1. EMAIL SECURITY
INTRODUCTION
E-mail now a days is a security hazard. Many viruses and worms use e-mail to spread
themselves throughout the Internet, and almost every day new types of worms and
viruses appear. It is of vital importance for administrators and users to keep mail security
up-to-date.
Hack:
1. To write program code.
2. To modify a program, often in an unauthorized manner, by changing the code itself.
1. Code that is written to provide extra functionality to an existing program.
2. An inelegant and usually temporary solution to a problem
Hacker: A slang term for a computer enthusiast, i.e., a person who enjoys learning
programming languages and computer systems and can often be considered an expert on
the subject(s). Among professional programmers, depending on how it used, the term can
be either complimentary or derogatory, although it is developing an increasingly
derogatory connotation. The pejorative sense of hacker is becoming more prominent
largely because the popular press has coopted the term to refer to individuals who gain
unauthorized access to computer systems for the purpose of stealing and corrupting data.
Hackers, themselves, maintain that the proper term for such individuals is cracker.
Email Viruses
Email viruses spread in two main ways:
Attachments. Viruses commonly hide in programs sent as email attachments, and run
when the user double-clicks on the program to start it. Therefore, you shouldn't run
programs received as email attachments unless you have a virus protection program
running and the attachment is from a trusted source.
For example, a greeting card program forwarded from a friend of a
friend is not from a trusted source, and there is nothing to stop it from running malicious
system programming code behind its animated presentation once you start it running on
1

2. your machine. You should also be wary of opening documents that might contain scripts
and macros (see below). Some attachments will have two extensions to try and trick you
into believing they are just a harmless data file and not a program, such as
"coolpicture.jpg. exe".
Scripts. One of the first script viruses was a MIME virus that attacked older versions of
programs like Netscape Mail, Microsoft Outlook, and Eudora, and could under certain
rare conditions run a damaging program as soon as the email was simply opened. In a
variation on an old hacker technique, the attached MIME file was given a very long name
that then triggered a bug that allowed the end of the name to be run as a series of
instructions, which could then be written to do damaging things to your computer.
However, Visual Basic (VBasic) script viruses became very real, and have
continued to do considerable damage across the Internet. VBasic is a very flexible and
deeply powerful program development environment used by Microsoft for their operating
system, office automation, and Internet applications. This means that VBasic viruses can
run from anywhere in the Microsoft software architecture and affect the entire system,
from email to operating system, giving them unprecedented reach and power.
The first widespread VBasic virus was Melissa, which brought down several of the
largest corporations in the world for several days in late March 1999. Melissa traveled in
a Microsoft Word document and was triggered when the document was opened, opened
the associated Microsoft Outlook email program, read the user's email address book, and
then sent copies of itself to the first fifty names. This clever architecture was quickly
followed by many variants programmed by hackers around the world, including the KAK
virus that triggered as soon as an email was opened, and the BubbleBoy virus that
triggered as soon as the email was viewed in the preview pane.
Various types to provide Email security.
1. Email filtering.
2. Web email vulnerabilities.
3. Reaper exploit.
4. Email encryption.
2

3. EMAIL FILTERING
There are three steps of filtering that every mail should be subjected to:
Attachment filters are used to block executable attachments, such as .exe files. Long
lists of other attachment types are also executable. Of late, exploits in image processing
libraries have been made public. This allows spreading viruses using image files, such as
gif or jpg. Attachment filters require little processing and little maintenance (they are
always up-to-date, but you must make sure you block all attachment types used as virus
carrier). However, they are ineffective if a virus author uses a more complex method of
spreading the infection by wrapping the virus into an archive file, e.g. a zip archive
(unless you choose to block archives as well).
Virus filters are used to scan all attachments for known viruses. The virus database must
be constantly updated to reliably detect the latest threats. As the update of virus filter
databases lags behind, there is a window of vulnerability where viruses can pass
undetected into users' mailboxes. By blocking executable attachments, an attachment
blocker can close this window, to a point: Users must still be instructed to be very careful
with the content of archive files that passed both the attachment blocker and the virus
checker
Spam filters :Finally, most mail traffic nowadays is Spam. Good Spam filters are able to
capture about 90% of all Spam mails, while at the same time false positives (a legitimate
mail incorrectly flagged as spam) are very rare.
WEB EMAIL
There is an unexpected vulnerability to confidentiality of personal information with some
web based email services. When you click a link on a web page, the HTTP protocol sends
the URL of the current page to the new page. Therefore, if you access your email through
a web based email service and click on a link in an email, the URL of the current web
page is passed to the new page. This can cause unexpected compromise of personal
information with web email services that put account information in the URL of the web
page, since this information is transmitted to the server of any third party web page you
access through your web email account. This information can include your email address,
login ID, and even your actual name. In most cases the information can't be used to
actually access your web email account, since most services have implemented password
3

