exposures (i.e., loss potential) based on estimated frequencies
and costs of occurrence, and (optionally) recommends how to
allocate resources to countermeasures so as to minimize total
exposure.
(C) The analysis lists risks in order of cost and criticality,
thereby determining where countermeasures should be applied first.
It is usually financially and technically infeasible to counteract
all aspects of risk, and so some residual risk will remain, even
after all available countermeasures have been deployed. [FP031,
R2196]
$ risk management
(I) The process of identifying, controlling, and eliminating or
minimizing uncertain events that may affect system resources.
(See: risk analysis.)
$ Rivest Cipher #2 (RC2)
(N) A proprietary, variable-key-length block cipher invented by
Ron Rivest for RSA Data Security, Inc. (now a wholly-owned
subsidiary of Security Dynamics, Inc.).
$ Rivest Cipher #4 (RC4)
(N) A proprietary, variable-key-length stream cipher invented by
Ron Rivest for RSA Data Security, Inc. (now a wholly-owned
subsidiary of Security Dynamics, Inc.).
$ Rivest-Shamir-Adleman (RSA)
(N) An algorithm for asymmetric cryptography, invented in 1977 by
Ron Rivest, Adi Shamir, and Leonard Adleman [RSA78, Schn].
(C) RSA uses exponentiation modulo the product of two large prime
numbers. The difficulty of breaking RSA is believed to be
equivalent to the difficulty of factoring integers that are the
product of two large prime numbers of approximately equal size.
(C) To create an RSA key pair, randomly choose two large prime
numbers, p and q, and compute the modulus, n = pq. Randomly choose
a number e, the public exponent, that is less than n and
relatively prime to (p-1)(q-1). Choose another number d, the
private exponent, such that ed-1 evenly divides (p-1)(q-1). The
public key is the set of numbers (n,e), and the private key is the
set (n,d).
(C) It is assumed to be difficult to compute the private key (n,d)
from the public key (n,e). However, if n can be factored into p
and q, then the private key d can be computed easily. Thus, RSA
security depends on the assumption that it is computationally
difficult to factor a number that is the product of two large
prime numbers. (Of course, p and q are treated as part of the
private key, or else destroyed after computing n.)
(C) For encryption of a message, m, to be sent to Bob, Alice uses
Bob's public key (n,e) to compute m**e (mod n) = c. She sends c to
Bob. Bob computes c**d (mod n) = m. Only Bob knows d, so only Bob
can compute c**d (mod n) = m to recover m.
(C) To provide data origin authentication of a message, m, to be
sent to Bob, Alice computes m**d (mod n) = s, where (d,n) is
Alice's private key. She sends m and s to Bob. To recover the
message that only Alice could have sent, Bob computes s**e (mod n)
= m, where (e,n) is Alice's public key.
(C) To ensure data integrity in addition to data origin
authentication requires extra computation steps in which Alice and
Bob use a cryptographic hash function h (as explained for digital
signature). Alice computes the hash value h(m) = v, and then
encrypts v with her private key to get s. She sends m and s. Bob
receives m' and s', either of which might have been changed from
the m and s that Alice sent. To test this, he decrypts s' with
Alice's public key to get v'. He then computes h(m') = v". If v'
equals v", Bob is assured that m' is the same m that Alice sent.
$ role-based access control (RBAC)
(I) A form of identity-based access control where the system
entities that are identified and controlled are functional
positions in an organization or process.
$ root
(I) A CA that is directly trusted by an end entity. Acquiring the
value of a root CA's public key involves an out-of-band procedure.
(I) Hierarchical PKI usage: The CA that is the highest level (most
trusted) CA in a certification hierarchy; i.e., the authority upon
whose public key all certificate users base their trust. (See: top
CA.)
(C) In a hierarchical PKI, a root issues public-key certificates
to one or more additional CAs that form the second highest level.
Each of these CAs may issue certificates to more CAs at the third
highest level, and so on. To initialize operation of a
hierarchical PKI, the root's initial public key is securely
distributed to all certificate users in a way that does not depend
on the PKI's certification relationships. The root's public key
may be distributed simply as a numerical value, but typically is
distributed in a self-signed certificate in which the root is the
subject. The root's certificate is signed by the root itself
because there is no higher authority in a certification hierarchy.
The root's certificate is then the first certificate in every
certification path.
(O) MISSI usage: A name previously used for a MISSI policy
creation authority, which is not a root as defined above for
general usage, but is a CA at the second level of the MISSI
hierarchy, immediately subordinate to a MISSI policy approving
authority.
(O) UNIX usage: A user account (also called "superuser") that has
all privileges (including all security-related privileges) and
thus can manage the system and its other user accounts.
$ root certificate
(I) A certificate for which the subject is a root.
(I) Hierarchical PKI usage: The self-signed public-key certificate
at the top of a certification hierarchy.
$ root key
(I) A public key for which the matching private key is held by a
root.
$ root registry
(O) MISSI usage: A name previously used for a MISSI policy
approving authority.
