Cryptography

Unconditional Security is a guarantee of security on ciphertext regardless of computational power or time. This means that the ciphertext cannot be broken in any condition, which usually means there are not enough information from the ciphertext to crack it down into plaintext.

Timing Attack is a form of #Side-Channel Attack which analyse the time taken to execute a decryption #algorithm to guess the size of an operand or any critical cryptographic information.

Symmetric Cryptography, or Private-Key Cryptography is a #Cryptographic system that uses the same key for encryption and decryption. However, you can already imagine the security risk of sharing the same secret over a network, requiring a secure channel (usually via IPsec#). If the key get compromised#, it means the need to generate a new key and distribute# it again. It also requires a strong encryption #algorithm for the intruder to not be able to guess the secret key easily. That being said, it is quite fast when comparing to Asymmetric Cryptography.

Substitution Cryptography is a #cryptographic method that encrypt a message by replacing every text with an alternate text based on their natural or mathematical relationship between each other.

S/MIME utilises several Cryptographic schemes to provide secrecy to the MIME email. For Digital Signature#, it uses DDS or Rivest-Shamir-Adleman (RSA)#. Hash Functions# used are SHA-1 and MD5. ElGamal or Rivest-Shamir-Adleman (RSA)# is used to encrypt session key. The message encryption is done by Advanced Encryption Standard (AES)#, Triple Data Encryption Standard (3DES)#, RC2/40 or others.

An association between client and server called SSL session will be established by SSL Handshake Protocol, which could be shared among multiple SSL connection that are transient, #p2p, communications links. Each SSL connection is private (encrypted with Symmetric Cryptographic algorithms#) and reliable (message integrity check by Message Authentication Code (MAC)# using SHA, MD5 etc. hash functions on compressed SSL data), and for each web component (provide suitable services). The session could define a set of Cryptographic parameters such as keys and algorithms used which could be shared by multiple connections. The session is kept alive by SSL Alert Protocol, where the peer’s identity can be authenticated with Asymmetric Cryptographic Scheme#. SSL Change Cipher Spec Protocol would be used if the peer wants the consequent messages to be encrypted for transmission. With SSL session, there is no need to exchange security parameters for each SSL connection which could be expensive.

SET is an open encryption and security specification designed to protect credit card transaction on the Internet. It provides secure communication channel in a transaction, X.509v3 digital certificates#, and privacy to the client with dual signature.

There are many use cases in Cryptography# relies on random numbers such as Nonce# in authentication protocols, session keys, public key generation, and keystream for One-Time Pad.

Permutation/Transposition Cryptography is a #Cryptographic method that encrypt a message by rearranging the plaintexts. This includes changing Encoding# system of the plaintexts. Since it doesn’t alter the frequency of letters from the original plaintext, it is vulnerable to Frequency Analysis#. It is even more dangerous to group the ciphertext in group that match the key size used by the cipher.

Peer Entity Authentication is a kind of #Security Service that utilises encryption#, Digital Signature# and Authentication Exchange# in order to counter Masquerade#.

Kerckhoff’s Principle stated that the #Cryptography method must be secure in an environment based on the following 2 assumptions:

IND-CCA is the highest security notion for an encryption scheme#. It is resistant to the most lenient Cryptanalytic Attack#, that is to distinguish two ciphertexts using chosen ciphertext attack.

Common in Cryptography#, \(GF(p)\) is a Set# where \(\{a \in P | a \in \mathbb{Z} \text{ and } 0 \le a \le p - 1 \}\) with modulo# prime \(p\) as its arithmetic operations. For example, \(GF(7)\) multiplication looks like the table below.

Feistel Cipher Structure, invented by Horst Feistel, is the most common basic #cipher structure adopted by various schemes.

Digital Signature is a #Security Mechanism where hashed# data is appended to (sometimes encrypted# using Rivest-Shamir-Adleman (RSA)#) a data unit, allowing a recipient of the data unit to prove the source and Integrity# of the data unit. It could protect against forgery# due to its Non-Repudiation# nature. At the receiver side, it will either reject (return value 0) or accept (return value 1) the signature.

Data Origin Authentication is a kind of #Security Service that utilises encryption# and Digital Signature# in order to counter Masquerade#.

Cryptology is a field of study that includes Cryptography# and Cryptanalysis#.

Cryptanalytic Attack is performed based on the nature of the cryptographic #algorithm with the complement from the general characteristic of the plaintext. It is essentially finding a relationship between the plaintext and the ciphertext. Some #Cryptanalysts would use the sample plaintext-ciphertext pairs in aid on cracking the algorithm down. The purpose of the Cryptanalytic Attack is to find the relationship between the information that the cryptanalyst has obtained.

Cryptanalysis is a study of principles or method of decrypting ciphertext# without knowing the key. People who study or practise cryptanalysis are known as cryptanalyst, intruder, or attacker. The results of a Cryptanalysis doesn’t necessary bad, as they are useful feedbacks to the cryptographers to improve their #algorithm.

Confidentiality is the protection of transmitted data from unauthorised disclosure. It serves as a #Security Service and utilises encryption# and Routing Control# in order to counter the release of message contents#.

Computational Security is a guarantee of security on ciphertext on assuming that computing resources are limited, and the time required or cost to decrypt the ciphertext is too long or too large to be valuable.

If a #Cryptanalysis could crack an encryption scheme with an attempts less than of the Brute Force Attack, then it is considered to be a Cryptanalytic Attack on the scheme.

Avalanche Effect happened when a slight change of input or key bit (plaintext) results in a significant change on the output bits (ciphertext, approximately half or more of them). It is a key desirable property of #encryption #algorithm.

Asymmetric Cryptography aka Public-Key Cryptography is a #Cryptographic system, first introduced by Whitefield Diffie and Martin Hellman in 1976, that involves usage of pair keys that perform unequal functions. Such keys are commonly denoted as: private key and public key. The generation of two keys typically requires very large numbers, thus rendering it slow when comparing to Symmetric Cryptography.