4. and other protections, but it can reveal more personal information than is available
through other normal web communications.
Reaper exploit
Email confidentiality can also be compromised by macro viruses like the reaper exploit,
where the virus waits in the background and sends your reply or forward of an email back
to the hacker, and then travels with your email to divulge copies of replies or forwards by
the recipients back to the hacker as well. This term is used mainly as an historical
reference because it sounds cool, and less because it is in common current use.
Encryption.
You should encrypt your e-mail for the same reason that you don't write all of your
correspondence on the back of a post card. E-mail is actually far less secure than the
postal system. With the post office,you at least put your letter inside an envelope to hide
it from casual snooping. Take a look at the header area of any e-mail message that
you receive and you will see that it has passed through a number of nodes on its way to
you. Every one of these nodes presents the opportunity for snooping. Encryption in no
way should imply illegal activity. It is simply intended to keep personal thoughts
personal.
Encrypting email is the only way to guarantee its confidentiality in transit. The most
widely used method of email encryption uses Pretty Good Privacy, which integrates
directly with your email application.
PRETTY GOOD PRIVACY (PGP)
PGP is a program that gives your electronic mail something that it otherwise
doesn't have: Privacy. It does this by encrypting your mail so that nobody but the
intended person can read it. When encrypted, the message looks like a meaningless
jumble of random characters. PGP has proven itself quite capable of resisting even the
most sophisticated forms of analysis aimed at reading the encrypted text. PGP can also be
used to apply a digital signature to a message without encrypting it. This is normally
used in public postings where you don't want to hide what you are saying, but rather want
to allow others to confirm that the message actually came from you. Once a digital
signature is created, it is impossible for anyone to modify either the message or the
signature without the modification being detected by PGP.
4

5. While PGP is easy to use, it does give you enough rope so that you can hang
yourself. You should become thoroughly familiar with the various options in PGP before
using it to send serious messages. For example, giving the command "PGP -sat
<filename>" will only sign a message, it will not encrypt it. Even though the output looks
like it is encrypted, it really isn't. Anybody in the world would be able to recover the
original text.
PGP provides a confidentiality and authentication service that can be used for
Electronic mail and file storage applications.It is available free worldwide in versions
that run on a variety of platforms ,including Windows, Unix Macintosh and many more
in addition , the commercial version satisfies uses who want a product to that comes with
vendor support.
Operational Description
The actual operation of PGP consists of five services.
1. Authentication
2. Confidentiality
3. Compression
4. E-Mail Compatibility
5. Segmentation
Authentication
1. The sender creates a message
2. Sha-1 is used to generate a 160-bit hash code of the message.
3. The hash code is encrypted with RSA using the sender’s private key and the result is
4. prepended to the message
5. The receiver uses RSA with the sender’s public key to decrypt and recover the hash
code.
6. The receiver generates a new hash code for the message and compares it with the
decrypted hash code. If the two match the message is accepted as Authentic.
The combination of SHA-1 and RSA provides and effective digital signature’s scheme.
5

