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Dec
4
awarded  Yearling
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
Countermeasures of replay attack en.wikipedia.org/wiki/Freshness_(cryptography)
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
Freshness is used to guarantee that a party is currently involved in a communication and not just replaying messagse. Freshness may be achieved by sequence numbers, timestamps or nonces (like in SSL). If you encrypt something that outputs always the same value, you can re-use that potentially. If the input has some sort of randomness (like a nonce), the encryption output will always be different and you cannot replay it.
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
It provides freshness once again. If you do Finish prf(kcs, hash(messageonewithnonce 1)) and Finish prf(kcs, hash(messageonewithnonce 2) the results are different. You cannot replicate this without knowing kcs. The results are different ONLY because of the nonces.
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
My bad. It is actually mutual Finish messages that you receive, as I said in my main answer. Both depend on the messages sent(including nonces) and the master key.
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
Messages 4 and 5 provide mutual entity authentication. It is like a mutual challenge-response protocol but not only challenges, but the whole messages (including the challenges that are inside the response)
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
It is not sent in plaintext. 7.4.8 is digitally signed, and 7.4.9 is a prf(mastersecret,messages). It is not that complicated if you are not obsessed on breaking an RFC. You cannot forge a digital signature, nor you know the master secret, so you cant complete the handshake without steps 4 and 5. The nonces form part of the encrypted data and allow you to provide freshness to both these messages avoiding replays.
May
21
comment Practical ways to prevent Denial Of Service attacks
MACs are calculated with a preshared key amongst two parties. If you dont have the key, you cannot forge it. These keys require secure distribution of course, but it was a bit out of scope of this question
May
21
comment According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
It is the same I said. My message 4 they call 7.4.8. Certificate Verify and message 5 is 7.4.9. Finished.
May
20
comment Using a TPM with Linux
Dont know if this is exactly what you want. But have you tried TrueCrypt? It can encrypt any volume.
May
20
awarded  Commentator
May
20
comment Practical ways to prevent Denial Of Service attacks
Never heard of egress filtering. Does it have anything to do with ingress filtering?
May
20
answered According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?
May
20
revised Practical ways to prevent Denial Of Service attacks
added 434 characters in body
May
20
suggested rejected edit on Is possible to exploit C#, Java, Python or any language that is running inside VM (i.e. managed runtime)
May
20
answered Practical ways to prevent Denial Of Service attacks
May
19
awarded  Citizen Patrol
May
19
answered Encryption and Layers understanding
May
18
comment Serpent cipher technical details in-depth
The block size for AES is always 128. Modes of operation address how to add message dependancy or position dependancy to more than one block of ciphertext.
May
18
awarded  Yearling