Hello. And Welcome back.
The last time we met (in the last post), we were talking about Caesar Cipher, a classical technique in which all the letters of the message are shifted by some number between 1 to 25, and the resultant text becomes unreadable at first glance, and the message gets hidden in that ciphertext.
That's not much secure. Not especially when we have a fast calculating machine like 'Computer'.
In the Brute force attack, you take the ciphertext (with cunning intention of cracking it), and then,
you try to enlist all the possible combinations of plaintext that it could've been possibly derived from.
In other words, you try to decrypt the message repeatedly, using all the keys from 1 to 25 (because you don't know which is the 'acutal' key!), until you get 'something' that makes sense. For example:
Suppose you got a message "VORD GRGVIJ CVRBVU RK RYR.TFD",
and you suspect it to be encrypted using Caesar Cipher.
So! What do you do!
You repeatedly try deciphering it using each key from 1 to 25, which in the end, gives you something like this:
1 UNQC FQFUHI BUQAUT QJ QXQ.SEC
2 TMPB EPETGH ATPZTS PI PWP.RDB
3 SLOA DODSFG ZSOYSR OH OVO.QCA
4 RKNZ CNCREF YRNXRQ NG NUN.PBZ
5 QJMY BMBQDE XQMWQP MF MTM.OAY
6 PILX ALAPCD WPLVPO LE LSL.NZX
7 OHKW ZKZOBC VOKUON KD KRK.MYW
8 NGJV YJYNAB UNJTNM JC JQJ.LXV
9 MFIU XIXMZA TMISML IB IPI.KWU
10 LEHT WHWLYZ SLHRLK HA HOH.JVT
11 KDGS VGVKXY RKGQKJ GZ GNG.IUS
12 JCFR UFUJWX QJFPJI FY FMF.HTR
13 IBEQ TETIVW PIEOIH EX ELE.GSQ
14 HADP SDSHUV OHDNHG DW DKD.FRP
15 GZCO RCRGTU NGCMGF CV CJC.EQO
16 FYBN QBQFST MFBLFE BU BIB.DPN
17 EXAM PAPERS LEAKED AT AHA.COM
18 DWZL OZODQR KDZJDC ZS ZGZ.BNL
19 CVYK NYNCPQ JCYICB YR YFY.AMK
20 BUXJ MXMBOP IBXHBA XQ XEX.ZLJ
21 ATWI LWLANO HAWGAZ WP WDW.YKI
22 ZSVH KVKZMN GZVFZY VO VCV.XJH
23 YRUG JUJYLM FYUEYX UN UBU.WIG
24 XQTF ITIXKL EXTDXW TM TAT.VHF
25 WPSE HSHWJK DWSCWV SL SZS.UGE
And, with close inspection, you find that the row at Key=17 makes some sense in English. (some blasting sense indeed!)
That's it. Using 'Brute Force Attack', you have successfully done the discovery of plaintext from some originally gibberish ciphertext.
This indeed proves, how 'fragile' caesar cipher is.
Although, if it's coupled with some other technique or some advanced manipulation is done to the technique, a large message (like 100000 characters) can be somewhat difficult to crack for a human alone. But for the fast computers (and clever algorithms), it's still a very weak method.
Wait...wait... one more thing!
Most of the times, when we brute force a ciphertext encrypted using caesar cipher, we get only 1 'text-that-makes-sense' out of 25 possibilities; and we believe that one to be the original plaintext.
But, what if, after brute force, you find 2 or more 'texts-that-make-sense'. Which will you decide to be the original plaintext? Will you try to analyze the context? or will you try to go by your intuition? or, is such a case even possible?
Worth thinking, isn't it!
It's not that Caesar cipher is the only popular classical technique. In fact, there are many classical techniques which are more powerful and stronger. We'll discuss some of them.
But before that, we will look into two encoding/decoding techniques, which take some plaintext and turn them into some unreadable gibberish.
Hint: One of these techniques is very-very popular and still in use, where dots and dashes are used to encode a message....
... and even, transmit it using flashes of light, or beeps of sound!
... anyone getting that?
... yes! :-) Cool!
... what! no! :-(
OK. Never mind. We are going to discuss that later anyway. (after the post after this post.)
Bye till then.
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