End to End Encryption

Cyber Security: Backup media

Backup media
Depending on the amount of data you need to backup, a range of technologies are available:



Optical storage
Optical storage is the same technology used for CDs, DVDs and Blu-Ray.

The most common technology for optical storage is writeable DVD standards including DVD-R, DVD+R, DVD-RW, DVD+RW and DVD-RAM. Most of these DVD formats can store 4.7 GB on a single disc, although newer, so-called, dual layer discs and drives can store twice that. Blu-Ray technology offers 25 GB and dual layer (50GB) formats with three layer 100GB discs, although they are expensive.

Advantages

• Optical drives and media are extremely cheap and widespread. Most computers have an optical drive or can accept a USB driver and the discs can be bought in supermarkets.
• There are a large number of manufacturers, so there should be no problem with future supplies of discs.
• More modern optical disc technologies (such as Blu-Ray) also support most older types of disc such as DVD and CD.
• The media is relatively small. Large amounts of data can be stored in a very small space.
• The media is robust. Discs can be posted and are able to survive regular use or being dropped. They are resistant to extremes of temperature and humidity, and immune to strong magnetic fields.

Disadvantages

• Optical drives are relatively slow compared to hard disks, especially when writing data.
• There are a large number of types of disc (especially recordable DVDs). Some of these discs are not widely supported.
• Their capacity is relatively low compared to hard disks. A 1TB hard disk is commonplace on modern computers, so it would take more than 200 DVDs to make a complete backup of the disk. Consequently, DVDs might be best suited to making backups of key data.

Magnetic disks
The magnetic hard disk at the heart of most computers can also be used as a backup device. Most PCs have sufficient internal space for a second hard disk that can be devoted to backups, or a relatively cheap external hard disk can be connected to a USB or Firewire port on a computer.

More expensive disks can be connected directly to a network using Ethernet or wi-fi in which case they are known as Network-Attached Storage (NAS). Disks can be made more resilient to failure by combining several disks together with copies of data stored on multiple disks so that even if one copy is damaged or the disk fails, it is not lost forever; the most common type of this ‘redundant’ storage is called a Redundant Array of Independent Disks (RAID).

Advantages

• Disks are relatively cheap and capacities are growing rapidly.
• External hard disks can be easily moved between computers.
• There are many disk manufacturers, all of whose products can be used in almost any computer.
• There are a large number of back-up programs designed to be used with hard disks. Many external disks are sold with applications to ease the back-up process, or offer a ‘one touch’ back-up button.

Disadvantages

• Hard disks are fragile and easily damaged if dropped or exposed to extremely high temperatures or magnetic fields.
• If hard disks are used once to make a back up then archived, the replacement cost is much higher than for tape or optical media.

Solid State Disks
Solid State Disks (SSDs) are storage devices that can store data in memory chips without the need for a power source. The name is somewhat misleading because these devices don’t actually contain physical disks. They can be commonly found in the USB memory sticks used for sharing files between computers. As the technology has advanced to increase the storage capacity of SSDs they are now being used in laptops and mobile devices as substitutes for magnetic disks.

Advantages
SSDs have the same advantages as magnetic disks when compared to optical storage technologies. Some additional advantages are:

• SSDs are more robust and are unlikely to be damaged if dropped or exposed to magnetic fields.
• It is possible to read and write data from SSDs much faster.
• There is no noise produced when SSDs operate because they have no moving parts.

Disdvantages

• SSDs are more expensive than equivalent capacity magnetic disks.
• At the moment, the maximum capacity of SSDs available on the market is 1TB although this will increase as the technology advances.

Remote backups
Large businesses and organisations insure themselves even further against failure by storing backups away from their centre of operation.

In the event of a disaster, there is much greater likelihood that they can return to normal operations within a short period of time – after all, it is much easier to buy new computers than recreate all of the records.

