testing_grounds/rsa-dec.py at master · mshoffner2/testing_grounds · GitHub

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
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
# coding: utf-8
# In[1]:

import sys
import os
import math

#finding the modular exponent
def mod_exp(b,e,n):
    bbin=bin(e)[2:]
    #print(bbin)
    blen=len(bbin)
    temp=1
    b1=1
    for i in range(blen-1,-1,-1):
        #print(i)
        b=(b*b1)%n;
        b1=b
        #print(b)
        if bbin[i]=='1':
            temp=(temp*b)%n
            #print (temp)
    return temp

def rsa_dec(ciphertext, N, d, size_N):
    padded_msg = mod_exp(ciphertext, d, N)
    temp = hex(padded_msg)[2:]
    #print(temp)
    #gotta remove padding: check for null byte

    #find size of the padded message in bits
    #temp = math.log(padded_msg, 2)

    #print(int(temp))
    i = padded_msg.bit_length()
    #print(int(i))
    #convert to bytes
    i = i + (8 - (i % 8))
    #print(i)
    i = int(i)
    #print(i)
    i = i / 8
    #print "i"
    #print(i)
    #print int(i)
    i = int(i)
    #print(i)
    i = i - 1

    #search for the null byte marking the changeover from r bytes to message bytes
    #while(int(padded_msg/(2**(i*8))) % 256 != 0):
    #    i = i - 1
    #print "i"
    #print(i)
    #print(padded_msg/(2**(i*8)) % 256)

    #remove r
    #temp = hex(padded_msg)[2:]
    #print(temp)


    #result = padded_msg % (2**(i*8))
    #change back to hex, remove extra characters added
    result = padded_msg
    result = hex(result)[2:]
    i = 0#len(result)-1
    keep_going = 1

    while(keep_going == 1 and i < len(result) - 1):
        if(result[i] == '0' and result[i + 1] == '0'):
            keep_going = 0
        i = i + 2
    result = result[i:]
    result = int(result, 16)
    result = hex(result)[2:]
    #print "result"
    print(result)

    return(result)


key_f_name = ""
in_f_name = ""
out_f_name = ""

if len(sys.argv) != 7:
    print('usage: rsa-enc -k <key file> -i <input file> -o <output file>')
    exit()

if(sys.argv[1] == '-k'):
    key_f_name = sys.argv[2]
elif(sys.argv[3] == '-k'):
    key_f_name = sys.argv[4]
elif(sys.argv[5] == '-k'):
    key_f_name = sys.argv[6]
else:
    print('usage: rsa-enc -k <key file> -i <input file> -o <output file>')
    exit()

if(sys.argv[1] == '-i'):
    in_f_name = sys.argv[2]
elif(sys.argv[3] == '-i'):
    in_f_name = sys.argv[4]
elif(sys.argv[5] == '-i'):
    in_f_name = sys.argv[6]
else:
    print('usage: rsa-enc -k <key file> -i <input file> -o <output file>')
    exit()


if(sys.argv[1] == '-o'):
    out_f_name = sys.argv[2]
elif(sys.argv[3] == '-o'):
    out_f_name = sys.argv[4]
elif(sys.argv[5] == '-o'):
    out_f_name = sys.argv[6]
else:
    print('usage: rsa-enc -k <key file> -i <input file> -o <output file>')
    exit()


in_file = open(in_f_name, "r")
my_text = in_file.read()
in_file.close()

key_file = open(key_f_name, "r")
size_N = key_file.readline()
main_N = key_file.readline()
main_d = key_file.readline()
key_file.close()

main_N = int(main_N)
main_d = int(main_d)

result = rsa_dec(int(my_text), main_N, main_d, int(size_N))
#open and write to output file

out_file = open(out_f_name, "w")
out_file.write(result)
out_file.close()