ISA 400 Management of Information Security Week #4 Cryptography Philip Robbins – October 24, 2015 Information Security & Assurance Program University of Hawai'i West Oahu 1

Cryptography Agenda Domain: Cryptography Quiz Assignment 2

Cryptology comes from “Crypto” Cryptography Cryptology comes from “Crypto” - Meaning: To Hide Definition: The science of hiding communications. Why? - Protect email, PII, transactions & data. Cryptographic systems use - Codes: “secret keys” - Ciphers: hiding the true meaning of a message 3

Cryptography & Encryption Confidentiality - The process of protecting plaintext messages from monitoring or eavesdropping. - Cryptography vs.. Encryption?? N1 LAN N2 - Algorithm - Key - Algorithm - Key DATA / PLAINTEXT CLEARTEXT DATA / PLAINTEXT CLEARTEXT ENCRYPTION DECRYPTION CIPHERTEXT 4

3 Basic Elements of Cryptography - Algorithm - Key - Data 5

Basic Elements: Algorithm Cryptography Basic Elements: Algorithm - Describes the process (instruction set) involved in producing a desired output. - In the case of Cryptography what is our desired output? Encryption / cipher text / Confidentiality Does more Complexity = (mean) more Security? 6

Cryptography Non-reputation Authentication - Sender can’t deny sending a message. Authentication - Associated with validating a user’s identity - Also associated with the integrity of the message 7

Cryptography Authentication Digital Signatures - Uses Hash Function & Encryption together Digital Certificates - Ensure identity of remote computer - Trust; who are you sending your information to? 8

Substitution Algorithm Cryptography Substitution Algorithm - Caesar’s Cipher - Rotate (shift) alphabet - Easy to decipher (frequency of common words, i.e. “the”) Key? Key Length? 9

Transposition Algorithm Cryptography Transposition Algorithm - Encryption by changing position of plaintext. - Rail Fence Cipher DATA: 'WE ARE DISCOVERED. FLEE AT ONCE‘ KEY: 3 ‘Rails’ (rows) CIPHERTEXT: 10

Steganography (not stenography) Cryptography Steganography (not stenography) - Security through obscurity – concealing content. - Not recommended as encryption substitute. Concealment Cipher - Not actually encrypted – just hidden. - A message (hidden) within a message. - Example: Message = Newspaper Page #, Word #, … Running Key Cipher - Text is used for a very long key stream. - Clever use of components in the world. - Example: Key = Every 3rd word from a book. 11

Cryptography Vernam Cipher - Gilbert Vernam - 1917 - Uses a basic Boolean XOR Function!! XOR Logic Gate Symbols XOR Truth Table 12

Cryptography Stream Cipher: Dividing the message into bits for processing (Encrypting data one bit at a time). 13

Cryptography Stream vs.. Block Cipher 14

Cryptography Block Cipher: Dividing the message into blocks for processing 1 Block 15

Cryptography Key & Algorithm Relationship - Algorithm’s are static mathematic functions. - Algorithm does not change; the key does. - The purpose of a key is to add randomization. - The key is a group of instructions for the algorithms. - Larger key space means better security: 128 bit strength = 2^128 = 3.4 x 10^38 possible keys (key space) - Processing power can brute force keys < 128 bit 16

Cryptography Key & Algorithm Relationship 17

Cryptography Symmetric (Private) Key Algorithm - The same key is used to encipher plaintext to produce cipher text Plaintext ⊕ Key = Ciphertext *and to* - decipher cipher text to yield the original plaintext Ciphertext ⊕ Key = Plaintext 18

Cryptography Symmetric (Private) Key Algorithm - How is confidentiality maintained? 19

Cryptography Symmetric Key Algorithm - Advantages Fast Hard to break if large key is used. - Disadvantages Only provides for confidentiality Key Management Distribution 20

= n(n-1)/2 Cryptography Symmetric Key Algorithm - Disadvantages Key Management Assume 10 people want to communicate with each other while ensuring confidentiality. How many keys would you need? # of communication channels = n(n-1)/2 21