$ router
(I) A computer that is a gateway between two networks at OSI layer
3 and that relays and directs data packets through that
internetwork. The most common form of router operates on IP
packets. (See: bridge.)
(I) Internet usage: In the context of the Internet protocol suite,
a networked computer that forwards Internet Protocol packets that
are not addressed to the computer itself. (See: host.)
$ RSA
See: Rivest-Shamir-Adleman.
$ rule-based security policy
(I) "A security policy based on global rules imposed for all
users. These rules usually rely on comparison of the sensitivity
of the resource being accessed and the possession of corresponding
attributes of users, a group of users, or entities acting on
behalf of users." [I7498 Part 2] (See: identity-based security
policy.)
$ safety
(I) The property of a system being free from risk of causing harm
to system entities and outside entities.
$ SAID
See: security association identifier.
$ salt
(I) A random value that is concatenated with a password before
applying the one-way encryption function used to protect passwords
that are stored in the database of an access control system. (See:
initialization value.)
(C) Salt protects a password-based access control system against a
dictionary attack.
$ sanitize
(I) Delete sensitive data from a file, a device, or a system; or
modify data so as to be able to downgrade its classification
level.
$ SASL
See: Simple Authentication and Security Layer.
$ SCA
See: subordinate certification authority.
$ scavenging
See: (secondary definition under) threat consequence.
$ screening router
(I) A synonym for "filtering router".
$ SDE
See: Secure Data Exchange.
$ SDNS
See: Secure Data Network System.
$ seal
(O) To use cryptography to provide data integrity service for a
data object. (See: sign, wrap.)
(D) ISDs SHOULD NOT use this definition; instead, use language
that is more specific with regard to the mechanism(s) used, such
as "sign" when the mechanism is digital signature.
$ secret
(I) (1.) Adjective: The condition of information being protected
from being known by any system entities except those who are
intended to know it. (2.) Noun: An item of information that is
protected thusly.
(C) This term applies to symmetric keys, private keys, and
passwords.
$ secret-key cryptography
(I) A synonym for "symmetric cryptography".
$ Secure Data Exchange (SDE)
(N) A local area network security protocol defined by the IEEE
802.10 standard.
$ Secure Data Network System (SDNS)
(N) An NSA program that developed security protocols for
electronic mail (Message Security Protocol), OSI layer 3 (SP3),
OSI layer 4 (SP4), and key management (KMP).
$ Secure Hash Standard (SHS)
(N) The U.S. Government standard [FP180] that specifies the Secure
Hash Algorithm (SHA-1), a cryptographic hash function that
produces a 160-bit output (hash result) for input data of any
length < 2**64 bits.
$ Secure Hypertext Transfer Protocol (Secure-HTTP, S-HTTP)
(I) A Internet protocol for providing client-server security
services for HTTP communications. (See: https.)
(C) S-HTTP was originally specified by CommerceNet, a coalition of
businesses interested in developing the Internet for commercial
uses. Several message formats may be incorporated into S-HTTP
clients and servers, particularly CMS and MOSS. S-HTTP supports
choice of security policies, key management mechanisms, and
cryptographic algorithms through option negotiation between
parties for each transaction. S-HTTP supports both asymmetric and
symmetric key operation modes. S-HTTP attempts to avoid presuming
a particular trust model, but it attempts to facilitate multiply-
rooted hierarchical trust and anticipates that principals may have
many public key certificates.
$ Secure/MIME (S/MIME)
(I) Secure/Multipurpose Internet Mail Extensions, an Internet
protocol [R2633] to provide encryption and digital signatures for
Internet mail messages.
$ Secure Sockets Layer (SSL)
(N) An Internet protocol (originally developed by Netscape
Communications, Inc.) that uses connection-oriented end-to-end
encryption to provide data confidentiality service and data
integrity service for traffic between a client (often a web
browser) and a server, and that can optionally provide peer entity
authentication between the client and the server. (See: Transport
Layer Security.)
(C) SSL is layered below HTTP and above a reliable transport
protocol (TCP). SSL is independent of the application it
encapsulates, and any higher level protocol can layer on top of
SSL transparently. However, many Internet applications might be
better served by IPsec.
(C) SSL has two layers: (a) SSL's lower layer, the SSL Record
Protocol, is layered on top of the transport protocol and
encapsulates higher level protocols. One such encapsulated
protocol is SSL Handshake Protocol. (b) SSL's upper layer provides
asymmetric cryptography for server authentication (verifying the
server's identity to the client) and optional client
authentication (verifying the client's identity to the server),
and also enables them to negotiate a symmetric encryption
algorithm and secret session key (to use for data confidentiality)
before the application protocol transmits or receives data. A
keyed hash provides data integrity service for encapsulated data.
$ secure state
(I) A system condition in which no subject can access any object
in an unauthorized manner. (See: (secondary definition under)
Bell-LaPadula Model, clean system.)