6. Confidentiality
Another basic service provided by PGP confidentiality, which is provided by encrypting
messages to be transmitted or to be stored locally as files. In both cases, the symmetric
encryption algorithm CAST-128 may be used . Alternatively IDEA or 3DES may be
used. The 64 -bit cipher feed back mode is used.
In PGP, each symmetric key is used only once i.e. a new key is generated in a
random 128-bit number for each message. Thus although this is referred to in the
documentation as in a session key. It is in reality in a one- time key. Because it is to be
used only once. The session key is bound to the message and transmitted with it .To
protect the key it is encrypted with the receiver’s public key.
1.The sender generates a message the random 128 bit number to be used as a session key
for this message only.
2.The message is encrypted using CAST-128 or 3 DES with the session key.
3.The session key is encrypted with RSA, using the recipient’s public key and prepended
to the message.
4.The receiver uses RSA with its private key to decrypt and recover the session key.
5.The session key is used to decrypt the message.
Compression:
As a default,PGP compresses the message after applying the signature but before
encryption.The placement of compression algorithm, indicated by Z for compression and
Z inverse for decompression.
1.The signature is generated before compression for two reasons:
a. It is preferable to sign an uncompressed message so that one can store only the
uncompressed message together with the signature for future verification. If one
signed a compressed document, then it would be necessary either to store a
compressed version of message for later verification or to recompress the message
when verification is required..
b. Even if one were willing to generate dynamically a recompressed message for
verification ,PGP’S compression algorithm presents a difficulty.The algorithm is not
6

7. deterministic;various implementations of the algorithm achieve different tradeoffs in
running speed versus compression ratio and ,as a result ,produce different compressed
Forms.However these different compression algorithms are interoperable because
any version of the algorithm can correctly decompress the output of any other version
.Applying the hash function and signature after compression would constrain all
PGP implementations to the same version of the compression algorithm.
2. Message encryption is applied after compression to strengthen cryptographic security.
Because the compressed message has less redundancy than the original
plaintext, cryptanalysis is more difficult.
E-Mail Compatibility
When PGP is used ,at least part of the block to be transmitted is encrypted. If only
the signature service is used,then the message digest is encrypted .If the confidentiality
service is used, the message plus signature are encrypted .Thus,part or all of the
resulting block consists of a stream of arbitrary 8-bit octets.However ,many electronic
mail systems only permit the use of blocks consisting of ASCII text. To accommodate
this restriction this restriction ,PGP provides the service of converting the raw 8-bit
binary stream to a stream of printable ASCII characters. The scheme used for this
purpose is radix-64 conversion.Each group of three octets of binary data is mapped into 4
ASCII codes .This format also appends a CRC to detect transmission errors.
The use of radix 64 expands a message by 33% .Fortunately ,the session key
and signature portions of the message are relatively compact,and the plaintext message
has been compressed.In fact,the compression should be more than enough to
componsate for the radix 64 for expansion.
One worthy aspect of the radix 64 algorithm is that blindly converts the input
stream to radix 64 format regardless of content, even if the input happens to be ASCII
text. Thus if a message is signed but not encrypted and the conversion is applied to the
entire block. And the output is unreadable to the causual observer, which provides a
certain level of confidentiality .As an option PGP can be configured to convert to radix
64 format only the signature portion of signed plain text messages. This enables the
human recipients to read the message without using PGP.
7

8. Segmentation:
E-mail facilities often are restricted to a maximum message length.For example ,
many of the facilities accessible through the Internet impose a maximum length of
50,000 octects. Any message longer than that must be broken up into a smaller segments.
Each of which is maild separately.
To accommodate this restriction, PGP automatically subdivides a message that is
too large into segments that are small enough to send via E-mail. The segmentation is
done after all of the other processing including the radix 64 conversion. Thus the session
key component and signature component appear only once, at the beginning of the first
segment. At the receiving end PGP must strip off all E-mail headers and reassemble the
entire original block .
MIME
Short for Multipurpose Internet Mail Extensions, a specification for formatting non-
ASCII messages so that they can be sent over the Internet. Many e-mail clients now
support MIME, which enables them to send and receive graphics, audio, and video files
via the Internet mail system. In addition, MIME supports messages in character sets other
than ASCII.There are many predefined MIME types, such as GIF graphics files and
PostScript files. It is also possible to define your own MIME types.
In addition to e-mail applications, Web browsers also support various MIME types. This
enables the browser to display or output files that are not in HTML format.
S/MIME
(Secure / Multipurpose Internet Mail Extensions) is a protocol that adds digital signatures
and encryption to Internet MIME (Multipurpose Internet Mail Extensions) messages
described in RFC 1521. MIME is the official proposed standard format for extended
Internet electronic mail. Internet e-mail messages consist of two parts, the header and the
body. The header forms a collection of field/value pairs structured to provide information
essential for the transmission of the message. The structure of these headers can be found
in RFC 822. The body is normally unstructured unless the e-mail is in MIME format.
MIME defines how the body of an e-mail message is structured. The MIME format
8

