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Cryptography Glossary

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Cryptography Glossary Cryptography Glossary A5/1 A stream cipher used in GSM mobile phone communication. 36 Active Attack A cryptanalysis attack that relies on actively disrupting communication 44 or forcefully getting access to data. Adaptive chosen-ciphertext Attack Similar to chosen-ciphertext attack but Eve can choose subsequent ci- 44 phertexts based on information learnt from previous encryptions. Adaptive chosen-plaintext Attack Similar to chosen-plaintext attack but Eve can choose subsequent plain- 44 texts based on information learnt from previous encryptions. AddRoundKey The round key addition operation used during AES encryption and de- 28 cryption. AES The advanced encryption standard that is the successor of DES. 26 Alice The sender of an encrypted message. 11 Asymmetric Cipher Cipher that uses different (not trivially related) keys for encryption and 11, 54 decryption. Asymmetric Cryptography The study of algorithms and protocols for asymmetric ciphers. 54 Birthday Paradox A probability theoretical fact stating that in a random group of ¢¡ people 47 the likelihood that two of them will have the same birthday is more than £¥¤§¦ Block A fixed-length group of bits. 11 Block Cipher A symmetric key cipher, which operates on fixed-length groups of bits, 11 named blocks. Bob The intended receiver of an encrypted message. Bob is assumed to have 11 the key to decrypt it. C2 Short for Cryptomeria. 24 CA Short for Certification Authority. 71 Caesar Cipher Shift cipher with fixed shift of ¡ . 6 © § ¨ © !¨ Carmichael Number A number ¨ for which for all but that is 64 nevertheless composite. CBC Short for Cipher Block Chaining 20 CBC-MAC A method to produce a MAC from a block cipher. 51 Certificate Also called Digital Certificate. 71 Certification Authority A trusted third party that issues and validates digital certificates 71 CFB Short for Cipher Feedback mode 21 Chosen-ciphertext Attack Eve can obtain the plaintexts corresponding to arbitrary ciphertexts of 44 her choice. Chosen-plaintext Attack Eve can obtain the ciphertexts corresponding to arbitrary plaintexts of 44 her choice. Cipher Substitution at the level of letters/characters/symbols. 4 Cipher Block Chaining mode A mode of operation for block ciphers that propagates context informa- 20 tion. Cipher Feedback mode A mode of operation that turns a block cipher effectively into a stream 21 cipher by using context information. Cipher-alphabet The alphabet used for encryption. 6 Ciphertext An enciphered message. 4 Ciphertext-only Attack Eve has access only to a collection of ciphertexts or codetexts. 44 Code Substitution at the level of words 4 Codetext An encoded message. 4 Collision Free Function A hash function is called collision free, if for any " it is computationally 46 %&'"$)(!%&'"*#+ infeasible to find an "$# such as . Commitment Scheme A method of sending secret information such that it cannot be altered at 73 a later stage; neither by the sender nor the receiver. Connection Polynomial Polynomial used to describe and analyse a LFSR based stream cipher. 34 Content Scrambling System A proprietary standard to encrypt multimedia DVDs for copy protection. 35 Counter mode A mode of operation that turns a block cipher effectively into a stream 23 cipher by using a counter. Cross-Certification Several CAs are linked by exchanging certificates directly with each 72 other. Cryptanalysis The science of breaking ciphertexts. 4 Cryptanalyst A practitioner of cryptanalysis. 4 Cryptographer A practitioner of cryptography. 4 Cryptographic Hash Function A function that transforms an arbitrarily long message into fixed lengths 46 string to authenticate it has not been tampered with. Cryptography The science of scrambling messages. 3, 4 Cryptologist A practitioner of cryptology. 4 Cryptology The branch of mathematics encompassing both cryptography and crypt- 4 analysis Cryptomeria A Feistel Cipher used as content protection mechanism for multimedia 24 DVDs. CSS Short for Content Scrambling System. 35 CTR Short for Counter mode 23, 31 Davies-Meyer A method to build hash functions from block ciphers. 50 Decipher The process of decrypting a message with respect to some cipher. 4 Decode The process of decrypting a message with respect to some code. 4 Decrypt The process of unscrambling a message. 4 Deletion Attack Data is modified by deleting parts of the ciphertext. 44 Denial of Service Attack This is an attempt to make a computer resource unavailable to its in- 45 tended users. Differential Cryptanalysis is the study of how differences in an input can affect the resulting differ- 44 ence at the output. Diffie-Hellman Key Exchange The very first asymmetric cryptography algorithm invented, that uses 56 discrete exponentiation to agree on a key. Diffie-Hellman Problem A computationally infeasible problem. 56 Digital Signature A cryptographic scheme to ensure message identity based on public key 66 cryptography. Digital Signature Algorithm A digital signature derived from RSA, whose security is based on the 67, 68 factorisation of numbers. Discrete Logarithm Problem A computationally infeasible problem. 