coen 350 ipsec, ssl, ssh,. ipsec rfc 1636 identified key areas where the internet needs to be made...
TRANSCRIPT
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COEN 350
IPSec, SSL, SSH,
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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.
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IPSec
Implemented below the transport layer.
No application needs to be rewritten.
Is part of the OS.Applications
TCP
IPsec
IP
lower layers
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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 Header IPSec header Secure IP Payload
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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.)
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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.
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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.
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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.
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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
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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.
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IPSec Transport mode
versus Tunnel mode
Original Packet IPsec Package in Transport Mode
IPSec Package in Tunnel Mode
IP header | rest IP header | IPsec header | rest new IP hdr | IPSec | IP header | rest
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IPSec
IPsec in tunnel mode for a VPN:
IP: src=R1, dst=R2 | ESP | IP: src=A, dst=B | packet
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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.
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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.
1 1 2 4 4
Next header
Payload length
Unused SPI Sequence Number
Authentication data
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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.
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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.
4 4 var. var. var. 1 1 var.
SPI Sequence
number
IV data padding padding length
Next header / protocol
type
Authentication data
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IPSec: IKE
Internet Key Exchange Needed for
mutual authentication to set up an SA …
Compromise based on Photuris and Skip
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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.
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PhoturisA
lice
Bob
CA
CA, CB, crypto
CA, CB, gb mod p, crypto selected
CA, CB, gb mod p
CA, CB, {Alice, sig of prev. message} gab mod p
CA, CB, {Bob, sig of prev. message} gab mod p
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Photuris Alice chooses cookie CA in order to
keep different login attempts separated.
Bob uses a stateless cookie CB 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.
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PhoturisA
lice
Bob
CA
CA, CB, crypto
CA, CB, gb mod p, crypto selected
CA, CB, gb mod p
CA, CB, {Alice, sig of prev. message} gab mod p
CA, CB, {Bob, sig of prev. message} gab mod p
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SKIP Simple Key Management for Internet
Protocols Principals have
Certified Diffie-Hellman public keys ga mod p Private key a. Alice wants to talk to Bob:
Alice takes Bob’s public key gb and raises it to the ath power.
Bob takes Alice’s public key ga and raises it to the bth power.
Both share the secret gab mod p.
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SKIP
SKIP derives a key KAlice,Bob from the mutually shared secret between Alice and Bob. Such as the lower bits of gab mod p.
Each packet is encrypted / authenticated with a randomly generated key Kpacket.
The key Kpacket is encrypted with KAlice, Bob and added to the packet.
The header of the packet is in clear text.
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SKIP SKIP packet
Clear IP Header KAlice,Bob{Kpacket} Kpacket{payload}
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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.
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SKIP
Make the master key KAlice,Bob dependent on a version that automatically updates:KAlice,Bob = hash(gab,counter-value) Allows still principals to get a brand-
new certified key. Prevents some replay attacks.
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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, …
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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.
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IPSec: IKE
Phase 1 Aggressive Mode:
Alice Bob
ga, Alice, crypto-proposal
gb, crypto-choice, proof I’m Bob.
Proof I’m Alice
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IPSec: IKE Phase 1 Main Mode:
Alice
Bob
crypto-suites I support
Crypto suites I choose.
ga
gb
gab{Alice, proof I’m Alice}
gab{Bob, proof I’m Bob}
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IPSec: IKE
Key Types Pre-shared secret Public key for encryption / decryption Public key for signing
8 variants of Phase 1!!!
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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.
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IPSec: IKE
Phase 1 protocols Read them!
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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.
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IPSec: IKE
Alice BobX,Y, Crypto-protocol, SPIA, nonceA,
SPI: Security Parameter Index
X,Y, Crypto-protocol accepted, SPIB, nonceB
X, Y Ack
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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.
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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.
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Secure Socket Layer
Various keys are formed from various random numbers exchanged during the protocol.
Negotiate crypto-protocols.
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Secure Socket Layer
SSL sessions are long-lived. Many SSL connections can be
derived from an SSL session.
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Secure Socket Layer:Session Connection
Alice BobHello. Ciphers I support. RAlice
Certificate. Ciphers I choose. RBob
{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 RAlice, RBob, S
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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.
Alice BobSession ID. Ciphers I support. RAliceSession ID. Certificate. Ciphers I choose.
RBob
{Keyed Hash of Messages}
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Secure Shell: SSH
Authentication phase starts: SSH1 tries out
Kerberos Rhosts RhostsRSA Public key TIS Password
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Secure Shell: SSH
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Secure Shell: SSH