Cryptography and Information Assurance - Assignment Example

Cryptography Name: Course Tutor Date: Table of Contents 1. Encryption of “MEET ME TONIGHT using Cipher methods 3 Rail Fence cipher 3 Route cipher 4 Caesar cipher: 4 Atbash cipher: 4 Monoalphabetic substitution cipher: 5 Vigenère Cipher: 5 Playfair cipher 6 Homophonic Substitution: 7 Stream cipher using PRS: 8 One-time pad: 8 2. Caesar cipher and Vigenere cipher 9 3. Cracking the ciphertexts 10 4.Three substantially different random number generators 15 Linear congruential generators (LGC), 15 Multiple recursive generators (MRG): 15 Mersenne Twister: 16 References 16 1. Encryption of “MEET ME TONIGHT using Cipher methods The message “MEET ME TONIGHT” can Encrypted using the following methods of encryption methods Rail Fence cipher, Route Cipher, Caesar cipher, Atbash cipher, a monoalphabetic substitution cipher, Vigenere cipher, Playfair cipher, a Homophonic Substitution Cipher, Stream cipher using a psuedo-random sequence, and One-time pad. For each cipher as Rail Fence cipher a)To encrypt a message using the Rail Fence Cipher, we need to have a key, which for this cipher is the number of rows, the more rows the more your cipher text will be scattered from the original message. The length of the message needs to be at least twice the key, but preferably 3 times. b)After we select the key (which is 4) then we write the message in zigzag lines across the page, and then read off each row M T T E E O H E M N G T I To get the cipher text we read off each line in turn. c)The cipher text: “MTTEEOHEMNGTI”. Route cipher a)To encrypt a message using the Route Cipher, we need to have a key, which in this case is the size of the block and the route assigned. The route should be the same on encryption and decryption. We choose the key to be 4 columns because our message is too short and if we increase it we may end up with large chunks of plaintext in the right order within the ciphertext. The route starting from the top left, from top to bottom this will scatter the letter of the word across the cipher text. b)We write the message in rows lines across the table. To get the cipher text start reading down the columns. M E E T M E T O N I G H T X X X Because the message is not fit exactly we use X as a null. c)The cipher text: “MMNTEEIXETGXTOHX”. Caesar cipher: a)The original Caesar cipher has a shift of 3; but the shift cipher has a key from 1 to 25. The key here will be 15 so the most frequent alphabet in English text “e” will be the second frequent alphabet in English text “t” and this will add some security to the cipher against frequency analyzer attack. b)We shift each alphabet in the message by 15 so “M” will become “B” and “E” Will become “T” c)The cipher text: “BTTI BT IDCXVWI”. Atbash cipher: a)There is no key in this cipher; the cipher simply reverses the plaintext alphabet to create the cipher text alphabet or a shift of 25.  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 z y x w V u t s r q p O n m l k j i h g f e d c b a b)To encrypt the message “MEET ME TONIGHT”, no simply it’s like substitution cipher; we look into the table and substitute each alphabet with the cross ponding cipher alphabet. “M” will become “N” “E” will become “V” c)The cipher text: “NVVG NV GLMRTSG”. Monoalphabetic substitution cipher: a)This method is also known as a simple substitution cipher and depends on a fixed replacement structure whereby the substitution for each letter of the alphabet is fixed (Ilie, 2011). The key in this case is selected randomly thus enhancing security of the key. Moreover, through the restriction of key