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RE: Signing before Encryption and Signing after Encryption
From: "David Gillett" <gillettdavid () fhda edu>
Date: Wed, 22 Mar 2006 15:26:08 -0800

  You're right, there's the entire additional dimension of tying
the private key to the entity it is supposed to represent.  That's
not part of the encryption, but it's a necessary part of the
legality.  I find it far too easy to get caught up in the
technical aspects....

David Gillett
 

-----Original Message-----
From: Craig Wright [mailto:cwright () bdosyd com au] 
Sent: Wednesday, March 22, 2006 1:53 PM
To: gillettdavid () fhda edu; shyaam () gmail com; 
security-basics () securityfocus com
Subject: RE: Signing before Encryption and Signing after Encryption


Hi David,
Non-repudiation has different requirements in different legal 
jurisdictions.

There needs to be a manner to verify the keys (i.e. PKI). I 
can get a verisign certificate calling myself Bill Gates. 
This does not mean for the purpose of legal contractual 
negotiations that I am Bill Gates. I could sign an email as 
such though.

For non-repudiation to work, there needs to be an attestation 
by the operator of the certificate authority.


The following are some guidelines for non-repudiation, based 
on locality of course:
Australia     National Electronic Authentication Council,

              Liability and other Legal Issues in the Use of 
PKI Digital Certificates (May 2002).

EC,           Directive 1999/93/EC of the European Parliament and of
the Council
Austria,      Signature Law, 2000

England, Scotland and Wales

              Electronic Communications Act, 2000

Germany       Signature Law, 2001

Sweden        Qualified Electronic Signatures Act (SFS 
2000:832) (in swedish).


India         Information Technology Act, 2000

New Zealand   Electronic Transactions Act, 2003 sections 22-24

USA           Electronic Signatures in Global and National Commerce
Act (E-SIGN),

              at 15 U.S.C. 7001 et seq
Switzerland   Federal Law on Certification Services Concerning the
Electronic Signature, 2003


To take a quote from the English Ministry associated with 
Digital Signature law:
"A private key authenticated by a digital certificate 
generated within a PKI can be considered as the electronic 
equivalent of a passport. Both establish identities for 
persons who have met the requisite identity checks. The 
community accepts the validity of the holder's identity 
because it trusts the issuer. The identity can be used to 
authenticate the holder in subsequent transactions without 
directly involving the issuer."

Web of trust models such as PGP can result in a signature, 
but the issue of non-repudiation is not fulfilled in that the 
issuer can not be held to account separately (as it is a self 
signed certificate).

In situations where the parties have had prior dealings, it 
may be possible to verify the owner of the public key, for 
example, at a personal meeting, parties may exchange public 
keys on floppy disks (eg key signing parties). However, if 
the parties are unknown to each other, and perhaps in 
different jurisdictions, the requisite level of confidence is 
not present. The solution to this lies in the public key 
infrastructure and is governed by different levels of trust.


Regards
Craig

-----Original Message-----
From: David Gillett [mailto:gillettdavid () fhda edu]

Sent: 23 March 2006 8:24
To: Craig Wright; shyaam () gmail com; security-basics () securityfocus com
Subject: RE: Signing before Encryption and Signing after Encryption

  Does non-repudiation require anything more than assurance 
that the private key (a) MUST have been used, and (b) HASN'T 
been compromised?
Are you just alluding to the measures which support those 
assertions, or to some additional requirement(s) that escapes me?

  [If your private key isn't really private, all bets are off.]

David Gillett


-----Original Message-----
From: Craig Wright [mailto:cwright () bdosyd com au]
Sent: Wednesday, March 22, 2006 12:56 PM
To: gillettdavid () fhda edu; shyaam () gmail com;

security-basics () securityfocus com
Subject: RE: Signing before Encryption and Signing after Encryption




True, but the argument was not one as to which is the better method.
There are several secure hashing algorithms.




Further there is more to verification to source than just asymmetric

keys. Non-repudiation is a complex field in itself and requires a

entire range of associated infrastructure.


Regards
Craig



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