Securing E-Mail (PGP)
PGP is a scheme to provide Authentication, Confidentiality, Compression, Email compatibility, Segmentation for electronic mail system.
Summary
PGP is a scheme to provide Authentication, Confidentiality, Compression, Email compatibility, Segmentation for electronic mail system.
Things to Remember
PGP offers:
- Authentication
- Confidentiality
- Compression
- Email compatibility
- Segmentation
MCQs
No MCQs found.
Subjective Questions
Q1:
Write a brief description of the alimentary tract.
Type: Long Difficulty: Easy
Show/Hide Answer
Answer: <h3>A. The alimentary tract</h3>
<h4>a) Mouth</h4>
<p>The starting and upper expanded portion of the alimentary tract are known as a mouth. It is also called buccal cavity or oral cavity. The mouth and oral cavity are lined with non -keratinized stratified squamous epithelium containing small mucous secreting glands, which helps to moist the oral cavity.<br /><br /><strong>i. The tongue</strong></p>
<p>– The tongue is highly mobile, a voluntary muscular structure which lies on the floor of the mouth. It is attached to the hyoid bone by its base and to the floor of the mouth by a fold of the mucous membrane covering, called the frenulum. Tips of a tongue are sensitive to sweet and salt, back of the tongue is sensitive to bitter and posterior half of each side of the tongue is sensitive to sour taste.<br /><br /><strong>ii. The teeth</strong> – The teeth are embedded in the alveoli or sockets of the alveolar ridges of the mandible and the maxillae. Each individual develops two sets of teeth during the life; the temporary teeth of childhood and the permanent teeth of an adult. <br /><br /><strong>1. The temporary teeth:</strong> The temporary teeth are also known as deciduous or milk teeth, these are 20 in number, 10 in each jaw. They begin to erupt from the age of 6months and should all be presented by all the end of 24 months.<br /><br /><strong>2. The permanent teeth</strong>: These begin to replace the deciduous teeth. They start to erupt from the age of 6years should be completed by the age of 24 years. There are 32 permanent teeth, 16 in upper and 16 in the lower jaw.</p>
<p><strong>Structure & function of teeth</strong>: The tooth has two anatomical parts. The crown of a tooth is that part of the tooth which is covered with enamel and this is the part usually visible in the mouth.<br />The root is the part embedded in the jaw. It anchors the tooth in its bony socket and is normally not visible.<br /><br /><strong>Enamel</strong>-The hard outer layer of the crown. Enamel is the hardest substance in the body.<br /><br /><strong>Dentine</strong> - Not as hard as enamel, forms the bulk of the tooth and can be sensitive if the protection of the enamel is lost.<br /><br /><strong>Pulp -</strong> Soft tissue containing the blood and nerve supply to the tooth. The pulp extends from the crown to the tip of the root.<br /><br /><strong>Cementum -</strong> The layer of bone-like tissue covering the root. It is not as hard as enamel.<br />Structures around the tooth<br /><br /><strong>Periodontal ligament:</strong> Made up of thousands of fibers which fasten the cementum to the bony socket. These fibers anchor the tooth to the jaw bone and act as shock absorbers for the tooth which is subjected to heavy forces during chewing. <br /><br /><strong>Oral Mucosa:</strong> This is the term used to describe the moist tissue that lines the mouth. <br /><br /><strong>Gingivae (gums)</strong>: Soft tissue that immediately surrounds the teeth and bone. It protects the bone and the roots of the teeth and provides an easily lubricated surface.</p>
<h4>b) Pharynx-</h4>
<p>The pharynx is expanded muscular tube lying behind the nose and mouth. It is about 13 cm (5inches) long and extends from the base of the skull to the level of the cricoid cartilage, where it becomes continuous with the esophagus. It lies just in front of cervical vertebrae.<br /><br />The pharynx is anatomically divided into 3 parts<br /><strong>i. Nasopharynx</strong> – It lies behind nose, passage for air only. Eustachian tube (auditory tube) connects it to the middle ear.<br /><strong>ii. Oropharynx –</strong> It extends from the soft palate to C3 and is a common passage for food and air. It has palatine tonsil. Waldeyer s ring is present around <strong>it.</strong><br /><strong>iii. Laryngopharynx</strong> – it extends from C3-C6, is a passage for food only. It has glottis which is anteriorly opening into larynx that is guarded by epiglottis.<br /><br /><strong>Function of pharynx is:</strong><br />- To passes the food from mouth to esophagus.</p>
