🚀 go-pugleaf

In article <1992Oct13.172459.28720@zip.eecs.umich.edu> ayman@eecs.umich.edu (Ayman I. Kayssi) writes:
>I posted a question on comp.unix.questions about how to get a shell by email,
>that is a shell that would execute what's in the body of an email message.
>All the details have been worked out except for one thing: security.
>Currently, security is obtained using the following:
>1- the subject of the message is a certain (fixed) special string
>2- a header line is added which contains an encrypted string
>You can see that the problem is that the message itself contains the security
>keys, and therefore anyone can intercept the email and fake a message...
>So, are there any suggestions on how to make this more secure?
>Email or post...

Sounds like an application of RSA digital signatures to me.

Have all of your "authorised users" generate a keypair. They each give
you their public keys, which you store in some sort of database.

Then the "authorised users" can sign the list of commands (script) they want
to have executed and mail it in.

You check the signature when the mail is received before you run
the script they send you. 

This scheme is such that, if the message is altered, or an unauthorised
user (without access to a secret key corresponding to a public key you
have on file) sends a script the signature shouldn't verify.

Problems:
1. You have to trust your authorised users to keep their private keys
secret.
2. Potential legal problems due to the fact that RSA is patented.
For commercial use, you'll certainly have to pay a licence fee.
3. You may have problems if the script is such that, if run more than
once, may do something you don't want. Nothing prevents some malicious
person from intercepting the mail and resending it some number of times.
4. others I haven't thought of.

PGP is an example of a program which could be used to implement this.
RSA Data Security, Inc. also sells tools which will enable you to do this.

Mark
-- 
Mark Henderson
markh@wimsey.bc.ca
RIPEM key available by key server/finger/E-mail