Storing a private key

microsoft.public.dotnet.security

26 Jul 2006 10:16 AM

pigeonrandle

Hi,
I have a server and client program. The client encrypts data being sent
to the server using the servers public key before it transmits it to
the server over a tcp connection.

The question i have though, is where do i store the private key on the
server so that it will be safe?! In my mind (at least for the moment
....) there is no place to put it that couldn't be compromised in one
way or another.

The server also uses the same public key to encrypt other files it has
stored containing database usernames and passwords - hence my concerns
about storing the private key somewhere safe.

I would have liked to just 'keep the key in memory', but we all know
what would happen when Windows got bored and decided it was time to
blue-screen-of-death :-0

Thanks in advance for your help,
James Randle.

26 Jul 2006 2:34 PM

Joe Kaplan (MVP - ADSI)

Storing secrets is a hard problem. There is an entire chapter about this
topic in "Writing Secure Code" which is well worth a read if you are serious
about understanding this in detail.

People typically use things like DPAPI for helping to store secrets, but
that doesn't provide a complete solution and also comes with its own issues.
Since you have a private key for a certificate, you can also store that in a
standard key container and apply extra security to it. However, there might
not be an easy way to use the password protection feature on the key and
still access it from a server application.

Storing encrypted passwords is generally regarded as a bad design that
introduces much more risk than storing a salted hash of the password
instead. When you encrypt, if your key is compromised, the user's plaintext
passwords can be recovereded directly. When you hash, you don't even know
the user's plaintext password. Only brute force techniques can be used to
try to get the plaintext, and a good design can typically make that effort
too expensive to contemplate.

Joe K.

--
Joe Kaplan-MS MVP Directory Services Programming
Co-author of "The .NET Developer's Guide to Directory Services Programming"
http://www.directoryprogramming.net
--

Show quoteHide quote

"pigeonrandle" <pigeonran***@hotmail.com> wrote in message
news:1153908969.044048.33770@i3g2000cwc.googlegroups.com...
> Hi,
> I have a server and client program. The client encrypts data being sent
> to the server using the servers public key before it transmits it to
> the server over a tcp connection.
>
> The question i have though, is where do i store the private key on the
> server so that it will be safe?! In my mind (at least for the moment
> ...) there is no place to put it that couldn't be compromised in one
> way or another.
>
> The server also uses the same public key to encrypt other files it has
> stored containing database usernames and passwords - hence my concerns
> about storing the private key somewhere safe.
>
> I would have liked to just 'keep the key in memory', but we all know
> what would happen when Windows got bored and decided it was time to
> blue-screen-of-death :-0
>
> Thanks in advance for your help,
> James Randle.
>

26 Jul 2006 2:38 PM

pigeonrandle

In answer to my self!

http://groups.google.com/group/microsoft.public.dotnet.security/browse_thread/thread/f1b6b4240771c8d2/80d4620876fa8b75?lnk=gst&q=storing+private+key&rnum=1#80d4620876fa8b75

unless of course anyone else feel like they should add something
specifically pertaining to my exmaple?

Cheers,
James Randle.

pigeonrandle wrote:
Show quoteHide quote

> Hi,
> I have a server and client program. The client encrypts data being sent
> to the server using the servers public key before it transmits it to
> the server over a tcp connection.
>
> The question i have though, is where do i store the private key on the
> server so that it will be safe?! In my mind (at least for the moment
> ...) there is no place to put it that couldn't be compromised in one
> way or another.
>
> The server also uses the same public key to encrypt other files it has
> stored containing database usernames and passwords - hence my concerns
> about storing the private key somewhere safe.
>
> I would have liked to just 'keep the key in memory', but we all know
> what would happen when Windows got bored and decided it was time to
> blue-screen-of-death :-0
>
> Thanks in advance for your help,
> James Randle.

26 Jul 2006 8:18 PM

Alun Jones

"pigeonrandle" <pigeonran***@hotmail.com> wrote in message
news:1153908969.044048.33770@i3g2000cwc.googlegroups.com...
> I have a server and client program. The client encrypts data being sent
> to the server using the servers public key before it transmits it to
> the server over a tcp connection.
>
> The question i have though, is where do i store the private key on the
> server so that it will be safe?! In my mind (at least for the moment
> ...) there is no place to put it that couldn't be compromised in one
> way or another.