$ security
(I) (1.) Measures taken to protect a system. (2.) The condition of
a system that results from the establishment and maintenance of
measures to protect the system. (3.) The condition of system
resources being free from unauthorized access and from
unauthorized or accidental change, destruction, or loss.
$ security architecture
(I) A plan and set of principles that describe (a) the security
services that a system is required to provide to meet the needs of
its users, (b) the system elements required to implement the
services, and (c) the performance levels required in the elements
to deal with the threat environment. (See: (discussion under)
security policy.)
(C) A security architecture is the result of applying the system
engineering process. A complete system security architecture
includes administrative security, communication security, computer
security, emanations security, personnel security, and physical
security (e.g., see: [R2179]). A complete security architecture
needs to deal with both intentional, intelligent threats and
accidental kinds of threats.
$ security association
(I) A relationship established between two or more entities to
enable them to protect data they exchange. The relationship is
used to negotiate characteristics of protection mechanisms, but
does not include the mechanisms themselves. (See: association.)
(C) A security association describes how entities will use
security services. The relationship is represented by a set of
information that is shared between the entities and is agreed upon
and considered a contract between them.
(O) IPsec usage: A simplex (uni-directional) logical connection
created for security purposes and implemented with either AH or
ESP (but not both). The security services offered by a security
association depend on the protocol selected, the IPsec mode
(transport or tunnel), the endpoints, and the election of optional
services within the protocol. A security association is identified
by a triple consisting of (a) a destination IP address, (b) a
protocol (AH or ESP) identifier, and (c) a Security Parameter
Index.
$ security association identifier (SAID)
(I) A data field in a security protocol (such as NLSP or SDE),
used to identify the security association to which a protocol data
unit is bound. The SAID value is usually used to select a key for
decryption or authentication at the destination. (See: Security
Parameter Index.)
$ security audit
(I) An independent review and examination of a system's records
and activities to determine the adequacy of system controls,
ensure compliance with established security policy and procedures,
detect breaches in security services, and recommend any changes
that are indicated for countermeasures. [I7498 Part 2, NCS01]
(C) The basic audit objective is to establish accountability for
system entities that initiate or participate in security-relevant
events and actions. Thus, means are needed to generate and record
a security audit trail and to review and analyze the audit trail
to discover and investigate attacks and security compromises.
$ security audit trail
(I) A chronological record of system activities that is sufficient
to enable the reconstruction and examination of the sequence of
environments and activities surrounding or leading to an
operation, procedure, or event in a security-relevant transaction
from inception to final results. [NCS04] (See: security audit.)
$ security class
(D) A synonym for "security level". For consistency, ISDs SHOULD
use "security level" instead of "security class".
$ security clearance
(I) A determination that a person is eligible, under the standards
of a specific security policy, for authorization to access
sensitive information or other system resources. (See: clearance
level.)
$ security compromise
(I) A security violation in which a system resource is exposed, or
is potentially exposed, to unauthorized access. (See: data
compromise, violation.)
$ security domain
See: domain.
$ security environment
(I) The set of external entities, procedures, and conditions that
affect secure development, operation, and maintenance of a system.
$ security event
(I) A occurrence in a system that is relevant to the security of
the system. (See: security incident.)
(C) The term includes both events that are security incidents and
those that are not. In a CA workstation, for example, a list of
security events might include the following:
- Performing a cryptographic operation, e.g., signing a digital
certificate or CRL.
- Performing a cryptographic card operation: creation, insertion,
removal, or backup.
- Performing a digital certificate lifecycle operation: rekey,
renewal, revocation, or update.
- Posting information to an X.500 Directory.
- Receiving a key compromise notification.
- Receiving an improper certification request.
- Detecting an alarm condition reported by a cryptographic
module.
- Logging the operator in or out.
- Failing a built-in hardware self-test or a software system
integrity check.
$ security fault analysis
(I) A security analysis, usually performed on hardware at a logic
gate level, gate-by-gate, to determine the security properties of
a device when a hardware fault is encountered.
$ security gateway
(I) A gateway that separates trusted (or relatively more trusted)
hosts on the internal network side from untrusted (or less
trusted) hosts on the external network side. (See: firewall and
guard.)
(O) IPsec usage: "An intermediate system that implements IPsec
protocols." [R2401] Normally, AH or ESP is implemented to serve a
set of internal hosts, providing security services for the hosts
when they communicate with other, external hosts or gateways that
also implement IPsec.
$ security incident
(I) A security event that involves a security violation. (See:
CERT, GRIP, security event, security intrusion, security
violation.)
(C) In other words, a security-relevant system event in which the
system's security policy is disobeyed or otherwise breached.
(O) "Any adverse event which compromises some aspect of computer
or network security." [R2350]
(D) ISDs SHOULD NOT use this "O" definition because (a) a security
incident may occur without actually being harmful (i.e., adverse)
and (b) this Glossary defines "compromise" more narrowly in
relation to unauthorized access.
$ security intrusion
(I) A security event, or a combination of multiple security
events, that constitutes a security incident in which an intruder
gains, or attempts to gain, access to a system (or system
resource) without having authorization to do so.
