Asymmetric Keys

Question

Can someone please validate that I'm on the right track with this line of thought?
I need to generate a private/public key pair using a user's PIN number.
So, I think I need to do the following.
1) Generate a private/public key pair from a PIN number (how, I don't know, as the current generatator uses a random seed).
2) Store the public key but throw away the private key (temporarily).
3) Encrypt data using the stored public key.
4) Later, when the user signs on again, the PIN number will be entered and I'll regenerate the private key dynamically from that PIN number. (I don't want to be able to regenerate the private key from the stored public key in step #2, however).
5) Decrypt data originally stored with the public key using the private key for display to the user.
Am I on the right track? Is this even possible? If so, can someone outline sligntly more detailed pseudocode for me so I know how to proceed? If not, is there another way to achieve my goal?
Message was edited by:
rpalm01

Answer 1

Well, this might make more sense if I explain the
real problem I'm trying to solve. I need to be able
to scan documents and encrypt them using a "public"
type key. Sounds insecure. If you scan them on your system then your client cannot be sure that you have not created an unencrypted copy.
These documents (files) will reside in a
repository on my system. I don't want to be able to
decrypt them, ever. Good. Except that you don't need to decrypt the documents since you had access to the unencrpted document when you scannned it so it is insecure as far as you client is concerned.
However, I'll have a web site
the "client" signs in to where they enter their PIN,Once again it is insecure as far as the client is concerned. He sends the PIN to you so you then know the PIN.
in addition to standard user/password security
information. Then, the document (file) reader can
regenerate the user's private key from the PIN and
decrypt the document (file) appropriately. Now as far as the client is concerned it is really really insecure since given the PIN you can regenerate the private key and decrypt the document.
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But, I guess this assumes that I won't be able to
decrypt the document with the "public" key I'm
storing. That's why I thought I needed an asymmetric
ciper solution. While ever the decryption takes place on your machine this solution is insecure as far as your clients are concerned. Once you have access to the PIN you have access to both the public and private keys.
A tenet of public key encryption is that only the owner of the private key ever has access to the private key. Since you are expecting to regenerate the private key from the PIN you have access to the private key hence as far as you clients are concerned your system is insecure.
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Can you tell I'm confused?Yes.
Your system is insecure regardless of the encryption method use.