Cryptography

Cryptography is the study and art of hiding meaningful information in an unreadable format. Cryptography and cryptographic (“crypto”) systems help in securing data from interception and compromise during online transmissions. Cryptography enables one to secure transactions, communications, and other processes performed in the electronic world, and is additionally used to protect confidential data such as email messages, chat sessions, web transactions, personal data, corporate data, e-commerce applications, etc.

Overview of Cryptography “Cryptography” comes from the Greek words kryptos, meaning “concealed, hidden, veiled, secret, or mysterious,” and graphia, “writing”; thus, cryptography is “the art of secret writing.”

Cryptography is the practice of concealing information by converting plain text (readable format) into cipher text (unreadable format) using a key or encryption scheme: it is the process of the conversion of data into a scrambled code that is sent across a private or public network.

There are two types of cryptography, determined by the number of keys employed for encryption and decryption:

• Symmetric Encryption: Symmetric encryption (secret-key, shared-key, and private-key) uses the same key for encryption as it does for decryption

• Asymmetric Encryption: Asymmetric encryption (public-key) uses different encryption keys for encryption and decryption; these keys are known as public and private keys

Hash functions calculate a unique fixed-size bit string representation, called a message digest, of any arbitrary block of information. Message digest (One-way Hash) functions distill the information contained in a file (small or large) into a single fixed-length number, typically between 128 and 256 bits. If any given bit of the function’s input is changed, every output bit has a 50% chance of changing. Given an input file and its corresponding message digest, it should be nearly impossible to find another file with the same message digest value, as it is computationally infeasible to have two files with the same message digest value.

MD2, MD4, MD5, and MD6 are message digest algorithms used in digital signature applications to compress documents securely before the system signs it with a private key. The algorithms can be of variable length, but the resulting message digest is always 128 bits.

The MD5 algorithm is a widely used cryptographic hash function that takes a message of arbitrary length as input and outputs a 128-bit (16-byte) fingerprint or message digest of the input. The MD5 algorithm is used in a wide variety of cryptographic applications and is useful for digital signature applications, file integrity checking, and storing passwords.

Self-signed certificates are widely used for testing servers. In self-signed certificates, a user creates a pair of public and private keys using a certificate creation tool such as Adobe Acrobat Reader, Java’s keytool, Apple’s Keychain, etc. and signs the document with the public key. The recipient requests the private key from the sender in order to verify the certificate. However, certificate verification rarely occurs due to the necessity of disclosing the private key: this makes self-signed certificates useful only in a self-controlled testing environment.

Email encryption hides the email content from eavesdroppers by encrypting it into an unreadable form. Emails can be encrypted and decrypted by means of a digital signature mechanism that uses public and private keys: the public key is shared, while the private key is kept private.

There are numerous methods that can be employed for email encryption, including:

• Digital Signature: Uses asymmetric cryptography to simulate the security properties of a signature in digital, rather than written form

• Secure Sockets Layer (SSL): Uses RSA asymmetric (public key) encryption to encrypt data transferred over SSL connections

• Transport Layer Security (TLS): Uses a symmetric key for bulk encryption, an asymmetric key for authentication and key exchange, and message authentication codes for message integrity

• Pretty Good Privacy (PGP): Used to encrypt and decrypt data that provides authentication and cryptographic privacy

• GNU Privacy Guard (GPG): Software replacement of PGP and free implementation of the OpenPGP standard that is used to encrypt and decrypt data

Overview of Cryptanalysis

Cryptanalysis can be performed using various methods, including the following:

• Linear Cryptanalysis: A known plaintext attack that uses a linear approximation to describe the behavior of the block cipher

• Differential Cryptanalysis: The examination of differences in an input and how this affects the resultant difference in the output

• Integral Cryptanalysis: This attack is useful against block ciphers based on substitution-permutation networks and is an extension of differential cryptanalysis

Perform Cryptanalysis using CrypTool

• CrypTool is a freeware program that enables you to apply and analyze cryptographic mechanisms, and has the typical look and feel of a modern Windows application. CrypTool includes a multitude of state-of-the-art cryptographic functions and allows you to both learn and use cryptography within the same environment. CrypTool is a free, open-source e-learning application used in the implementation and analysis of cryptographic algorithms.

Perform Cryptanalysis using AlphaPeeler

• AlphaPeeler is a powerful tool for learning cryptology. It can be useful as an instructor’s teaching aid and to create assignments for classical cryptography. You can easily learn classical techniques such as frequency analysis of alphabets, mono-alphabetic substitution, Caesar cipher, transposition cipher, Vigenere cipher, and Playfair cipher. AlphaPeeler Professional (powered by crypto++ library) also includes DES, Gzip/Gunzip, MD5, SHA-1, SHA-256, RIPEMD-16, RSA key generation, RSA crypto, RSA signature & validation, and generation of secret share files.