<h4>c) Esophagus –</h4>
<p>The esophagus or gullet is a collapsible muscular tube extending from the pharynx to the cardiac orifice of the stomach. It is about 25cm (10inches) long and 2cm diameter. It lies in the median plane in the thorax in front of the vertebral column and behind the trachea and the heart. It passes between the muscle fibers of the diaphragm behind the central tendon at the level of 10th thoracic vertebrae (where inferior vena cava crosses the diaphragm at 8th thoracic vertebrae and aorta at 12th thoracic vertebrae level).</p>
<p><strong>The structure of the esophagus:</strong> The esophagus is formed by four layers of tissues.<br /><strong>1) The outer layer:</strong> covered with elastic fibrous tissue.<br /><strong>2) The muscle layer</strong>: it consists of outer coat longitudinal and inner coat circular layer of fiber. The muscle of upper third of the esophagus is skeletal muscle but their action is involuntary while that of the middle third is mixed skeletal and visceral muscle and the lower third contains only visceral muscle fibers. <br /><strong>3) The submucous layer:</strong> consists of alveolar tissue, which contains blood and lymph vessels, and nerves of the autonomic nervous system.<br /><strong>4) The inner lining mucous membrane:</strong> the proximal third is lined with stratified squamous epithelium with mucous secreting glands, which have tiny ducts leading to the surface, and distal third by columnar epithelium and middle third by mixed of both.<br /><br /><strong>Functions of the esophagus:</strong><br />- The esophagus transports food from pharynx to stomach or acts as passages way.<br /><br /><strong>d) Stomach</strong> – stomach is the widest and the most dilatable part of a digestive system, situated between the esophagus and the beginning of the small intestine. It lies in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity.<br />It is muscular and distensible organ and its shape and size vary according to the amount and types of its contents, and to the pressure exerted on it by surrounding organs even though it has a capacity of 1.5 to 2 liters. The stomach is ‘J’ shaped structure having 25cm long.</p>
<p><strong>Structure of stomach:</strong><br />The stomach has two openings: <br /><strong>(a) the cardiac orifice </strong><br /><strong>(b) the pyloric orifice.</strong><br /><br />It has also two curvatures: <br /><strong>(a) the greater curvature</strong><br /><strong>(b) the lesser curvature.<br /></strong><br />The esophagus enters the stomach at the cardiac orifice, which is situated at the upper end of the lesser curvature which terminates at the pyloric orifice. The greater curvature begins where the esophagus enters the stomach and extends over the fundus, the curves downwards to the pylorus. The lesser curvature is shorter and extends from the cardiac orifice to the pylorus.<br /><br /><strong>Parts of the stomach:</strong><br /><strong>1. Fundus</strong> – the part of the stomach above the cardiac orifice is fundus. It is dome shaped, which generally contains a bubble of air.<br /><strong>2. Body</strong> – the main parts of the stomach is a body.<br /><strong>3. Pyloric antrum</strong> – This is a narrow part after the body. From this point, the stomach joins with the duodenum.<br /><br /><strong>Functions of the stomach:</strong><br />i. The stomach acts as a temporary reservoir for food, allowing the digestive enzymes to act.<br />ii. It produces gastric juice, which begins the chemical digestion of protein.<br />iii. Churns the food into small pieces, which help for complete digestion.<br />iv. A secrete intrinsic factor which is necessary for binding vit.B12 in the stomach and needed for its absorption in the terminal ileum.<br />v. Although iron absorption takes places in the small intestine it is dissolved out of foods most effectively in the stomach in the presence of hydrochloric acid.</p>
<h4>e) The small intestine –</h4>