Offsite backups
Specialised companies offer specialised facilities where companies can hire storage space or machinery to hold backups. These offsite facilities might be nothing more than an extremely secure vault where tapes or disks can be deposited; but increasingly they are large server farms connected to extremely high-speed networks. Users can copy files to these servers as if they were part of their own network; the only bottleneck is the speed of the network between the offsite facility and the user.



The UK’s largest such site is Telehouse UK in London’s Docklands which has partner sites in the United States and Japan. The London facility covers some 45,000 square metres and is used by over 700 large companies and internet service providers.

Backing up to the Cloud
For many years, offsite backup was restricted to organisations which could afford relatively large monthly fees. Cloud technology allows anyone to have offsite storage, and in many cases a certain amount of storage is completely free. Most cloud services are designed for convenience, to allow users to share files between computers, and with other users, rather than specifically as backup services, but they can also offer you some additional security (especially when you encrypt files before putting them in the Cloud) if your computer is stolen or stops working.



One strong word of warning if you do use the Cloud as a backup, with only a few exceptions, these services will not protect you if a file is deleted. Most Cloud services are synchronised – that is, when a file is deleted on your computer, the copy on the Cloud server is either immediately, or very shortly afterwards, also deleted.

Cloud backups are obviously limited by the bandwidth of your internet connection. If you have a slow uplink (that is sending data to the Cloud) you may not be able to make backups of all your data in a reasonable amount of time. Instead you might have to prioritise which data is backed up to the Cloud and which is stored locally.

Cloud security
Unless you take further steps, once data is stored in the Cloud you can no longer be sure that it is entirely secure from prying eyes. Most suppliers have policies claiming that your data will be secure, but they cannot provide absolute insurance from attackers, as experienced by some celebrity users of Apple’s iCloud service in 2014. You can read more about this incident, if you are interested, via the link at the bottom of this page.



Some businesses have policies forbidding employees from storing information in the Cloud as it may not be secure, or it may be stored outside the legal protection of the company’s country of origin.

Using encryption to scramble the contents is the only way you can guarantee that your data is safe in the Cloud.

Cyber Security: Firewall - VPN

VPN basics
In some ways, our local networks resemble forts sitting in the Wild West of a Hollywood movie. Inside strong walls, life goes on as normal, with data being exchanged freely between trusted machines. Meanwhile, beyond the firewall there is the lawless frontier of the internet; traffic crossing the internet must make a risky journey largely unprotected.

The problem of secure data transmission is especially acute for organisations based in several physical locations, such as those who need to exchange information with sub-contractors or those with a dispersed workforce such as sales teams or home workers.



Traditionally, companies invested in private communications links (usually called leased lines) whose cost might run to thousands of pounds per month. Most organisations cannot justify such an investment and in any case, leased lines cannot serve a mobile or highly dispersed workforce. So the lawless frontier of the internet is our only choice – this is where VPNs come to the rescue!

A VPN, as the name implies, is a means of creating a private network across an untrusted network such as the internet. VPNs can be used for a number of different purposes such as:

• to securely connect isolated Local Area Networks (LANs) across the internet
• to allow mobile users remote access to a corporate network using the internet
• to control access within an intranet environment.

VPN concepts
VPNs are typically implemented using dedicated network devices (sometimes this might be a firewall), and software. There are two parts to the software; the first, called a VPN client, is installed on the computer of anyone who wants to be part of the VPN. The client is responsible for connecting users to the VPN so that it can send and receive information in a secure manner with, in this example, a corporate network. The second part is the VPN server which is part of a dedicated network device, usually located on the perimeter of an organisation’s network. The server software typically performs the authentication of users and route traffic to the corporate network.

The VPN software creates a path known as a ‘tunnel’ between the VPN client and the VPN server. It can establish this ‘tunnel’ by using any third party or untrusted network such as the internet. Unlike other paths through the internet, information which passes through this ‘tunnel’ can be encrypted to protect it from inspection or modification. So we can use these tunnels to protect our data while it crosses the lawless frontier of the internet back to the safety of our forts!

Securing the tunnels
The VPN path or tunnel between the VPN client and the VPN server relies on encryption to protect the data from interception or modification as it travels across the internet.



