Ported PHP cipher behaves differently than its Python counterpart

Solution:

I'm not sure how Python works, but you can't indefinitely add or subtract from the index of an array in PHP. Once you get to 0 and start subtracting more (assuming the indexes are zero-based and numerical), you're going to get an undefined offset error because that index doesn't exist. The same happens if you increase it more than the maximum index. You might want to do something like modulo to make sure that the value is always in the range of the indexes of the array.

I whipped up a quick PHP script that should do this:

function Offset($offset) {
    $array = ["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","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","1","2","3","4","5","6","7","8",
    "9","0",".",",","'","?","!","@","_","-"];

    // Make sure the offset is a +/- value of the indexes of $array
    // by taking the modulo
    $offset = $offset % (count($array)-1) ;

    // If it is a negative number, subtract it from the end instead
    if ($offset < 0) {
        $offset = count($array)-1 + $offset;
    }

    // Get the index from your array
    return $array[$offset];
}


for ($i=-200; $i<200; $i++) {
    echo "$i => ".(Offset($i))."<br>";
}
Copy code

This outputs:

-200 => K
-199 => L
-198 => M
-197 => N
-196 => O
-195 => P
-194 => Q
-193 => R
-192 => S
-191 => T
-190 => U
-189 => V
-188 => W
-187 => X
-186 => Y
-185 => Z
-184 => a
-183 => b
-182 => c
-181 => d
-180 => e
-179 => f
-178 => g
-177 => h
-176 => i
-175 => j
-174 => k
-173 => l
-172 => m
-171 => n
-170 => o
-169 => p
-168 => q
-167 => r
-166 => s
-165 => t
-164 => u
-163 => v
-162 => w
-161 => x
-160 => y
-159 => z
-158 => 1
-157 => 2
-156 => 3
-155 => 4
-154 => 5
-153 => 6
-152 => 7
-151 => 8
-150 => 9
-149 => 0
-148 => .
-147 => ,
-146 => '
-145 => ?
-144 => !
-143 => @
-142 => _
-141 => -
-140 => A
-139 => B
-138 => C
-137 => D
-136 => E
-135 => F
-134 => G
-133 => H
-132 => I
-131 => J
-130 => K
-129 => L
-128 => M
-127 => N
-126 => O
-125 => P
-124 => Q
-123 => R
-122 => S
-121 => T
-120 => U
-119 => V
-118 => W
-117 => X
-116 => Y
-115 => Z
-114 => a
-113 => b
-112 => c
-111 => d
-110 => e
-109 => f
-108 => g
-107 => h
-106 => i
-105 => j
-104 => k
-103 => l
-102 => m
-101 => n
-100 => o
-99 => p
-98 => q
-97 => r
-96 => s
-95 => t
-94 => u
-93 => v
-92 => w
-91 => x
-90 => y
-89 => z
-88 => 1
-87 => 2
-86 => 3
-85 => 4
-84 => 5
-83 => 6
-82 => 7
-81 => 8
-80 => 9
-79 => 0
-78 => .
-77 => ,
-76 => '
-75 => ?
-74 => !
-73 => @
-72 => _
-71 => -
-70 => A
-69 => B
-68 => C
-67 => D
-66 => E
-65 => F
-64 => G
-63 => H
-62 => I
-61 => J
-60 => K
-59 => L
-58 => M
-57 => N
-56 => O
-55 => P
-54 => Q
-53 => R
-52 => S
-51 => T
-50 => U
-49 => V
-48 => W
-47 => X
-46 => Y
-45 => Z
-44 => a
-43 => b
-42 => c
-41 => d
-40 => e
-39 => f
-38 => g
-37 => h
-36 => i
-35 => j
-34 => k
-33 => l
-32 => m
-31 => n
-30 => o
-29 => p
-28 => q
-27 => r
-26 => s
-25 => t
-24 => u
-23 => v
-22 => w
-21 => x
-20 => y
-19 => z
-18 => 1
-17 => 2
-16 => 3
-15 => 4
-14 => 5
-13 => 6
-12 => 7
-11 => 8
-10 => 9
-9 => 0
-8 => .
-7 => ,
-6 => '
-5 => ?
-4 => !
-3 => @
-2 => _
-1 => -
0 => A
1 => B
2 => C
3 => D
4 => E
5 => F
6 => G
7 => H
8 => I
9 => J
10 => K
11 => L
12 => M
13 => N
14 => O
15 => P
16 => Q
17 => R
18 => S
19 => T
20 => U
21 => V
22 => W
23 => X
24 => Y
25 => Z
26 => a
27 => b
28 => c
29 => d
30 => e
31 => f
32 => g
33 => h
34 => i
35 => j
36 => k
37 => l
38 => m
39 => n
40 => o
41 => p
42 => q
43 => r
44 => s
45 => t
46 => u
47 => v
48 => w
49 => x
50 => y
51 => z
52 => 1
53 => 2
54 => 3
55 => 4
56 => 5
57 => 6
58 => 7
59 => 8
60 => 9
61 => 0
62 => .
63 => ,
64 => '
65 => ?
66 => !
67 => @
68 => _
69 => -
70 => A
71 => B
72 => C
73 => D
74 => E
75 => F
76 => G
77 => H
78 => I
79 => J
80 => K
81 => L
82 => M
83 => N
84 => O
85 => P
86 => Q
87 => R
88 => S
89 => T
90 => U
91 => V
92 => W
93 => X
94 => Y
95 => Z
96 => a
97 => b
98 => c
99 => d
100 => e
101 => f
102 => g
103 => h
104 => i
105 => j
106 => k
107 => l
108 => m
109 => n
110 => o
111 => p
112 => q
113 => r
114 => s
115 => t
116 => u
117 => v
118 => w
119 => x
120 => y
121 => z
122 => 1
123 => 2
124 => 3
125 => 4
126 => 5
127 => 6
128 => 7
129 => 8
130 => 9
131 => 0
132 => .
133 => ,
134 => '
135 => ?
136 => !
137 => @
138 => _
139 => -
140 => A
141 => B
142 => C
143 => D
144 => E
145 => F
146 => G
147 => H
148 => I
149 => J
150 => K
151 => L
152 => M
153 => N
154 => O
155 => P
156 => Q
157 => R
158 => S
159 => T
160 => U
161 => V
162 => W
163 => X
164 => Y
165 => Z
166 => a
167 => b
168 => c
169 => d
170 => e
171 => f
172 => g
173 => h
174 => i
175 => j
176 => k
177 => l
178 => m
179 => n
180 => o
181 => p
182 => q
183 => r
184 => s
185 => t
186 => u
187 => v
188 => w
189 => x
190 => y
191 => z
192 => 1
193 => 2
194 => 3
195 => 4
196 => 5
197 => 6
198 => 7
199 => 8
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