Tag Info

Hot answers tagged

23

Non-repudiation is about having a proof that the announced author really wrote the message -- and such the proof can be verified even without the consent of the said author: the author must not be able to repudiate his message. This calls for asymmetric cryptography (since verification can be done without the author consent, it cannot use whatever secret ...


19

No. Digital signatures are not sufficient for non-repudiation -- not by a long shot. Non-repudiation is a legal concept. It means that, if there is a dispute, in a lawsuit it will be possible to hold one party to their commitments. For example, mathematical schemes that claim to provide non-repudiation have to withstand the "jury attack". Some expert ...


10

Authenticity is about one party (say, Alice) interacting with another (Bob) to convince Bob that some data really comes from Alice. Non-repudiation is about Alice showing to Bob a proof that some data really comes from Alice, such that not only Bob is convinced, but Bob also gets the assurance that he could show the same proof to Charlie, and Charlie would ...


8

Non-repudiation is not done with public keys; non-repudiation is done with a legal framework which defines responsibilities and duties. Though details depend on the jurisdiction, most will more or less follow the following scheme: A signature that you perform is binding as long as you did it. That's the definition. The rest is about what happens in case of ...


6

One simple protocol that can be verified by a certain target user but not by third party: Use a Diffe-Hellman keyexchange on your key and the receivers key Use the shared key to encrypt a message and add a MAC This protocol offers the first three properties, but not the fourth. So the answer is NO. Everybody who knows the shared secret can forge the ...


6

Unless there is some special configuration I'm not familiar with: Joe user. There is an Edit function, hiding right there under Other Actions (in Outlook 2007, at least...). Note you can only see this when you open it in full message view, and not in the preview pane (as I usually read it...). Note also that this is not available via OWA. It may be ...


5

Encryption with a secret symmetric key does not prove authenticity unless you use an authenticated encryption mode of operation such as GCM. Authenticated encryption algorithms generate a Message Authentication Code (MAC) in addition to encrypting the message, and if the shared key is properly secured this can be used to prove the authenticity and integrity ...


5

Authentication and non-repudiation are two different sorts of concepts. Authentication is a technical concept: e.g., it can be solved through cryptography. Non-repudiation is a legal concept: e.g., it can only be solved through legal and social processes (possibly aided by technology). Some people have been taught that non-repudiation can be provided ...


4

Search this site on non-repudiation. You'll find lots of information about the topic. In particular, you'll discover that non-repudiation is not a technical property (contrary to what cryptographers might tell you); it is primarily a socio-legal property. Thus, non-repudiation cannot be assured through technical means alone: it can only be achieved ...


4

Why would you want authentication? To know that an e-mail, piece of software, web site, or other item originated from a specific person, computer system, or company. Generally you are using the identity of origin as part of a decision about trust. If an e-mail comes from your bank and you authenticate the e-mail, you place a certain amount of trust in the ...


4

Encryption does not protect against malicious alterations. If you encrypt some data with a stream cipher like RC4 or AES-CTR, then an attacker can decide to flip any bit he wants on the ciphertext, and, upon decryption, this flips the corresponding bit in the plaintext. This allows surgical modifications. With block ciphers in CBC mode, things are a bit less ...


4

This setup does not provide non-repudiation. Non-repudiation is very challenging to achieve, and based on what I am hearing, you are nowhere near it. Based on your description, you're not going to be able to prove the validity of the emails through technical arguments alone. You will have to use non-technical arguments. You might find other witnesses to ...


4

MasterCard and VISA enforce very strict regulations on any system which operates in any way in the vicinity of their precious credit cards. If a bank or an ATM operator lets the communication be tapped, then the VISA thugs will skin them alive, trample their organs, then expose their dismembered bodies on the Wall Street Bull, as a warning for other banks. ...


3

The answer to your question would be: no. The reason behind it being that the only one losing a bit of money if all of your previous mentioned exploits were possible, would be the bank. A bit of money you say? Yes a bit of money, the money you can loose with an ATM are rather low compared to, for instance, SWIFT transactions. Now does that mean there ...


3

Legal matters depend on jurisdiction, and there are a lot of those. However, in many of them, a signature is "legally-binding" if the signer really did it. When you sign, how you do it does not matter as far as legal binding is defined; putting your name at the end of an email is also a legally binding signature. Several cases have shown that an oral ...


2

Firstly, I am interpreting your question to mean that end-users will not be using digital signatures. They can't be bothered, etc. I do answer this with the use of non-interactive signatures on the server that the end-user would never see or be affected by. Question 1: ... how easy is it for suspect employees to alter un-signed e-mail evidence... in their ...


1

PKI can be used to generate digital signatures. These can be used to provide non-repudiation. As referred to in the previous answer, the burden of proof is what is important where non-repudiation is concerned. The ability to prove non-repudiation which has been assured through cryptography (specifically PKI) can be aided by demonstrating that the bearer of ...


1

If your back end requires the plain text password, why not cache the password on a secure API proxy server? client --- oauth---> [Data Center] ---> HTTP/S ---> App that caches passwords ---> backend There are many ways to do OAuth 2.0, and I would suggest using the normal token that already includes an expiration, scope, and signature ...


1

If your original construction gives you the security properties you want, then simply replacing Alice_PU[KS] with Bob_PU[KS] should do the job. Think of the database as a communication channel to your future self. Future Bob should still have his keypair, so can both decrypt the session key and verify the signature.



Only top voted, non community-wiki answers of a minimum length are eligible