56 DoS Short for Denial of Service attack. 45 DSA Short for Digital Signature Algorithm. 68 ECB Short for Electronic Codebook mode 19 Electronic Codebook mode A na¨ıve mode of operation for block ciphers that encrypts every block 19 independently. ElGamal A public key cipher based on discrete exponentiation. 57 Encipher The process of encrypting a message with respect to some cipher. 4 Encode The process of encrypting a message with respect to some code. 4 Encrypt The process of scrambling a message. 4 Encryption Schemes Techniques to introduce a degree of randomness into public key ciphers 63 often by preprocessing the messages. Eve The eavesdropper who tries to intercept and to cryptanalyse messages 11 passed between Bob and Alice. Feedback Function A function that determines a new bit for a shift register by tapping the 33 content of some of the registers. Feistel Cipher A basic block cipher developed by Horst Feistel at IBM. It forms the 12 bases of many modern block ciphers. Feistel function The function applying the round key in the Feistel cipher, thereby effec- 12 tively parameterising the round function. Fermat’s Test A probabilistic test algorithm to establish the likelihood that a given 63 number is a prime, based on Fermat’s little theorem. Finalisation Function A final function applied to strengthen an output hash in the Merkle- 47 Damgard˚ Construction. Fingerprint The result of a hash function. Also known as hash sum. 46 Frequency Analysis A statistical method to decipher messages based on the frequency of 7 occurrences of letters in particular languages. Hash The result of a hash function. 46 Hierarchical CAs Several CAs are certified by a single root CA. 72 HMAC A method to produce a MAC from a hash function. 51 Initial Value An arbitrary value used to kick off encryption in block cipher modes. 20 Initial values are normally denoted as ¢¡ and do not need to be kept secret. Initialisation Vector See Initial Value. 20 Insertion Attack Data is modified by inserting parts into the ciphertext. 44 Integer Factorisation A computationally infeasible problem for large integers. 56 InverseMixColumns A column manipulation operations used during AES decryption. Inverse 28 of MixColumns. InverseShiftRows A byte permutation used during AES decryption. Inverse of Shift Rows. 28 InverseSubBytes An S-Box like substitution algorithm used during AES decryption. The 27 inverse of SubBytes. IP Spoofing A computer poses as another computer by illegitimately assuming its IP 45 address. Kerberos A symmetric key exchange protocol derived from Needham-Schroeder, 42 but based on timestamps. It is used in Windows 2000. Key Auxiliary information that is used to vary the encryption procedure 6 Key Exchange Protocols Precisely defined communication methods to exchange keys for crypto- 39 graphic algorithms. Key Generator A function that generates keys that can be used in a public key cipher. 55, 66 Key management Problems related to choosing, distributing, and securely storing keys for 11 symmetric ciphers. Key Schedule A function to generate round keys from one input key. 14, 16 Keystream A stream of bits used of encryption by xor-ing it with the plaintext in a 31 stream cipher. Known-plaintext Attack Eve has a set of ciphertexts to which she knows the corresponding plain- 44 text. Lamport Signatures A generic signature scheme that is based on one-way functions. It is 67, 69 considered secure even against quantum cryptanalysis, since it uses sig- natures exactly once. LFSR Short for Linear Feedback Shift Register. 33 Linear Cryptanalysis is the approximation of the action of a cipher by some function. 44 Linear Feedback Shift Register A shift register with a linear feedback function that is a building block 33 for many modern stream ciphers. Lucifer Cipher First simple Feistel cipher. 12 MAC Short for Message Authentication Code. 51, 66 Mallory A malicious attacker, who can modify messages, substitute her own mes- 39 sages, replay old messages, and so on. Man-in-the-Middle Attack Mallory spoofs Alice into believing she’s Bob, and spoofs Bob into be- 45 lieving she’s Alice, thus gaining access to all messages in both directions without the trouble of any cryptanalytic effort. Masquerading Attack An attack in which one person or program successfully masquerades as 45 another by falsifying data and thereby gaining an illegitimate advantage. Matyas-Meyer-Oseas A method to build hash functions from block ciphers. 50 MD Short for Message-Digest. 48 MD4 A hash function of the MD family producing 128-bit hashes. 48 MD5 A hash function of the MD family producing 128-bit hashes. 49 Mental Coin Flipping A commitment scheme for making a binary decision. 73 Mental Poker A commitment scheme to play poker without physically exchanging 74 cards. Merkle-Damgaard Construction A method to extend a fixed size compression function to an arbitrary size 47 compression function. Merkle-Damgaard strengthening A padding method that adds a bit representation of the message length 47 at the end of a message before applying a hash function.
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