See Triple-DES.
Advanced Encryption Standard. A symmetric block data encryption technique. The U.S. government adopted the Rijndael variant of the algorithm as its encryption standard in October 2000. AES replaces DES encryption as the government standard.
An encryption system in which the sender and receiver of a message use different keys to encrypt and decrypt the message. Asymmetric keys are used to establish a secure channel for symmetric key encryption. The Diffie-Hellman algorithm is an example of an asymmetric key protocol. Contrast with symmetric key cryptography.
An extension header that provides authentication and integrity, without confidentiality, to IP packets.
A symmetric block cipher algorithm that takes a variable-length key from 32 bits to 448 bits. Its author, Bruce Schneier, claims that Blowfish is optimized for applications where the key does not change often.
IPv4 network addresses with the host portion of the address having all zeroes (10.50.0.0) or all one bits (10.50.255.255). A packet that is sent to a broadcast address from a machine on the local network is delivered to all machines on that network.
A trusted third-party organization or company that issues digital certificates used to create digital signatures and public-private key pairs. The CA guarantees the identity of the individual who is granted the unique certificate.
A list of public key certificates that have been revoked by a CA. CRLs are stored in the CRL database that is maintained through IKE.
In X.509 certificates, the assurance from the certificate authority that the certificates from the trust anchor to the user's certificate provide an unbroken chain of authentication.
See IP packet.
Data Encryption Standard. A symmetric-key encryption method developed in 1975 and standardized by ANSI in 1981 as ANSI X.3.92. DES uses a 56-bit key.
A digital code that is attached to an electronically transmitted message that uniquely identifies the sender.
A standardized method of using ordinary strings to represent shared information. Distinguished names are used in LDAP and in X.509 certificates, as well as in other technologies. For more information, see A String Representation of Distinguished Names.
A DOI defines data formats, network traffic exchange types, and conventions for naming security-relevant information. Security policies, cryptographic algorithms, and cryptographic modes are examples of security-relevant information.
Digital Signature Algorithm. A public key algorithm with a variable key size from 512 to 4096 bits. The U.S. Government standard, DSS, goes up to 1024 bits. DSA relies on SHA-1 for input.
Also known as “public key” cryptography. An asymmetric cryptographic key agreement protocol that was developed by Diffie and Hellman in 1976. The protocol enables two users to exchange a secret key over an insecure medium without any prior secrets. Diffie-Hellman is used by the IKE protocol.
Elliptic Curve Digital Signature Algorithm. A public key algorithm that is based on elliptic curve mathematics. An ECDSA key size is significantly smaller than the size of a DSA public key needed to generate a signature of the same length.
An extension header that provides integrity and confidentiality to packets. ESP is one of the five components of the IP Security Architecture (IPsec).
The process of a header and payload being placed in the first packet, which is subsequently placed in the second packet's payload.
Any device or software that isolates an organization's private network or intranet from the Internet, thus protecting it from external intrusions. A firewall can include packet filtering, proxy servers, and NAT (network address translation).
A number that is generated from a string of text. Hash functions are used to ensure that transmitted messages have not been tampered with. MD5 and SHA-1 are examples of one-way hash functions.
Keyed hashing method for message authentication. HMAC is a secret key authentication algorithm. HMAC is used with an iterative cryptographic hash function, such as MD5 or SHA-1, in combination with a secret shared key. The cryptographic strength of HMAC depends on the properties of the underlying hash function.
A packet sent to a machine on the Internet to solicit a response. Such packets are commonly known as “ping” packets.
Internet Key Exchange. IKE automates the provision of authenticated keying material for IPsec security associations (SAs).
The method or protocol by which data is sent from one computer to another on the Internet.
See Internet Protocol (IP), IPv4, IPv6.
A packet of information that is carried over IP. An IP packet contains a header and data. The header includes the addresses of the source and the destination of the packet. Other fields in the header help identify and recombine the data with accompanying packets at the destination.
Twenty bytes of data that uniquely identify an Internet packet. The header includes source and destination addresses for the packet. An option exists within the header to allow further bytes to be added.
A communication facility or medium over which nodes can communicate at the link layer. The link layer is the layer immediately below IPv4/IPv6. Examples include Ethernets (simple or bridged) or ATM networks. One or more IPv4 subnet numbers or prefixes are assigned to an IP link. A subnet number or prefix cannot be assigned to more than one IP link. In ATM LANE, an IP link is a single emulated LAN. When you use ARP, the scope of the ARP protocol is a single IP link.
TCP/IP is frequently referred to as a “stack.” This refers to the layers (TCP, IP, and sometimes others) through which all data passes at both client and server ends of a data exchange.
Internet Protocol, version 4. IPv4 is sometimes referred to as IP. This version supports a 32-bit address space.
The name that an administrator gives to the storage area, or keystore, on a network interface card (NIC). The keystore name is also called the token or the token ID.
1. An IKEv2 rule's keyword whose value must match the value of the label keyword in a preshared key file if the auth_method is preshared.
2. A keyword used when creating an IKEv2 certificate. This value is convenient for locating all parts of the certificate (private key, public key, and public key certificate) in the keystore.
3. A mandatory access control (MAC) indication of the level of sensitivity of an object or process. Confidential and Top Secret are sample labels. Labeled network transmissions contain MAC labels.
4. An IKEv1 rule's keyword whose value is used to get the rule.
In IPv6, a designation that is used for addressing on a single link for purposes such as automatic address configuration. By default, the link-local address is created from the system's MAC address.