9. permits e-mail to include enhanced text, graphics, audio, and more in a standardized
manner via MIME-compliant mail systems. However, MIME itself does not provide any
security services. The purpose of S/MIME is to define such services, following the syntax
given in PKCS #7 (see Question 5.3.3) for digital signatures and encryption. The MIME
body section carries a PKCS #7 message, which itself is the result of cryptographic
processing on other MIME body sections. S/MIME standardization has transitioned into
IETF, and sets of documents describing S/MIME version 3 have been published there.
Public Key Cryptography
Public Key Cryptography (PKC) is a near magical property of information arising from
the underlying mathematical structure of the universe that also conveniently enables
creation of modern-day secure communication channels on the Internet.
The main feature of PKC is the use of two keys for each person, a public key and a
private key, where either key can decrypt a message encrypted with the other. Each key is
almost impossible to find out from the other, and if the keys are long enough the method
is effectively unbreakable -- according to the known laws of science.
The elegant PKC architecture enables clever creation of a secure communications system
for distributed participants, which is exactly what is needed for the Internet. The
technology is the basis of the field of Public Key Infrastructure (PKI), and the basis of the
industry standard Rivest, Shamir, Adleman (RSA) encryption algorithm
Public Key Cryptography (PKC) History
Public Key Cryptography (PKC) uses two keys, a "public key" and a "private key", to
implement an encryption algorithm that doesn't require two parties to first exchange a
secret key in order to conduct secure communications. In a nice mathematical twist, this
conceptual breakthrough also enables an elegant implementation of digital signatures.
In a classic cryptosystem, we have encryption functions E_K and decryption
functions D_K such that D_K(E_K(P)) = P for any plaintext P. In a public-key
cryptosystem, E_K can be easily computed from some ``public key'' X which in turn is
computed from K. X is published, so that anyone can encrypt messages. If decryption
9

10. D_K cannot be easily computed from public key X without knowledge of private key K,
but readily with knowledge of K, then only the person who generated K can decrypt
messages. That's the essence of public-key cryptography,introduced by Diffie and
Hellman in 1976.
Role of the session key in public key schemes:
In virtually all public key systems, the encryption and decryption
times are very lengthy compared to other block-oriented algorithms such as DES for
equivalent data sizes. Therefore in most implementations of public-key systems, a
temporary, random `session key' of much smaller length than the message is generated
for each message and alone encrypted by the public key algorithm. The message
is actually encrypted using a faster private key algorithm with the session key. At the
receiver side, the session key is decrypted using the public-key algorithms and the
recovered `plaintext' key is used to decrypt the message.
The session key approach blurs the distinction between `keys'
and `messages' -- in the scheme, the message includes the key, and the key itself is treated
as an encryptable `message'. Under this dual-encryption approach, the overall
cryptographic strength is related to the security of either the public- and private-key
algorithms.
How Public Key Cryptography (PKC) Works
The security of the standard Public Key Cryptography (PKC) algorithm
RSA is founded on the mathematical difficulty of finding two prime factors of a very
large number.
Historically, most encryption systems depended on a secret key that two or more parties
used to decrypt information encrypted by a commonly agreed method. The main idea of
PKC is the use of two unique keys for each participant, with a bi-directional encryption
mechanism that can use either key to decrypt information encrypted with the other key,
as described below:
Public key. One of the keys allocated to each person is called the "public key", and is
published in an open directory somewhere where anyone can easily look it up, for
example by email address.
10