$ security kernel
(I) "The hardware, firmware, and software elements of a trusted
computing base that implement the reference monitor concept. It
must mediate all accesses, be protected from modification, and be
verifiable as correct." [NCS04] (See: reference monitor.)
(C) That is, a security kernel is an implementation of a reference
monitor for a given hardware base.
$ security label
(I) A marking that is bound to a system resource and that names or
designates the security-relevant attributes of that resource.
[I7498 Part 2, R1457]
(C) The recommended definition is usefully broad, but usually the
term is understood more narrowly as a marking that represents the
security level of an information object, i.e., a marking that
indicates how sensitive an information object is. [NCS04]
(C) System security mechanisms interpret security labels according
to applicable security policy to determine how to control access
to the associated information, otherwise constrain its handling,
and affix appropriate security markings to visible (printed and
displayed) images thereof. [FP188]
$ security level
(I) The combination of a hierarchical classification level and a
set of non-hierarchical category designations that represents how
sensitive information is. (See: (usage note under) classification
level, dominate, lattice model.)
$ security management infrastructure (SMI)
(I) System elements and activities that support security policy by
monitoring and controlling security services and mechanisms,
distributing security information, and reporting security events.
The associated functions are as follows [I7498-4]:
- Controlling (granting or restricting) access to system
resources: This includes verifying authorizations and
identities, controlling access to sensitive security data, and
modifying access priorities and procedures in the event of
attacks.
- Retrieving (gathering) and archiving (storing) security
information: This includes logging security events and
analyzing the log, monitoring and profiling usage, and
reporting security violations.
- Managing and controlling the encryption process: This includes
performing the functions of key management and reporting on key
management problems. (See: public-key infrastructure.)
$ security mechanism
(I) A process (or a device incorporating such a process) that can
be used in a system to implement a security service that is
provided by or within the system. (See: (discussion under)
security policy.)
(C) Some examples of security mechanisms are authentication
exchange, checksum, digital signature, encryption, and traffic
padding.
$ security model
(I) A schematic description of a set of entities and relationships
by which a specified set of security services are provided by or
within a system. (See: (discussion under) security policy.)
(C) An example is the Bell-LaPadula Model.
$ security parameters index (SPI)
(I) IPsec usage: The type of security association identifier used
in IPsec protocols. A 32-bit value used to distinguish among
different security associations terminating at the same
destination (IP address) and using the same IPsec security
protocol (AH or ESP). Carried in AH and ESP to enable the
receiving system to determine under which security association to
process a received packet.
$ security perimeter
(I) The boundary of the domain in which a security policy or
security architecture applies; i.e., the boundary of the space in
which security services protect system resources.
$ security policy
(I) A set of rules and practices that specify or regulate how a
system or organization provides security services to protect
sensitive and critical system resources. (See: identity-based
security policy, rule-based security policy, security
architecture, security mechanism, security model.)
(O) "The set of rules laid down by the security authority
governing the use and provision of security services and
facilities." [X509]
(C) Ravi Sandhu notes that security policy is one of four layers
of the security engineering process (as shown in the following
diagram). Each layer provides a different view of security,
ranging from what services are needed to how services are
implemented.
What Security Services Should Be Provided?
^
| + - - - - - - - - - - - +
| | Security Policy |
| + - - - - - - - - - - - + + - - - - - - - - - - - - - - +
| | Security Model | | A "top-level specification" |
| + - - - - - - - - - - - + <- | is at a level below "model" |
| | Security Architecture | | but above "architecture". |
| + - - - - - - - - - - - + + - - - - - - - - - - - - - - +
| | Security Mechanism |
| + - - - - - - - - - - - +
v
How Are Security Services Implemented?
$ Security Protocol 3 (SP3)
(O) A protocol [SDNS3] developed by SDNS to provide connectionless
data security at the top of OSI layer 3. (See: NLSP.)
$ Security Protocol 4 (SP4)
(O) A protocol [SDNS4] developed by SDNS to provide either
connectionless or end-to-end connection-oriented data security at
the bottom of OSI layer 4. (See: TLSP.)
$ security-relevant event
See: security event.
$ security service
(I) A processing or communication service that is provided by a
system to give a specific kind of protection to system resources.
(See: access control service, audit service, availability service,
data confidentiality service, data integrity service, data origin
authentication service, non-repudiation service, peer entity
authentication service, system integrity service.)
(O) "A service, provided by a layer of communicating open systems,
which ensures adequate security of the systems or the data
transfers." [I7498 Part 2]
(C) Security services implement security policies, and are
implemented by security mechanisms.
$ security situation
(I) ISAKMP usage: The set of all security-relevant information--
e.g., network addresses, security classifications, manner of
operation (normal or emergency)--that is needed to decide the
security services that are required to protect the association
that is being negotiated.
$ security token
See: token.
$ security violation
(I) An act or event that disobeys or otherwise breaches security
policy. (See: compromise, penetration, security incident.)