Correct. The same is true if you store the certificate in a safe. The
person who has access to the safe and its combination could very easily open
the safe, pull out the certificate, and use it.

> The server also uses the same public key to encrypt other files it has
> stored containing database usernames and passwords - hence my concerns
> about storing the private key somewhere safe.

How about the certificate store? Seems like a good place to store a
certificate and its private key.

> I would have liked to just 'keep the key in memory', but we all know
> what would happen when Windows got bored and decided it was time to
> blue-screen-of-death :-0

What you're touching on here is the "rouge admin" theory of computer
security, exemplified by the question "what software / settings do I use to
protect my systems and their data from the system administrators?"

The answer is "none". Your administrators are administrators. The people
who view the memory dump on your system are administrators. The people who
can expose keys from the certificate store are administrators.

Administrators are trustworthy individuals who can be entrusted with
complete control of all data and operations on the systems that they
administer.

If you cannot state that about your administrators, demote and / or fire
them, replacing them with people that you are willing to trust - or, remove
the sensitive data from the systems that they administer.

The certificate store is an adequate place to store private keys. Learn how
to protect your private keys using NTFS rights on the Crypto\RSA directory.
And trust - or remove - your administrators.

Alun.
~~~~
[Please don't email posters, if a Usenet response is appropriate.]

--
Texas Imperial Software | Find us at http://www.wftpd.com or email
23921 57th Ave SE | a***@wftpd.com.
Woodinville WA 98072-8661 | WFTPD, WFTPD Pro are Windows FTP servers.
Fax/Voice +1(425)807-1787 | Try our NEW client software, WFTPD Explorer.

27 Jul 2006 8:19 AM

pigeonrandle

Alun,
Thanks for your insight. I guess i can trust them, and i presume (as a
precaution) that i can enter a clause in the EULA stating that it is
their responsibility to ensure their network is secure..?

Cheers,
James.

Alun Jones wrote:
Show quoteHide quote

> "pigeonrandle" <pigeonran***@hotmail.com> wrote in message
> news:1153908969.044048.33770@i3g2000cwc.googlegroups.com...
> > I have a server and client program. The client encrypts data being sent
> > to the server using the servers public key before it transmits it to
> > the server over a tcp connection.
> >
> > The question i have though, is where do i store the private key on the
> > server so that it will be safe?! In my mind (at least for the moment
> > ...) there is no place to put it that couldn't be compromised in one
> > way or another.
>
> Correct. The same is true if you store the certificate in a safe. The
> person who has access to the safe and its combination could very easily open
> the safe, pull out the certificate, and use it.
>
> > The server also uses the same public key to encrypt other files it has
> > stored containing database usernames and passwords - hence my concerns
> > about storing the private key somewhere safe.
>
> How about the certificate store? Seems like a good place to store a
> certificate and its private key.
>
> > I would have liked to just 'keep the key in memory', but we all know
> > what would happen when Windows got bored and decided it was time to
> > blue-screen-of-death :-0
>
> What you're touching on here is the "rouge admin" theory of computer
> security, exemplified by the question "what software / settings do I use to
> protect my systems and their data from the system administrators?"
>
> The answer is "none". Your administrators are administrators. The people
> who view the memory dump on your system are administrators. The people who
> can expose keys from the certificate store are administrators.
>
> Administrators are trustworthy individuals who can be entrusted with
> complete control of all data and operations on the systems that they
> administer.
>
> If you cannot state that about your administrators, demote and / or fire
> them, replacing them with people that you are willing to trust - or, remove
> the sensitive data from the systems that they administer.
>
> The certificate store is an adequate place to store private keys. Learn how
> to protect your private keys using NTFS rights on the Crypto\RSA directory.
> And trust - or remove - your administrators.
>
> Alun.
> ~~~~
> [Please don't email posters, if a Usenet response is appropriate.]
> --
> Texas Imperial Software | Find us at http://www.wftpd.com or email
> 23921 57th Ave SE | a***@wftpd.com.
> Woodinville WA 98072-8661 | WFTPD, WFTPD Pro are Windows FTP servers.
> Fax/Voice +1(425)807-1787 | Try our NEW client software, WFTPD Explorer.