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Cryptography > TLS 1.3 and IPsec > Flashcards

TLS 1.3 and IPsec Flashcards

1
Q

What is TLS 1.3?

A

The latest TLS version
Significant changes from earlier versions affecting security and efficiency

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2
Q

What is IPsec?

A

Framework for ensuring secure communications over IP (internet protocol) networks

Similar security services as TLS, but at a lower layer in the communications protocol stack

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3
Q

What are the 7 layers of the OSI model?

A

Application

Presentation

Session

Transport

Network

Data link

Physical

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4
Q

What layer does TLS operate on?

A

Application layer

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5
Q

What layer does IPsec operate on?

A

Network layer

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6
Q

What efficiency and security problems in earlier versions, does TLS 1.3 fix?

A

Efficiency: Needing 2 round trip times before data can be sent

Sec: Too complex protocol, supported old and weak cipher suites

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7
Q

What does TLS 1.3 aim to achieve?

A

Provable security

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8
Q

What items in TLS was removed from version 1.2 to 1.3? (6)

A

Static RSA and DH key exchange

Renegotiation

SSL 3.0 negotiation

DSA in finite fields

data compression

non-AEAD cipher suites

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9
Q

What items was added in TLS 1.3 from 1.2? (3)

A

Zero round-trip-time (0-RTT) mode from pre-shared keys

Post-handshake client authentication through “certificate verify” signature

More AEAD cipher suites

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10
Q

Describe the TLS 1.3 handshake protocol: Hello messages

A

Client sends keyshare field in client hello for one or more anticipated cipher suites

Server can obtains session key on receipt of client hello if:
- server accepts one of the cipher suites
- the keyshare matches the accepted ciphersuite

If the conditions above fail:
- Server sends an optional Hello Retry Request
- Client responds is these in an acceptable cipher suite

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11
Q

In TLS 1.3 what messages are encrypted?

A

After hello - all later parts of the protocol are encrypted using the keys from the handshake

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12
Q

What messages in TLS 1.3 handshake are not cryptographically protected?

A

Client and sever hello/keyshare messages

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13
Q

How does TLS 1.3 derive individual keys?

A

HKDF standard (hash key derivation function)

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14
Q

What different key types can be derived from the master secret?

A

Handshake traffic keys
Application traffic keys
Early data keys

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15
Q

What are Application traffic keys used for?

A

Protect client-server traffic

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15
Q

What are Handshake traffic keys used for?

A

Protect handshake protocol

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16
Q

What are early data keys used for?

A

Used for 0-RTT data

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17
Q

In TLS 1.2 and 1.3, what does the CertificateVerify message do?

A

Used by the client to send a certificate and authenticate using the message

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18
Q

What does the CertificateVerify message contain?

A

A signature which can be verified using the public key in the certificate

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19
Q

What is the post-handshake client authentication extension in TLS 1.3?

A

If used, the server may request client authentication at any time after the handshake completed

The client then responds with its certificate and a signature in the form of CertificateVerify

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20
Q

What is early-data?

A

Application data that parties can start sending immediately, in 0-RTT key establishments

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21
Q

Describe 0-RTT in TLS 1.3

A

0-RTT is based on a pre-shared key (PSK), that is either agreed outside TLS or from an earlier TLS session

At the end of the handshake protocol, the server can send to the client one or more new session tickets as PSKs

A client may start a new PSK sesion without negotiating version and ciphersuite

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22
Q

What is one thing needed to make 0-RTT possible, and what is this used for?

A

Pre shared key

PSK is used to authenticate Diffie Hellman

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23
Q

What secrecy does early data lack?