$ self-signed certificate
(I) A public-key certificate for which the public key bound by the
certificate and the private key used to sign the certificate are
components of the same key pair, which belongs to the signer.
(See: root certificate.)
(C) In a self-signed X.509 public-key certificate, the issuer's DN
is the same as the subject's DN.
$ semantic security
(I) An attribute of a encryption algorithm that is a formalization
of the notion that the algorithm not only hides the plaintext but
also reveals no partial information about the plaintext. Whatever
is efficiently computable about the plaintext when given the
ciphertext, is also efficiently computable without the ciphertext.
(See: indistinguishability.)
$ sensitive (information)
(I) Information is sensitive if disclosure, alteration,
destruction, or loss of the information would adversely affect the
interests or business of its owner or user. (See: critical.)
$ separation of duties
(I) The practice of dividing the steps in a system function among
different individuals, so as to keep a single individual from
subverting the process. (See: dual control, administrative
security.)
$ serial number
See: certificate serial number.
$ server
(I) A system entity that provides a service in response to
requests from other system entities called clients.
$ session key
(I) In the context of symmetric encryption, a key that is
temporary or is used for a relatively short period of time. (See:
ephemeral key, key distribution center, master key.)
(C) Usually, a session key is used for a defined period of
communication between two computers, such as for the duration of a
single connection or transaction set, or the key is used in an
application that protects relatively large amounts of data and,
therefore, needs to be rekeyed frequently.
$ SET
See: SET Secure Electronic Transaction(trademark).
$ SET private extension
(O) One of the private extensions defined by SET for X.509
certificates. Carries information about hashed root key,
certificate type, merchant data, cardholder certificate
requirements, encryption support for tunneling, or message support
for payment instructions.
$ SET qualifier
(O) A certificate policy qualifier that provides information about
the location and content of a SET certificate policy.
(C) In addition to the policies and qualifiers inherited from its
own certificate, each CA in the SET certification hierarchy may
add one qualifying statement to the root policy when the CA issues
a certificate. The additional qualifier is a certificate policy
for that CA. Each policy in a SET certificate may have these
qualifiers:
- A URL where a copy of the policy statement may be found.
- An electronic mail address where a copy of the policy statement
may be found.
- A hash result of the policy statement, computed using the
indicated algorithm.
- A statement declaring any disclaimers associated with the
issuing of the certificate.
$ SET Secure Electronic Transaction(trademark) or SET(trademark)
(N) A protocol developed jointly by MasterCard International and
Visa International and published as an open standard to provide
confidentiality of transaction information, payment integrity, and
authentication of transaction participants for payment card
transactions over unsecured networks, such as the Internet. [SET1]
(See: acquirer, brand, cardholder, dual signature, electronic
commerce, issuer, merchant, payment gateway, third party.)
(C) This term and acronym are trademarks of SETCo. MasterCard and
Visa announced the SET standard on 1 February 1996. On 19 December
1997, MasterCard and Visa formed SET Secure Electronic Transaction
LLC (commonly referred to as "SETCo") to implement the SET 1.0
specification. A memorandum of understanding adds American Express
and JCB Credit Card Company as co-owners of SETCo.
$ SETCo
See: (secondary definition under) SET Secure Electronic
Transaction.
$ SHA-1
See: Secure Hash Standard.
$ shared secret
(I) A synonym for "keying material" or "cryptographic key".
$ S-HTTP
See: Secure HTTP.
$ sign
(I) Create a digital signature for a data object.
$ signature
See: digital signature, electronic signature.
$ signature certificate
(I) A public-key certificate that contains a public key that is
intended to be used for verifying digital signatures, rather than
for encrypting data or performing other cryptographic functions.
(C) A v3 X.509 public-key certificate may have a "keyUsage"
extension which indicates the purpose for which the certified
public key is intended.
$ signer
(N) A human being or an organization entity that uses its private
key to create a digital signature for a data object. [ABA]
$ SILS
See: Standards for Interoperable LAN/MAN Security.
$ simple authentication
(I) An authentication process that uses a password as the
information needed to verify an identity claimed for an entity.
(See: strong authentication.)
(O) "Authentication by means of simple password arrangements."
[X509]
$ Simple Authentication and Security Layer (SASL)
(I) An Internet specification [R2222] for adding authentication
service to connection-based protocols. To use SASL, a protocol
includes a command for authenticating a user to a server and for
optionally negotiating protection of subsequent protocol
interactions. The command names a registered security mechanism.
SASL mechanisms include Kerberos, GSSAPI, S/KEY, and others. Some
protocols that use SASL are IMAP4 and POP3.
$ Simple Key-management for Internet Protocols (SKIP)
(I) A key distribution protocol that uses hybrid encryption to
convey session keys that are used to encrypt data in IP packets.
[R2356] (See: IKE, IPsec.)
(C) SKIP uses the Diffie-Hellman algorithm (or could use another
key agreement algorithm) to generate a key-encrypting key for use
between two entities. A session key is used with a symmetric
algorithm to encrypt data in one or more IP packets that are to be
sent from one of the entities to the other. The KEK is used with a
symmetric algorithm to encrypt the session key, and the encrypted
session key is placed in a SKIP header that is added to each IP
packet that is encrypted with that session key.
