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EncryptionEncryptionandand

Key Distribution Key DistributionMethodsMethods

APPLIED DATA COMMUNICATION Tallinn University of Technology

Gülçin Yıldırım - Team #12

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What is Encryption?What is Encryption?

Encryption is the process of encodingmessages or information in such a waythat only authorized parties can read it.

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Why Encryption?Why Encryption?

ConfidentialityAuthentication

Message IntegrityAccess and Availability

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EavesdroppingEavesdropping

Intercept messages

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Inserting messagesInserting messages

Actively insert messages into connection

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ImpersonationImpersonation

Can fake (spoof) source address in packet (orany field in packet)

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HijackingHijacking

"Take over" ongoing connectionby removing sender or receiver by inserting

himself in place

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Denial of ServiceDenial of Service

Prevent service from being used by others(e.g, by overloading resources)

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Insecure CommunicationInsecure Communication

Sender IntendedReceiver

MITM

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Secure ChannelSecure Channel

Sender IntendedReceiver

MITM

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Encrypted MessageEncrypted Message

Sender IntendedReceiver

MITM

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A Secret Message

371c79266d08ca124f3f8ea8ebb5d368

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EncryptionEncryption

Generates a ciphertext from a plaintext using anencryption key and an encryption algorithm (cipher)

It is a two way process:an encrypted data is expected to be decrypted later.

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A Secret Message

371c79266d08ca124f3f8ea8ebb5d368

Plaintext

Ciphertext

Cipher

Key

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Encryption TypesEncryption Types

SymmetricKey

Encryption

PublicKey

Encryption

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Symmetric Key EncryptionSymmetric Key Encryption

All communicating parties usethe same key Key is used both for encryptionand decryption

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Symmetric Key Encryption Symmetric Key Encryption Faster compared to public key encryption

Key needs to be stored securely (only accessed when required)

Secure channel required to transfer the key

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Public Key EncryptionPublic Key EncryptionRequires two keys:

Public Key: used for encryption

Private Key: used for decryption

All communicating parties exchange their public keys Sender encrypts the plaintext using receiver's public key

Receiver decrypts the ciphertext using their own private key

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Public Key EncryptionPublic Key Encryption

Slower compared to Symmetric Key Encryption Public key & ciphertext can be sent over aninsecure channel More secure because there is no need to shareprivate keys with anyone

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Public Key EncryptionPublic Key Encryption

Public Key(share with pink)

Private Key (keep it secret)

Public Key(share with blue)

Private Key(keep it secret)

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Public Key EncryptionPublic Key Encryption

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Logic Behind the KeysLogic Behind the Keys

Trying to find a prize behind a series of number of doors

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Public & Symmetric Key Mix Public & Symmetric Key Mix

Performance ? Security ?

Public key encryption used to exchange keysSymmetric key encryption used to encrypt data

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Encryption AlgorithmsEncryption Algorithms

Block Cipher and Stream Cipher

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Encryption AlgorithmsEncryption Algorithms

An encryption algorithm is called "cipher" There are two types of ciphers:

Block cipherStream cipher

Two concepts are very important for both of them:Prime numbersEntropy for random number generation

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Block CipherBlock CipherOperates on fixed-size blocks (N bits) and uses fixed-size keys (K bits)

1. Reads N-bits of data from the plaintext2. Uses the key and applies the encryption algorithm3. Produces ciphertext in size of N-bits4. Repeats steps 1-4 until all plaintext is processed

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Block Cipher - AESBlock Cipher - AESOne of the most popular block ciphers is the AES algorithm.

Some other examples are: DES, Blowfish, RC5, ...

AES stands for Advanced Encryption StandardWorks on 128 bits (16 bytes) of blocksUses 128, 192 or 256 bits of keysOperates on a 4x4 matrix of bytes

There are four stages in the algorithm:

1. KeyExpansions: Keys are derived from the provided key

2. InitialRound: AddRoundKey

3. Rounds: SubBytes, ShiftRows, MixColumns, AddRoundKey

4. FinalRound: SubBytes, ShiftRows, AddRoundKey

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Block Cipher - AESBlock Cipher - AES

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Stream CipherStream CipherOperates on variable-size blocks (N bits) and uses random-size keys

1. Generates a random number N2. Reads N-bits of data from the plaintext3. Uses the key and applies the encryption algorithm4. Produces ciphertext in size of N-bits5. Repeats steps 1-5 until all plaintext is processed

A popular stream cipher algorithm is RC4.

However, it is replaced by RC5, a block cipher algorithm.

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Key Distribution MethodsKey Distribution Methods

The main concern of a key distribution method is how to securelysupply keys between all communicating parties

There are some important security questions we must consider:

Symmetric Key Encryption

Is the shared key stored securely? Is it compromised?Is the communication channel secure?

Public Key EncryptionAm I encrypting for the intended receiver?

A key distribution method helps us with those concerns.

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Key Distribution MethodsKey Distribution Methods

There are various different key distribution methods for differentencryption types:

In symmetric key encryption, trusted key distributioncenter (KDC) is acting as intermediary between parties In public key encryption, public key servers are used for bothuploading and downloading public keys One another method is using a public key infrastructure (PKI)to share SSL certificates. A Certificate Authority (CA) providespublic keys and also validates SSL certificates

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Use-Case: GPGUse-Case: GPG

GPG (GNU Privacy Guard) is a very popular applicationthat uses public key encryption Most commonly used for encryption / decryption offiles & email messages Available for many platforms: Linux, Mac OS X,Microsoft Windows, BSD, etc... There are very large key servers to distribute publickeys (e.g., MIT PGP Public Key Server)

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Demo - SenderDemo - Sender

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Demo - ReceiverDemo - Receiver

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ReferencesReferenceshttps://dribbble.com/shots/2295470-Encryption-Key-Zoom

https://dribbble.com/shots/2321171-Secure-Area

https://pixabay.com/p-369540/?no_redirect

https://www.istockphoto.com/illustrations/one+burglar

https://dribbble.com/shots/1708900-Encryption-Keys-Animation

https://dribbble.com/shots/1883333-Lock-and-Key

https://dribbble.com/shots/2028614-Cripto

https://dribbble.com/shots/1512967-The-Key

https://dribbble.com/shots/1386297-Gold-Key-GIF

https://www.cs.rit.edu/~ark/lectures/https02/https.shtml

https://en.wikipedia.org/wiki/Advanced_Encryption_Standard

http://people.ee.duke.edu/~romit/courses/f07/material/7-security.pdf

https://www.youtube.com/watch?v=ERp8420ucGs

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Thank you!Thank you!