![]() Click here - for non-technical blog posts I've written about on topics related to information security (infosec).After giving up Pastebin for posting IOCs, I started using Github, so click here for posts from my Github account.From December 2018 through December 2020, I ocassionally posted information to Pastebin, so click here for posts from my Pastebin account.Click here - for some tutorials that will help for these exercises. Click here - for training exercises to analyze pcap files of network traffic.Almost every post on this site has pcap files or malware samples (or both). ![]() Since the summer of 2013, this site has published over 2,200 blog entries about malicious network traffic. I just highlighted the Hash here to reinforce the fact that since both peers were authenticated in Phase 1, all subsequent messages are authenticated and a new hash (HMAC) is generated for each packet.A source for packet capture (pcap) files and malware samples. Then, in frame #8 we see that Responder picked one of the Proposals:įrame #9 is just an ACK to the picked proposal confirming that Initiator accepted it: Note: Identification payload carries source and destination tunnel IP addresses and if this doesn't match what is configured on both peers then IPSec negotiation will not proceed. ![]() Now, Initiator sends its proposals to negotiate the security parameters for production traffic as mentioned (the highlighted yellow proposal is just a sample as the rest is collapsed - this is frame #7): ![]() The purpose of this phase is to establish the security parameters that will be used for production traffic (IPSec SA): Responder also sends a similar packet back to Initiator in frame #6 but I skipped for brevity. The responder performs the same calculation and confirms the hash is correct. In packet #5 the Initiator sends a hash generated using pre-shared key set as key material so that only those who possess pre-master key can do it: In our case, this is done via pre-shared keys: If it is RSA certificate then peers exchange RSA certificates and assuming the CA that signed each side is trusted then verification complete successfully. If we said we're going to do this using pre-shared keys then verification consists of checking whether both sides has the same pre-shared key. The purpose of this exchange is to confirm each other's identity. Nonce is just to protect against replay attacks by adding some randomness to key generation As selected encryption algorithm for this phase was AES-CBC (128-bits) then we use AES with this key to symmetrically encrypt further data. SKEYID_e (e for encryption): you'll see that the next 2 packets are also encrypted. Yes, I know, we verify the integrity by using a hash but throwing a key into a hash adds stronger security to hash and it's called HMAC. SKEYID_a (a for authentication): this key is used to protect message integrity in every subsequent packets as soon as both peers are authenticated (peers will authenticate each other in next 2 packets). seed key for production traffic keys in Plain English. It is used as seed key for Phase2 keys, i.e. SKEYID_d (d for derivative): not used by Phase 1. With DH public key value and the nonce both peers will generate a seed key called SKEYID.Ī further 3 session keys will be generated using this seed key for different purposes: Then, next 2 Identity Protection packets both peers exchange Diffie-Hellman public key values and nonces (random numbers) which will then allow both peers to agree on a shared secret key: 71) can pick if it matches its local policies:įair enough, in frame #2 the Responder (. 70) sends a set of Proposals containing a set of security parameters ( Transforms) that Responder (. Sample pcap: IPSEC-tunnel-capture-1.pcap (for instructions on how to decrypt it just go to website where I got this sample capture: )īoth peers add a unique SPI just to uniquely identify each side's Security Association (SA): We call first 6 messages Phase 1 and last 3 messages as Phase 2. The Big Pictureįirst 6 Identity Protection (Main Mode) messages negotiate security parameters to protect the next 3 messages (Quick Mode) and whatever is negotiated in Phase 2 is used to protect production traffic (ESP or AH, normally ESP for site-site VPN). Understanding IPSec IKEv2 negotiation on Wireshark 1.
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