Added RSA Algorithm used in cryptography (#61)

* Added RSA Algorithm

* Update README.md

* Create README.md

* Update README.md

* Add files via upload

* Update README.md

* Added RSA Algorithm

Co-authored-by: Ayush Bhardwaj <classicayush@gmail.com>

README.md

@@ -67,6 +67,7 @@ So far, the following projects have been integrated to this repo:
 |[Youtube video downloader](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/Youtube_Video_Downloader)|[Christopher He](https://github.com/hecris)|
 |[Zabbix API](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/zabbix_api)|[msg4sunny](https://github.com/msg4sunny)|
 |[Zip password cracker](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/zip_password_cracker)|[umar abdullahi](https://github.com/umarbrowser)|
+|[RSA Algorithm](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/RSA_Algorithm)|[Chinmay Rane](https://github.com/Chinmayrane16)
 |[CLI Calculator](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/cli_calculator)|[Willian GL](https://github.com/williangl) |
 |[Find PhoneNumber in String](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/Find-PhoneNumber-in-String)|[Austin Zuniga](https://github.com/AustinZuniga)|
 |[IMDB TV Series Info Extractor](https://github.com/hastagAB/Awesome-Python-Scripts/tree/master/imdb_episode_ratings)|[Yash Raj Sarrof](https://github.com/yashYRS) |

RSA_Algorithm/README.md

@@ -0,0 +1,25 @@
+# RSA Algorithm
+* Python script that encrypts and decrypts a text based on [RSA algorithm](https://people.csail.mit.edu/rivest/Rsapaper.pdf)
+* It involves the concept of modular arithmatic and euler's theorem.
+* It is also based on the idea that factorizing large numbers requires years.
+* Here, the (a,n) are kept public and (p,q,b) are kept private.
+
+![](https://github.com/Chinmayrane16/Awesome-Python-Scripts/blob/master/RSA_Algorithm/RSA_Algorithm.png)
+
+## Usage
+For Windows users:
+
+```bash
+$ python RSA_Algorithm.py
+```
+
+For Mac/Linux/Unix users:
+
+```bash
+$ ./RSA_Algorithm.py
+```
+
+## References
+[Blog](https://www.di-mgt.com.au/rsa_alg.html) <br>
+[Paper](https://people.csail.mit.edu/rivest/Rsapaper.pdf) <br>
+[Video](https://www.youtube.com/watch?v=wXB-V_Keiu8)

RSA_Algorithm/RSA_algorithm.py

@@ -0,0 +1,185 @@
+"""
+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