Two tidbits of potential interest

David Shaw dshaw at
Thu Sep 24 19:21:48 CEST 2009

On Sep 24, 2009, at 12:30 PM, M.B.Jr. wrote:

> Hi David,
> about the first "tidbit":
> On Tue, Sep 22, 2009 at 6:08 PM, David Shaw <dshaw at>  
> wrote:
>> First of all, someone has factored a 512-bit RSA key (the one used to
>> protect a TI programmable calculator, it seems).  It took 73 days  
>> on a
>> dual-core 1900Mhz Athlon64.  It took just under 5 gigs of storage  
>> and around
>> 2.5 gigs of RAM.  In other words: not much at all.  It's not some big
>> distributed project - rather it's a single guy who wanted to factor  
>> it and
>> just left it running in the background for 2 and a half months.   
>> (This is
>> actually a month old - forgot to send it before now).
> dummy question:
> by factoring a public key integer, one can get somehow to its
> corresponding private key?

Yes, that's exactly what happens.  If you factor the public key, you  
can derive the private key.

In the case above, it seems TI was using that 512-bit key to ensure  
that only TI could generate software images for their calculator.   
With the key factored, anyone can sign a software image.


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