3.5
6 bit string (pre-encryption)
J
A
_
U
10
1
0
21
.
27
X
24
U
21
!
30
01010 00001
00000 10101
11011
11000 10101
11110
0101
0100
0101
1101
0010
0000
Encryption keys:
1010 0111 0011
10
00
10
(init)
42
28
14
28
0111
00
14
0011
10
0
0000
00
Encrypted 6 bit string
01010 00000 01000
0
0
0
01110 00111 00000
0
0
0
00100 00111 01000
0
0
0
0010 0011
0100
0001
1110
1011
0000
00
1100
10
1001
00
0101
10
0010
00
1110
10
1011
00
0
50
36
22
8
58
44
50
1100
10
36
1001
00
22
0101
10
8
0010
00
58
1110
10
44
1011
00
30
0111
10
00010
0
11001
0
11011
0
1101
01010
0
10010
0
11000
0
1100
11010
0
01011
0
10001
0
1000
11100
0
00100
0
11000
0
1100
00100
0
11101
0
11001
0
1100
10110
0
10110
0
00000
0
0000
1110
Uitleg
Omzetten
naar
decimale
represent
atie
Omzetten
naar binair
Omzetten
naar 4 bit
strings
Omzetten naar
decimaal
+50 mod 64
Omzetten naar
binair
11100
0
01111
0
10011
0
1001
string
key
XOR
Encrypted
string
3.6
3.7 (bonus)
3.8
The message sent is some sort of a welcoming message, so we can guess some of the formal first
and last lines of the encrypted message: The first line could be something like ‘welcome customer,’
‘dear mr.x.’ In this case, ‘dear customer’ matches the amount of characters on the first line.
HYNZQZLPSZXV
SILTSTEJCGHTPAPPHQACZWOEEHREQZLPSZXVKJLEAQ
MZLWIHTJVRTHPLTUZQXNRZHMXZIPKCLXTQBAJIHZAJLOETX
YOMYIMAYLFMQWXPORRAKVVGREYWPMGXYQPYR
JNSXPCISHLWIHTJYFXCKYCRSDWIAIZXXYVRMOACQQFMRS
CZWATPIPHQIYYKQMXCBVKNMDYF
KICECFG
MGGRKCRIWRL
HYNZQZLPSZXV
Dear customer
This translates to the key; eunioftwe
A guess we made is that a part of the key is: e uni of twente
When we use this key to decode our text, we see that the key isn’t correct, yet we find some
valuable information:
dearcustomer
ooyleolnytoplgchtlhgvjvaanewcustomergpywml
tdhjpdppijfcwpphgmtterthedecryhdginvqmdmhfhurlj
tvquvtwursecretkeywgbiydzfalzntuwcqd
euwtcjeonyoucanuseygepjeydmwvgtteijyjhgmdminy
privatecomeelcchegxirjijlx
wdjiysn
icmecompany
The last line looks awfully familiar to the company name; acme company. The line above it could be
a formal ending of the letter. Our guess is that the line can be decrypted to ‘regards’
So;
KICECFG
Regards
MGGRKCRIWRL
Acme company
When we use the ceasar system on each character, we get that the key used for this bit is:
‘tewelcomeunioftwen’
When we look back to the key we got from the first line, we find that part of the key matches.
‘tewelcomeunioftwen’
Considering that the key has to start with ‘eunioftwente’, we guess that the key must be
‘eunioftwentewelcom’
When we decrypt using this key, we get:
dearcustomer
wearehappytowelcomeyouasanewcustomerofacme
ifyoucanreadthisletterthedecryptionofourmessage
usingyoursecretkeyworkedsuccessfully
fromnowonyoucanuseyourpersonalsecretkeyforany
privatecommunicationwithus
regards
acmecompany
Which, with some formatting, looks like this:
Dear customer,
We are happy to welcome you as a new customer of ACME.
If you can read this letter the decryption of our message using your secret key worked
successfully.
From now on you can use your personal secret key for any private communication with us.
Regards,
acme company
3.9