generation, unauthorized users cannot access data from device source by generating the key during runtime operations. Although the cipher is weak for cipher text only attack. An example is shown below; 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 q p o k I h w s e d c y x l u t b a g v j z r f n m b)The message MEET ME TONIGHT will be encrypt by replacing each letter of the message with the corresponding letter from randomly generated letters above for the alphabets. This will be done as “M” will be “X”, “E” will be “I”, V for T, U for O, L for N, W for G and S for H. c)This will give cipher text of “XIIV XI VUIYWSV”. Vigenère Cipher: a)To encrypt a message using the Vigenère Cipher, we need to have a key, which can be any phrases. The key will be repeated over and over until it is the same length as the plaintext. The key will be “CRYPTO” the key here is chosen to be 6 in the length this will give a good protection because the message is short, if the message were long the key should be more than 8 in the length . b)The idea about this method is to add the plain text to the key and take module 26. Where “A” is “0” and “Z” is “25”. 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 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Key C R Y P T O C R Y P T O C Text M E E T M E T O N I G H T cipher O V C I F S V F L X Z V V (M + C) % 26 = (12 + 2) % 26 = 14: O (Y + E) % 26 = (24 + 4) % 26 = (28) % 26 = 2: C c)The cipher text: “OVCI FS VFLXZVV”. Playfair cipher a)To encrypt a message using the Playfair cipher we need to have a key which in this case drawing up a  square (Ilie, 2011). It consists of 25 alphabets so we need to ignore one from the English alphabets either “Q” or “J”. Key: G H R E U N V T C B W P S L K Y Z A I Q X M D F O We just combine “I” and “J” to “I”. b)The encryption starts by split the plaintext up pairs of letters, if any letter left by itself at the end of the plaintext then inserts the letter "X" at the end. Message: MEET ME TONIGHT: ME ET MT TO NI GH TX Rules of encryption: 1) If the two letters appear in the same column in the square, then replace each letter by the letter of the right side in the square. 2) Otherwise, form the rectangle for which the two plaintext letters are two opposite corners. Then replace each plaintext letter with the letter that forms the other corner of the rectangle. ME: FH G H R E U N V T C B W P S L K Y Z A I Q X M D F O GH:HR G H R E U N V T C B W P S L K Y Z A I Q X M D F O c)The cipher text formed will be ” FHRC FH BDCYHRD” Homophonic Substitution: a)A Homophonic substitution cipher, is different from simple substitution cipher, it replaces plaintext with any of several different ciphertext letters. alphabet to represent the higher frequent alphabet like “I” and “t”.’ in this case numbers 0 to 9 to get the key and letter 'E' might be replaced by any of 5 different symbols. They are generally much more difficult to break than standard substitution ciphers. Key: b)The encryption here it’s just normal substitution but for the alphabet that has more than one cipher text we try to change the cipher text. “M” will be “G” “E” we can choose either “Z”,”7”,”2”,”1” or “1”. c)The cipher text:”GZ72Y G1 UQAVHC6. Stream cipher using PRS: a) Stream cipher is usually done bit by bit, but here for simplicity we will use as character by character. The key here is the PRG and the seeds. The key was chosen to be linear random generator just for simplicity and demonstration; in real application it should be change it to be more random and secure. 