Encryption
In a VPN, encryption and decryption is typically performed by the client and server software. Early VPN solutions used proprietary encryption techniques, but shortcomings in many of these methods has forced a switch to public encryption standards.

Authenticity and integrity
It is vital to ensure that information can be trusted – that it is coming from an authenticated user and that it has not been altered in transit. VPNs use a number of methods to ensure authenticity:

• hashes (see Week 5)
• digital signatures (see Week 5)
• message authentication codes (MACs).

MACs are appended to messages and act as an authenticator. They are similar in principle to digital signatures, but the hash is encrypted and decrypted using the same secret key, (symmetric encryption).

VPN protocols
There are three main forms of VPN protocol currently in use, these are:

• PPTP (Point to Point Tunnelling Protocol)

PPTP was designed in a consortium led by Microsoft, which included an implementation of the protocol as a standard component of Windows NT 4. Microsoft also released PPTP as a free add-on to Windows 95 and Windows 98, allowing users of (at the time) the most popular version of Windows to access corporate networks.



PPTP proved unsuited to large companies (being limited to 255 connections per server), but more seriously, the PPTP standard did not settle on a single form of user authentication or encryption; therefore two companies could offer software supporting PPTP, yet each product would be incompatible with the other! From Windows 2000 onwards, Microsoft replaced PPTP with L2TP (see below).

• L2TP (Layer 2 Tunnelling Protocol)

This is an adaptation of a VPN protocol known as L2F originally developed by Cisco to compete with PPTP. In an attempt to improve L2F, a successor was devised by a group composed of the PPTP Forum, Cisco and the Internet Engineering Task Force (IETF). L2TP combines features of both PPTP and L2F.

• IPSec (Internet Protocol Security)

IPSec was designed by an international committee (The Internet Engineering Task Force (IETF)) between 1992 with a first draft standard published in 1995, the revised standard was published in 1998. IPSec is now the most widely supported protocol with backing from Intel, IBM, HP/Compaq and Microsoft (among others).

                               

IPSec has gained a reputation for security thanks to its use of well-known and trusted technologies. Rather than invent new techniques for encryption, the designers of the protocol built their system on top of existing encryption technologies, which had, in themselves been subjected to intense scrutiny.   

Cyber Security: Cryptography - Encrypted network connections

Web traffic is not encrypted by default. Web pages pass as plain text across the internet and are vulnerable to interception.
Obviously, this was a problem when companies first began to consider online shopping. At first companies had to ask customers to browse online and then make a telephone call so the company could accept credit card information.



The solution came in 1995 when the web browser pioneer Netscape announced the Secure Socket Layer (SSL) protocol (this has now been replaced by Transport Layer Security (TLS), which would allow web browsers to exchange secure data. It is supported by all modern browsers and allows confidential information to be exchanged over an insecure link.

TLS/SSL
TLS/SSL uses a combination of asymmetric and symmetric encryption to exchange data. When a web browser connects to a server and requests a secure communication the two computers first engage in what is known as a handshake and agree how future communications will be conducted, including the type of cryptography that will be used.



After agreeing how to communicate, the server transmits its own public key and a digital certificate of authenticity to the user’s computer which checks that the certificate is genuine and has not expired. If the certificate is genuine, the user’s computer then generates a master secret, encrypts it with the copy of the server’s public key and sends that to the server.

The server decrypts the encrypted master secret with its own private key. Both the server and the computer now have copies of the secret and use that to generate identical copies of a symmetric encryption key. Crucially, the key itself has not been transmitted across the network.

Each computer now informs the other that all other transactions in this session will be conducted using the symmetric key (called the session key), by sending ‘finished’ handshake messages using each other’s session keys. The two computers can now perform the secure transaction itself, including sensitive information such as bank account details, addresses, credit card numbers and receipts using the high-speed symmetric key.

At the end of the secure session, the two computers say goodbye to one another and each deletes their copies of the symmetric session key. If the user starts another secure session a completely new key will be used.



