Merge pull request #2588 from Kalivarapubindusree/RSA

RSA_Algorithm_Script added

Author: avinashkranjan

RSA_Algorithm_Script/README.md

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+# RSA_Algorithm_Script
+
+Short description of package/script
+
+- This Script Was simple to setup
+- Just run the main file
+
+## Setup instructions
+
+Just Need to run the RSA_Algorithm_Script.py file and for running  python3 is must be installed! 
+
+## Detailed explanation of script, if needed
+
+This Script Is Only for RSA_Algorithm_Script use only!  

RSA_Algorithm_Script/RSA_Algorithm_Script.py

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+def is_prime(n):
+    if n < 2:
+        return False
+    for i in range(2, int(n**0.5) + 1):
+        if n % i == 0:
+            return False
+    return True
+
+def gcd(a, b):
+    while b != 0:
+        a, b = b, a % b
+    return a
+
+def multiplicative_inverse(a, b):
+    s1, s2, m = 1, 0, b
+    while b != 0:
+        q, r = divmod(a, b)
+        a, b = b, r
+        s1, s2 = s2, s1 - q * s2
+    return s1 % m
+
+def powermod(x, y, p):
+    res = 1
+    x = x % p
+    while y > 0:
+        if y % 2 == 1:
+            res = (res * x) % p
+        y //= 2
+        x = (x * x) % p
+    return res
+
+def 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 = int(input('Enter a prime number: '))
+                if is_prime(p):
+                    break
+                else:
+                    print(p, 'is not a prime number')
+            
+            while True:
+                q = int(input('Enter a different prime number: '))
+                if is_prime(q) and p * q > 26:
+                    break
+                else:
+                    print('Both prime numbers are the same or the product is less than 26!')
+            
+            n = p * q
+            phi_n = (p - 1) * (q - 1)
+            
+            while True:
+                a = int(input(f'Enter a number such that Greatest Common Divisor with {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): ').lower()
+
+            encrypted_string = ""
+            encrypted_num = []
+
+            for ch in message:
+                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 ch in encrypted_string:
+                    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, q, a, b = 13, 17, 5, 77
+            n = p * q
+            message = input('Enter the message to be encrypted (lower case): ').lower()
+
+            encrypted_string = ""
+            encrypted_num = []
+
+            for ch in message:
+                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 ch in encrypted_string:
+                    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
+
+if __name__ == '__main__':
+    main()