A

Forward secrecy

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24
What option does the TLS handshakes always use?
Diifie-Hellman option
25
In TLS 1.3, what does the cipher suites specify?
Which AEAD cipher to use in Record layer Hash function to use for KDF
26
What ciphersuite is mandatory to implement in TLS 1.3?
TLS_AES_128_GCM_SHA256
27
What is the ChaCha algorithm?
Stream cipher with MAC Faster than AES 256-bit key Combines XOR, addition modulo 2^32, rotation operations over 20 rounds Produces 512 bits of keystream
28
What are the efficiency improvements of TLS 1.3?
Saving of one round trip time in handshake Can set up follow-on session with 0-RTT
29
What security improvements came with TLS 1.3?
Only forward-secret key exchange now allowed Many legacy cipher suite no longer allowed Renegotiation option removed Formal security proof
30
What does the Selfie attack on TLS break?
Mutual authentication in PSK mode
31
How does the selfie attack on TLS work?
Victim party A must be prepared to act as client and a server A shares a PSK with B The attacker reflects messages back to herself so client A believes she is talking to B while actually taking with server A
32
How can the selfie attack on TLS be prevented?
Forbidding to share a PSK between more than one server and one client
33
What types of algorithms does IPsec use?
Encryption, authentication and key management
34
What is IPsec most commonly used for?
To provide VPN Provides a security architecture for both IPv4 and IPv6
35
What is message confidentiality?
Protects against unautherised data disclosure by the use of encryption
36
What is message integrity?
Detects if data has been changed by using a MAC or authenticated ancryption
37
What is message replay protection?
The same data is not replayed and data is not delivered badly out of order
38
What is Limited traffic analysis protection?
Eavesdropper on network traffic should not know which parties communicate, how often or how much data is sent
39
What is Peer authentication?
Each IPsec endpoint confirms the identity of the other IPsec endpoint
40
What 5 security services does IPsec provide?
Message confidentiality Message integrity Message replay protection Limited traffic analysis protection Peer authentication
41
What is a gateway-to-gateway architecture?
Provides secure network communications between two networks Traffic is routed through the IPsec connection, protecting it appropriately Only protects data between 2 gateways
42
What is a gateway-to-gateway architecture most often used for?
When connecting two secured networks, such as linking a branch office to headquarters over the internet
43
What is a Host-to-gateway architecture?
The organization deploys a VPN gateway onto their network Each remote user establishes a VPN connection between the local computer (host) and the gateway The VPN gateway may be a dedicated device or part of another network device
44
When are host-to-gateway architectures mostly used?
When connecting hosts on unsecured networks to resources on secured networks. Commonly used to provide secure remote access
45
What are host-to-host architectures?
Provide end-to-end protection for data (throughout its transit) resource-intensive to implement/maintain in terms of user and host management. All user systems and servers that will participate in VPNs need to have VPN software installed and/or configured Key management through a manual process
46
What are host-to-host architectures typically used for?
For special purpose needs, such as system administrators performing remote management of a single server
47
What are the 3 IPsec protocol types?
ESP: Encapsulating Security Payload AH: Authentication Header IKE: Internet Key Exchange
48
What does the IPsec protocol provide: Encapsulating Security Payload?
Provides: - confidentiality - authentication - integrity - replay protection
49
What is the IPsec protocol: Authentication Header
Provides: - authentication - integrity - replay protection No confidentiality and because of that deprecated
50
What is the IPsec protocol: Internet Key Exchange
Takes care of negotiating, creating and managing session keys in so-called security associations
51
How are IPsec connections set up?
Key exchange: IKEv2 protocol IKEv2 uses DH authenticated using signatures with public keys in X.509 certificates Includes cookies: client must return a time-dependent cookie value before the server proceeds
52
What attacks does using cookies when setting up a IPsec connection mitigate, and what do they provide?
The cookies mitigates denial-of-service attacks The cookies provide proof of reachability before any expensive cryptographic processing is completed
53
What is a Security Association (SA)?
Contains info needed by an IPsec endpoint to support an IPsec connection SA tells the endpoint how to process inbound IPsec packets or how to generate outbound packets SAs are needed for each direction of connection
54
What can SAs include?
cryptographic keys and algorithms Key lifetimes Security parameter index (SPI): included in the IPsec header to associate a packet with the appropriate SA Security protocol identifier (ESP or AH)
55
What is used to establish keys to use in SAs?
IKEv2
56
Name 2 modes of operation in IPsec
Transport and tunnel mode (both protocol ESP and AH can operate in both)
57
What is transport mode in IPsec?
Maintains IP header of the original packet and protects payload Generally only used in host-to-host architectures
58
What is tunnel mode in IPsec?
Original packet encapsulated into a new one, meaning payload is the original packet Typical use is gateway-to-gatewat architecure
59
What are the components of the ESP protocol in IPsec?
ESP header: contains SPI identifying the SA and sequence numbers ESP trailer: Contains padding and padding length, may include extra padding to enhance traffic flow confidentiality ESP auth: Contains MAC of the encrypted data and ESP header, may not be required if an authenticated encryption mode is used
60
What does a IP packet look like when protected by Transport-ESP?
Original IP packet: [ IP header ] [ Data ] Protected: [IP header] [ESP header] [Data] [ESP trailer] [ESP auth] Data and ESP trailer are encrypted ESP header, Data and ESP trailer are authenticated
61
What does a IP packet look like when protected by Tunnel-ESP?
Original IP packet: [ IP header ] [ Data ] Protected: [New IP header] [ESP header] [IP header] [Data] [ESP trailer] [ESP auth] Encrypted: IP header, data, ESP trailer Authenticated: ESP header, IP header, data, ESP trailer
62
Describe outbound packet processing in ESP transport mode
Padding of data after original IP header: add ESP trailer and result encrypted using the symmetric cipher and key in the SA ESP header is prepended ESP MAC calculated over the data prepared so far and appended (if an SA uses the authentication service) Original IP header is prepended but some fields must be changed: - Protocol fields from TCP to ESP - Total length changes to reflect addition of ESP header - Checksum recalculated
63
Describe outbound packet processing in ESP tunnel mode
Entire original packet is padded by adding an ESP trailer The result is encrypted using the symmetric cipher and key agreed in the SA ESP header prepended ESP MAC calculated and appended, if SA uses auth service New outer IP header is prepended - Inner IP header of the original IP packet carries the ultimate src and dst addresses - Outer IP header may contain distinct IP addresses such as addresses of security gateways - Outer IP header protocol field is set to ESP
64
Describe the security of IPsec
Providing enc without integrity is insecure - active attacks have been demonstrated ESP applies enc before MAC in normal usage Using AH, a MAC can be applied before enc. Attacks have been demonstrated on such configs IPsec key exchange protocol (IKEv2) has no significant weaknesses

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