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Steganography

Hiding a message in a text or an image is called steganography. Hidden messages become visible when treated with special chemicals or exposed to Ultra Violet light (used in spy work). UV light is used to detect counterfeit currency. Using photographic technique, a message can be reduced to a 'micro dot' and placed in a text or the micro dot can be hidden on the envelope, under the postal stamp etc.

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Cryptography is a science of coding and decoding messages for secrecy. Confident and secret messages are sent from one party to another. An enemy can intercept the messenger and can access the message content. To avoid such an incident, messages are normally coded.

There is an old story of a king who send a message to his army general in a very special way. The messenger's head was shaved and a message is painted on his head. He was sent to the general with the message on his head after a month time !.

In public key crypto system, the keys for encryption (coding) and decryption (decoding) are different. e.g. - RSA (Rivest Shamir Adleman) public key system.

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Cryptography

In Transposition crypto system message is coded using transposition of alphabets.

Message : this is a secret between us

Encrypted 1 : htsi si a esrcte ebwteen su (2 alphabets are grouped and interchanged it's position)

Encrypted 2 : htsisiaesrcteebwteensu (2 alphabets are grouped and interchanged it's position. Space is removed fronm the coded word).

Encrypted 3 : htsi siae srct eebw teen su (2 alphabets are grouped and interchanged it's position. Then it is grouped with 4 alphabets).

Two or three or four rail system code

Message : this is a secret between us

Encrypting using two rail system

t i i a e r t e w e u
hs s s c e b t e n s

Encrypted message : tiiaerteweuhssscebtens or group it as tiiaert eweuhs ssceb tens

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Substitution ciphers : Here each letter reains it's position, but is substituted by another letter. A three place shift left forms the cipher in the example below.

Plain alphabet : a b c d e f g h i j k l m n o p q r s t u v w x y z

Cipher alphabet : d e f g h i j k l m n o p q r s t u v w x y z a b c

Message : this is our secret

Encrypted message : vjku ku qwt ugetgv

Crypt analyst uses short cut techniques like frequency analysis to decrypt (decipher) a message. The frequency of occurance of English alphabets in a message are as etaonrlshdifcmugpywbvkrjqz.

So 'e' is the most frequently used alphabet, while 'z' is used less. Code books are used to decode messages. Normally, there will be an understanding between the sender and receiver about the code of the algorithm used in encrypting.

e.g.- Lion means Head of the organization, off shoot means department.

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Vignare square, is an excellent cryptostystem.

Plain alphabet
a b c d e f g h i j k l m n o p q r s t u v w x y z

Cipher alphabet
b c d e f g h i j k l m n o p q r s t u v w x y z a
c d e f g h i j k l m n o p q r s t u v w x y z a b
d e f g h i j k l m n o p q r s t u v w x y z a b c
-----------------------------------------------------
u v w x y z a b c d e f g h i j k l m n o p q r s t
-----------------------------------------------------
a b c d e f g h i j k l m n o p q r s t u v w x y z

Ciphering
Message : i love you (selected for simplicity)

Keyword : u want win (it should be similar to the message in alphabet count)

Cipher text : c haix uwh

Here the message's 'i' is coded using keyword's 'u' with the help of Vignare square. Consider the last line's alpahbet 'i' and the line starting with keyword 'u'. The intercept gives 'c'. Similarly other alphabets are coded.

Try the above method of coding using another keyword plane plane. Decoding is difficult without knowing the keyword.

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Data Encryption System

Based on the IBM techniques the National Bureau of Standards (USA) developed standard cipher system for commercial use named as DES - Data Encryption System. 64/128 bit key encryption make decoding difficult in DES. Still, it can be cracked by today's powerful PCs connected parallelly equipped with special softwares. Bigger the key, stronger is the
encryption. For most secure transaction, use 512 bit key.

RSA public key crypto system uses different keys for encryption and decryption. In RSA system key used for coding is called public key as it is available to public while the key used for decoding is a secret one - private key. As RSA is too slow (coding and decoding), so it is used to code the key of DES.

Cryptographic algorithms

Symmetric key : IDEA, DES, Tripple DES, Blowfish, RC4, RC5 etc.
Public key : RSA, Elgamal, DSS, Diffie-Hellman key exchange, MD5, SHA etc.

Cryptographic systems in use for E-mail are Secure Socket Layer (SSL), Pretty Good Privacy (PGP), Multipurpose Internet Mail Extensions (MIME) etc.

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Virus threat

Before opening (unzipping) E-mail attachments, Floppy or CD scan it for viruses. Virus e-mail attachments has file extensions like .vbs, .hta, .ocx, .shs etc. Common viruses are written to exploit softwares like MS Word and Outlook.

Formatting cannot remove boot sector viruses like 'stoned'. Use anti virus software to remove the virus. Virus fills a PC with it's own copy while a Worm replicate only to new computers through networks. Stealth viruses try to hide from OS and anti virus software while retro virus attacks the anti virus software and can disable it's files.

Info on Virus hoax : www.vmyths.com, www.icsalabs.com, www.virusbtn.com

Anti virus software : www.symantec.com, www.f-secure.com, www.antivirus.com

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Computer Security

Computer can accept 40 to 80 characters as password. Construct a complicated password with alpha numerals and special characters, so that cracking the password will be difficult. Normal passwords are cracked with built in dictionary. Use acronyms related to self as password. e.g. - date of birth, first 3 letters of name, last 4 letters of favorite movie etc.

A 36 character password takes minimum 12*10^8 years to discover !. Use truly random combination, hard to remember & longer passwords. Change the default password at the earliest. e.g. - system, test, demo, instrument, hello, admin, guest, sysadmin etc.

In windows 95, Escape key bypasses the password.

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Computer Security

Change password after a specified time period. Store the info and passwords at a different place in a file with password to open (Password filename with extension removed : 9instma). Information can be buried in vast amount of other data.

Two words can be combined to form a password. e.g. - demoment takes 1140 year to crack.

Mix initials with an reverse date. e.g. - BZpY2002bef10 takes 12*10^7 year to discover.

Line of a poem or poems. e.g. - orayiramkinakkalalhalleluya takes 3*10^21 year to discover !.

Physical threats to data are theft, vengeance of an employee - dust, magnetism, breaking, lightning, tea, scratches and even urination ! etc., fire, bombing, electromagnetic pulse due to nuclear explosions, power fluctuations, temperature variations, humidity, static electricity (due to friction - carpets, shoes and earthing are remedies).

Data can be secured using offsite data storage, sonar intruder alarm, identification of employee using one or more of the following - fingerprint, voice, identity card, weight, writing style, colour of eye, geometry of hand, secret codes etc.

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Encryption (making codes)

n th alphabet in a word is encrypted using an integer m. Such action will be repeated p times. Deciphering (decoding) is done using key or computer programs. Computer generated random numbers can also be used.

'Cat' will be coded as 'Knv' using the random numbers (8, 13, 2).

Once a standard coding system is made, it is benchmarked by experts. Encrypted communication using computer softwares lie DES (Data Encryption Standard), 3DES and PKE are difficult to crack.

Transfer of encrypted message : Remove n th letter from each word and send it separate.