June 6, 2016 this week Message confidentiality HOM Purpose - PDF document

June 6, 2016 this week Message confidentiality HOM Purpose Terminology Message confidentiality block Using Mathematical Operations Pieter van den Hombergh stream study Fontys Hogeschool voor Techniek en Logistiek June 6, 2016 HOM/FHTenL Message confidentiality June 6, 2016 1/16 Message Purpose of Encryption Purpose of Encryption confidentiality HOM Maintain confidentiality Maintain confidentiality Purpose Best way to keep something secret is not to share it. Best way to keep something secret is not to share it. Terminology Effective against gossip, Effective against gossip, block but not very useful sharing the information is essential. but not very useful sharing the information is essential. Using Mathematical Think bank information, account, pin but also business plans or strategic Think bank information, account, pin but also business plans or strategic Operations stream Thinking military is a good starting point: Paranoid. study HOM/FHTenL Message confidentiality June 6, 2016 2/16 Terminology Message confidentiality HOM Plaintext - original message Purpose Ciphertext - coded message Terminology Cipher - algorithm for transforming plaintext to block Using ciphertext Mathematical Operations Key - info used in cipher known only to sender/receiver stream Encipher (encrypt) - converting plaintext to ciphertext study Decipher (decrypt) - recovering ciphertext from plaintext Cryptography - study of encryption principles/methods Cryptanalysis (code breaking) - study of principles/methods of deciphering ciphertext without knowing key Cryptology - field of both cryptography and cryptanalysis HOM/FHTenL Message confidentiality June 6, 2016 3/16 Message Simplified diagram symmetric encryption confidentiality Secret key shared by Secret key shared by HOM sender and recipient sender and recipient Purpose K K Terminology Transmitted block X ciphertext Using Y = E( K , X ) X = D[ K , Y ] Mathematical Operations Plaintext Plaintext Encryption algorithm Decryption algorithm input output stream (e.g., AES) (reverse of encryption algorithm) study Same keys use at both transmitting and receiving end. Both key must be kept secret, making sharing the keys risky. source: Network Security Essentials. W. Stallings HOM/FHTenL Message confidentiality June 6, 2016 4/16 1

June 6, 2016 this week Old Cipher Message confidentiality HOM Purpose Terminology block Using Mathematical Operations stream study HOM/FHTenL Message confidentiality June 6, 2016 5/16 Message Caesar cipher explained confidentiality HOM Based on substitution of characters of characters over Purpose fixed distance or rotation. (See picture on previous Terminology page). block Used by Julius for private correspondence. Using Mathematical Easily broken, no communication security. Operations stream Is application of modulo arithmetic. study Encryption E n ( x ) = ( x + n ) mod 26. Decryption: D n ( x ) = ( x + 26 − n ) mod 26. source https://en.wikipedia.org/wiki/Caesar_cipher HOM/FHTenL Message confidentiality June 6, 2016 6/16 Enigma Message confidentiality HOM The military version of the Purpose enigma had some important Terminology block modifications over the Using original, mainly the patch Mathematical Operations panel (plug board). stream The encryption was actually study quite strong. It was mainly the flaws in the procedures, predictability of the plain text, and the availability of key tables and the hardware that helped crack the code. see NumberPhile on Enigma HOM/FHTenL Message confidentiality June 6, 2016 7/16 Message Advantages and disadvantages of Symmetric confidentiality Encryption HOM Purpose ✓ Can be used for broadcast (multiple receivers for one Terminology encryption.) block Using ✗ Distributing keys can be complex. Mathematical Operations ✓ Typically cheaper (faster) stream study HOM/FHTenL Message confidentiality June 6, 2016 8/16 2

