried about it, although
the cause for worry is not immediate.  It's good enough for 
data in flight and no 1024-bit modulus has yet been factored 
(at least not publicly), but it is no longer adequate to 
protect data at rest.  

IOW, your clients don't need to be worried about someone 
listening in on the traffic in real time unless you're 
making a key management, padding, or protocol mistake 
somewhere.  On the other hand, if your clients assume 
the encrypted text messages get recorded somewhere, they 
are reasonable to be worried that someone who cares a 
whole lot and is willing to devote substantial resources 
to it might break them a relatively short time (less than 
five years) in the future.

Bear