From ngps at POST1.COM  Mon Jun  2 18:06:00 2003
From: ngps at POST1.COM (Ng Pheng Siong)
Date: Tue, 3 Jun 2003 00:06:00 +0800
Subject: [PYTHON-CRYPTO] AES in M2Crypto advice
In-Reply-To: <200305311336.38234.jason@oes.co.th>
References: <200305311336.38234.jason@oes.co.th>
Message-ID: <20030602160600.GA572@vista.netmemetic.com>

On Sat, May 31, 2003 at 01:36:31PM +0700, Jason H. Smith wrote:
> First, a quick question, if I may.  I did not follow the instructions in
> INSTALL saying to modify distutils.  Instead, I simply symlinked swig/ to
> SWIG, and it looks fine.  Did I mess anything up?

Hi,

Yes, it's fine. I should do that for my source, too. ;-)

> But mainly, I want to solicit advice for using AES in CBC mode to send an
> entire hard drive image over TCP.

Let's talk a little higher-level:

Content security: encrypting your disk image so that its content is secure
should the encrypted image fall into the wrong hands.

Communication security, a la SSH or SSL: your content is secure while it is
moving across the wire; at the end points the content is in the clear.

Of course, you can transmit secured content, say, a PGP message, over SSH
or SSL.

What are you attempting to do? What are you protecting against? Must you
write a new program to do the low-level crypto? Can you not compose
existing tools to achieve your objectives?


> Thus far, I am basically using this procedure:
> 1) key = md5 hash of a passphrase
> 2) iv = whatever
> 3) create a BIO.MemoryBuffer object
>   4) read a 10MB chunk
>   5) a) create a BIO.CipherStream object
>      b) set_cipher('aes_128_cbc', key, iv, 1)
>   6) encrypt the block, following demo/bio_ciph_test.py
>   7) write the ciphertext
>   7) set new iv = ciphertext[-16:]
>   8) go back to step 4

Some thoughts:

1. There aren't unit tests for BIO.CipherStream, meaning it may be buggy.  ;-)

2. I think evp_ciph_test.py has an easier model:

    def cipher_filter(cipher, inf, outf):
        while 1:
            buf=inf.read()
            if not buf:
                break
            outf.write(cipher.update(buf))
        outf.write(cipher.final())
        return outf.getvalue()

    def test_cipher(algo):
        otxt='against stupidity the gods themselves contend in vain'
        print 'testing', algo, '...',

        k=EVP.Cipher(algo, 'goethe','12345678', enc, 1, 'sha1', 'salt', 5)
        pbuf=cStringIO.StringIO(otxt)
        cbuf=cStringIO.StringIO()
        ctxt=cipher_filter(k, pbuf, cbuf)
        pbuf.close()
        cbuf.close()

The function cipher_filter, with variation, is what I use in my own code.
Set up the cipher as in test_cipher.  Pass in file objects for inf and
outf. (Remove the last line that says outf.getvalue(). Maybe also remove
the next-to-last line, depending on your calling code.)

But do first consider the high-level issues of what you're doing.

Cheers.

--
Ng Pheng Siong <ngps at netmemetic.com>

http://firewall.rulemaker.net  -+- Manage Your Firewall Rulebase Changes
http://www.post1.com/home/ngps -+- Open Source Python Crypto & SSL



From jason at OES.CO.TH  Mon Jun  2 19:13:17 2003
From: jason at OES.CO.TH (Jason H. Smith)
Date: Tue, 3 Jun 2003 00:13:17 +0700
Subject: [PYTHON-CRYPTO] AES in M2Crypto advice
In-Reply-To: <20030602160600.GA572@vista.netmemetic.com>
References: <200305311336.38234.jason@oes.co.th>
            <20030602160600.GA572@vista.netmemetic.com>
Message-ID: <200306030013.22666.jason@oes.co.th>

On Monday 02 June 2003 11:06 pm, Ng Pheng Siong wrote:
> Let's talk a little higher-level:
>
> Content security: encrypting your disk image so that its content is
> secure should the encrypted image fall into the wrong hands.
>
> Communication security, a la SSH or SSL: your content is secure while
> it is moving across the wire; at the end points the content is in the
> clear.

To clarify, I can explain the project.  I recently posted to the Python 
newsgroup, but I will briefly explain here, too.

Basically, I'm writing a Knoppix derivitive that uses zeroconf and SLP to 
easily do a full backup or restore of e.g. your laptop's hard drive, 
storing the image on a network file server.  The server part can be 
implemented farily easily by a Unix admin; but it works out of the box 
with my company's upcoming file servers.

The problem is, the system administrator, or an intruder, should not have 
access to, say, the CEO's laptop image; so there's the encryption 
requirement.  Also, I want this to be compatible with any SMB (mabye NFS) 
file server, so encryption is done on the client machine before it hits 
the wire.  So, with that requirement, I get on-the-wire encryption for 
free.  And of course, the image sits on the server protected via AES and 
an ostensibly strong passphrase.

(Although a TODO of mine is to use a random encryption key; and once the 
backup is made, the file server burns a custom restore CD exactly like 
the original except with the key hard-coded into the restore software.  
This way, the security is not a matter of good or bad passphrases.  Now, 
it's a matter of keeping an important CDROM safe, which is much more 
intuitive to your average employee.)

> What are you attempting to do? What are you protecting against? Must
> you write a new program to do the low-level crypto? Can you not compose
> existing tools to achieve your objectives?

