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Copy of Cryptography

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Tanvi Patel

on 29 April 2013

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Transcript of Copy of Cryptography

The Agenda What is Cryptography? Cryptography Eg: RSA AES Modern-day standard symmetric-key encryption
Developed by Belgian cryptographers Joan Daemen and Vincent Rijmen
Used by NSA for SECRET and TOP SECRET information http://startpad.googlecode.com/hg/labs/js/enigma/enigma-sim.html Credits Riley Thomasson Jacob Lee Everything: Works Cited C. H. Bennett, F. Bessette, G. Brassard, L. Salvail and J. Smolin "Experimental Quantum Cryptography" Journal of Cryptology vol.5, no.1, 1992, pp. 3-28.
Joan Daemen, Vincent Rijmen, "The Design of Rijndael: AES - The Advanced Encryption Standard." Springer, 2002. ISBN 3-540-42580-2.
Kahn, David. The Codebreakers; the Story of Secret Writing. New York: Macmillan, 1967. Print.
Singh, Simon. The Code Book: the Science of Secrecy from Ancient Egypt to Quantum Cryptography. New York: Anchor, 2000. Print. Literature Survey PAST Scytales Enigma TODAY RSA PGP DES FUTURE QUATUM CRYPTOGRAPHY ALGORITHMS
Increasingly used to protect information.
Can ensure Confidentiality,
Integrity and Authenticity too. History Early cryptography was solely concerned with converting messages into unreadable groups of figures to protect the message’s content during the time the message was being carried from one place to another.

In the modern era, cryptography has grown from basic message confidentiality to include some phases of message integrity checking, sender/receiver identity authentication, and digital signatures, among other things What is CRYPTOGRAPHY? Literature Survey on Cryptography Substitution cipher: Eg:CEASER CIPHER (Julius Ceaser): Around 50 B.C Transposition cipher: Eg:SCYTALE (Greeks and Spartans): 500 B.C
Encrypted message:HKSUTSILEYBE C A T
3 1 20
L U E Rotor machine: Eg:ENIGMA MACHINE (GERMANS): During World War 2 Private/Symmetric key cipher: Eg 1: DATA ENCRYPTION STANDARD (DES):IBM-1977 Eg 2:ADVANCED ENCRYPTION STANDARD (AES): Joan Daemen, Vincent Rijmen 1998 a.Symmetric key block cipher b.Symmetric key stream ciphers:

Eg: RC4 Ron Rivest 1987 Public key/Assymetric cipher: RSA = Rivest-Shamir-Adelman 1978
Clifford Cocks
Uses a one-way function (multiplying/factoring large primes)
Example of public-key encryption Quantum cryptography the final battle ??? Algorithm and Implementation Caesar cipher (shift cipher) is a simple substitution cipher based on a replacement of every single character of the open text with a character, which is fixed number of positions further down the alphabet.

In the times of Julius Caesar was used only the shift of 3 characters, but nowadays the term Caesar cipher refers to all variants (shifts) of this cryptosystem.

The encryption can be described with the following formula:
C_{i} = (T_{i} + k) \pmod{m}

Ci - i-th character of the closed text
Ti - i-th character of the open text
k - shift
m - length of the alphabet

The process of decryption uses reverted procedure:
T_{i} = (C_{i} - k) \pmod{m} Caesar Cipher Encryption terminology:

* plaintext: message to be sent, in readable form
* ciphertext: message in coded form, unreadable without special information such as a key
* encrypt: turn plaintext into ciphertext
* decrypt: turn ciphertext back into plaintext
* cryptanalysis: cracking a code - attempting to decrypt without the required special information
* cryptography: study of codes and code-breaking Implementation ??? Blowfish Blow fish Algorithm Implementation
??? Pretty Good privacy data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication.

used for signing, encrypting and decrypting texts, e-mails, files, directories and whole disk partitions to increase the security of e-mail communications.

Phil Zimmermann in 1991

PGP offers 5 services:
E-mail compatibility
Segmentation Blowfish algorithm:
Two parts:
Expansion of the key.
Encryption of the data.
Expansion of the key:
Break the original key into a set of subkeys.
Key of no more than 448 bits is separated into 4168 bytes.
P-array and four 32-bit S-boxes.
P-array contains 18 32-bit subkeys.
Each S-box contains 256 entries.
The encryption of the data:
64-bit input is denoted with an x
P-array is denoted with a Pi (where i is the iteration).
64-bit block size
Key length - 32 bits to 448 bits (32-448 bits in steps of 8 bits; default 128 bits).
16-round Feistel cipher
Large key-dependent S-boxes
Each line - 32 bits.
Algorithm keeps two sub-key arrays:
The 18-entry P-array
Four 256-entry S-boxes.
S-boxes accept 8-bit input
Produce 32-bit output.
One entry of P-array is used every round.
After final round, each half of data block is XORed with one of the two remaining unused P-entries.
Initialize the P-array and S-boxes
XOR subkey with plaintext.
(example) P1 XOR (first 32 bits of key), P2 XOR (second 32 bits of key), ...
New output of XL is apply to function .
Output of function is XOR with XR bits
Then perform swap operation.
Repeat 16 times.

Blowfish's F-function.
Splits the 32-bit input into four eight-bit quarters, and uses the quarters as input to the S-boxes.
Outputs are added modulo 232 and XORed to produce the final 32-bit output.

Key schedule
Initialize the P-array and S-boxes with values derived from the hexadecimal digits of pi, which contain no obvious pattern.
Secret key
XORed with the P-entries in order.
Resultant ciphertext
Replaces P1 and P2.
Encrypted again with the new subkeys
P3 and P4 are replaced by the new ciphertext.
Continues, replacing the entire P-array and all the S-box entries.
Algorithm will run 521 times to generate all the subkeys - 4KB of data is processed.

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