chapter 8

symmetric encryption

A cryptographic method in which the same algorithm and secret key are used both to encipher and decipher the message.

asymmetric encryption

A cryptographic method that incorporates mathematical operations involving both a public key and a private key to encipher or decipher a message. Either key can be used to encrypt a message, but then the other key is required to decrypt it.

transposition cipher

A cryptographic operation that involves simply rearranging the values within a block based on an established pattern. Also known as a permutation cipher.

Vernam cipher

A cryptographic technique developed at AT&T and known as the "one-time pad," this cipher uses a set of characters for encryption operations only one time and then discards it.

exclusive OR operation (XOR)

A function within Boolean algebra used as an encryption function in which two bits are compared. If the two bits are identical, the result is a binary 0; otherwise, the result is a binary 1.

Diffie-Hellman key exchange

A hybrid cryptosystem that facilitates exchanging private keys using public-key encryption.

secret key

A key that can be used in symmetric encryption both to encipher and decipher the message.

message authentication code (MAC)

A key-dependent, one-way hash function that allows only specific recipients (symmetric key holders) to access the message digest.

Secure Electronic Transactions (SET)

A protocol developed by credit card companies to protect against electronic payment fraud.

Secure Sockets Layer (SSL)

A security protocol developed by Netscape to use public-key encryption to secure a channel over the Internet.

Secure Multipurpose Internet Mail Extensions (S/MIME)

A security protocol that builds on the encoding format of the Multipurpose Internet Mail Extensions (MIME) protocol and uses digital signatures based on public-key cryptosystems to secure e-mail.

Link encryption

A series of encryptions and decryptions between a number of systems, wherein each system in a network decrypts the message sent to it and then reencrypts the message using different keys and sends it to the next neighbor. This process continues until the message reaches the final destination.

Secure Hash Standard (SHS)

A standard issued by the National Institute of Standards and Technology (NIST) that specifies secure algorithms, such as SHA-1, for computing a condensed representation of a message or data file.

Privacy-Enhanced Mail (PEM)

A standard proposed by the Internet Engineering Task Force (IETF) that uses 3DES symmetric key encryption and RSA for key exchanges and digital signatures.

polyalphabetic substitution

A substitution cipher that incorporates two or more alphabets in the encryption process.

monoalphabetic substitution

A substitution cipher that only incorporates a single alphabet in the encryption process.

message digest

A value representing the application of a hash algorithm on a message that is transmitted with the message so it can be compared with the recipient's locally calculated hash of the same message. If both hashes are identical after transmission, the message has arrived without modification. Also known as a hash value.

Vigenère cipher

An advanced type of substitution cipher that uses a simple polyalphabetic code.

substitution cipher

An encryption method in which one value is substituted for another.

Bit stream cipher

An encryption method that involves converting plaintext to cipher-text one bit at a time.

Block cipher

An encryption method that involves dividing the plaintext into blocks or sets of bits and then converting the plaintext to ciphertext one block at a time.

Secure HTTP (S-HTTP)

An extended version of Hypertext Transfer Protocol that provides for the encryption of protected Web pages transmitted via the Internet between a client and server.

public key infrastructure (PKI)

An integrated system of software, encryption methodologies, protocols, legal agreements, and third-party services that enables users to communicate securely through the use of digital certificates.

digital signatures

Encrypted message components that can be mathematically proven as authentic.

encapsulating security payload (ESP) protocol

In IPSec, a protocol that provides secrecy for the contents of network communications as well as system-to-system authentication and data integrity verification.

application header (AH) protocol

In IPSec, a protocol that provides system-to-system authentication and data integrity verification, but does not provide secrecy for the content of a network communication.

transport mode

In IPSec, an encryption method in which only a packet's IP data is encrypted, not the IP headers themselves; this method allows intermediate nodes to read the source and destination addresses.

tunnel mode

In IPSec, an encryption method in which the entire IP packet is encrypted and inserted as the payload in another IP packet. This requires other systems at the beginning and end of the tunnel to act as proxies to send and receive the encrypted packets and then transmit the packets to their ultimate destination.

certificate revocation list (CRL)

In PKI, a published list of revoked or terminated digital certificates.

certificate authority (CA)

In PKI, a third party that manages users' digital certificates.

registration authority (RA)

In PKI, a third party that operates under the trusted collaboration of the certificate authority and handles day-to-day certification functions.

session keys

Limited-use symmetric keys for temporary communications during an online session.

hash functions

Mathematical algorithms that generate a message summary or digest (sometimes called a fingerprint) to confirm message identity and integrity.

hash algorithms

Public functions that create a hash value, also known as a message digest, by converting variable-length messages into a single fixed-length value.

digital certificates

Public-key container files that allow PKI system components and end users to validate a public key and identify its owner.

Decipher

See Decryption.

Encipher

See Encryption.

public-key encryption

See asymmetric encryption.

hash value

See message digest.

private-key encryption

See symmetric encryption.

permutation cipher

See transposition cipher.

Digital Signature Standard (DSS)

The NIST standard for digital signature algorithm usage by federal information systems. DSS is based on a variant of the ElGamal signature scheme.

Work factor

The amount of effort (usually expressed in units of time) required to perform cryptanalysis on an encoded message.

Advanced Encryption Standard (AES)

The current federal standard for the encryption of data, asspecified by NIST. AES is based on the Rijndael algorithm, which was developed by Vincent Rijmen and Joan Daemen.

Keyspace

The entire range of values that can be used to construct an individual key.

cryptology

The field of science that encompasses cryptography and cryptanalysis.

Key or cryptovariable

The information used in conjunction with the algorithm to create the ciphertext from the plaintext; it can be a series of bits used in a mathematical algorithm or the knowledge of how to manipulate the plaintext. Sometimes called a cryptovariable.

Algorithm

The mathematical formula or method used to convert an unencrypted mes-sage into an encrypted message. This sometimes refers to the programs that enable the cryptographic processes.

Plaintext or cleartext

The original unencrypted message that is encrypted and is the result of successful decryption.

IP Security (IPSec)

The primary and now dominant cryptographic authentication and encryption product of the IETF's IP Protocol Security Working Group. A framework for security development within the TCP/IP family of protocol standards, IPSec provides application support for all uses within TCP/IP, including virtual private networks.

Decryption

The process of converting an encoded or enciphered message (ciphertext)back to its original readable form (plaintext). Also referred to as deciphering.

Encryption

The process of converting an original message (plaintext) into a form that cannot be used by unauthorized individuals (ciphertext). Also referred to as enciphering.

Code

The process of converting components (words or phrases) of an unencrypted message into encrypted components.

Steganography

The process of hiding messages; for example, hiding a message within the digital encoding of a picture or graphic so that it is almost impossible to detect that the hidden message even exists.

steganography

The process of hiding messages; for example, hiding a message within the digital encoding of a picture or graphic so that it is almost impossible to detect that the hidden message even exists.

cryptography

The process of making and using codes to secure information.

cryptanalysis

The process of obtaining the plaintext message from a ciphertext message without knowing the keys used to perform the encryption.

nonrepudiation

The process of reversing public-key encryption to verify that a message was sent by the sender and thus cannot be refuted.

Ciphertext or cryptogram

The unintelligible encrypted or encoded message resulting from an encryption.

Cipher

When used as a verb, the transformation of the individual components (characters, bytes, or bits) of an unencrypted message into encrypted components or vice versa (see decipher and encipher); when used as a noun, the process of encryption or the algorithm used in encryption, and a term synonymous with cryptosystem.