<p>The small intestine is a convoluted tube, extending from the pylorus of the stomach to the ileum-cecal valve, where it joins the large intestine. It is approximately 5m (16feet) long and lies in the abdominal cavity, surrounded by the large intestine. The chemical digestion of the food, absorption of most nutrient materials takes place in this parts. <br /><br />The small intestine can be divided into three parts:<br /><strong>1. Duodenum:</strong> it is about 25cm long and C-shaped which curves around the head of the pancreas.<br /><strong>2. Jejunum:</strong> jejunum is the middle parts of the small intestine and is about 2m long. It starts from the point where the intestine turns abruptly towards the abdominal wall and downwards and continues.<br /><strong>3. Ileum –</strong> it is terminal part of small intestine and is about 3m long. It starts from the end of jejunum to ileocaecal valve. <br /><br />The structure of small intestine: there are four layers of tissues forming the wall of the intestine.<br /><strong>I. The outer layer</strong> – covering of peritoneum called the mesentery.<br /><strong>II. The muscle layer</strong> – there are two layers of smooth muscle fibers under the serous membrane.<br />1) Superficial layer of longitudinal<br />2) Deeper layer of circular fiber</p>
<p><strong>Functions of the small intestine:</strong><br />I. To onward movement of its contents, which is produced by peristaltic, segmental and pendular movement.<br />II. Secretion of intestinal juice<br />III. To complete the digestion of carbohydrates, proteins and gets in the enterocytes of the villi<br />IV. To protect against the infection by microbes that have survived the antimicrobial action of the hydrochloric acid in the stomach<br />V. To secretes the hormones: a) cholecystokinin – pancreozymins (CCK-PZ) and b) secretin<br />VI. To absorb the end product of nutrient materials.</p>
<h4>f) The large intestine –</h4>
<p>The large intestine or colon is about 1.5 m (5ft) long and extends from the ileocecal valve to the anus. Its lumen is larger than that of the small intestine. It forms an arch around the coiled up small intestine. For descriptive purpose, it can be divided into following parts: <br />I. Caecum and vermiform appendix<br />II. Ascending colon<br />III. Transverse colon<br />IV. Descending colon<br />V. Pelvic or sigmoid colon<br />VI. Rectum and canal<br /><br /><strong>Structures of the large intestine:</strong> <br />a. The outer layer – covering of peritoneum<br />b. The muscle layer - There are two layers of muscles fibers <br />a) The longitudinal fibers do not form a smooth continuous layer of tissue but are collected into three bands called taeniae coil which is situated at a regular interval around the colon.<br />b) The circular muscle fibers form a thin layer, which completely surrounds the colon.<br />Functions of the large intestine:<br />I. Absorption of water, electrolytes and salts<br />II. Acts as temporary reservoir for feces and excreta of feces as needed<br />III. Microbial activity: there are a large number of microbes in the colon, which synthesize Vit. K and folic acid.</p>
<h4> </h4>
<p> </p>
<h4>a) Mouth</h4>
<p>The starting and upper expanded portion of the alimentary tract are known as a mouth. It is also called buccal cavity or oral cavity. The mouth and oral cavity are lined with non -keratinized stratified squamous epithelium containing small mucous secreting glands, which helps to moist the oral cavity.<br /><br /><strong>i. The tongue</strong></p>
<p>– The tongue is highly mobile, a voluntary muscular structure which lies on the floor of the mouth. It is attached to the hyoid bone by its base and to the floor of the mouth by a fold of the mucous membrane covering, called the frenulum. Tips of a tongue are sensitive to sweet and salt, back of the tongue is sensitive to bitter and posterior half of each side of the tongue is sensitive to sour taste.<br /><br /><strong>ii. The teeth</strong> – The teeth are embedded in the alveoli or sockets of the alveolar ridges of the mandible and the maxillae. Each individual develops two sets of teeth during the life; the temporary teeth of childhood and the permanent teeth of an adult. <br /><br /><strong>1. The temporary teeth:</strong> The temporary teeth are also known as deciduous or milk teeth, these are 20 in number, 10 in each jaw. They begin to erupt from the age of 6months and should all be presented by all the end of 24 months.<br /><br /><strong>2. The permanent teeth</strong>: These begin to replace the deciduous teeth. They start to erupt from the age of 6years should be completed by the age of 24 years. There are 32 permanent teeth, 16 in upper and 16 in the lower jaw.</p>