As well as ecommerce sites, TLS/SSL is supported by other websites that supply confidential information including banks and some email clients. Its use means that end users can benefit from the confidentiality and integrity provided by cryptography without having to worry about the technical details of configuring their software or managing keys.


How secure is your browsing
Web browsers have made it easy to determine if a website is using TLS/SSL by:

• making all secure addresses begin ‘https://’ (rather than ‘http://’) with the s standing for ‘secure’. Examples include Gmail, at https://mail.google.com/; Google defaults to Google Safe Search at https://www.google.com/, which means that your search requests and results cannot be seen by others.
• showing a closed padlock symbol in or near the top of your browser window.

Visit a website that you use regularly (it could be this one!) and find a page that you would expect to use a secure network connection. A common example would be your webmail account or online banking website. Use your browser’s help feature and click on the padlock icon to find out about its meaning.

© The Open University  

Cyber Security: Cryptography - Encryption Key

Encryption keys
Keys are pieces of information that determine the output from an encryption (or decryption) process. A single cipher can produce an almost limitless number of different outputs with different key values; allowing secure communication even if the cipher itself is known to hostile third parties.



It might surprise you to know that almost all ciphers are published in the scientific press or in standards documents, having them available for widespread scrutiny allows many people to check that they are secure and do not contain weaknesses which could be exploited to compromise the security of the data encrypted using that cipher.

A computer encryption key is nothing more than a string of bits where each bit can have a value of either 0 or 1. The number of possible values for a key is simply the total number of values that the key can have. So our one-bit long key can only have two possible values – 0 and 1. If we chose to have a two-bit key it could have one of four possible values – 00, 01, 10 and 11. In fact every time we increase the length of the key by one bit we double the number of possible keys – so a three-bit key has eight possible values – 000, 001, 010, 011, 100, 101, 110 and 111.



The total number of keys can be written in scientific form as 2key length; so a key with a length of eight has 28 – that is 256 – values.

But how long should a key be? How short is too short?

The problem with short keys
Short keys are vulnerable to what is known as a brute force attack about passwords. A brute force attack is where a computer, or a number of computers, try every possible value for a key until they produce recognisable plaintext.



Since computers can work through key values extremely rapidly, keys must be sufficiently long that they offer a very large number of possible values.

Keys may be known to the user in the form of passwords, or they may be stored in a computer’s hardware (such as the decryption keys stored on a DVD player that allow it to play the encrypted data stored on the movie disk), or they can be generated by a computer as and when they are needed (such as conducting a secure transaction on a shopping site).

The key distribution problem
Traditionally, symmetric encryption suffered one enormous shortcoming – it was necessary for either the sender or the recipient to create a key and then send it to the other party. While the key was in transit, it could be stolen or copied by a third party who would then be able to decrypt any ciphertexts encrypted with that key.
Another problem is that a large number of key pairs are needed between communicating parties. This quickly becomes difficult to manage the more there are. This can be calculated as n(n-1)/2 where n is the number of communicating parties.

For example, if ten parties want to communicate with each other securely they would need 45 different key pairs: 10(10-1)/2 = 45. This would increase to 4,950 if there were 100 communicating parties!

This problem, called the key distribution problem, affected anyone wishing to use encryption until the 1970s when a method of distributing keys without actually sending the keys themselves was developed independently by GCHQ in the United Kingdom and Whitfield Diffie and Martin Hellman in the United States. The British discovery was kept secret for many years, so today the solution is known as the Diffie–Hellman key exchange method.

Symmetric encryption methods have the advantage that encryption and decryption is extremely fast, making them ideal for transmitting large amounts of secure data.







Asymmetric or public key cryptography
Asymmetric cryptography, better known as public key cryptography, sidesteps the key distribution problem as each user creates their own keys:

• the private key which they keep safe and never distribute
• the public key which can be sent to anyone with whom they want exchange encrypted information.

Together the two keys are known as a key pair, which is what was used by Alice and Bob.

