Main Aspects of Email Working - Coursework Example

Computing - Internet Technology (Email Working) This paper will discuss how an email is sent and received by sender (Tom) and receiver (Jane). The paper will discuss the full path that is travelled by an email from sending to receiving. In addition, encryption used for encrypting and decrypting messages , various email communication protocols (such as application, network and transport protocols) for transferring and receiving an email will be also discussed in paper. Finally, various components (hardware, etc) such as router, DNS, mail sever and ISP will be discussed in brief. Below figure1, show how email actually works after Tom clicks ‘send’ button and Jane accept it. Figure 1: How Email Works (Path) The various steps from sending to receiving an email are explained below: Step A. Tom Create, Encrypt and Send an Email Tom creates an email in his Mail User Agent (MUA)1, encrypts with Jane’s Public Key and clicks Send. Tom’s MUA formats the message in Internet e-mail format and uses the Simple Mail Transfer Protocol (SMTP) to send the message to Tom’s Mail Server (MTA). Step B. Toms MDA/MTA Routes the Email Toms MUA transfers the email to a Mail Delivery Agent (MDA). Frequently, the Toms MTA also handles the responsibilities of an MDA. The MDA/MTA accepts the email, and forwards it. In figure 1, an MDA forwards the email to an MTA and it enters the first of a series of "network clouds," labeled as a "Company Network (LAN)" cloud. Step C. Network Cloud An email can encounter a network cloud within a large company (LAN) or ISP, or the Internet2. The network cloud may encompass a multitude of mail servers, DNS servers, routers, and other devices and services. These devices may be protected by firewalls, spam filters and malware detection software that may bounce or even delete an email. Step D. Email Queue The email in figure 1 is addressed to Jane at another company network (LAN) which is physically separated by 4000 kilometres, so it enters an email queue with other outgoing email messages. Step E. MTA to MTA Transfer When transferring an email, the sending MTA (Tom’s Mail Server) handles all aspects of mail delivery until the message has been either accepted or rejected by the receiving MTA ((Jane’s Mail Server). As the email clears the queue, it enters the Internet network cloud, where it is routed along a host-to-host chain of servers. Each MTA in the Internet network cloud needs to "stop and ask directions (IP address)" from the Domain Name System (DNS) in order to identify the next MTA in the delivery chain. To find the Janes IP address and mailbox, the MTA must drill down through the Domain Name System (DNS), which consists of a set of servers distributed across the Internet (e.g., .org, .com, .edu, .gov, .net, etc.). DNS Resolution and Transfer Process: The MTA looks at the destination address provided in the SMTP protocol and asks the appropriate DNS server which Mail Exchange (MX) servers have knowledge of the subdomain or local host in the email address. The DNS server responds with an MX record. The MTA contacts the MX servers on the MX record in order of priority until it finds the designated host for that address domain. The sending MTA (Tom’s) asks if the host accepts messages for the recipients username (Jane’s) at that domain (i.e., jane@b.org) and transfers the message. Step F. Firewalls, Spam and Virus Filters An email may be transferred to more than one MTA within a network cloud and is likely to be passed to at least one firewall before it reaches its destination (Jane’s Mail Server). An email in a firewall is tested by spam and virus filters before it is allowed to pass inside the firewall. These filters test to see if the message qualifies as spam or malware. If the message contains malware, the file is usually quarantined and Tom is notified. If the message is identified as spam, it will be deleted without notifying Tom. Delivery In figure 1, the email makes it past the hazards of the spam trap, filter, and is accepted for delivery by the Janes MTA. The MTA calls a local MDA to deliver the mail to the correct mailbox (Jane’s), where it will sit until it is retrieved by the Janes MUA. Jane may pick up her email in many ways, for example using the Internet Message Access Protocol, by logging into her Mail Server and reading it directly, or by pressing the "get mail" button in his MUA, which picks up the message using the Post Office Protocol (POP3). Now Jane will decrypt with her Private Key and will read the message sent by Tom. The various protocols used for communication (sending and receiving an email) are: Simple Mail Transfer Protocol (SMTP) SMTP is used to distribute mail between servers, and by the mail client to send the message initially. It is the