June 6, 2016 this week Mathematical operations Message confidentiality HOM ✗ Bit wise OR and AND loose information. Purpose Addition (also subtraction) increase the amount of Terminology information. block Using (integer) division looses information. Mathematical Operations Multiplication increases the amount of information. stream ✓ Bit wise XOR does not . It is in fact modulo 2 addition. study HOM/FHTenL Message confidentiality June 6, 2016 9/16 Message Feistel Circuit, block cipher confidentiality HOM The stream run from top Purpose to bottom in both cases. Terminology The keys in decryption block are in reversed order Using Mathematical w.r.t. the encryption. Operations { { In every round, half of stream round study the block is encrypted with K i and xor-ed with the other half then swaps places with the other half for the next round. The “key“ is a/the combination of all K i . source Feistel Cipher HOM/FHTenL Message confidentiality June 6, 2016 10/16 AES /Rijndael Message confidentiality HOM Developed by Dr. Joan Daemen and Dr. Vincent Rijmen of Belgium, and selected as the winner of the NIST Purpose Terminology competition for finding a replacement of DES and 3DES. block AES is a slight modification of Rijndael. Using AES is based on a design principle known as a Mathematical Operations substitution-permutation network, combination of both stream substitution and permutation, and is fast in both software study and hardware. Unlike its predecessor DES, AES does not use a Feistel network source https://en.wikipedia.org/wiki/Advanced_ Encryption_Standard HOM/FHTenL Message confidentiality June 6, 2016 11/16 Message Crypto strength confidentiality Time at 10 9 / s Time at 10 13 / s HOM Key size (bits) Cipher Key space 2 56 ≈ 7.2E16 2 55 ns = 1 . 125 yr 56 DES 1 hr 2 128 ≈ 73 . 4 E 38 2 127 ns = 5 . 3 E 21 yr 128 AES 5.3E17 yr Purpose 2 168 ≈ 3 . 7 E 50 2 167 ns = 5 . 8 E 33 168 3DES 5.8E29 yr Terminology 2 192 ≈ 6 . 3 E 57 2 191 ns = 9 . 8 E 40 192 AES 9.8E36 yr 2 256 ≈ 1 . 2 E 77 2 255 ns = 1 . 8 E 60 256 AES 1.8E56 yr block Using Mathematical Operations stream study HOM/FHTenL Message confidentiality June 6, 2016 12/16 3

June 6, 2016 this week The importance of Random numbers Message confidentiality HOM The generation of random numbers is essential to Purpose cryptography. Terminology One of the most difficult aspect of cryptographic algorithms block is in depending on or generating, true random information. Using This is problematic, since there is no known way to produce Mathematical Operations true random data, and most especially no way to do so on a stream finite state machine such as a computer. study HOM/FHTenL Message confidentiality June 6, 2016 13/16 Message Stream Cipher confidentiality HOM Encrypt the data as they pass by, not in blocks but Purpose typically as bits (real serial stream) or bytes (which are Terminology tiny blocks). block Bit streams are easily done in hardware, but unnatural Using Mathematical for modern byte or word oriented general purpose Operations CPU’s. stream study Application: streaming data, audio, video. Use of Linear Feedback Shift Registers (LFSR) is common, again in combination with XOR. Combined with a one time pad (of the same length as the message) makes it unbreakable (proof by CE Shannon, 1949) This one time pad needs to be transported using another route, making this approach unworkable, but for most critical applications. HOM/FHTenL Message confidentiality June 6, 2016 14/16 A5/1, GSM cipher Message confidentiality HOM 18 17 16 13 8 0 Purpose Terminology block Using Mathematical Operations 21 20 10 0 stream study 22 21 20 10 7 0 The GSM A5/1 cipher, now considered insecure. From wikipedia. https://en.wikipedia.org/wiki/Stream_cipher HOM/FHTenL Message confidentiality June 6, 2016 15/16 Message Study for this week confidentiality HOM Study the mentioned wikipedia pages Purpose https://en.wikipedia.org/wiki/Cryptographic_primitive Terminology https://en.wikipedia.org/wiki/Stream_cipher block https://en.wikipedia.org/wiki/Caesar_cipher Using https://en.wikipedia.org/wiki/Feistel_cipher Mathematical https://en.wikipedia.org/wiki/Advanced_Encryption_Standard Operations stream Watch the videos at youtube (Numberphile and study Computerphile): https://www.youtube.com/watch?v=8ZtInClXe1Q https://www.youtube.com/watch?v=G2_Q9FoD-oQ https://www.youtube.com/watch?v=V4V2bpZlqx8 HOM/FHTenL Message confidentiality June 6, 2016 16/16 4