$ Simple Mail Transfer Protocol (SMTP)
(I) A TCP-based, application-layer, Internet Standard protocol
[R0821] for moving electronic mail messages from one computer to
another.
$ Simple Network Management Protocol (SNMP)
(I) A UDP-based, application-layer, Internet Standard protocol
[R2570, R2574] for conveying management information between
managers and agents.
(C) SNMP version 1 uses cleartext passwords for authentication and
access control. (See: community string.) Version 2 adds
cryptographic mechanisms based on DES and MD5. Version 3 provides
enhanced, integrated support for security services, including data
confidentiality, data integrity, data origin authentication, and
message timeliness and limited replay protection.
$ simple security property
See: (secondary definition under) Bell-LaPadula Model.
$ single sign-on
(I) A system that enables a user to access multiple computer
platforms (usually a set of hosts on the same network) or
application systems after being authenticated just one time. (See:
Kerberos.)
(C) Typically, a user logs in just once, and then is transparently
granted access to a variety of permitted resources with no further
login being required until after the user logs out. Such a system
has the advantages of being user friendly and enabling
authentication to be managed consistently across an entire
enterprise, and has the disadvantage of requiring all hosts and
applications to trust the same authentication mechanism.
$ situation
See: security situation.
$ S/Key
(I) A security mechanism that uses a cryptographic hash function
to generate a sequence of 64-bit, one-time passwords for remote
user login. [R1760]
(C) The client generates a one-time password by applying the MD4
cryptographic hash function multiple times to the user's secret
key. For each successive authentication of the user, the number of
hash applications is reduced by one. (Thus, an intruder using
wiretapping cannot compute a valid password from knowledge of one
previously used.) The server verifies a password by hashing the
currently presented password (or initialization value) one time
and comparing the hash result with the previously presented
password.
$ SKIP
See: Simple Key-management for IP.
$ SKIPJACK
(N) A Type II block cipher [NIST] with a block size of 64 bits and
a key size of 80 bits, that was developed by NSA and formerly
classified at the U.S. Department of Defense "Secret" level. (See:
CAPSTONE, CLIPPER, FORTEZZA, Key Exchange Algorithm.)
(C) On 23 June 1998, NSA announced that SKIPJACK had been
declassified.
$ slot
(O) MISSI usage: One of the FORTEZZA PC card storage areas that
are each able to hold an X.509 certificate and additional data
that is associated with the certificate, such as the matching
private key.
$ smart card
(I) A credit-card sized device containing one or more integrated
circuit chips, which perform the functions of a computer's central
processor, memory, and input/output interface. (See: PC card.)
(C) Sometimes this term is used rather strictly to mean a card
that closely conforms to the dimensions and appearance of the kind
of plastic credit card issued by banks and merchants. At other
times, the term is used loosely to include cards that are larger
than credit cards, especially cards that are thicker, such as PC
cards.
(C) A "smart token" is a device that conforms to the definition of
smart card except that rather than having standard credit card
dimensions, the token is packaged in some other form, such as a
dog tag or door key shape.
$ smart token
See: (secondary definition under) smart card.
$ SMI
See: security management infrastructure.
$ S/MIME
See: Secure/MIME.
$ SMTP
See: Simple Mail Transfer Protocol.
$ smurf
(I) Software that mounts a denial-of-service attack ("smurfing")
by exploiting IP broadcast addressing and ICMP ping packets to
cause flooding. (See: flood, ICMP flood.)
(D) ISDs SHOULD NOT use this term because it is not listed in most
dictionaries and could confuse international readers.
(C) A smurf program builds a network packet that appears to
originate from another address, that of the "victim", either a
host or an IP router. The packet contains an ICMP ping message
that is addressed to an IP broadcast address, i.e., to all IP
addresses in a given network. The echo responses to the ping
message return to the victim's address. The goal of smurfing may
be either to deny service at a particular host or to flood all or
part of an IP network.
$ sniffing
(C) A synonym for "passive wiretapping". (See: password sniffing.)
(D) ISDs SHOULD NOT use this term because it unnecessarily
duplicates the meaning of a term that is better established. (See:
(usage note under) Green Book.
$ SNMP
See: Simple Network Management Protocol.
$ social engineering
(I) A euphemism for non-technical or low-technology means--such as
lies, impersonation, tricks, bribes, blackmail, and threats--used
to attack information systems. (See: masquerade attack.)
(D) ISDs SHOULD NOT use this term because it is vague; instead,
use a term that is specific with regard to the means of attack.
$ SOCKS
(I) An Internet protocol [R1928] that provides a generalized proxy
server that enables client-server applications--such as TELNET,
FTP, and HTTP; running over either TCP or UDP--to use the services
of a firewall.
