1. COEN 350 IPSec, SSL, SSH,

2. IPSec RFC 1636 identified key areas where the internet needs to be made more secure. Spoofing: Creating packets with false addresses. Eavesdropping / packet sniffing. Works for both IPv4 and IPv6.

3. IPSec Implemented below the transport layer. No application needs to be rewritten. Is part of the OS. Applications TCP IPsec IP lower layers

4. IPSec An IPSec packet in tunnel mode completely encapsulates the payload. IP Header is either an Authentication Header ESP Encapsulating Security Payload that tells the user which Security Association to use. IP HeaderIPSec headerSecure IP Payload

5. IPSec Developed by the Internet Engineering Task Force IETF Architecture ESP (Encapsulating Security Payload) AH (Authentication Header) Encryption Algorithm Authentication Algorithm Key Management DOI (Domain of Interpretation) (How to fit the work together.)

6. IPSec Security Association Cryptographically protected connection. Paradigm to manage authentication and confidentiality between sender and receiver. Unidirectional. IPSec header contains SPI (Security Parameter Index) that identifies the security association. Allows partner to look up the necessary data such as the key in SA database.

7. IPSec Security Association Database When X transmits to Y in IPSec, X looks up Y in the SA database. Provides key Provides SPI Provides algorithms to be used Provides sequence number When Y receives a transmission, Y uses the SPI and the destination address to find the SA.

8. IPSec Security Policy Database Specifies what to do with packets: Dropping Forwarded and accepted without IPSec protection Forwarded and protected by IPSec Decision based on fields in the IPsec packet.

9. IPSec Two types of IPsec headers. AH Authentication header. Provides integrity protection only. Allows firewalls to peek at TCP ports. ESP Encapsulating Security Payload Optional integrity protection Optional encryption

10. IPSec Two modes Transport mode Adding IPsec information between IP header and remainder of package. Tunnel mode Keeps the original IP packet intact, but put it into a new packet with new IP header and IPsec data.

11. IPSec Transport mode versus Tunnel mode Original PacketIPsec Package in Transport ModeIPSec Package in Tunnel Mode IP header | restIP header | IPsec header | restnew IP hdr | IPSec | IP header | rest

12. IPSec IPsec in tunnel mode for a VPN: IP: src=R1, dst=R2 | ESP | IP: src=A, dst=B | packet

13. IPSec NAT Network address translation NAT boxes takes IP traffic from the outside. Based on port number, repackages packet to be send to an internal address and vice versa. Allows organization to make to do with few IP addresses.

14. IPSec AH Header Next header: protocol of encapsulated package Payload length: Size of AH header in words. SPI Sequence number: Used by AH to recognize replayed packages Authentication data: Cryptographic integrity check on the payload data. 11244 Next headerPayload length UnusedSPISequence Number Authentication data

15. IPSec AH Some IP header fields get reset by NATs and routers. Mutable fields can be changed: Type of service Flags Fragment offset Time to live Header checksum Immutable fields cannot be changed: Payload length Needed to reassemble fragmented AH packets.

16. IPSec ESP SPI Sequence Number (same as for AH) IV Initialization Vector (used by some cryptographic algorithms Data: protected data, possibly encrypted Padding: needed to make data multiple of block size. Padding length Next header: Protocol field in IPv4 or next header in IPv6 Authentication data: Cryptographic integrity check. 44var. 11 SPISequence number IVdatapaddingpadding length Next header / protocol type Authentica tion data

17. IPSec: IKE Internet Key Exchange Needed for mutual authentication to set up an SA … Compromise based on Photuris and Skip

18. Photuris Uses Cookies Different from web browser cookies. When Alice connects to Bob, Bob chooses a cookie and sends it to Alice. Bob only honors further requests from Alice with the cookie. Foils very simple DoS attacks. To keep cookie stateless, the cookie is a function of Alice’s address and a secret known by Bob only.

19. Photuris Alice Bob CACA C A, C B, crypto C A, C B, g b mod p, crypto selected C A, C B, g b mod p C A, C B, {Alice, sig of prev. message} g ab mod p C A, C B, {Bob, sig of prev. message} g ab mod p

20. Photuris Alice chooses cookie C A in order to keep different login attempts separated. Bob uses a stateless cookie C B in order to keep DoD attacks at bay. Messages 3 and 4 consists of a Diffie- Hellman encryption. Messages 5 and 6 serve for authentication.

21. Photuris Alice Bob CACA C A, C B, crypto C A, C B, g b mod p, crypto selected C A, C B, g b mod p C A, C B, {Alice, sig of prev. message} g ab mod p C A, C B, {Bob, sig of prev. message} g ab mod p

22. SKIP Simple Key Management for Internet Protocols Principals have Certified Diffie-Hellman public keys g a mod p Private key a. Alice wants to talk to Bob: Alice takes Bob’s public key g b and raises it to the a th power. Bob takes Alice’s public key g a and raises it to the b th power. Both share the secret g ab mod p.

23. SKIP SKIP derives a key K Alice,Bob from the mutually shared secret between Alice and Bob. Such as the lower bits of g ab mod p. Each packet is encrypted / authenticated with a randomly generated key K packet. The key K packet is encrypted with K Alice, Bob and added to the packet. The header of the packet is in clear text.

24. SKIP SKIP packet Clear IP HeaderK Alice,Bob {K packet }K packet {payload}

25. SKIP Changing a principal’s key is a difficult, but needed operation. Minimizes exposure of the key and makes crypt-analysis more difficult. Updating the master key prevents reusing compromised traffic keys. Each new key needs to be certified.