11. Private key. Each person keeps their other key secret, which is then called their "private
key".
If John wants to send an encrypted email to Mary, he encrypts his message with Mary's
public key, and then sends it to her. He doesn't need to be worried about interception or
eavesdropping since the only person that can read the message is Mary, because she is the
only one that has the corresponding private key that can decrypt it. This powerful
architecture has three profound consequences:
Geography. The sender and the recipient no longer need to meet or use some other
potentially insecure method to exchange a common secret key. Since everyone has their
own set of keys, then anyone can securely communicate with anyone else by first looking
up their public key and using that to encrypt the message, enabling secure communication
even across great distances over a network (like the Internet).
Digital signatures. A sender can digitally sign their message by encrypting their name
(or some other meaningful document) with their secret key and then attaching it to a
message. The recipient can verify that the message came from the sender by decrypting
their signature with their public key. If the decryption works and produces a readable
signature, then the message came from the sender because only they could have
encrypted the signature with their private key in the first place.
Security. The disclosure of a key doesn't compromise all of the communications on a
network, since disclosure of public keys is intended, and only messages sent to one
person are affected by the disclosure of a private key.
Details. The algorithms on which both RSA's and Cock's algorithms are based uses a
mathematical expression built on the multiplication of two large prime numbers (a
number that is the product of only 1 and itself). For example, the following numbers are
the product of two prime numbers:
Product Primes
15 = 3 x 5
77 = 7 x 11
221 = 13 x 17
While RSA's and Cock's algorithms are similar, RSA's is described in the following
because it is the more general case and was published first. Essentially, the public key is
the product of two randomly selected large prime numbers, and the secret key is the two
11

12. primes themselves. The algorithm encrypts data using the product, and decrypts it with
the two primes, and vice versa.
A mathematical description of the encryption and decryption expressions is shown
below:
Encryption: C = M^e (modulo n)
Decryption: M = C^d (modulo n)
Where:
M = the plain-text message expressed as an integer number.
C = the encrypted message expressed as an integer number.
n = the product of two randomly selected, large primes p and q.
d = a large, random integer relatively prime to (p-1)*(q-1).
e = the multiplicative inverse of d, that is:
( e * d ) = 1 ( modulo ( p - 1 ) * ( q - 1 ) )
The public key is the pair of numbers ( n, e ).
The private key is the pair of numbers ( n, d ).
This is prime factors of a large number, and of finding the private key d from the public
key n. difficult This algorithm is secure because of the great mathematical difficulty of
finding the two because the only known method of finding the two prime factors of a
large number is to check all the possibilities one by one, which isn't practical because
there are so many prime numbers. For example, a 128 bit public key would be a number
between 1 and 340,282,366,920,938,000,000,000,000,000,000,000,000
Now, first Euclid proved that there are an infinite number of primes. Then, the work of
Legendre, Gauss, Littlewood, Te Riele, Tchebycheff, Sylvester, Hadamard, de la Vallée
Poussin, Atle Selberg, Paul Erdös, Hardy, Wright, and Von Koch showed that the number
of prime numbers between one and n is approximately n / ln(n). Therefore, there are
about: 2^128 / ln( 2^128 ) = 3,835,341,275,459,350,000,000,000,000,000,000,000
different prime numbers in a 128 bit key. That means that even with enough computing
power to check one trillion of these numbers a second, it would take more than
121,617,874,031,562,000 years to check them all. That's about 10 million times longer
than the universe has existed so far.
12