(C) SOCKS is layered under the application layer and above the
transport layer. When a client inside a firewall wishes to
establish a connection to an object that is reachable only through
the firewall, it uses TCP to connect to the SOCKS server,
negotiates with the server for the authentication method to be
used, authenticates with the chosen method, and then sends a relay
request. The SOCKS server evaluates the request, typically based
on source and destination addresses, and either establishes the
appropriate connection or denies it.
$ soft TEMPEST
(O) The use of software techniques to reduce the radio frequency
information leakage from computer displays and keyboards. [Kuhn]
(See: TEMPEST.)
$ software
(I) Computer programs (which are stored in and executed by
computer hardware) and associated data (which also is stored in
the hardware) that may be dynamically written or modified during
execution. (See: firmware, hardware.)
$ SORA
See: SSO-PIN ORA.
$ source authentication
(D) ISDs SHOULD NOT use this term because it is ambiguous. If the
intent is to authenticate the original creator or packager of data
received, then say "data origin authentication". If the intent is
to authenticate the identity of the sender of data, then say "peer
entity authentication". (See: data origin authentication, peer
entity authentication).
$ source integrity
(I) The degree of confidence that can be placed in information
based on the trustworthiness of its sources. (See: integrity.)
$ SP3
See: Security Protocol 3.
$ SP4
See: Security Protocol 4.
$ spam
(I) (1.) Verb: To indiscriminately send unsolicited, unwanted,
irrelevant, or inappropriate messages, especially commercial
advertising in mass quantities. (2.) Noun: electronic "junk mail".
[R2635]
(D) This term SHOULD NOT be written in upper-case letters, because
SPAM(trademark) is a trademark of Hormel Foods Corporation. Hormel
says, "We do not object to use of this slang term [spam] to
describe [unsolicited commercial email (UCE)], although we do
object to the use of our product image in association with that
term. Also, if the term is to be used, it should be used in all
lower-case letters to distinguish it from our trademark SPAM,
which should be used with all uppercase letters."
(C) In sufficient volume, spam can cause denial of service. (See:
flooding.) According to the SPAM Web site, the term was adopted as
a result of the Monty Python skit in which a group of Vikings sang
a chorus of 'SPAM, SPAM, SPAM . . .' in an increasing crescendo,
drowning out other conversation. Hence, the analogy applied
because UCE was drowning out normal discourse on the Internet.
$ SPC
See: software publisher certificate.
$ SPI
See: Security Parameters Index.
$ split key
(I) A cryptographic key that is divided into two or more separate
data items that individually convey no knowledge of the whole key
that results from combining the items. (See: dual control, split
knowledge.)
$ split knowledge
(I) A security technique in which two or more entities separately
hold data items that individually convey no knowledge of the
information that results from combining the items. (See: dual
control, split key.)
(O) "A condition under which two or more entities separately have
key components which individually convey no knowledge of the
plaintext key which will be produced when the key components are
combined in the cryptographic module." [FP140]
$ spoofing attack
(I) A synonym for "masquerade attack".
$ SSH
(I) A protocol for secure remote login and other secure network
services over an insecure network.
(C) Consists of three major components:
- Transport layer protocol: Provides server authentication,
confidentiality, and integrity. It may optionally also provide
compression. The transport layer will typically be run over a
TCP/IP connection, but might also be used on top of any other
reliable data stream.
- User authentication protocol: Authenticates the client-side
user to the server. It runs over the transport layer protocol.
- Connection protocol: Multiplexes the encrypted tunnel into
several logical channels. It runs over the user authentication
protocol.
$ SSL
See: Secure Sockets Layer, Standard Security Label.
$ SSO
See: system security officer.
$ SSO PIN
(O) MISSI usage: One of two personal identification numbers that
control access to the functions and stored data of a FORTEZZA PC
card. Knowledge of the SSO PIN enables the card user to perform
the FORTEZZA functions intended for use by an end user and also
the functions intended for use by a MISSI certification authority.
(See: user PIN.)
$ SSO-PIN ORA (SORA)
(O) MISSI usage: A MISSI organizational RA that operates in a mode
in which the ORA performs all card management functions and,
therefore, requires knowledge of the SSO PIN for an end user's
FORTEZZA PC card.
$ Standards for Interoperable LAN/MAN Security (SILS)
(N) (1.) The IEEE 802.10 standards committee. (2.) A developing
set of IEEE standards, which has eight parts: (a) Model, including
security management, (b) Secure Data Exchange protocol, (c) Key
Management, (d) [has been incorporated in (a)], (e) SDE Over
Ethernet 2.0, (f) SDE Sublayer Management, (g) SDE Security
Labels, and (h) SDE PICS Conformance. Parts b, e, f, g, and h are
incorporated in IEEE Standard 802.10-1998.
$ star property
(I) (Written "*-property".) See: "confinement property" under
Bell-LaPadula Model.
$ Star Trek attack
(C) An attack that penetrates your system where no attack has ever
gone before.
$ steganography
(I) Methods of hiding the existence of a message or other data.
This is different than cryptography, which hides the meaning of a
message but does not hide the message itself. (See: cryptology.)