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 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Si+1=(a*Si+b) mod 25 S0: initial seeds. b) Choose a=6 , b=9 ,S0=11 S1= (6*11+9) mod 26 = 0 : A S2= (6*0+9) mod 26 = 9 : J S3= (6*9+9) mod 26 = 13 : N S4= (6*13+9) mod 26 = 12 : M S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 A J N M G U E I H B P Y D Cipher text = Mi+Si mod 26 = M+A mod 26 = (12 + 0) mod 26 = 4: M c) Cipher text: “MNRF SY XWUJVFW”. One-time pad: a)One-time pad is a type of stream cipher with the key should be used only one time and the key should be equal or garter than the message. Randomly we choose the key:”RGULAXBEVGHUI”. The key is taken from a random table after we applay module 26 on the numbers. b) Cipher text = Mi+Si mod 26 = M+S mod 26 = (12 + 17) mod 26 = 3: D c) Cipher text: “DKYE MB USIONBB”. 2. Caesar cipher and Vigenere cipher ANSWER: Stream cipher encrypt bits individually (bit by bit) this differ from block cipher that encrypt block of bits at once. Stream cipher is achieved by adding a bit from a key stream to a plaintext bit and takes the module of the sum. That lead us to the different usage to block and stream cipher, if we want a fast and real time encryption we will choose stream cipher rather block cipher. The key of the shift (or Caesar) cipher are constant for each letter on the plain text that’s make it a weak secure cipher. Because the key is constant it makes is an easy cipher to break either by brute force attack or by frequency analysis attack (cipher text only attack). The key of the Vigenère Cipher is repeated over and over until is the same length as the message. The more length of the key the more secure you will get. Actually if the key length is the same as the plain text length we will get a secure cipher (if the key has random properties). This cipher can be attack by try to guess a key length (try and error) then by apply frequency analysis to get the key.in general this cipher is not a secure cipher but it will gives more security that Caesar cipher. The key of the Pseudo-Random Stream ciphers is based on pseudo random number generator method that used to get the random number and the security is dependent on the PRG and its randomness.to attack this cipher is by attacking the PRG used on it. The length of the key of the OTP is the same as the plain text that’s make it a perfect secrecy although it’s not a practical. The attack on tis cipher is only by using brute force attack unless the key was used more than one then we can use the two time pad attack. 3. Cracking the ciphertexts Each of the following ciphertexts have been enciphered using historical ciphers: Caesar cipher, monoalphabetic substitution cipher (not Caesar cipher), Vigenere cipher, transposition cipher and Scytale cipher. Crack each of the ciphertexts; include details of your method of attack. If a computer program or online tool has been used/written include details of that program. ANSWER: One will begin by logging in into http://www.richkni.co.uk/php/crypta/freq.php decipher the characters Caesar cipher: Choose Caesar shifts in site mentioned above then type in the space provided “enter your ciphertext below” Cipher text: ” WH WG GWADZWQWHM WHGSZT GOWR VS AM SMSG HSZZ AS HVOH CB HVS WBGWRS CT MCIF ZSTH GVCS XIGH KVSFS HVS TWFSZWUVH GHFWYSG WH HVS ZSOHVSF WG GQCFSR PM GWL OZACGH DOFOZZSZ QIHG CPJWCIGZM HVSM VOJS PSSB QOIGSR PM GCASCBS KVC VOG JSFM QOFSZSGGZM GQFODSR FCIBR HVS SRUSG CT HVS GCZS WB CFRSF HC FSACJS QFIGHSR AIR TFCA WH VSBQS MCI GSS AM RCIPZS RSRIQHWCB HVOH MCI VOR PSSB CIH WB JWZS KSOHVSF OBR HVOH MCI VOR O DOFHWQIZOFZM AOZWUBOBH PCCH GZWHHWBU GDSQWASB CT HVS ZCBRCB GZOJSM OG HC MCIF DFOQHWQS WT O USBHZSAOB