13. Therefore, unless someone makes a very large and unexpected mathematical
breakthrough, it's practically impossible to find out the private key from a public key with
RSA encryption, making it one of the most secure methods ever invented. However,
please note that like almost all encryption systems, the RSA algorithm is still vulnerable
to plain-text attacks, when a third party can repeatedly choose (or otherwise knows) some
of the text to be encrypted and can examine the result. In addition, the promised
development of quantum computers over the next several decades that can effectively
perform many calculations simultaneously may be able to break the RSA algorithm
relatively quickly.
RSA algorithm:
RSA is a public-key cryptosystem defined by Rivest, Shamir, and Adleman.
For example,Plaintexts are positive integers up to 2^{512}. Keys are quadruples
(p,q,e,d), with p a 256-bit prime number, q a 258-bit prime number,and d and e large
numbers with (de - 1) divisible by (p-1)(q-1). We define E_K(P) = P^e mod pq, D_K(C)
= C^d mod pq. All quantities are readily computed from classic and modern number
theoretic algorithms (Euclid's algorithm for computing the greatest common divisor
yields an algorithm for the former, and historically newly explored computational
approaches to finding large `probable' primes, such as the Fermat test, provide the latter.)
Now E_K is easily computed from the pair (pq,e)---but, as far as anyone knows,
there is no easy way to compute D_K from the pair (pq,e). So whoever generates K can
publish (pq,e). Anyone can send a secret message to him; he is the only one who can
read the messages.
How to Choose a Good Password
Do not use:
1. Names:
a. of yourself, including nicknames;
b. of your spouse or significant other, of your parents, children, siblings,
pets, or other family members;
c. of fictional characters, especially ones from fantasy or sci-fi stories like
the Lord of the Rings or Star Trek;
13

14. d. of any place or proper noun;
e. of computers or computer systems;
f. any combination of any of the above.
2. Numbers, including:
a. your phone number;
b. your social security number;
c. anyone's birthday;
d. your driver's licence number or licence plate;
e. your room number or address;
f. any common number like 3.1415926 or 1.618034;
g. any series such as 1248163264;
h. any combination of any of the above.
3. Any username in any form, including:
a. capitalized (Joeuser);
b. doubled (joeuserJoeuser);
c. reversed (resueoJ);
d. reflected (joeuserResueoj);
e. with numbers or symbols appended (Joeuser!).
4. Any word in any dictionary in any language in any form.
5. Any word you think isn't in a dictionary, including:
a. any slang word or obscenity;
b. any technical term or jargon (BartleMUD, microfortnight, Oobleck).
6. Any common phrase:
a. ``Go ahead, make my day.''
b. ``Brother, can you spare a dime?''
c. ``1 fish, 2 fish, red fish, blue fish.''
7. Simple patterns, including:
14

15. a. passwords of all the same letter;
b. simple keyboard patterns (qwerty, asdfjkl);
c. anything that someone might easily recognize if they see you typing it.
8. Any information about you that is easily obtainable:
a. favorite color;
b. favorite rock group.
9. Any object that is in your field of vision at your workstation.
10. Any password that you have used in the past.
There are programs (and they are easy to write) which will crack passwords that are
based on the above.
Do:
1. Change your password every three to six months. Changing once every term
should be considered an absolute minimum frequency.
2. Use both upper and lower case letters.
3. Use numbers and special symbols (!@#$) with letters.
4. Create simple mnemonics (memory aids) or compounds that are easily
remembered, yet hard to decipher:
a. ``3laR2s2uaPA$$WDS!'' for ``Three-letter acronyms are too short to use
as passwords!''
b. ``IwadaSn,atCwt2bmP,btc't.'' for ``It was a dark and stormy night, and the
crackers were trying to break my password, but they couldn't.''
c. ``HmPwaCciaCccP?'' for ``How many passwords would a cracker crack if
a cracker could crack passwords?''
5. Use two or more words together (Yet_Another_Example).
6. Use misspelled words (WhutdooUmeenIkan'tSpel?).
7. Use a minimum of eight characters. You may use up to 255 characters on Athena,
and generally the longer the password, the more secure it is.
Never!
Finally, NEVER write your password down anywhere, nor share your password with
anyone, including your best friend, your academic advisor, or an on-line consultant!
15

16. CONCLUSION
E-mail now a days is a security hazard. Many viruses and worms use e-mail to spread
themselves throughout the Internet, and almost every day new types of worms and
viruses appear. It is of vital importance for administrators and users to keep mail security
up-to-date.
There are three steps of filtering that every mail should be subjected to: Attachment
filters, Virus filters, Spam filters.
You should encrypt your e-mail for the same reason that you don't write all of your
correspondence on the back of a post card. E-mail is actually far less secure than the
postal system. With the post office,you at least put your letter inside an envelope to hide
it from casual snooping.
16