IPsec

Why might you want to use authentication prior to encryption?

- it is impossible for anyone to intercept the message and alter the authentication data without detection -It may be desirable to store the authentication information with the message at the destination for later reference

Summarize Transport mode of operation

1. At the source, the block of data containing the ESP trailer plus the entire transport layer segment is encrypted and the plaintext of this block is replaced with its ciphertext to form the IP packet for transmission. Authentication is optionally added. 2. The packet is then routed to the destination. Each intermediate router needs to examine and process the IP header plus any plaintext IP extension headers but does NOT need to examine the ciphertext. 3. The destination node examines and processes the IP header plus any plaintext IP extension headers. Then, on the basis of the SPI in the ESP header, the destination node decrypts the remainder of the packet to recover the plaintext transport layer segment.

List the 5 features of the IKE determination algorithm

1. It employs a mechanism known as cookies to thwart clogging attacks 2. It enables 2 parties to negotiate a group; this in essence, specifies the global parameters of the Diffie-Hellman Key exchange 3. It uses nonces to ensure against replay attacks It enables the exchange of Diffie Hellman public key values 5. It authenticates the Diffie-Hellman exchange to thwart man-in-the-middle attacks

How many keys are typically required for communication between 2 applicants in Internet Key Exchange (IKE)

4 keys

What is a Security Association (SA) ?

A one way logical connection between sender and a receiver that affords security services to the traffic carried on it.

Is the Integrity Check Value (ICV) in the ESP computed before or after encryption is performed?

After

List and briefly define different categories of IPsec documents.

Architecture: The general concepts, security requirements, definitions and mechanisms defining IPsec technology Authentication Header (AH): An extension header to provide message authentication Encapsulating Security Payload (ESP): Consists of am encapsulating header and trailer used to provide encryption or combined encryption/authentication Internet Key Exchange(IKE): The key management schemes for use with IPsec Cryptographic Algorithms: Algorithms for encryption, message authentication, psuedorandom functions, and cryptographic key exchange

Where does encryption occur in a tunnel mode SA?

Encryption occurs only between an external host and security gateway or between 2 security gateways.

What are the types of secret key algorithm used in IPsec?

Encryption: For encryption, the cipher block chaining (CBC) mode is used. Message authentication: For message authentication, VPN-A relies on HMACwith SHA-1 with the output truncated to 96 bits. VPN-B relies on a variant ofCMAC with the output truncated to 96 bits. Pseudorandom function: IKEv2 generates pseudorandom bits by repeated use of the MAC used for message authentication.

List and briefly describe some benefits of IPsec

IPsec provides the capability to secure communication across a LAN, private and public WANs, and the internet. It can encrypt and/or authenticate all traffic at the IP level.

Is tunnel mode vulnerable to traffic analysis? Why or why not?

It is not vulnerable to traffic analysis because the original packet is encapsulated and the the new, larger packet may have totally different source and destination addresses.

Name the two types of key management the IPsec architecture supports.

Manual and automated

What are the roles of the Oakley Key determination protocol and ISAKMP in IPsec?

Oakley Key Determination Protocol: key exchange protocol based on the Diffie Hellman algorithm but providing added security. Generic in that it does not dictate specific formats. Internet Security Association and Key Management Protocol (ISAKMP): Provides a framework for Internet key exchange management and provides the specific protocol supports, including formats for negotiation of security attributes. Consists of a set of message types that enable the use of a variety of key exchange algorithms.

What are the pros and cons of transport mode operation?

Pro: Provides confidentiality for any application that uses it, thus avoiding the need to implement confidentiality in every individual application. Con: It is possible to do traffic analysis on the transmitted packets

Summarize the alternative cryptographic suites approved for use with IPsec

RFC 4308 defines two cryptographic suites for establishing virtual private net-works. Suite VPN-A matches the commonly used corporate VPN security used in older IKEv1 implementations at the time of the issuance of IKEv2 in 2005. Suite VPN-B provides stronger security and is recommended for new VPNs that implement IPsecv3 and IKEv2.

What is a security association bundle?

Refers to a sequence of SAs through which traffic must be process to provide a desired set of IPsec services

What parameters identify an SA and what parameters characterize the nature of a particular SA?

SA (Security Association) is uniquely defined by 3 parameters: Security Parameters Index (SPI) - A 32 bit unsigned integer assigned to an SA having local significance only Security Protocol Identifier - Indicates whether the association is an AH or ESP security association IP destination address - Address of the destination endpoint of the SA, which may be an end user system or a network system such as a firewall or router. A Security Association Database (SAD): Defines the parameters associated with each SA

What is the difference between a Security Association Database (SAD) and a Security Policy Database (SPD) ?

Security Association Database defines the actual parameters of an SA like the type of encryption used, the key, if it's tunnel or transport mode, its sequence number etc. The Security Policy Database contains information on where a packet is actually going based on its SA, contains values such as remote IP address, local IP address, next layer protocol, name, and local/remote ports

Briefly define the Security Policy Database (SPD)

The Security Policy Database (SPD) contains a set of rules that determines whether a packet is subject to IPsec processing and governs the processing details. Each entry in the SPD represents a policy that defines how the set of traffic covered under the policy will be processed. It basically directs traffic at the IP level.

Why does ESP include a padding field?

The padding field serves several purposes: -If an encryption algorithm requires the plaintext to be a multiple of some number of bytes, the padding field is used to expand the plaintext to the required length -Used to assure alignment of pad length and next header fields -Additional padding may be added to provide partial traffic flow confidentiality by concealing the actual length of the pay load

What is the role of the selectors in a security policy database?

The selectors are a set of of IP and upper layer protocol field values that define an SPD entry. They are used to filter outgoing traffic in order to map it to a particular SA

What is the difference between transport mode and tunnel mode?

These are the two modes of operation for IPsec. Tunnel Mode: the entire original IP packet is encapsulated to become the payload of a new IP packet. Additionally, a new IP header is added on top of the original IP packet. Since a new packet is created using the original information, tunnel mode is useful for protecting traffic between different networks. Transport Mode: The main difference in transport mode is that it retains the original IP header. In other words, payload data transmitted within the original IP packet is protected, but not the IP header. In transport mode, encrypted traffic is sent directly between two hosts that previously established a secure IPsec tunnel.

What are the basic approaches to bundling SAs?

Transport Adjacency: Refers to applying more than one security payload to the secure IP packet without invoking tunneling. Allows for only one level of combination. Iterated Tunneling: Refers to the application of multiple layers of security protocols effected through IP tunneling. Allows for multiple levels of nesting.

What mode of IPsec operation can be used to implement a secure virtual private network (VPN) ?

Tunnel mode

Summarize Tunnel mode of operation

Tunnel mode provides protection to the IP packet. To acheive this, 1. After the AH and ESP fields are added to the IP packet, the entire packet plus security fields is treated as the payload of the new outer IP packet with a new outer IP header. 2. The entire original, inner, packet travels through a tunnel from one point of an IP network to another; no routers along the way are able to examine the IP header.