Cryptography Reference
In-Depth Information
We look at this file to see where we find this text string, using a hexdump
program (the first four characters give the hexadecimal address from the begin-
ning of the file, followed by 16 characters both in hexadecimal and ASCII
representations).
..'X.P#....S..#
|
0650
00 e7 27 58 02 50 23 00
01 d1 9f 53 ad 08 23 7c
0660
00 67 00 00 00 00 00 41
41 41 41 41 41 41 41 41
.g.....AAAAAAAAA
0670
41 41 41 41 41 41 41 41
41 41 41 41 41 41 41 41
AAAAAAAAAAAAAAAA
*
0690
41 41 41 41 41 41 41 41
41 41 41 0a 41 41 41 41
AAAAAAAAAAA.AAAA
06a0
41 41 41 41 41 41 41 41
41 41 41 41 41 41 41 41
AAAAAAAAAAAAAAAA
*
Now, let's encrypt this file. The trick to be found here is to again select 'A' as
the password. The part of the file considered here now looks as follows:
.."
\
.V*...._..2l
0650
03 e5 22 5c 05 56 2a 08
0a db 92 5f a2 06 32 6c
.u.....YZ[
\
]^_'a
0660
13 75 15 14 17 16 19 59
5a 5b 5c 5d 5e 5f 60 61
0670
62 63 64 65 66 67 68 69
6a 6b 6c 6d 6e 6f 70 71
bcdefghijklmnopq
rstuvwxyz{
|
}
∼
...
0680
72 73 74 75 76 77 78 79
7a 7b 7c 7d 7e 7f 80 81
0690
82 83 84 85 86 87 88 89
8a 8b 8c c6 8e 8f 90 91
................
06a0
92 93 94 95 96 97 98 99
9a 9b 9c 9d 9e 9f a0 a1
................
It virtually leaps to your eyes that there are ascending numbers, which is not
the case when selecting 'B' for the password:
..!_.U)....
\
..1o
0650
00 e6 21 5f 06 55 29 0b
09 d8 91 5c a1 05 31 6f
.v.....ZYX_
\
]
\
cb
0660
10 76 16 17 14 15 1a 5a
59 58 5f 5e 5d 5c 63 62
0670
61 60 67 66 65 64 6b 6a
69 68 6f 6e 6d 6c 73 72
a'gfedkjihonmlsr
qpwvut{zyx.
∼
}
|
..
0680
71 70 77 76 75 74 7b 7a
79 78 7f 7e 7d 7c 83 82
0690
81 80 87 86 85 84 8b 8a
89 88 8f c5 8d 8c 93 92
................
06a0
91 90 97 96 95 94 9b 9a
99 98 9f 9e 9d 9c a3 a2
................
Obviously, the two 'A' characters have somehow 'lifted themselves off', but
not by subtraction, for then the last file would look different: the difference
between 'A' and 'B' is 1, and this would probably not have had such a big
influence. It seems that the plaintext is XORed with the keyword, and an
ascending number sequence is additionally superimposed. Let's find out what
the outcome would be if we used the password 'AB':
