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RSA_algorithm.py
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185 lines (157 loc) · 5.08 KB
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"""
For more information on the algorithm, refer the following links:
https://www.di-mgt.com.au/rsa_alg.html
https://people.csail.mit.edu/rivest/Rsapaper.pdf
https://www.youtube.com/watch?v=wXB-V_Keiu8
"""
def isPrime(n):
prime = [True for i in range(n+1)]
p = 2
while p*p<=n:
if prime[p]==True:
for i in range(p*p,n+1,p):
prime[i]=False
p+=1
return prime[n]
def gcd(a,b):
while b!=0:
r = a%b
a=b
b=r
return a
def Multiplicative_inverse(a,b):
s1 = 1
s2 = 0
m = b
while b!=0:
q=a//b
r=a%b
a=b
b=r
s=s1-q*s2
s1=s2
s2=s
if s1<0:
s1+=m
return s1
def powermod(x,y,p):
res = 1
x = x%p
while (y>0):
if (y%2) == 1:
res = (res*x)%p
y = y//2
x = (x*x)%p
return res
if __name__ == '__main__':
while (True):
res = input('Do you want to enter prime numbers (y) or let the algorithm do it for you (n) or exit (e)? (y/n/e): ')
if res == 'y':
while True:
p = 13
p = int(input('Enter a prime number: '))
if isPrime(p):
break
else:
print(p,'is not a prime number')
continue
while True:
q = 17
q = int(input('Enter a different prime number: '))
if isPrime(q) and (p*q>26):
break
else:
print('Both the prime numbers are same!! or product of both the prime numbers is less than 26!!')
continue
n = p*q
phi_n = (p-1)*(q-1)
a = 19
while True:
a = int(input('Enter a number such that Greatest Common Divisor of that number with '+ str(phi_n) + ' is 1: '))
if gcd(a,phi_n)!=1:
continue
else:
break
b = Multiplicative_inverse(a,phi_n)
message = input('Enter the message to be encrypted (lower case): ')
message = message.lower()
encrypted_string = ""
encrypted_num = []
for i in range(len(message)):
ch = message[i]
if ch!=' ':
m = ord(ch) - 97
e = powermod(m,a,n)
encrypted_num.append(e)
encrypted_string += chr(e%26 + 97)
else:
encrypted_string +=' '
print('Encrypted message is:', encrypted_string)
print(encrypted_num)
res = input("Do you want to decrypt it too? (y/n): ")
if res == 'y':
decrypted = ''
j=0
for i in range(len(encrypted_string)):
ch = message[i]
if ch != ' ':
e = encrypted_num[j]
m = powermod(e,b,n)
ch = chr(m+97)
decrypted+=ch
j+=1
else:
decrypted+=' '
print("Decrypted message is:",decrypted)
else:
ans = input("Do you want to continue? (y/n): ")
if ans == 'y':
continue
else:
break
elif res == 'n':
p = 13
q = 17
n = p*q
a = 5
b = 77
message = input('Enter the message to be encrypted (lower case): ')
message = message.lower()
encrypted_string = ""
encrypted_num = []
for i in range(len(message)):
ch = message[i]
if ch!=' ':
m = ord(ch) - 97
e = powermod(m,a,n)
encrypted_num.append(e)
encrypted_string += chr(e%26 + 97)
else:
encrypted_string +=' '
print('Encrypted message is:', encrypted_string)
res = input("Do you want to decrypt it too? (y/n): ")
if res == 'y':
decrypted = ''
j=0
for i in range(len(encrypted_string)):
ch = encrypted_string[i]
if ch != ' ':
e = encrypted_num[j]
m = powermod(e,b,n)
ch = chr(m+97)
decrypted+=ch
j+=1
else:
decrypted+=' '
print("Decrypted message is:",decrypted)
else:
ans = input("Do you want to continue? (y/n): ")
if ans == 'y':
continue
else:
break
elif res == 'e':
break
else:
print('Invalid command!')
continue