# secure memory

Steve Burnett (burnettS@RSA.COM)
Tue, 24 Jun 1997 10:27:10 -0700

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    Message-Id: <c=US%a=_%p=RSA_Data_Securit%l=LOBESTER-970624172710Z-7344@LOBESTER.rsa.com>

    From: Steve Burnett <burnettS@RSA.COM>

    To: "'JavaSoft crypto questions'" <java-security@web2.javasoft.com>

    Subject: secure memory

    Date: Tue, 24 Jun 1997 10:27:10 -0700

In cryptography, we are always concerned about leaving "memory
footprints". Suppose I use my private key. I have it stored securely,
but I need to, at some point, load that key in the clear in memory to
perform my operations. When I'm done using that key, if my operating
system does not overwrite memory (simply marks the area as available),
then my private key may still be sitting there in memory after I release
it.

Hence, an attacker may be able to "take a snapshot of the memory" and
see any data left over (this used to be a common technique among college
crackers to steal passwords).

So we in the crypto business want to overwrite memory when we are
done with it.

But if I overwrite something in Java, I may have only overwritten one
copy of the data. Java may have, without my knowledge, copied my key
from one location in memory to another. It may also have done some
memory/disk swapping, so that my key is now sitting on a hard drive
somewhere.

How do I prevent an attacker from looking at my memory when I'm done
with it? And remember, the attacker will use something other than Java
to look at my memory. In other words, don't say that when the attacker
grabs hold of the memory, Java will zero it out first, because the
attacker is not using Java to grab hold.

One suggestion is to provide a key word (such as "secure") that
indicates the data is secure, and cannot be copied or swapped (or if it
is, the previous location must be overwritten).

secure byte[ ] keyData = new byte[16];

So my overall question is, what is JavaSoft doing about this issue?
What are you doing in your version of DSA? What do you suggest we do
with our Java code?

--Steve Burnett
burnetts@rsa.com

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