Why do some scenarios require both ciphering and integrity whereas some scenarios require only ciphering ? What are the factors that decide this in the case of networking domain ?
A:
Encryption protects your text in transport, but it doesn't prove who you are. Adding an integrity control also proves your identity.
A scenario:
I can encrypt data between an ATM and a bank's server. No-one can sniff this traffic and decrypt it, so you can assume that it's "secure". But there's nothing to stop an intermediary from replaying those transactions. Or from replaying traffic seen at a different ATM location, even if the attacker doesn't know what the transaction actually contains. The transactions are not linked to any specific ATM as an entity. So if I withdraw $100 then an intermediary can replay the traffic exchange 10 times from multiple locations and cause me to withdraw $1000.
Adding an integrity control to the exchange can lock the transaction to only a single system and also prove that the transaction was not modified. So, for example, I can get the ATM to sign a digitally timestamped copy of each transaction. Now when the encrypted traffic is replayed, the server can tell that it's a false transaction as the timestamp will be old. Or if the a transaction from a similar ATM at a different location is replayed, then the server can also ascertain that it's talking to a different identity than the one actually expected. So while encryption secures the transaction channel, integrity makes sure that the two end-point decrypting the traffic are actually talking to the party that they expect.
Simon @ http://blog.LabSlice.com
Simon Ellis
2010-10-22 03:44:18
Integrity is about the *message content.* You are talking about authentication and authorization.
EJP
2010-10-22 04:48:44
A:
Most systems that do ciphering also provide message integrity along the way, so your question is really posing a false dichotomy.
EJP
2010-10-22 04:50:14
A:
Ciphering is needed when you want that only authorized people can ACCESS TO SEE the data. Integrity is when authorized people can ACCESS TO MODIFY the data.
As you can see, both ciphering and integrity need an authentication and authorization phase before.
Ex: Data could be chipered with different private keys and deciphered with the relative different public keys. These phases depend onto the authentication & authorization phase.
Ex: when you connect via HTTPS, the first phase is a negotiation of the correct certificate. Typically the client authorize the server checking the trust of the certificate chain.
Ex: You have to access to data in your central DB. Data could be ciphered or not, but the access to the key and/or the data must be done only after an authentication and authorization check.
I hope my considerations help you
robob
2010-10-22 05:23:24
You are mistaken about this. Ciphering provides secrecy. Integrity provides tamper-evidence. Neither of these have anything to do with authentication or authorization.
EJP
2010-10-22 06:53:39
Yes, Ciphering provides secrecy, but you need authentication and authorization to SEE the data. Or better, you need auth and auth to get the key to see the data
robob
2010-10-22 11:38:51
EJP
2010-10-23 01:00:03
robob
2010-10-23 07:25:57
Integrity is still about the message content. The article you cite is rather confused on this point, as are you. There are four classical aspects: privacy, integrity, authentication, and authorization.
EJP
2010-10-23 08:52:35
robob
2010-10-23 14:47:05