<p><strong>Structure & function of teeth</strong>: The tooth has two anatomical parts. The crown of a tooth is that part of the tooth which is covered with enamel and this is the part usually visible in the mouth.<br />The root is the part embedded in the jaw. It anchors the tooth in its bony socket and is normally not visible.<br /><br /><strong>Enamel</strong>-The hard outer layer of the crown. Enamel is the hardest substance in the body.<br /><br /><strong>Dentine</strong> - Not as hard as enamel, forms the bulk of the tooth and can be sensitive if the protection of the enamel is lost.<br /><br /><strong>Pulp -</strong> Soft tissue containing the blood and nerve supply to the tooth. The pulp extends from the crown to the tip of the root.<br /><br /><strong>Cementum -</strong> The layer of bone-like tissue covering the root. It is not as hard as enamel.<br />Structures around the tooth<br /><br /><strong>Periodontal ligament:</strong> Made up of thousands of fibers which fasten the cementum to the bony socket. These fibers anchor the tooth to the jaw bone and act as shock absorbers for the tooth which is subjected to heavy forces during chewing. <br /><br /><strong>Oral Mucosa:</strong> This is the term used to describe the moist tissue that lines the mouth. <br /><br /><strong>Gingivae (gums)</strong>: Soft tissue that immediately surrounds the teeth and bone. It protects the bone and the roots of the teeth and provides an easily lubricated surface.</p>
<h4>b) Pharynx-</h4>
<p>The pharynx is expanded muscular tube lying behind the nose and mouth. It is about 13 cm (5inches) long and extends from the base of the skull to the level of the cricoid cartilage, where it becomes continuous with the esophagus. It lies just in front of cervical vertebrae.<br /><br />The pharynx is anatomically divided into 3 parts<br /><strong>i. Nasopharynx</strong> – It lies behind nose, passage for air only. Eustachian tube (auditory tube) connects it to the middle ear.<br /><strong>ii. Oropharynx –</strong> It extends from the soft palate to C3 and is a common passage for food and air. It has palatine tonsil. Waldeyer s ring is present around <strong>it.</strong><br /><strong>iii. Laryngopharynx</strong> – it extends from C3-C6, is a passage for food only. It has glottis which is anteriorly opening into larynx that is guarded by epiglottis.<br /><br /><strong>Function of pharynx is:</strong><br />- To passes the food from mouth to esophagus.</p>
<h4>c) Esophagus –</h4>
<p>The esophagus or gullet is a collapsible muscular tube extending from the pharynx to the cardiac orifice of the stomach. It is about 25cm (10inches) long and 2cm diameter. It lies in the median plane in the thorax in front of the vertebral column and behind the trachea and the heart. It passes between the muscle fibers of the diaphragm behind the central tendon at the level of 10th thoracic vertebrae (where inferior vena cava crosses the diaphragm at 8th thoracic vertebrae and aorta at 12th thoracic vertebrae level).</p>
<p><strong>The structure of the esophagus:</strong> The esophagus is formed by four layers of tissues.<br /><strong>1) The outer layer:</strong> covered with elastic fibrous tissue.<br /><strong>2) The muscle layer</strong>: it consists of outer coat longitudinal and inner coat circular layer of fiber. The muscle of upper third of the esophagus is skeletal muscle but their action is involuntary while that of the middle third is mixed skeletal and visceral muscle and the lower third contains only visceral muscle fibers. <br /><strong>3) The submucous layer:</strong> consists of alveolar tissue, which contains blood and lymph vessels, and nerves of the autonomic nervous system.