Cryptography Symmetric Key Algorithm - Disadvantages (Most serious deficiency) Distribution How would we transfer symmetric keys securely? What if someone is monitoring our comms? If sent in clear text someone can intercept. 22

Key Pair {Public Key, Private Key} Cryptography Asymmetric (Public Key) Encryption - One key is required to encrypt. Plaintext ⊕ Public Key = Ciphertext *and* - another key is required to decrypt. Ciphertext ⊕ Private Key = Plaintext Key Pair {Public Key, Private Key} 23

Cryptography Asymmetric (Public Key) Encryption Key Pair {Public Key, Private Key} 24

Cryptography Asymmetric Encryption given to anyone kept secret 25

Cryptography Asymmetric Encryption - SENDER Messages are encrypted with either the public or private key. The public key can be given to anyone. - RECIEVER Only the matching key pair will decrypt it. The private key is kept secret. 26

Cryptography Asymmetric Encryption - Mathematically, It should not be possible to get a key pair’s private key from the public key. - Anyone with a private key can generate its public pair. - This is done using one-way (hash) functions. 27

Cryptography Asymmetric Encryption - Advantages Key Management Distribution Confidentiality, Integrity, and Non-repudiation - Disadvantages Can’t encrypt large amounts of data. 28

Cryptography Asymmetric Encryption - Advantages Solves Key Management Problem!! Assume you wanted to communicate with 10 other people while ensuring confidentiality. How many keys would you need now? 29

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Cryptography Hashing - Taking variable amounts of data and compressing it into a fixed length value, producing unique outputs. - A different MD5 hash would indicate the file has been altered or corrupted. - Message digest helps to verify integrity. - Integrity and/or nonrepudiation 31

Cryptography Digital Signatures Message goes through a Hashing algorithm. The message and the message digest is encrypted with the sender’s private key. The receiver validates the digital signature by decrypting it with the sender’s public key. Provides integrity, authenticity, and non-repudiation. If I use my private key to encrypt something then it proves it came from me. 32

Cryptography Understanding Digital Signatures 33

How is integrity and non-repudiation maintained? Cryptography Understanding Digital Signatures How is integrity and non-repudiation maintained? 34

Cryptography Cryptographic Algorithms 35

Cryptography Cryptographic Algorithms Symmetric Key Cryptography: Encryption Standards 36

Cryptography Characteristics of Strong Algorithms: - Confusion Changing a char in plaintext doesn’t create predictable cipher text. Reverse Engineering process is difficult. Contains Complexity. - Diffusion Changes in plaintext creates large change in cipher text; avoiding discovery of key. 37

Cryptography Characteristics of Strong Algorithms: - Complexity A flat cipher is created by distributing the frequency of characters evenly. 38

Cryptography Kerckoff’s Principal: “…the security of a cipher system should depend on the key and not the algorithm…” Why would it be advantageous to release the cipher algorithm to the public? Why wouldn’t it be…? 39

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How did they do that??? They sell you the private key. 41

Cryptography Attacks Birthday Attack - Used to find the same hash value for two different inputs Reveals any mathematical weaknesses in the hashing algorithm. Total Hashes Input attempts required for 50% chance of output collision 42

Cryptography Attacks Brute-Force Attack - Tries all possible keys in a key space. 43

Cryptography Attacks Mathematical Attacks Properties of the algorithm are attacked. MAIN CATAGORIES Chosen-plaintext attack: access to PT and CT to determine key. Known plaintext attack: access to “known” PT and CT forms. Chosen-ciphertext attack: access to the CT ready to be decrypted. Ciphertext-only attack: access to CT but not the PT. Side-channel attack: misc info, EM emissions, noise, vibrations, ... 44

Review Questions Question #1 What is Cryptography? 45

Review Questions Question #1 What is Cryptography? The science of hiding communications. 46

Review Questions Question #2 What is encryption? 47

Review Questions Question #2 What is encryption? Transforming data into an unreadable format. 48

Review Questions Question #3 What is an algorithm? 49

Review Questions Question #3 What is an algorithm? Describes the process (instruction set) involved in producing a desired output. 50

Review Questions Question #4 What is a Cryptographic Key? 51

Review Questions Question #4 What is a Cryptographic Key? Piece of information that controls how the cryptographic algorithm functions (works). 52