1. A module in the diffserv architecture and IPQoS that marks the DS field of an IP packet with a value that indicates how the packet is to be forwarded. In the IPQoS implementation, the marker module is dscpmk.
2. A module in the IPQoS implementation that marks the virtual LAN tag of an Ethernet packet with a user priority value. The user priority value indicates how packets are to be forwarded on a network with VLAN devices. This module is called dlcosmk.
An iterative cryptographic hash function that is used for message authentication, including digital signatures. The function was developed in 1991 by Rivest.
MAC provides assurance of data integrity and authenticates data origin. MAC does not protect against eavesdropping.
An IPv6 address that identifies a group of interfaces in a particular way. A packet that is sent to a multicast address is delivered to all of the interfaces in the group. The IPv6 multicast address has similar functionality to the IPv4 broadcast address.
A system that has more than one physical interface and that does not perform packet forwarding. A multihomed host can run routing protocols.
The translation of an IP address used within one network to a different IP address known within another network. Used to limit the number of global IP addresses that are needed.
Network adapter card that is an interface to a network. Some NICs can have multiple physical interfaces, such as the igb card.
A group of information that is transmitted as a unit over communications lines. Contains an IP header plus a payload.
A firewall function that can be configured to allow or disallow specified packets through a firewall.
See IP header.
The data that is carried in a packet. The payload does not include the header information that is required to get the packet to its destination.
In PFS, the key that is used to protect transmission of data is not used to derive additional keys. Also, the source of the key that is used to protect data transmission is never used to derive additional keys. Therefore, PFS can prevent the decryption of previously recorded traffic.
PFS applies to authenticated key exchange only. See also Diffie-Hellman algorithm.
A system's attachment to a link. This attachment is often implemented as a device driver plus a network interface card (NIC). Some NICs can have multiple points of attachment, for example, igb.
Public Key Infrastructure. A system of digital certificates, Certificate Authorities, and other registration authorities that verify and authenticate the validity of each party involved in an Internet transaction.
A server that sits between a client application, such as a Web browser, and another server. Used to filter requests – to prevent access to certain web sites, for instance.
A cryptographic system that uses two different keys. The public key is known to everyone. The private key is known only to the recipient of the message. IKE provides public keys for IPsec.
In IPsec, an attack in which a packet is captured by an intruder. The stored packet then replaces or repeats the original at a later time. To protect against such attacks, a packet can contain a field that increments during the lifetime of the secret key that is protecting the packet.
A system that usually has more than one interface, runs routing protocols, and forwards packets. You can configure a system with only one interface as a router if the system is the endpoint of a PPP link.
The process of routers advertising their presence together with various link and Internet parameters, either periodically or in response to a router solicitation message.
The process of hosts requesting routers to generate router advertisements immediately, rather than at their next scheduled time.
A method for obtaining digital signatures and public key cryptosystems. The method was first described in 1978 by its developers, Rivest, Shamir, and Adleman.
Security Associations Database. A table that specifies cryptographic keys and cryptographic algorithms. The keys and algorithms are used in the secure transmission of data.
An association that specifies security properties from one host to a second host.
An integer that specifies the row in the security associations database (SADB) that a receiver should use to decrypt a received packet.
Database that specifies the level of protection to apply to a packet. The SPD filters IP traffic to determine whether a packet should be discarded, should be passed in the clear, or should be protected with IPsec.
Secure Hashing Algorithm. The algorithm operates on any input length less than 264 to produce a message digest. The SHA-1 algorithm is input to DSA.
To use ICMP echo request packets directed to an IP broadcast address or multiple broadcast addresses from remote locations to create severe network congestion or outages.
To eavesdrop on computer networks – frequently used as part of automated programs to sift information, such as clear-text passwords, off the wire.
To gain unauthorized access to a computer by sending a message to it with an IP address indicating that the message is coming from a trusted host. To engage in IP spoofing, a hacker must first use a variety of techniques to find an IP address of a trusted host and then modify the packet headers so that it appears that the packets are coming from that host.
A packet filter that can monitor the state of active connections and use the information obtained to determine which network packets to allow through the firewall. By tracking and matching requests and replies, a stateful packet filter can screen for a reply that does not match a request.
A transport layer protocol that provides connection-oriented communications in a manner similar to TCP. Additionally, SCTP supports multihoming, in which one of the endpoints of the connection can have more than one IP address.
An encryption system in which the sender and receiver of a message share a single, common key. This common key is used to encrypt and decrypt the message. Symmetric keys are used to encrypt the bulk of data transmission in IPsec. AES is one example of a symmetric key.
TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet).
Triple-Data Encryption Standard. A symmetric-key encryption method. Triple-DES requires a key length of 168 bits. Triple-DES is also written as 3DES.
In X.509 certificates, the root certificate from the certificate authority. The certificates from the root certificate to the end certificate establish a chain of trust.
The path that is followed by a packet while it is encapsulated. See encapsulation.
In IPsec, a configured tunnel is a point-to-point interface. The tunnel enables one IP packet to be encapsulated within another IP packet.
Network interfaces that provide traffic forwarding at the Ethernet (datalink) level of the IP protocol stack.
A combination of software and hardware network resources and functionality that are administered together as a single software entity. An internal virtual network consolidates network resources onto a single system, sometimes referred to as a “network in a box.”