KOZYG WBHC AM FCCAG GASZZWBU CT WCRCTCFA KWHV O PZOQY AOFY CT BWHFOHS CT GWZJSF IDCB VWG FWUVH TCFSTWBUSF OBR O PIZUS CB HVS FWUVH GWRS CT VWG HCD VOH HC GVCK KVSFS VS VOG GSQFSHSR VWG GHSHVCGQCDSWAIGH PS RIZZ WBRSSR WT W RC BCH DFCBCIBQS VWA HC PS OB OQHWJS ASAPSF CT HVS ASRWQOZ DFCTSGGWCB” Caesar cipher is not easy to attack since there are 25 shift keys that mean even brute attack can’t crack it. Toughest two pairs are “WH” and “WG” so “W” it’s more likely to be “I”, for this assumption the shift will be 14. Plain text: “it is simplicity itself said he my eyes tell me that on the inside of your left shoe just where the firelight strikes it the leather is scored by six almost parallel cuts obviously they have been caused by someone who has very carelessly scraped round the edges of the sole in order to remove crusted mud from it hence you see my double deduction that you had been out in vile weather and that you had a particularly malignant boot slitting specimen of the London slavey as to your practice if a gentleman walks into my rooms smelling of iodoform with a black mark of nitrate of silver upon his right forefinger and a bulge on the right side of his top hat to show where he has secreted his stethoscopeimust be dull indeed if i do not pronounce him to be an active member of the medical profession” Monoalphabetic substitution cipher: Choose frequency analyser in site mentioned above then type in the space provided “enter your ciphertext below” Cipher text: “VS VPN XSSK UK JVS VPXUJ YD FUHVJUKH VUN QUQS PJ FPTQN PKB HPN LSJN CYW EPK NSS JVPJ UJ UN MWUJS EVPZZSB PFF BYOK YKS NUBS YD EYWZNS P TPJEV EYWFB KYJ VPIS BYKS JVPJ OVC NVYWFB P TPK VYFB P TPJEV JY JVS NUBS YD VUN QUQS XWJ CYW EPKKYJ FUHVJ UJ PJ P FPTQ OUJVYWJ HSJJUKH JVS XYOF EVPZZSB PKB UJ UN PFF YK JVS ZUHVJ NUBS YD JVS QUQS DZYT JVPJ U HPJVSZ JVPJ VS UN P FSDJ VPKBSB TPK CYW VYFB CYWZ YOK QUQS JY JVS FPTQ PKB NSS VYO KPJWZPFFC CYW XSUKH ZUHVJ VPKBSB VYFB JVS FSDJ NUBS JY JVS DFPTS CYW TUHVJ BY UJ YKES JVS YJVSZ OPC XWJ KYJ PN P EYKNJPKEC JVUN VPN PFOPCN XSSK VSFB NY JVSK VS VPN XUJJSK JVZYWHV VUN PTXSZ UJ JPRSN P TWNEWFPZ SKSZHSJUE DSFFYO PKB YKS OUJV P HYYB NSJ YD JSSJV JY BY JVPJ XWJ UD U PT KYJ TUNJPRSK U VSPZ VUT WQYK JVS NJPUZ NY OS NVPFF VPIS NYTSJVUKH TYZS UKJSZSNJUKH JVPK VUN QUQS JY NJWBC”. To crack this cipher we use cipher text only attack. By running online frequency analyzer (Decrypting Text - code breaking software, 2014), this online program will analyze the cipher text and give the frequency of occurrence of each letter. Found: To found “E” and “T” we have to check the most common frequency of the letters J: 12 %, S: 10.8. And we want to find “E” and “T”. We try to find “THE” one of the common three letters on English “JVS” happen 14 times So now we have “J” as “T”, “V” as “H” and “S” as “E”. Now we have to use trial and error to get the rest of them, one of helpful online tool (Decrypting Text - code breaking software, 2014b) can make you plug what you find and substitute it in the original cipher text and make the ones not found as dot. Letter “P” occur by itself so it will be “A”. The cipher “VS VPN” after you enter it to online tool will become “he hA.”, from this we can now that “N” is “S”. And so on to get the entire message. 