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RE: Signing before Encryption and Signing after Encryption
From: "Craig Wright" <cwright () bdosyd com au>
Date: Thu, 23 Mar 2006 08:52:43 +1100

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

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

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.


-----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.


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