Cryptography IS Lecture 5 PDF

Cryptography Asma Amjad  What Is Cryptography? “Scrambling” data so that it cannot be read is a process known as cryptography. Cryptography is the science of transforming information into a secure form so that unauthorized persons cannot access it. It enables you to store sensitive...

Cryptography Asma Amjad  What Is Cryptography? “Scrambling” data so that it cannot be read is a process known as cryptography. Cryptography is the science of transforming information into a secure form so that unauthorized persons cannot access it. It enables you to store sensitive information and transmit it across the insecure network (like the internet) so that it cannot be read by anyone except the intended recipient. Changing the original text into a secret message using cryptography is known as Encryption. When the process is , reversed the to change the secret message back to its original form. This is called Decryption. Data in an unencrypted form is called cleartext data. Plaintext data is cleartext data. The science of encryption, known as cryptology, encompasses cryptography and cryptanalysis. Terminology of Cryptography Algorithm: The mathematical formula or method used to convert an unencrypted message into an encrypted message. This sometimes refers to the programs that enable the cryptographic processes. Bit stream cipher: An encryption method that involves converting plaintext to ciphertext one bit at a time. Block cipher: An encryption method that involves dividing the plaintext into blocks or sets of bits and then converting the plaintext to ciphertext one block at a time.  Key terms Monoalphabetic substitution A substitution cipher that only incorporates a single alphabet in the encryption process. (Ceaser cipher) Polyalphabetic substitution A substitution cipher that incorporates two or more alphabets in the encryption process. (Vigenère cipher) Substitution cipher An encryption method in which one value is substituted for another. A substitution cipher exchanges one value for another—for example, it might exchange a letter in the alphabet with the letter three values to the right, or it might substitute one bit for another bit four places to its left. A three-character substitution to the right results in the following transformation of the standard English alphabet. Initial alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ yields Encryption alphabet: DEFGHIJKLMNOPQRSTUVWXYZABC Within this substitution scheme, the plaintext MOM would be encrypted into the ciphertext PRP.