de facto standard for email transmissions across the Internet. The protocol used today is also known as ESMTP and defined in RFC 2821. SMTP is a relatively simple, text-based protocol, in which one or more recipients of a message are specified along with the message text and possibly other encoded objects. The message is then transferred to a remote server using a procedure of queries and responses between the client and server. An end-users email client, MUA, or a relaying servers MTA can act as an SMTP client. Post Office Protocol (POP3) POP (Post Office Protocol version 3) is used by the mail client to download messages and headers to a local computer from the mail server. POP is useful if user to read his/her mail offline as it downloads and stores user email on his/her computer. It is an application-layer Internet standard protocol to retrieve email from a remote server over a TCP/IP connection. Although most clients have an option to leave mail on server, e-mail clients using POP3 generally connect, retrieve all messages, store them on the users PC as new messages, delete them from the server, and then disconnect. Internet Message Access Protocol (IAMP) IMAP is used by clients to access mail directly on the mail server. With IMAP, the mail usually stays stored on the recipients server until it is deleted. The mail client only views the mail, rather than downloading it. IMAP is an application layer Internet protocol operating on port 143 that allows a local client to access e-mail on a remote server. IMAP supports both connected (online) and disconnected (offline) modes of operation. Email clients using IMAP generally leave messages on the server until the user explicitly deletes them. Asymmetric Cryptosystem (Public Key and Private Key) Figure 2: Public Key Encryption Email message is encrypted to keep it private and only the intended recipient able to decipher (decrypt) the message. Public key encryption is a special case of encryption that operates using a combination of two keys: a private key and a public key, which together form a pair of keys. The private key is kept secret since it is used for decryption (on Jane computer). The public key, which is used for encryption, is given to anybody (Tom) who wants to send encrypted mail (to Jane). It has six major parts: Plaintext - This is the text message to which an algorithm is applied. Encryption Algorithm - It performs mathematical operations to conduct substitutions and transformations to the plaintext. Public and Private Keys - These are a pair of keys where one is used for encryption and the other for decryption. Ciphertext - This is the encrypted or scrambled message produced by applying the algorithm to the plaintext message using key. Decryption Algorithm - This algorithm generates the ciphertext and the matching key to produce the plaintext. The Public Key encryption is shown above in figure 2. In figure 2: Ke is Alice’s public key, Kd is Alice’s private key The public key is accessible to Tom whereas the private key is only known to Jane It is computationally infeasible to compute the private key from the public key. Encryption: C = E(Ke, m), Decryption: P = D(Kd, C) Choose Keys Using RSA Algorithm Choose 2 large prime numbers p, q Compute n = p*q Choose e relatively prime to (p-1)(q-1) Compute d such that e*d =1 mod (p-1)*(q-1) For Example: Let p = 47, q = 71, then n = p*q = 3337, (p-1)(q-1) = 3220 Let e =79, and (p-1)(q-1) = 3220 = 2´2 ´ 5 ´ 7 ´ 23 Solve d from d*79= 1 mod 3220, d = 1019 Let P = 688, then C = mod n = mod 3337 = 1570 P = mod n = mod 3337 Local Area Network (LAN) LAN is a term for the internal network of an organisation, building or home. A LAN is often used as an extension of the Internet, but may also carry other protocols which may be restricted from entering the wider Internet. Router A router is a device that extracts the destination of a packet it receives, selects the best path to that destination, and forwards data packets to the next device along this path. It connect networks together; a LAN to a WAN for example, to access the Internet. Internet Service Provider (ISP) or Internet Access Provider (IAP) ISP or IAP is a business or organization that provides consumers or businesses access to the Internet and related services. IT may provide a combination of services including Internet transit, domain name registration and hosting, web hosting, and colocation. Domain Name Server (DNS) The Domain Name Server (DNS) distributes the responsibility for assigning domain names and mapping them to IP networks by allowing an authoritative server for each domain to keep track of its own changes, avoiding the need for a central registrar to be continually consulted and updated. The most basic task of DNS is to translate hostnames to IP addresses. Read More