19.1 Cryptography

And this is Module19 – Cryptography, Section 19.1 - Introduction to Cryptography Cryptography is study of secure communication that prevent third parties or the public from reading private messages. Cryptography means ‘hidden’ ‘writing’ and its features: – Cryptography is synonymous with encryption, the conversion of readable information to non-readable (Ciphertext) format. Decryption is the reverse process. – Cryptography takes care of data confidentiality, integrity, authentication and non-repudiation. – Applications include e-commerce, payment cards, DRM etc. – Cryptography is a technique of transforming and transmitting confidential data in an encoded way so that only authorized and intended users can obtain or work on it. – Cryptanalysis is process of breaking the work of cryptography. – Cryptology is the study of cryptography and cryptanalysis both. In cryptography, a cipher or Code is an algorithm for performing encryption or decryption. Modern encryption methods can be divided by two criteria: – by type of key used – by type of input data Classical Ciphers: Ciphers written hard using simple substitutions of a letter code or a word. – 20th century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution. – Secret communication requirement is there since age and methods vary as per need of the times. – Symmetric key algorithms (Private-key cryptography), where the same key is used for encryption and decryption. – Asymmetric key algorithms (Public-key cryptography), where two different keys are used for encryption and decryption. By type of input data – Block ciphers, which encrypt block of data of fixed size – Stream ciphers, which encrypt continuous streams of data Symmetric key algorithm – In symmetric key algorithms same key is used for encryption and decryption. (e.g., DES and AES) – The sender and receiver must have a shared key in advance exchanged secretly. – Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key. – Symmetric key ciphers are implemented as either block ciphers or stream ciphers. – A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a stream cipher. – Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are block cipher designs. In asymmetric key algorithms two different keys are used for encryption and decryption. (e.g. RSA) There are two separate keys: – a public key is published and enables any sender to perform encryption – a private key is kept secret by the receiver and can be used to perform decryption. Asymmetric systems - RSA (Rivest-Shamir-Adleman) - ECC (Elliptic Curve Cryptography) Symmetric systems - AES (Advanced Encryption Standard) - DES (Data Encryption Standard) Cryptographic hash functions are a third type of cryptographic algorithm. – They take a message of any length as input, and output a short, fixed length hash, which can be used in a digital signature. – MD5 is widely used hashing. – SHA series is more secure than MD5. SHA-2 improves SHA1 – 2012 - NIST announced that Keccak would be the new SHA-3 hash algorithm. – Cryptographic hash functions are used to verify the authenticity of data retrieved from a source.