The topic is about blowfish concept that is used in COMPUTER NETWORKS AND SECURITY

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RC4 Algorithm :
 RC4 is a Stream cipher designed in 1987 by Ron Rivets for RSA Security.
 It is variable key –size stream cipher with byte-oriented operations.
 The algorithm is based on the use of random permutation.
o K- is Key
o S- S is State vector having plain text.
INITIALIZATION OF S :
To begin,the entriesof Sare setequal tothe valuesfrom0 through255 in ascendingorder;that
is, S[0] 0, S[1] 1, . . ., S[255] 255.
A temporary vector,T, is also created.
If the length of the key K is 256 bytes, then K is transferred to T. Otherwise, for a key of length
keylenbytes,the firstkeylenelements of T are copied from K, and then K is repeated as many times as
necessary to fill out T.These preliminary operations can be summarized as:
Figure 1 Initialization of S
Initial Permutation of S:
Nextwe use T to produce the initial permutationof S.Thisinvolvesstarting with S[0] and going through
to S[255] and, foreach S[i],swappingS[i]with another byte in S according to a scheme dictated by T[i]:
STREAM GENERATION: Once the S vector is initialized, the input key is no longer used. Stream
generationinvolvescyclingthroughall the elementsof S[i] and,foreachS[i],swappingS[i] with another
byte in S according to a scheme dictated by the current configuration of S. After S[255] is reached, the
process continues, starting over again at S[0]:

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BLOWFISH:
BLOWFISH isa symmetricblockcipherdevelopedbyBruce Schneier.BLOWFISH wasdesignedtohave
the followingcharacteristics:
Fast: Blowfishencryptsdataon 32 bit microprocessorsata rate of 18 clock cyclesperbyte.
Compact:Blowfishcanrun inlessthan5K of memory.
Simple:Blowfish’ssimple structure iseasytoimplementandeasesthe taskof determiningthe strength
of the algorithm.

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Variable secure:The keylengthisvariable andcanbe as longas 448 bits.Thisallowsa tradeoff between
higherspeedandhighersecurity.
Subkeyand S-Box Generation:
Blowfishmakesuse of akeythat rangesfrom32 bitsto 448 bits( 1 to 14 32 bitwords).
Keyisusedto generate 18 sub keyseachof 32 bitsandfour 8*32 S-boxes.
The keysare storedinK-array:

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IDEA (INTERNATIONAL DATA ENCRYPTION ALGORITHM):

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Keygenerationanduse of subkeys:
The processcontinuesforrestof the rounds.(Look additional informationforbetterclarification)
OperationsusedinEverysingle round:
1. Multiplication
2. Addition
3.Bitwise XOROperator

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ADDITIONAL INFORMATIONFOR BETTER UNDAERSTANDING OF ALGORITHM
What happensin each single round:

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