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Computer Science
Computer Security and Reliability
Ethical Hacking and Security - Chapter 12 - Cryptography
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KEY TERM CH 12
Terms in this set (44)
Advanced Encryption Standard (AES)
A symmetric block cipher standard from NIST that replaced DES. See also Data Encryption Standard (DES).
asymmetric algorithm
Encryption methodology that uses two keys that are mathematically related; also referred to as public key cryptography.
authentication
The process of verifying that the sender or receiver (or both) is who he or she claims to be; this function is available in asymmetric algorithms but not symmetric algorithms.
birthday attacks
Attacks used to find the same hash value for two different inputs and reveal mathematical weaknesses in a hashing algorithm.
block cipher
A symmetric algorithm that encrypts data in blocks of bits. These blocks are used as input to mathematical functions that perform substitution and transposition of the bits, making it difficult for someone to reverse-engineer the mathematical functions that were used.
Blowfish
A block cipher that operates on 64-bit blocks of plaintext, but its key length can be as large as 448 bits.
brute-force attack
An attack in which the attacker uses software that attempts every possible combination of characters to guess passwords.
certificate
A digital document that verifies whether two parties exchanging data over the Internet are really who they claim to be. Each certificate has a unique serial number and must follow the X.509 standard.
certification authority (CA)
A third party, such as VeriSign, that vouches for a company's authenticity and issues a certificate binding a public key to a recipient's private key.
cipher
A key that maps each letter or number to a different letter or number.
ciphertext
Plaintext (readable text) that has been encrypted.
cryptanalysis
A field of study devoted to breaking encryption algorithms. data at rest Any data not moving through a network or being used by the OS; usually refers to data on storage media.
Data Encryption Algorithm (DEA)
The encryption algorithm used in the DES standard; a symmetric algorithm that uses 56 bits for encryption. See also Data Encryption Standard (DES).
Data Encryption Standard (DES)
A NIST standard for protecting sensitive but unclassified data; it was later replaced because the increased processing power of computers made it possible to break DES encryption.
dictionary attack
An attack in which the attacker runs a password-cracking program that uses a dictionary of known words or passwords as an input file against the attacked system's password file.
digital signature
A method of signing messages by using asymmetric encryption that ensures authentication and nonrepudiation. See also authentication and nonrepudiation.
encryption algorithm
A mathematical formula or method for converting plaintext into ciphertext.
hashing algorithm
A function that takes a variable-length string or message and produces a fixed-length hash value, also called a message digest. See also message digest.
International Data Encryption Algorithm (IDEA)
A block cipher that operates on 64-bit blocks of plaintext and uses a 128-bit key; used in PGP encryption software.
key
A sequence of random bits used in an encryption algorithm to transform plaintext into ciphertext, or vice versa.
keyspace
The range of all possible key values contained in an encryption algorithm. See also key.
man-in-the-middle attack
An attack in which attackers place themselves between the victim computer and another host computer, and then intercept messages sent from the victim to the host and pretend to be the host computer.
mathematical attack
An attack in which properties of the encryption algorithm are attacked by using mathematical computations. Categories of this attack include ciphertextonly attack, known plaintext attack, chosen-plaintext attack, chosen-ciphertext attack, and side-channel attack.
message digest
The fixed-length value that a hashing algorithm produces; used to verify that data or messages haven't been changed.
Message Digest 5 (MD5)
A 128-bit cryptographic hash function; still used, even though its weaknesses make finding collisions practical with only moderate computing power. Most useful for file integrity checking.
nonrepudiation
The process of ensuring that the sender and receiver can't deny sending or receiving the message; this function is available in asymmetric algorithms but not symmetric algorithms.
OpenPGP
The Internet public key encryption standard for PGP messages; can use AES, IDEA, RSA, DSA, and SHA algorithms for encrypting, authenticating, verifying message integrity, and managing keys. The most common free version is GNU Privacy Guard (GnuPG or GPG), and a commercial version that's compliant with the OpenPGP standard is available.
plaintext
Readable text that hasn't been encrypted; also called cleartext.
Pretty Good Privacy (PGP)
A free e-mail encryption program that allows typical users to encrypt e-mails.
private key
In a key pair, the secret key used in an asymmetric algorithm that's known only by the key owner and is never shared. Even if the public key that encrypted a message is known, the owner's private key can't be determined.
public key
In a key pair, the key that can be known by the public; it works with a private key in asymmetric key cryptography, which is also known as public key cryptography.
public key cryptography
Also known as asymmetric key cryptography, an asymmetric algorithm that uses two mathematically related keys.
public key infrastructure (PKI)
A structure consisting of programs, protocols, and security policies. PKI uses public key cryptography to protect data traversing the Internet.
rainbow table
A lookup table of password hash values that enables certain programs to crack passwords much faster than with brute-force methods.
RC4
A stream cipher created by Ronald L. Rivest that's used in WEP wireless encryption.
RC5
A block cipher created by Ronald L. Rivest that can operate on different block sizes: 32, 64, and 128 bits. The key size can reach 2048 bits.
replay attack
An attack in which the attacker captures data and attempts to resubmit the data so that a device, such as a workstation or router, thinks a legitimate connection is in effect.
Secure Hash Algorithm (SHA)
The NIST standard hashing algorithm that's much stronger than MD5 but has demonstrated weaknesses. For sensitive applications, NIST recommends not using SHA-1, and federal agencies are replacing it with longer digest versions, collectively called SHA-2.
Secure Multipurpose Internet Mail Extension (S/MIME)
A public key encryption standard for encrypting and digitally signing e-mail. It can also encrypt e-mails containing attachments and use PKI certificates for authentication.
steganography
The method of hiding data in plain view in pictures, graphics, or text.
stream cipher
A symmetric algorithm that operates on plaintext one bit at a time.
symmetric algorithm
An encryption algorithm that uses only one key to encrypt and decrypt data. The recipient of a message encrypted with a key must have a copy of the same key to decrypt the message.
substitution cipher
A cipher that maps each letter of the alphabet to a different letter. The Book of Jeremiah was written by using a substitution cipher called Atbash.
Triple Data Encryption Standard (3DES)
A standard developed to address the vulnerabilities of DES; it improved security, but encrypting and decrypting data take longer.
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