Re: An Honest and Simple Question.
- From: gordonb.xppxp@xxxxxxxxxxx (Gordon Burditt)
- Date: Fri, 16 Jul 2010 15:59:34 -0500
In my view a cipher should be able to go solo completely on the back
of a theoretically unbreakable mathematical algorithm, that is by
being used in the hands of a non-specialist office worker with minimal
training (that means no user-assistance whatever).
Unfortunately, these two parts have nothing to do with each other.
The encryption algorithm is something you can change out with a
software algorithm and the users don't have to care at all. The
strength of the algorithm has nothing to do with the amount of
administration an office worker needs to do. The *type* of the
algorithm (symmetric vs. asymmetric, for example) may affect this.
That means that if the user clicks on a PDF, MP3, or video file to
attach to an email, you need to handle it correctly, not quietly
corrupt it, and not have to have someone around to explain that
encryption is for the printable subset of ASCII only.
You will have these problems with user/manager administration using
*ANY* crypto system:
1. You have to keep the key secret. Don't fall for phishing requests
for a copy of whatever file a key is kept in.
2. For two users to communicate by encrypted email, they need to
set up a key first. New users (e.g. new hires) will enter the
group. Asymmetric cryptography, which yours is *not*, has the
advantage that it can send the public key with a message, so anyone
receiving it can send an encrypted reply using a crypto-aware email
client that stores keys for correspondents. No setup, it Just
Works. Also, you can set up public key registries without blowing
Now explain how two users set up to communicate by encrypted mail,
using your cryptography. You can't send the secret key with the
message, that would blow all your security. Of course, your answer
is "Duh, that's a management problem". Of course it is, but it's
very relevant to the problem that your crytography (and any symmetric
cipher) takes a lot more administration than an asymmetric one.
3. You have to educate users about what must be sent encrypted and
what need not be. You will have cases where you need to send email
to someone who has no key set up (e.g. ordering pizza). A smart
email client can automatically encrypt if a key is available, and
warn if it's about to send something unencrypted, but users have
to understand the warning and deal with the fact that it's OK to
order pizza unencrypted but not send client lists and sales reports
to the home office unencrypted.
4. Somehow the user, or email client program, has to figure out
what key to use for what message, both encrypting and decrypting.
Email client programs can be pretty smart but they have to have
something to go on. That includes contending with the fact that
users may have multiple e-mail addresses, and users may have multiple
keys for various purposes (such as "work" and "home").
Clearly that is
not going to be the case ever with either AES (that you are so
obsessively single-minded about) and even more so the RSA cipher.
I didn't mention AES in my post. It deserves mention that it is a
proof-of-concept that you *can* read plaintext as bytes and output
plaintext as bytes, without mangling the message. That code still
works even if AES is broken and can only be trusted for 99-cent app
These are always going to be costly to run in that they require
specialist management that must be provided by a highly informed,
Why interactive? Periodic key changes, adding and deleting users,
and updating the email client program and encryption program don't
have to be kept that up to date.
The hip-pocket nerve is most sensitive to cost in the world of e-
commerce security of information.
e-commerce (and particularly SSL) uses RSA for a very significant
reason: It's an asymmetric cipher. An email client can include
my encrypted mail certificate in my outgoing email, and the recipient
can then reply with no further information. An asymmetric cipher
can also be used to authenticate identity with certificates. A
symmetric cipher cannot do that. RSA beats the snot out of any
symmetric cipher for some very important properties crucial to
Remember, SSL needs to be able to encrypt images.
You *still* haven't explained how two users who want to communicate
using your ciphers set up a key. Especially if the only communication
method they have is the Internet.
This a very discerning market that
unlike the national security arm of cryptography is not a captive one
and is not bound by so-called 'advanced' 'standard' (neither of these
is true) - they will kick the 'standard' bit (pardon the pun) into
touch at the drop of a hat if it is demonstarted to them that they can
go it alone in managing their own network - that is now a distinct
They will need an asymmetric cipher. Yours is not one. If you do come
up with a theoretically unbreakable *asymmetric* cipher, the world will
beat a path to your door. Assuming, of course, that it handles images
I wouldn't take any bets on AES or RSA ciphers being around more than
another ten years. Old ciphers are as useless as old newspapers.
True. But a symmetric cipher cannot replace RSA for use in e-commerce.
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