<br /><strong>4) The inner lining mucous membrane:</strong> the proximal third is lined with stratified squamous epithelium with mucous secreting glands, which have tiny ducts leading to the surface, and distal third by columnar epithelium and middle third by mixed of both.<br /><br /><strong>Functions of the esophagus:</strong><br />- The esophagus transports food from pharynx to stomach or acts as passages way.<br /><br /><strong>d) Stomach</strong> – stomach is the widest and the most dilatable part of a digestive system, situated between the esophagus and the beginning of the small intestine. It lies in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity.<br />It is muscular and distensible organ and its shape and size vary according to the amount and types of its contents, and to the pressure exerted on it by surrounding organs even though it has a capacity of 1.5 to 2 liters. The stomach is ‘J’ shaped structure having 25cm long.</p>
<p><strong>Structure of stomach:</strong><br />The stomach has two openings: <br /><strong>(a) the cardiac orifice </strong><br /><strong>(b) the pyloric orifice.</strong><br /><br />It has also two curvatures: <br /><strong>(a) the greater curvature</strong><br /><strong>(b) the lesser curvature.<br /></strong><br />The esophagus enters the stomach at the cardiac orifice, which is situated at the upper end of the lesser curvature which terminates at the pyloric orifice. The greater curvature begins where the esophagus enters the stomach and extends over the fundus, the curves downwards to the pylorus. The lesser curvature is shorter and extends from the cardiac orifice to the pylorus.<br /><br /><strong>Parts of the stomach:</strong><br /><strong>1. Fundus</strong> – the part of the stomach above the cardiac orifice is fundus. It is dome shaped, which generally contains a bubble of air.<br /><strong>2. Body</strong> – the main parts of the stomach is a body.<br /><strong>3. Pyloric antrum</strong> – This is a narrow part after the body. From this point, the stomach joins with the duodenum.<br /><br /><strong>Functions of the stomach:</strong><br />i. The stomach acts as a temporary reservoir for food, allowing the digestive enzymes to act.<br />ii. It produces gastric juice, which begins the chemical digestion of protein.<br />iii. Churns the food into small pieces, which help for complete digestion.<br />iv. A secrete intrinsic factor which is necessary for binding vit.B12 in the stomach and needed for its absorption in the terminal ileum.<br />v. Although iron absorption takes places in the small intestine it is dissolved out of foods most effectively in the stomach in the presence of hydrochloric acid.</p>
<h4>e) The small intestine –</h4>
<p>The small intestine is a convoluted tube, extending from the pylorus of the stomach to the ileum-cecal valve, where it joins the large intestine. It is approximately 5m (16feet) long and lies in the abdominal cavity, surrounded by the large intestine. The chemical digestion of the food, absorption of most nutrient materials takes place in this parts. <br /><br />The small intestine can be divided into three parts:<br /><strong>1. Duodenum:</strong> it is about 25cm long and C-shaped which curves around the head of the pancreas.<br /><strong>2. Jejunum:</strong> jejunum is the middle parts of the small intestine and is about 2m long. It starts from the point where the intestine turns abruptly towards the abdominal wall and downwards and continues.<br /><strong>3. Ileum –</strong> it is terminal part of small intestine and is about 3m long. It starts from the end of jejunum to ileocaecal valve. <br /><br />The structure of small intestine: there are four layers of tissues forming the wall of the intestine.<br /><strong>I. The outer layer</strong> – covering of peritoneum called the mesentery.<br /><strong>II. The muscle layer</strong> – there are two layers of smooth muscle fibers under the serous membrane.<br />1) Superficial layer of longitudinal<br />2) Deeper layer of circular fiber</p>
<p><strong>Functions of the small intestine:</strong><br />I. To onward movement of its contents, which is produced by peristaltic, segmental and pendular movement.<br />II. Secretion of intestinal juice<br />III. To complete the digestion of carbohydrates, proteins and gets in the enterocytes of the villi<br />IV. To protect against the infection by microbes that have survived the antimicrobial action of the hydrochloric acid in the stomach<br />V. To secretes the hormones: a) cholecystokinin – pancreozymins (CCK-PZ) and b) secretin<br />VI. To absorb the end product of nutrient materials.</p>