What do you mean by low-level crypto?  This is Python, after all! :p  
Hopefully, though, I've clarified above.

Thanks for the implementation advice, as well.  I'm relatively new to 
Python and GUI programming.  So I'm still boggling over the correct 
approach.

Best.

-- 
GPG: 03EE 9EB8 E500 874A F509  7B95 9B9A 84A1 26E9 4F79
http://www.ece.utexas.edu/~jhs/public_key.gpg
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From ngps at POST1.COM  Thu Jun  5 08:46:05 2003
From: ngps at POST1.COM (Ng Pheng Siong)
Date: Thu, 5 Jun 2003 14:46:05 +0800
Subject: [PYTHON-CRYPTO] AES in M2Crypto advice
In-Reply-To: <200306030013.22666.jason@oes.co.th>
References: <200305311336.38234.jason@oes.co.th>
            <20030602160600.GA572@vista.netmemetic.com>
            <200306030013.22666.jason@oes.co.th>
Message-ID: <20030605064605.GB712@vista.netmemetic.com>

On Tue, Jun 03, 2003 at 12:13:17AM +0700, Jason H. Smith wrote:
Content-Description: signed data
> The problem is, the system administrator, or an intruder, should not have
> access to, say, the CEO's laptop image; so there's the encryption
> requirement.

IMHO, it is more important that the thief who steals the CEO's laptop or
the subsequent black market buyer do not get access to the files on it.

Install a crypto filesystem type thingy on the laptop and train the CEO to
use it properly. Then just backup the disk image normally; sensitive stuff
should already be secured by the crypto filesystem. You can escrow the
passphrase with the corporate lawyers or, ahem, a trusted third party. (Not
your $25 SSL cert vendor, fer sure. ;-)


> Thanks for the implementation advice, as well.  I'm relatively new to
> Python and GUI programming.  So I'm still boggling over the correct
> approach.

Yes, having fun is important too. ;-)

--
Ng Pheng Siong <ngps at netmemetic.com>

http://firewall.rulemaker.net  -+- Manage Your Firewall Rulebase Changes
http://www.post1.com/home/ngps -+- Open Source Python Crypto & SSL



From jason at OES.CO.TH  Thu Jun  5 09:12:02 2003
From: jason at OES.CO.TH (Jason H. Smith)
Date: Thu, 5 Jun 2003 14:12:02 +0700
Subject: [PYTHON-CRYPTO] AES in M2Crypto advice
In-Reply-To: <20030605064605.GB712@vista.netmemetic.com>
References: <200305311336.38234.jason@oes.co.th>
            <200306030013.22666.jason@oes.co.th>
            <20030605064605.GB712@vista.netmemetic.com>
Message-ID: <200306051412.06696.jason@oes.co.th>

On Thursday 05 June 2003 01:46 pm, Ng Pheng Siong wrote:
> IMHO, it is more important that the thief who steals the CEO's laptop
> or the subsequent black market buyer do not get access to the files on
> it.
>
> Install a crypto filesystem type thingy on the laptop and train the CEO
> to use it properly. Then just backup the disk image normally; sensitive

Surely.  But these days, that might be a tall order.  CEOs aren't known 
for openly accepting security technology (and its implied 
inconveniences).  So we'll start small; and when it dawns on him or her 
that the backups are more secure than the laptop itself, that's when we 
make our move!

But joking aside, I think your average corporate executive understands 
meatspace security much better.  For example, most will implement a good 
security system, perhaps with guards.  They will lock their office when 
they leave, and (presumably) they will never let their laptop out of 
their site, because they know how important it is.

But computer security is more mysterious and confusing, so I think it's 
harder for some executives to make a good informed decision (witness IIS 
deployment statistics).  That's why it's very important for crypto and 
security in general to be as user-friendly as possible as the mainstream 
world becomes dependent on it.  For example, bad passwords are human 
nature; and I think no amount of education will solve it.  That's why 
token-based authentication is smarter.  People know not to  lend out 
their credit card or house keys; and so they'll naturally guard their 
smart ID card for accessing the financial database or whatever.  
Personally, I can't wait for every PC to come with a smart card reader.

Anyway, that's enough OT for me for one day ;)

-- 
GPG: 03EE 9EB8 E500 874A F509  7B95 9B9A 84A1 26E9 4F79
http://www.ece.utexas.edu/~jhs/public_key.gpg
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From ngps at POST1.COM  Mon Jun 23 20:47:41 2003
From: ngps at POST1.COM (Ng Pheng Siong)
Date: Tue, 24 Jun 2003 02:47:41 +0800
Subject: [PYTHON-CRYPTO] [Announce] M2Crypto 0.11
Message-ID: <20030623184741.GA1536@vista.netmemetic.com>

Hi,

M2Crypto 0.11 is now available.

What's new:

- Fixes to memory leaks. (Thanks Dave Berkeley and Brent Chun.)
- ZServerSSL updated for Zope 2.6.1.
- ZSmime on Zope 2.6.1 interoperates with Mozilla 1.1. (No code change.)


As usual, M2Crypto is here:

    http://www.post1.com/home/ngps/m2

Cheers.


--
Ng Pheng Siong <ngps at netmemetic.com>

http://firewall.rulemaker.net  -+- Manage Your Firewall Rulebase Changes
http://www.post1.com/home/ngps -+- Open Source Python Crypto & SSL