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 d y f c l g h t n j q s w a p k e m i h u b o r Plain text: “HE HAS BEEN IN THE HABIT OF LIGHTING HIS PIPE AT LAMPS AND GAS JETS YOU CAN SEE THAT IT IS QUITE CHARRED ALL DOWN ONE SIDE OF COURSE A MATCH COULD NOT HAHE DONE THAT WHY SHOULD A MAN HOLD A MATCH TO THE SIDE OF HIS PIPE BUT YOU CANNOT LIGHT IT AT A LAMP WITHOUT GETTING THE BOWL CHARRED AND IT IS ALL ON THE RIGHT SIDE OF THE PIPE FROM THAT I GATHER THAT HE IS A LEFT HANDED MAN YOU HOLD YOUR OWN PIPE TO THE LAMP AND SEE HOW NATURALLY YOU BEING RIGHT HANDED HOLD THE LEFT SIDE TO THE FLAME YOU MIGHT DO IT ONCE THE OTHER WAY BUT NOT AS A CONSTANCY THIS HAS ALWAYS BEEN HELD SO THEN HE HAS BITTEN THROUGH HIS AMBER IT TAKES A MUSCULAR ENERGETIC FELLOW AND ONE WITH A GOOD SET OF TEETH TO DO THAT BUT IF I AM NOT MISTAKEN I HEAR HIM UPON THE STAIR SO WE SHALL HAHE SOMETHING MORE INTERESTING THAN HIS PIPE TO STUDY”. Vigenère Cipher: Choose Vigenère Cipher in site mentioned above then type in the space provided “enter your ciphertext below” Cipher text: “WPRR M WLVR PPTN ZV WZLZIH QOE SKPR AMCP WRIZD UAGDYSPMDFS NRS CAIMCR WVXW MRNMC QEIIG TF VX WLD ASI MERR UZR ZMHD HNVGTSBR WPRR ECO FBV ISE QSREOE W RLRR M HSOHPS YOG FT DPREZTNT XD JOH RDH SUI WLS AYGDEQ QT MY QEN LNQ E WTRRH CFRFI WLS YSDVEQ EUEEE QT MY AMVST SSG TN ZC BLD SMID I JEH NACEQWE BJ PYYGLXYG FPDHLL QN CENWDY HNW RWENVTO BHX XE IF SCWY QYGTNT XWP LNWI EHEIT OALW ISAG QN XEZSGJ HNW FFIGI GPTHVCPD FSBPTVQTD I JMHS TUEI TT AIKPR UES EHR JXCSG XWTNT XWLT V HXO WNW IZ WVVT EO ZV UZROIH HHB LPO TUI RLSR MC SAAH WP CNQT ZUG ECO AFWJCEF QT EHNX ISOHKW PVRVNEHVRV SAF FTPN QSCP NB XGLCR SU L CYYT SAF FTPN QMHNOIIGPD GLT NOZQXDSVSCYAVVT LNQ LXD WVJT SAII QPEA IMLMVRTO IA IKPRL APJ WVXWZUG ECJ LVKWE BRMCR TUVDHN HTDY TUI BLTGIG EHR WJDPVGXZNF SU HER TDWIPI ISEA VTDTRH JAOA CDFNT KDCOG AWZ AF CDF MNC GPMRQQPR FXPJEQ SKPR GMBP IA XWP OSJXNE GLPE NVKWE HVW GPMNMCTNT FTSIAH PYD UMH QRRRRS NNQT HEEI GPAYPN EHR SCWY GAD AOVRID WUMRS CBYAO SHKVPSG WJDPVGXZN OYI LS N QPETRV DQ FNGI T DVH CZT OIVTN JSGV UAXXW HR LPO GBRT LNQ LXD PRSEWE NVT ZF UYVFEASI PXGVPNTVSC MUG EH PNTPXDH VR HJMCEISY NRS ERNHXEIBR PD YBY PYD V EGP NBXWTNT APD FBYCO TB MBALVGPEE UMB TN NRN HAL ECO TUIGP TUI BLTGIG ORBTEPD V XJCN GS NZU ZV WZLZIH LS NFHZLHXTWY ZC ALSG LDAE VJ NZU SEXW MR XWPN ZC WZNBV PD WRPA LS ZC EZSVXXZN NVT QOEIKPR SSGQEVXTO”. By using [http://www.mygeocachingprofile.com/codebreaker.vigenerecipher.aspx] ,The idea here is to predict the length of the key (by try and error), then for each block you take the first letter and see the frequency of that letter; the most common one will be the decryption of letter “E”. So when we take block of 5 , the most frequent letter in the first letter of the block is t. So we have: t + (the first letter of the key) = e the first letter of the key = p. and we do the same for all the letters of the key. We found the key is “plane” Plain text: “here i have lain mr holmes for over nine weeks unconscious and raving with brain fever if it had not been for miss harrison here and for the doctor s care i should not be speaking to you now she has nursed me by day and a hired nurse has looked after me by night for in my mad fits i was capable of anything slowly my reason has cleared but it is only during the last three days that my memory has quite returned sometimes i wish that it never had the first thing that i did was to wire to mr forbes who had the case in hand he came out and assures me that though everything has been done no trace of a clue has been discovered the commissionnaire and his wife have been examined in every way without any light being thrown upon the matter the suspicions of wee police then rested upon young gorot who as you may remember stayed over time in the office that night his remaining behind and his French name were really the only two points which could suggest suspicion but as a matter of fact i did not begin work until he had gone and his people