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RE: Signing before Encryption and Signing after Encryption
From: "Craig Wright" <cwright () bdosyd com au>
Date: Tue, 28 Mar 2006 07:36:16 +1100


Fairly much.

There are hash based signature schemes for example, but having ones that
may not be repudiated are difficult.

Also comes to good practice. Why sign a message if it may be repudiated
later (though there may be some reasons)?

Craig

-----Original Message-----
From: Gregory Rubin [mailto:grrubin () gmail com]
Sent: 25 March 2006 7:15
To: Craig Wright
Cc: gillettdavid () fhda edu; shyaam () gmail com;
security-basics () securityfocus com
Subject: Re: Signing before Encryption and Signing after Encryption

So it sounds to me that this is more a legal and contractual issue than
a technical issue, or am I misreading this?

Greg Rubin

On 3/22/06, Craig Wright <cwright () bdosyd com au> wrote:

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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those States and Territories of Australia where such legislation exists.

DISCLAIMER
The information contained in this email and any attachments is confidential. If you are not the intended recipient, you 
must not use or disclose the information. If you have received this email in error, please inform us promptly by reply 
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Any views expressed in this message are those of the individual sender. You may not rely on this message as advice 
unless it has been electronically signed by a Partner of BDO or it is subsequently confirmed by letter or fax signed by 
a Partner of BDO.

BDO accepts no liability for any damage caused by this email or its attachments due to viruses, interference, 
interception, corruption or unauthorised access.

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The Norwich University program offers unparalleled Infosec management
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