Dang Thanh Binh Explain general cryptography concepts Explain basic hashing concepts. Basic encryption concepts. Explain and implement protocols Explain core concepts of public key cryptography Cryptography – science of encrypting information. “scrambles” data so only authorized parties can “unscramble” and read data using two methods Can substitute – change one letter with a different letter Can transpose – scramble the order of letters, without actually changing one for another. The best cryptosystems both substitute and transpose.
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�
Dang Thanh Binh
� Explain general cryptography concepts
� Explain basic hashing concepts.
� Basic encryption concepts.
� Explain and implement protocols
� Explain core concepts of public key cryptography
� Cryptography – science of encrypting information.
� “scrambles” data so only authorized parties can
“unscramble” and read data using two methods
�Can substitute – change one letter with a different letter
�Can transpose – scramble the order of letters, without actually
changing one for another.
� The best cryptosystems both substitute and transpose.
� Cryptography - a method of storing and transmitting data
in a form only intended for authorized parties to read or
process.
� Cryptanalysis - science of studying, breaking, and
reverse engineering algorithms and keys.
� Encryption – the method of transforming data (plaintext)
into an unreadable format.
� Plain text – the format (usually readable) of data before
being encrypted
� Cipher text – the “Scrambled” format of data after being
encrypted
� Decryption – the method of turning cipher text back into
plain text
� Encryption algorithm – a set or rules or procedures that
dictates how to encrypt and decrypt data. Also called an
encryption “cipher”
� Key – (crypto variable) a values used in the encryption
process to encrypt and decrypt
� Key space – the range of possible values used to
construct keys
� example:
�if a key can be 4 digits (0-9)
�key space = 10,000 (0000 – 9999)
�if it can be 6 digits
�key space = 1,000,000 (000,000 – 999,999)
� Key Clustering – Instance when two different keys
generate the same cipher text from the same plaintext
� Work factor – estimated time and resources to break a
cryptosystem
� Romans used a shift cipher called a “CEASAR” cipher.
Shift Ciphers simply shift characters in an alphabet.
� Jumbles up the ordering of characters in a message. The
Spartans of Greece used a form of this called the “Scytale”
Cipher.
� Hiding one message in another
� “Meet the mini me that ate later.”
� “Meet me later.”
� The Vigenère cipher is named for Blaise de Vigenère,
although Giovan Battista Bellaso had invented the cipher
earlier. Vigenère did invent a stronger autokey cipher.
� Vigenère cipher is a method of encrypting alphabetic text
by using a series of different Caesar ciphers based on the
letters of a keyword. It is a simple form of polyalphabetic
substitution.
� This cipher is well known because while it is easy to
understand and implement, it often appears to beginners
to be unbreakable.
� For example, suppose that the plaintext to be encrypted is:ATTACKATDAWN
� The person sending the message chooses a keyword andrepeats it until it matches the length of the plaintext, forexample, the keyword "LEMON": LEMONLEMONLE
� The first letter of the plaintext, A, is enciphered using thealphabet in row L, which is the first letter of the key. This is doneby looking at the letter in row L and column A of the Vigenèresquare, namely L. The rest of the plaintext is enciphered in asimilar fashion.
� Plaintext: ATTACKATDAWN
� Key:LEMONLEMONLE
� Ciphertext: LXFOPVEFRNHR
� Take the message and break it up into fixed sized blocks,
encrypt each block using the given key.
� Often with block encryption, we include a value in addition
to the key that changes for each block, so we don’t get
repetitive cipher text blocks. This is called Cipher Block
Chaining (see next slide)
� Initialization Vectors are used with the first block in CBC
� XORing is a Boolean mathematical “function” which
creates an output bit based on two input bits. It outputs a 1
IF and ONLY if one bit of input is 1 and the other is a 0.