26. SKIP Make the master key K Alice,Bob dependent on a version that automatically updates: K Alice,Bob = hash(g ab,counter-value) Allows still principals to get a brand-new certified key. Prevents some replay attacks.

27. IPSec: IKE Phases Phase 1: Does mutual authentication and establishes session keys. Known as KSAKMP SA / IKE SA Phase 2: Establishes an ESP or AH SA Phase 1 is necessarily expensive. The two phases try to have phase 2 profit from a phase 1 interchange used for another protocol, connection, …

28. IPSec: IKE Phase 1 IKE: Aggressive mode Use a single crypto-proposal Main mode Negotiate the strongest crypto-proposal that both parties can agree to.

29. IPSec: IKE Phase 1 Aggressive Mode: AliceBob g a, Alice, crypto-proposal g b, crypto-choice, proof I’m Bob. Proof I’m Alice

30. IPSec: IKE Phase 1 Main Mode: Alice Bob crypto-suites I support Crypto suites I choose. gaga gbgb g ab {Alice, proof I’m Alice} g ab {Bob, proof I’m Bob}

31. IPSec: IKE Key Types Pre-shared secret Public key for encryption / decryption Public key for signing 8 variants of Phase 1!!!

32. IPSec: IKE Phase 1 establishes two session keys: Integrity key Encryption key for the last exchange in phase 1 and all exchanges in phase 2. Establishes a pair of cookies to keep different sessions different.

33. IPSec: IKE Phase 1 protocols Read them!

34. IPSec: IKE Phase 2: A.k.a. quick mode. Uses a pair X of cookies generated in phase 1. Session nonce for phase 2 session. All messages are encrypted with Phase 1 encryption key SKEYID_e All messages are integrity protected with Phase 1 intergrity key SKEYID_a. Can be initiated by either participant of Phase 1.

35. IPSec: IKE AliceBob X,Y, Crypto-protocol, SPI A, nonce A, SPI: Security Parameter Index X,Y, Crypto-protocol accepted, SPI B, nonce B X, Y Ack

36. Secure Socket Layer 1995: deployed in Netscape Navigator as SSLv2. 1995: Microsoft fixes SSLv2 and introduces a similar protocol Private Communication Technology (PCT) 1996: Netscape introduces SSLv3 1999: IETF introduces Transport Layer Security. SSLv3 remains the most implemented protocol.

37. Secure Socket Layer SSL is built on top of TCP. TCP provides reliable packet delivery. Rogue packet problem: Maliciously introduced TCP packet. Easy to do, since it only needs to satisfy the non- cryptographic TCP checksum. SSL disregards the package. TCP however will not accept the true packet, because it looks like a double to it. SSL will have to start over.

38. Secure Socket Layer Various keys are formed from various random numbers exchanged during the protocol. Negotiate crypto-protocols.

39. Secure Socket Layer SSL sessions are long-lived. Many SSL connections can be derived from an SSL session.

40. Secure Socket Layer: Session Connection AliceBob Hello. Ciphers I support. R Alice Certificate. Ciphers I choose. R Bob {S} Public Key of Bob. {Keyed Hash of Messages} {Keyed Hash of Messages} S is a random number, the pre-master secret. K is the master secret, calculated from R Alice, R Bob, S

41. Secure Socket Layer: Session Resumption If Bob wants to have multiple connections per session, he sends in Message 2 a session id. If Alice presents in Message 1 a session id, they skip the handshake. Alice can still negotiate ciphers with Bob who might have changed policies. AliceBob Session ID. Ciphers I support. R Alice Session ID. Certificate. Ciphers I choose. R Bob {Keyed Hash of Messages}

42. Secure Socket Layer SSL comes deployed with public keys of various trusted organizations. User can modify this list. User verifies public keys by sending certificate requests to the organizations in the list.

43. Secure Socket Layer SSLv3 upgrades: Protects against the “downgrade attack” Active attacker replaces the initial messages with ones containing weak crypto. Protects against the “truncation attack” Active attacker sends a TCP close (FIN) message. TCP is not protected, so the connection is abnormally terminated without SSL being aware of it.

44. Secure Shell: SSH SSH client and server are applications (running on top of OS). SSH consists of a bunch of applications. But SSH is not a UNIX shell.

45. Secure Shell: SSH Client contacts server. Client and server disclose the SSH versions they support. Client and server switch to a packet based protocol. Packet consists of 4B length, 1-8B of random padding, one-byte packet type code, packet payload data, four-byte integrity check field.

46. Secure Shell: SSH Server identifies itself by sending Host key Server key 8 random bytes (use as cookie) List of encryption, compression, authentication methods. Both sides compute a 128b session identifier.

47. Secure Shell: SSH When the client receives the host key, the client looks into the known host database. If the host key matches the one in the database then the client proceeds. If the host is in the database but with a different key, then the client queries the user. Otherwise, the client warns the user and proposes to add host and key to the known host database.

48. Secure Shell: SSH Client randomly generates a session key. Clients sends the session key encrypted with the server key and then with the host’s public key. Together with the choice of crypto-suites. Both sides now use the session key for encryption. Server sends confirmation message encrypted with the session key. This proves the server’s authenticity to the client.

49. Secure Shell: SSH Authentication phase starts: SSH1 tries out Kerberos Rhosts RhostsRSA Public key TIS Password

50. Secure Shell: SSH