Hopping in here (because I can not see he original post):
As I understand it, a digital signature is just a number which is
computed from a message as follows:
- compute a cryptographic hash of the message;
- encrypt that hash with the author's private key;
- append the encrypted hash to the message.
Then, any recipient of the message can confirm that it has not been
altered:
- recompute the cryptographic hash of the message;
- decrypt the appended encrypted hash, with the auhor's public key;
- compare the two hashes for equality.
It is impossible to alter a message (without being detected) unless you
know the author's private key. Knowing his /public/ key, is not enough.
I'm using the terms private & public key here, with their meaning in an
asymmetric encryption process such as RSA.
In a database environment, the "message" might be the content of a memo
field, and the "author" would be the person or program who placed the
original content into that field. You could sign that content as
described above, and store the signature (ie. appeneded encrypted
message hash) in a seperate field, or even within the memo field
itself.
So, your problem is really not an Access one. Your problem is to
understand what a digital signature is, and how to create and manage
them appropriately. Do not just implement what I wrote above! You
really need some expert advice by a competent cryptographer.
HTH,
TC
