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Linux Networking and Security. Chapter 8 Making Data Secure. Making Data Secure. Explain commonly used cryptographic systems Understand digital certificates and certificate authorities Use the PGP and GPG data-encryption utilities
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Linux Networking and Security Chapter 8 Making Data Secure
Making Data Secure • Explain commonly used cryptographic systems • Understand digital certificates and certificate authorities • Use the PGP and GPG data-encryption utilities • Describe different ways in which cryptography is applied to make computer systems more secure
Cryptography and Computer Security • Computer security is about making certain that the only people accessing resources or data are those whom should have access • Cryptography is the science of encoding data so that it cannot be read without special knowledge or tools; it is a key part of network applications and normally hidden from view • Network connections can be tapped to allow for viewing of transmitted data - called sniffing the network, and encryption can block this
Basic Encoding Techniques • The process of cryptography is as follows: • Begin with the message to transmit - called the plaintext • Apply a technique or rule called a cipher to change the plaintext • The result is ciphertext, an encrypted message • The most elementary example of encryption is letter-substitution where a different letter of the alphabet is substituted for each letter in the message
Key Systems • Rules, known as algorithms, allow letter-substitution to convert plaintext to ciphertext • The level of complexity of an algorithm can be increased by using a key, a code necessary to encrypt or decrypt a message correctly using the algorithm • Knowing the algorithm (the cipher) should not enable readability; good security assumes an eavesdropper knows the cipher, but the key must be kept secret
DES • The Data Encryption Standard (DES) was developed in the 1970s and uses a 56-bit key to encrypt data using various algorithms • 56 bits provide for 256 possible keys • It now takes 20 hours to break a DES key • DES is being phased out, but it is still widely used since relatively few people have the equipment to break the key, 20 hours is still a relatively long time in the Internet age, and it was a widely implemented U.S. standard
Skipjack and Triple DES • There were several responses to the cracking of DES: • DES keys were increased to 1024 bits • Creation of a new algorithm called Skipjack, which uses an 80 bit key • Triple DES relies on DES, but encodes each message three times using three different keys • Advanced Encryption Standard (AES) can provide roughly 1077 possible keys, and was approved for use by U.S. government agencies in May 2002
Symmetric and Asymmetric Encryption • Symmetric encryption algorithms • Use the same key and algorithm to encrypt and decrypt a message • The key used is called a private key, because it must be kept secret for the message to be secure • Asymmetric encryption algorithms • Use one key to encrypt and another to decrypt • The key you can reveal to everyone is called a public key
Signatures and Certificates • Authentication is the process of proving that you are in fact the person you say you are • Signatures let you authenticate a public key • You sign another person’s public key with your own private key to verify that the key really belongs to that person • Certificates provide the same type of verification as signatures • A certificate is a numeric code that is used to identify an organization
Fingerprints • A fingerprint is a smaller number that is derived from a very lengthy public key • Fingerprints are created by hashing the public key, a process by which a mathematical function is used that converts larger numbers into smaller numbers • Two commonly used hashes: • Message digest hash (MD5) provides 128 bits • Secure hash algorithm (SHA-1) provides 160 bits
Using Cryptography in a Browser • Whenever you visit a Web page that has been transmitted to your computer using encryption, you see a small lock or key in the lower left corner of the browser window • Most encrypted Web pages, such as order-entry screens, shopping carts, and similar data, appear with a URL that starts with https • The encrypted protocol for Web pages is Secure Socket Layer (SSL)
Kerberos Authentication • Kerberos authentication is a special kind of authentication for organizational networks • Kerberos was developed at MIT and is widely used around the world • Kerberos secures a network by providing a system that makes users prove who they are before they can use a service and also makes services prove who they are • It uses both public-key cryptography and a symmetric cipher
Using Encryption Utilities • Pretty Good Privacy (PGP) is the first utility to provide public-key encryption to all • Although PGP software was formerly included in Linux, it has been replaced with GPG • Gnu Privacy Guard (GPG) is a public-key encryption utility and uses non-patented algorithms • GPG operates from the command line, but there are graphical utilities to make it easier to use
Other Security Applications • RPM security can check a public-key signature on any package to verify that it came from its stated creator • Cryptographic File System (CFS) enforces cryptographic authentication on all users who want to share files across the network • Transparent Cryptographic File System (TCFS) operates transparently to users • IPSec and CIPE provide for IP packet encryption
Secure Shell • Secure Shell (SSH) is an encrypted version of Telnet, which provides secure remote access • SSH allows other protocols to ride on top of it • A Virtual Private Network (VPN) is a secure organizational network that uses an insecure public network (Internet) for communications • VPNs are often created with the aid of specially designed software that integrates many networking functions with cryptographic protocols and system management software
Chapter Summary • Cryptography is the science of encoding data, typically using a key, so that people without the key cannot read the data • Cryptography protects computer networks against sniffers, programs that allow crackers to see data passing along a network • Many different algorithms are used to encrypt data and they are either symmetric or asymmetric • DES was a popular standard algorithm for years, until Triple DES and AES began to replace it
Chapter Summary • Public-key encryption does not require that you openly exchange a secret key with the recipient of an encrypted message • RSA is the most familiar public-key algorithm • Signatures on a document show that the sender is the only one who could have sent the document • Certificates are issued and signed by certificate authorities such as VeriSign to vouch for the identity of the organization holding the certificate
Chapter Summary • A hash is a mathematical function that creates a small number from a very large number and it is used to create a fingerprint • Browsers such as Netscape and Mozilla use cryptography via the Secure Sockets Layer (SSL) protocol to allow secure e-commerce transactions • Kerberos provides a network-wide user and service authentication scheme to limit network access to authorized users • PGP was the first freely available public-key encryption software and remains an industry standard on which GPG is based
Chapter Summary • The Gnu Privacy Guard (GPG) is a free public-key encryption utility that lets you manage keys and encrypt, sign and decrypt documents • Keys should be signed only when the identity of the person providing the key has been ascertained with certainty • The rpm utility can check a public key signature on any package to verify that it came from the person or organization that claims to have created it
Chapter Summary • Other security protocols built on the same principles of cryptography as GPG include IPsec, CIPE, CFS and TCFS • The Secure Shell (SSH) provides encrypted remote access via a utility that functions like Telnet. SSH also lets other protocols work with it to create secure connections for many purposes
