Description
Q1. (15%) A sentence is encrypted using substitution cipher. Following is the encrypted
sentence (spaces between words are suppressed):
ftqdq uezae gotft uzsme msdqm ffmxq zfiuf tagfs dqmfi uxxba iqd
Analyze the encryption to answer the following questions:
(a) What is the substitution being used in the above cipher?
(b) Recover the cipher text into plain text.
Q2. (15%) Suppose that the cipher text “ssthiihttrefissaensigmtncuoforbyueerscirrotycues” is
encrypted using transposition cipher. The encryption key (permutation) is � =
(6 4 1 2 3 5 8 7).
(a) What is the inverse permutation (decryption key)?
(b) Decrypt the cipher text into plain text.
Q3. (40%) Referring to the lecture notes on DES, there are one Expansion Permutation (Table1),
eight Substitution S-Boxes and one Permutation P-Box (Table 2) in the function f(Ki, Ri) for
round i in DES encryption. Given that the input plain text is A7E2BC3FD4C896D2 and the
encryption key is 1A5D6D895B4B66DB in hexadecimal representation. Implement round 1
encryption manually and list L1 and R1. The initial permutation for input is shown in table 3.
Table 1: Expansion Permutation
Table 2: Permutation P-Box
Table 3: Input Permutation
Q4. (30%) An English prose quotation is encrypted with an unknown method. Below is the
encrypted quotation (where spaces between words are suppressed).
fjwvs yfvbl hfwdu skevm wiodm bmiff wmhhu vzsxj iqjvs zfvhv
bvvjp hepqe dfrjs swtif zolmp hzzhz xiyxe wliem wrhww ubufi
ylubh rbryt jdths revbr rwwjl hkcvi wyofd jimuw zcfwi csjka
xiuvz osren kvdsg jzltd svucf lzsvm swyfg yhbdj ssrbh gkvwt
bwlww umtfd erkjp lxdhz vfybv ojwba rrikx suozo kidou vrsrj
hdlum vbfvv oleun kvssw uuvzo kyngl ktgpm izzby mumdt qwwtc
rehgx iywis sxzii raaxz uquqg sqyur hasou xjhje mcdzg sqfge
vfgju bhtce qphzv odxii ieolm phvzb oljwk kvwgp gpfbo ibfwy
vweem rwugz flqds fxnyh kwfkt jufja hfnkv asmoz riiej plffc
hisuw zcfev mwiod mbbdj sfisa hkwue mfbgi jwvyg kvwgb ovvcx
monhi bsxji qrzlv bxhcw tisuo zgsxj iqrik xsuoz odien kvtgv
nuwzc fsgnk vqsms hvxfg yququ okmbj dtwxm dyffb gqjwf fchis
uwzcf mucvr awqcy uftll fiuxo fmtuw zcfjp lhtcf sncft cgtfl
dkwgr bhgus nimis dsfxb hgkvw aplou hjeey riusr jtdkw grubh
issvf mhmsj emgda cjfjf dksje mzuvs lvbxh rujif ghehk evmwi
odmbb djdmv tohua gwulh tsfxm swyss ytnur zaevh lksvw uuwvg
xvfyw iovib auvse ionde ruppm hisus oipzq jimuw zcfwx cwybw
aaydc ofhbz rlbvm oapva tiswr lblvz iikvw yocwv rfeuc regsy
tnurz aebfv fasmo ndzbk eocqk sjrbn lfbsp bcggf gksup lbvis
qkzqz wpghj wpxzw rlblv jyvis uijph rgkmt ndeqw xiyel ryiuj
ufjah fmrms jxxid erslb fiswd pjiqw cjhfp hcchq fhwrg kmtnd
eqwet usvfu iondx sgjhx skvaw diqkf afvnl fbawm yvjhz eonkr
hgjub hlbem mfheb aynxh msdsq ghehy sbfv
Analyze the encryption to answer the following questions:
(a) What type of cipher is it? (Monoalphabetic / Polyalphabetic)
(b) Give the permutation(s) (if any) or the substitution(s) used in the cipher.
(c) Recover the cipher text into plain text.
In your answers, you should show the detailed steps of your solution instead of listing the
plain text only.