are of huguenot extraction but as english in sympathy and tradition as you and i are nothing was found to implicate him in any way and there the matter dropped i turn to you mr holmes as absolutely my last hope if you fail me then my honor as well as my position are forever forfeited” Transposition cipher: Choose Transposition cipher in site mentioned above then type in the space provided “enter your ciphertext below” Cipher text: “TYREVE APGNIH VESESS IHTYRE RAEWGN VETUOS IHTYRE AERBGN SK” Because they are blocks of six, one will use this tool [http://tholman.com/other/transposition/] until one gets a key of 543210 Plain text: “EVERY THING PASSES EVERY THING WEAR SOUT EVERY THING BREAKS”. Scytale cipher: Cipher text: “WOBESM TOEUYS EUEUIR VOLSSM MSIVFT TUPECE TBSSRL TRHEAT OVOOEC NWVERU RODIES IRENYN” By try and error with using [http://tholman.com/other/transposition/] the key found to be 8. Basically to decrypt this cipher, you start by assumption the key length say 8 , then you should take the first letter then ignore the 7 letters after it and take the eighth letter and ignore the 7 letters after it and take the eighth letter, do this until u reach the end of the cipher text. Then take the second letter for the cipher text ignore the 7 letters after it and take the eighth letter and ignore the 7 letters after it and take the eighth letter. You should do this until you complete all of the letters. Plaint text: “We improve ours elves by victories over our self, there must be contests and you must win”. 4.Three substantially different random number generators The methods to be discussed are Linear congruential generators, Multiple recursive generators and Mersenne Twister. This discussed as Linear congruential generators (LGC), Is an algorithm that produces a sequence of pseudo-randomized numbers calculated with a discontinuous linear equation.  This represented as Si+1=(a*Si+b) mod m Where a represents multiplier, b represents increment, S0 represents seed and m represents number space (random number Є [0 , m-1]) To produce a pseudo-random number this will extremely depend on choice of (a,b,m). If bad value are chosen LGC will not generate numbers on the full period [0,m-1] rather it will generate a set of numbers then will be repeated over and over again and some number will not be generated. To make sure that LGC produce the full set some condition must be meet. b and m  are relatively prime. a-1  is divisible by all prime factors of m. a-1 is a multiple of 4 if m is a multiple of 4. LGC does not have a property of highly randomness number generator. Multiple recursive generators (MRG): A MRG are multiple recursive generators of LGC’s. They are based on the following recurrences Si+1=(ai*Si+bi + ai-1*Si-1+bi-1 + ai-2*Si-2+bi-2 + … ) mod m MRG has a better randomness than LGC. Mersenne Twister: It’s one of the most widely used PRNG; it was the first PRNG to provide fast generation of high-quality pseudorandom integers. It works on finite set {0,1} , so the generated number will be a sequence of bits zeros or ones. Mersenne Twister passes numerous randomness tests that make it one of the best choice for high quality randomness. MT generates the bit vectors of fixed word size by the recurrence: n >m: fixed positive integers. xk ,k = 0,1,…sequence of bit vectorwith fixed width W. , concatenation of r most significant bits of Xk and w− r least significant bits of Xk+1 References Decrypting Text - code breaking software, 2014a. Frequency analizer. Retrieved December 6, 2014 Decrypting Text - code breaking software, 2014b. Letter replacment. Retrieved December 6, 2014 Read More