(C) An example of a steganographic method is "invisible" ink.
(See: digital watermark.)
$ storage channel
See: (secondary definition under) covert channel.
$ stream cipher
(I) An encryption algorithm that breaks plaintext into a stream of
successive bits (or characters) and encrypts the n-th plaintext
bit with the n-th element of a parallel key stream, thus
converting the plaintext bit stream into a ciphertext bit stream.
[Schn] (See: block cipher.)
$ strong authentication
(I) An authentication process that uses cryptography--particularly
public-key certificates--to verify the identity claimed for an
entity. (See: X.509.)
(O) "Authentication by means of cryptographically derived
credentials." [X509]
$ subject
1. (I) In a computer system: A system entity that causes
information to flow among objects or changes the system state;
technically, a process-domain pair. (See: Bell-LaPadula Model.)
2. (I) Of a certificate: The entity name that is bound to the data
items in a digital certificate, and particularly a name that is
bound to a key value in a public-key certificate.
$ subnetwork
(N) An OSI term for a system of packet relays and connecting links
that implement the lower three protocol layers of the OSIRM to
provide a communication service that interconnects attached end
systems. Usually the relays operate at OSI layer 3 and are all of
the same type (e.g., all X.25 packet switches, or all interface
units in an IEEE 802.3 LAN). (See: gateway, internet, router.)
$ subordinate certification authority (SCA)
(I) A CA whose public-key certificate is issued by another
(superior) CA. (See: certification hierarchy.)
(O) MISSI usage: The fourth-highest (bottom) level of a MISSI
certification hierarchy; a MISSI CA whose public-key certificate
is signed by a MISSI CA rather than by a MISSI PCA. A MISSI SCA is
the administrative authority for a subunit of an organization,
established when it is desirable to organizationally distribute or
decentralize the CA service. The term refers both to that
authoritative office or role, and to the person who fills that
office. A MISSI SCA registers end users and issues their
certificates and may also register ORAs, but may not register
other CAs. An SCA periodically issues a CRL.
$ subordinate distinguished name
(I) An X.500 DN is subordinate to another X.500 DN if it begins
with a set of attributes that is the same as the entire second DN
except for the terminal attribute of the second DN (which is
usually the name of a CA). For example, the DN <C=FooLand, O=Gov,
OU=Treasurer, CN=DukePinchpenny> is subordinate to the DN
<C=FooLand, O=Gov, CN=KingFooCA>.
$ superencryption
(I) An encryption operation for which the plaintext input to be
transformed is the ciphertext output of a previous encryption
operation.
$ survivability
(I) The ability of a system to remain in operation or existence
despite adverse conditions, including both natural occurrences,
accidental actions, and attacks on the system. (See: availability,
reliability.)
$ symmetric cryptography
(I) A branch of cryptography involving algorithms that use the
same key for two different steps of the algorithm (such as
encryption and decryption, or signature creation and signature
verification). (See: asymmetric cryptography.)
(C) Symmetric cryptography has been used for thousands of years
[Kahn]. A modern example of a symmetric encryption algorithm is
the U.S. Government's Data Encryption Algorithm. (See: DEA, DES.)
(C) Symmetric cryptography is sometimes called "secret-key
cryptography" (versus public-key cryptography) because the
entities that share the key, such as the originator and the
recipient of a message, need to keep the key secret. For example,
when Alice wants to ensure confidentiality for data she sends to
Bob, she encrypts the data with a secret key, and Bob uses the
same key to decrypt. Keeping the shared key secret entails both
cost and risk when the key is distributed to both Alice and Bob.
Thus, symmetric cryptography has a key management disadvantage
compared to asymmetric cryptography.
$ symmetric key
(I) A cryptographic key that is used in a symmetric cryptographic
algorithm.
$ SYN flood
(I) A denial of service attack that sends a host more TCP SYN
packets (request to synchronize sequence numbers, used when
opening a connection) than the protocol implementation can handle.
(See: flooding.)
$ system
(C) In this Glossary, the term is mainly used as an abbreviation
for "automated information system".
$ system entity
(I) An active element of a system--e.g., an automated process, a
subsystem, a person or group of persons--that incorporates a
specific set of capabilities.
$ system high
(I) The highest security level supported by a system at a
particular time or in a particular environment. (See: system high
security mode.)
$ system high security mode
(I) A mode of operation of an information system, wherein all
users having access to the system possess a security clearance or
authorization, but not necessarily a need-to-know, for all data
handled by the system. (See: mode of operation.)
(C) This mode is defined formally in U.S. Department of Defense
policy regarding system accreditation [DOD2], but the term is
widely used outside the Defense Department and outside the
Government.
$ system integrity
(I) "The quality that a system has when it can perform its
intended function in a unimpaired manner, free from deliberate or
inadvertent unauthorized manipulation." [NCS04] (See: system
integrity service.)
$ system integrity service
(I) A security service that protects system resources in a
verifiable manner against unauthorized or accidental change, loss,