Bit Cipher 1

Example of bit Cipher 2

Practical Stream Cipher 3

Block Cipher 4

Substitution Cipher: Caesar Cipher 5

Vigenère Cipher Example  Suppose that the plaintext to be encrypted is: ATTACKATDAWN  The person sending the message chooses a keyword and repeats it until it matches the length of the plaintext, for example, the keyword "LEMON": LEMONLEMONLE  For successive letters of the message, we are going to take successive letters of the key string, and encipher each message letter using its corresponding key row.  Choose the next letter of the key, go along that row to find the column heading that matches the message character; the letter at the intersection of [key-row, msg-col] is the enciphered letter. 6

Vigenère cipher Example  For example, the first letter of the plaintext, A, is paired with L, the first letter of the key. So use row L and column A of the Vigenère square, namely L.  Similarly, for the second letter of the plaintext, the second letter of the key is used; the letter at row E and column T is X. The rest of the plaintext is enciphered in a similar fashion:  PlaintextATTACKATDAWN  Key: LEMONLEMONLE  Cipher text:LXFOPVEFRNHR 7

Transposition cipher example  For example, the word ZEBRAS is of length 6 (so the rows are of length 6), and the permutation is defined by the alphabetical order of the letters in the keyword. In this case, the order would be " ".  The message is read off in columns, in the order specified by the keyword.  Suppose we use the keyword ZEBRAS and the message WE ARE DISCOVERED. FLEE AT ONCE. In a regular columnar transposition, we write this into the grid as Follows: W E A R E D I S C O V E R E D F L E E A T O N C E  The ciphertext is then read off as: EVLNA CDTES EAROF ODEEC WIREE 8

Vernam cipher 9 Vernam proposed a bit-wise exclusive or of the message stream with a truly random zero-one stream which was shared by sender and recipient. Example: SENDING message: pad: XOR cipher: RECEIVING cipher: pad: XOR message:

Hashing using SHA224 SHA224("The quick brown fox jumps over the lazy dog")The quick brown fox jumps over the lazy dog 0x730e109bd7a8a32b1cb9d9a09aa2325d d dbc0c38bad SHA224("The quick brown fox jumps over the lazy dog.")The quick brown fox jumps over the lazy dog 0x619cba8e8e05826e9b8c519c0a5c68f4fb653e8a3d 8aa04bb2c8cd4c 10

Message Authentication Code MAC  In cryptography, a message authentication code (often MAC) is a short piece of information used to authenticate a message and to provide integrity and authenticity assurances on the message.  Integrity assurances detect accidental and intentional message changes, while authenticity assurances affirm the message's origin.  A MAC algorithm, sometimes called a keyed (cryptographic) hash function accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC (sometimes known as a tag).  The MAC value protects both a message's data integrity as well as its authenticity, by allowing verifiers (who also possess the secret key) to detect any changes to the message content. 11

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MAC vs. Digital Signature MACs differ from digital signatures as MAC values are both generated and verified using the same secret key. This implies that the sender and receiver of a message must agree on the same key before initiating communications, as is the case with symmetric encryption. 13