Whereas symmetric encryption only provides confidentiality of the messages exchanged, the use of two different keys allows asymmetric encryption to provide both confidentiality and authenticity. To get confidentiality Alice encrypts the message with Bob’s public key. This message can only be decrypted with the Bob’s private key so Alice and Bob can be sure that nobody else will be able to read it. However, if Alice also wants to prove to Bob that the message is authentically from her, she can first encrypt it using her private key, and encrypt the resulting message again using Bob’s public key. Once Bob decrypts the message using his private key, he can try to decrypt the result again using Alice’s public key. If this is successful, he can be confident that message must have come from Alice (since nobody else should know her private key).

   

So an important property of asymmetric cryptography is that the private key is the only key that can decrypt ciphertext encrypted using the corresponding public key and the public key is the only key capable of decrypting files encrypted with the corresponding private key. Crucially, the value of one key cannot easily be determined from the other, so even if the public key falls into hostile hands, the value of the private key cannot be determined.

Public keys can be distributed using email attachments or through public key chain servers which act as distributors for large numbers of public keys. The creator of a public key uploads their key to the key chain server and it is freely available to anyone who wants to use it.

Although the mathematics behind public key cryptography is incredibly complex, the process of using it is relatively simple. To send a message using public key cryptography is simple. The sender obtains a copy of the recipient’s public key, either by email or from a key chain server, and uses it to encrypt the message. The resulting ciphertext is then sent to the recipient who uses their corresponding private key to restore the original plaintext.

Public key cryptography is popular because there does not have to be any initial secure exchange of secret keys for an encrypted message to be sent (remember, users only ever exchange their public keys). However, it is generally far slower than symmetric encryption; and because of a quirk in the underlying mathematics, traditional public key cryptographic techniques require far longer keys to offer the same level of protection as symmetric encryption.

A newer type of public key cryptography, known as ‘elliptic curve cryptography’, can be just as secure as symmetric encryption using similar key lengths.

 

Cyber Security: Cryptography - Hidden Messages

Cryptography is a specialised area of mathematics concerned with protecting information so that it can be transmitted and received securely even when there is a risk that a hostile third party might intercept or modify the data.

     

The secret of keeping secrets
There have been many applications of cryptography throughout history, ranging from simple ciphers used by Julius Caesar to send military orders to his generals, to the more sophisticated medieval ciphers that withstood most attacks until the late 19th century and the famous Enigma codes of World War II.

The development of computers in the 20th century allowed for far more complex means of encryption. Computers could perform:

• the mathematical operations that underpin all cryptography
• much more complex mathematics than could be reasonably expected of a human
• much faster than a human
• on much more data than a human could handle.

Any data that could be represented in binary format, i.e. using 0s and 1s, can be encrypted by a computer. It is not an exaggeration to say that encryption makes much of the modern world possible. Some commonplace applications for cryptography include:

     

• secure banking and payments systems – cryptography ensures your money is safe when it is transferred between accounts, issued at ATMs or used to shop online
• protecting conversations made over mobile telephones
• safeguarding wireless networks that give access to the internet
• securing files on hard disks and memory sticks
• authenticating electronic documents
• electronic voting
• securing media files such as music or movies from piracy, where it is known as Digital Rights Management (DRM).

Plaintext and ciphertext
As in previous weeks, there is some terminology we need to introduce:

• plaintext – information that can be directly read by humans or a machine (this article is an example of plaintext). Plaintext is a historic term pre-dating computers, when encryption was only used for hardcopy text, nowadays it is associated with many formats including music, movies and computer programs
• ciphertext – the encrypted data
• a cipher – the mathematics (or algorithm) responsible for turning plaintext into ciphertext and reverting ciphertext to plaintext. (You might also see the word ‘code’ used. There is a technical difference between the two but it need not concern us now.)
• encryption – the process of converting plaintext to ciphertext (occasionally you may see it called ‘encipherment’)
• decryption – the process of reverting ciphertext to plaintext (occasionally ‘decipherment’).