Review Questions Question #5 What is Cryptanalysis? 53

Review Questions Question #5 What is Cryptanalysis? Breaking cryptography; act of obtaining plain text from cipher text. 54

Review Questions Question #6 Which of the following is a disadvantage of symmetric key encryption? Key Size Speed Key Management Key Strength 55

Review Questions Question #6 Which of the following is a disadvantage of symmetric key encryption? Key Size Speed Key Management Key Strength 56

Review Questions Question #7 Which of the following attacks requires an attacker to obtain several encrypted messages that have been encrypted using the same encryption algorithm? Know plain text attack Cipher text attack Clear text attack Replay attack 57

Review Questions Question #7 Which of the following attacks requires an attacker to obtain several encrypted messages that have been encrypted using the same encryption algorithm? Know plain text attack Cipher text attack Clear text attack Replay attack 58

Review Questions Question #8 Why does a digital signature contain a message digest? To detect any alteration of the message To indicate the encryption algorithm To confirm the identity of the sender To enable transmission in a digital format 59

Review Questions Question #8 Why does a digital signature contain a message digest? To detect any alteration of the message To indicate the encryption algorithm To confirm the identity of the sender To enable transmission in a digital format 60

Review Questions Question #9 Which is NOT a property of a one-way hash function? It converts a message of a fixed length into a message digest of arbitrary length It is computationally infeasible to construct two messages with the same digest It converts a message of arbitrary length into a message of a fixed length Given a digest value, it is computationally infeasible to find the corresponding message 61

Review Questions Question #9 Which is NOT a property of a one-way hash function? It converts a message of a fixed length into a message digest of arbitrary length It is computationally infeasible to construct two messages with the same digest It converts a message of arbitrary length into a message of a fixed length Given a digest value, it is computationally infeasible to find the corresponding message 62

Review Questions Question #10 What are the three most important functions that digital signatures perform? Integrity, Confidentiality, and Authorization Integrity, Authentication, and Nonrepudiation Authorization, Authentication, and Nonrepudiation Authorization, Detection, and Accountability 63

Review Questions Question #10 What are the three most important functions that digital signatures perform? Integrity, Confidentiality, and Authorization Integrity, Authentication, and Nonrepudiation Authorization, Authentication, and Nonrepudiation Authorization, Detection, and Accountability 64

Review Questions Question #11 What is the result of a hash algorithm being applied to a message? A digital signature A cipher text A message digest A plaintext 65

Review Questions Question #11 What is the result of a hash algorithm being applied to a message? A digital signature A cipher text A message digest A plaintext 66

Review Questions Question #12 A hash value is a fixed-length string used to verify message integrity? TRUE FALSE 67

Review Questions Question #12 A hash value is a fixed-length string used to verify message integrity? TRUE FALSE 68

Review Questions Question #13 Why did the NSA decide to drop support for DES? The cost was too high. The encryption algorithm was too slow. The processing power of computers had increased. It was too difficult for government agencies to use. 69

Review Questions Question #13 Why did the NSA decide to drop support for DES? The cost was too high. The encryption algorithm was too slow. The processing power of computers had increased. It was too difficult for government agencies to use. 70

Review Questions Question #14 Two different messages producing the same hash value results in which of the following? Duplicate key Corrupt key Collision Message digest 71

Review Questions Question #14 Two different messages producing the same hash value results in which of the following? Duplicate key Corrupt key Collision Message digest 72

Review Questions Question #15 Which of the following is an asymmetric algorithm? DES AES RSA Blowfish 73

Review Questions Question #15 Which of the following is an asymmetric algorithm? DES AES RSA Blowfish 74

Review Questions Question #16 (last one) What type of cryptographic algorithm is being used? 75

Review Questions Question #16 (last one) What type of cryptographic algorithm is being used? Caesar Cipher / Substitution Algorithm / ROT 76

Quiz Short answer, closed book, closed notes. 77

probbins@hawaii.edu Questions? www2.hawaii.edu/~probbins https://www.dorkatron.com/docs/ISA400/ 78