<h4>f) The large intestine –</h4>
<p>The large intestine or colon is about 1.5 m (5ft) long and extends from the ileocecal valve to the anus. Its lumen is larger than that of the small intestine. It forms an arch around the coiled up small intestine. For descriptive purpose, it can be divided into following parts: <br />I. Caecum and vermiform appendix<br />II. Ascending colon<br />III. Transverse colon<br />IV. Descending colon<br />V. Pelvic or sigmoid colon<br />VI. Rectum and canal<br /><br /><strong>Structures of the large intestine:</strong> <br />a. The outer layer – covering of peritoneum<br />b. The muscle layer - There are two layers of muscles fibers <br />a) The longitudinal fibers do not form a smooth continuous layer of tissue but are collected into three bands called taeniae coil which is situated at a regular interval around the colon.<br />b) The circular muscle fibers form a thin layer, which completely surrounds the colon.<br />Functions of the large intestine:<br />I. Absorption of water, electrolytes and salts<br />II. Acts as temporary reservoir for feces and excreta of feces as needed<br />III. Microbial activity: there are a large number of microbes in the colon, which synthesize Vit. K and folic acid.</p>
<h4> </h4>
<p> </p>
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Human Digestive System
Securing E-Mail (PGP)
Securing E-mail
Security of an e-mail is a vital issue because of the highly growing number of businesses utilizing this form of communication. There are two main schemes which are specially designed to provide confidentiality and authentication of electronic mail systems that are currently being used. These two types of e-mail types are PGP (Pretty Good Privacy) and S/MIME (Secure/Multipurpose Internet Mail Extension).
PGP (Pretty Good Privacy)
PGP is developed by Phil Zimmerman in 1995. Pretty Good Privacy (PGP) is an e-mail encryption scheme (technique) that has become a de-facto standard that is being used widely, by thousands of users all over the globe. Depending on the version, the PGP software was supposed to use MD5 or SHA for calculating the message digest such as CAST, Triple-DES or IDEA. In addition, PGP provides data compression. The documentation and source code used in this process are freely available to use it. The package is independent of operating system and processor. PGP doesn't rely on the "establishment" and its popularity and use have grown extensively since 1995.The used PGP are supposed to combine with the best available cryptographic algorithms to achieve secure e-mail communication.
When PGP is installed, the software creates a public key pair for the user. The public key can be posted on the user's Web site or placed on a public key server. The private key is protected by the use of a password. To maintain the security of the system the password has to be entered every time the user accesses the private key. PGP gives the user the option of digitally sign the (sent/received) messages, encryption of those messages, or both digitally signing and encrypting. It is assumed that all users are using the public key cryptography and they have generated a private/public key pair. Either RSA (with RSA digital signatures) or El Gamel (with DSA) can be used. All users also use a symmetric key system such as triple DES or Rijndael.PGP encrypts data using block cipher called IDEA (International Data Encryption Algorithm) which uses 128-bit keys.
Services offered by PGP:
- Authentication
- Confidentiality
- Compression
- Email compatibility
- Segmentation
Working of PGP
References:
- A.S. Tanenbaum, “Computer Networks”, 3rd Edition, Prentice Hall India, 1997.
- W. Stallings, “Data and Computer Communication”, Macmillan Press, 1989.
- Kurose Ross, “Computer Networking: A top-down approach”, 2nd Edition, Pearson Education
- Larry L. Peterson, Bruce S. Davie, “Computer Networks: A Systems Approach”, 3rd Edition, Morgan Kaufmann Publishers
Lesson
Network Security
Subject
Computer Engineering
Grade
Engineering
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