https://github.com/sangamcse/computer-security
https://github.com/sangamcse/computer-security
Last synced: 2 months ago
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- Host: GitHub
- URL: https://github.com/sangamcse/computer-security
- Owner: sangamcse
- Created: 2019-05-25T10:54:42.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2019-05-25T10:54:59.000Z (almost 6 years ago)
- Last Synced: 2025-01-24T12:14:49.843Z (4 months ago)
- Language: Python
- Size: 3.91 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
## Assignment Computer Security
### 1. One Time Pad
---
```py
import string
abc = string.ascii_lowercase
one_time_pad = list(abc)
def encrypt(msg, key):
'''
Method to encrypt message using OTP.
:param msg: Plain message to encrypt
:param key: Key of encryption
:return: Encrypted cypher text
'''
ciphertext = ''
for idx, char in enumerate(msg):
charIdx = abc.index(char)
keyIdx = one_time_pad.index(key[idx])
cipher = (keyIdx + charIdx) % len(one_time_pad)
ciphertext += abc[cipher]
return ciphertext
def decrypt(ciphertext, key):
'''
Method to decrypt message using OTP.
:param ciphertext: Cypher text to decrypt
:param key: Key of decryption
:return: Decrypted plain text
'''
if ciphertext == '' or key == '':
return ''
charIdx = abc.index(ciphertext[0])
keyIdx = one_time_pad.index(key[0])
cipher = (charIdx - keyIdx) % len(one_time_pad)
char = abc[cipher]
return char + decrypt(ciphertext[1:], key[1:])
```
### 2. Stream Cipher
---
```py
msg = map(int, input("Enter the message: ").split(" "))
key = map(int, input("Enter key: ").split(" "))
encrypted = []
decrypted = []
for i in range(len(msg)):
encrypted.append(msg[i] ^ key[i%len(key)])
e = ' '.join(map(str,encrypted))
print("Encrypted message: " + e)
for j in range(len(encrypted)):
decrypted.append(encrypted[j] ^ key[j%len(key)])
d = ' '.join(map(str,decrypted))
print("Decrypted message: " + d)
```
### 3. RC4
---
```py
msg = map(int, input("Enter the message: ").split(" "))
key = map(int, input("Enter key: ").split(" "))
s = [0]*8
t = []
for i in range(8):
s[i] = i
t.append(key[i % len(key)])
j = 0
for i in range(8):
j = (j+s[i]+t[i]) % 8
temp = s[i]
s[i] = s[j]
s[j] = temp
i = j = 0
c = []
x = []
for _ in range(len(msg)):
i = (i+1)%8
j = (j+s[i])%8
temp = s[i]
s[i] = s[j]
s[j] = temp
k = (s[i] + s[j])%8
x.append(s[k])
c.append(msg[i] ^ s[k])
cipher = ' '.join(map(str,c))
print(cipher)
for i in range(len(c)):
print(c[i] ^ x[i],)
```
### 4. RSA
---
```py
def rsa_algo(p: int, q: int, msg: str):
n = p * q
z = (p-1)*(q-1)
e = find_e(z)
d = find_d(e, z)
cypher_text = ''
for ch in msg:
cypher_text += chr((ord(ch) ** e) % n)
plain_text = ''
for ch in cypher_text:
plain_text += chr((ord(ch) ** d) % n)
return cypher_text, plain_text
def find_e(z: int):
e = 2
while e < z:
if gcd(e, z) is 1:
return e
e += 1
def find_d(e: int, z: int):
d = 2
while d < z:
if ((d*e) % z) is 1:
return d
d += 1
def gcd(x: int, y: int):
small, large = (x, y) if x 1e20 or self.x < -1e20
def neg(self):
return Point(self.x, -self.y)
def dbl(self):
if self.is_zero():
return self.copy()
try:
L = (3 * self.x * self.x) / (2 * self.y)
except ZeroDivisionError:
return Point()
x = L * L - 2 * self.x
return Point(x, L * (self.x - x) - self.y)
def add(self, q):
if self.x == q.x and self.y == q.y:
return self.dbl()
if self.is_zero():
return q.copy()
if q.is_zero():
return self.copy()
try:
L = (q.y - self.y) / (q.x - self.x)
except ZeroDivisionError:
return Point()
x = L * L - self.x - q.x
return Point(x, L * (self.x - x) - self.y)
def mul(self, n):
p = self.copy()
r = Point()
i = 1
while i <= n:
if i&n:
r = r.add(p)
p = p.dbl()
i <<= 1
return r
def __str__(self):
return "({:.3f}, {:.3f})".format(self.x, self.y)
def show(s, p):
print(s, "Zero" if p.is_zero() else p)
def from_y(y):
n = y * y - Point.b
x = n**(1./3) if n>=0 else -((-n)**(1./3))
return Point(x, y)
a = from_y(1)
b = from_y(2)
show("a =", a)
show("b =", b)
c = a.add(b)
show("c = a + b =", c)
d = c.neg()
show("d = -c =", d)
show("c + d =", c.add(d))
show("a + b + d =", a.add(b.add(d)))
show("a * 12345 =", a.mul(12345))
```
### 6. Diffie-Hellman Key Exchange Algorithm
```c
/* Diffie-Hellman Key exchange algorithm */
#include
#include
long long int power(long long int a, long long int b, long long int P) {
if (b == 1)
return a;
else return (((long long int)pow(a, b)) % P);
}
int main() {
long long int P, G, x, a, y, b, ka, kb;
// Both the persons will be agreed upon the
// public keys G and P
P = 23; // A prime number P is taken
printf("The value of P : %lld\n", P);
G = 9; // A primitve root for P, G is taken
printf("The value of G : %lld\n\n", G);
// Alice will choose the private key a
a = 4; // a is the chosen private key
printf("The private key a for Alice : %lld\n", a);
x = power(G, a, P); // gets the generated key
// Bob will choose the private key b
b = 3; // b is the chosen private key
printf("The private key b for Bob : %lld\n\n", b);
y = power(G, b, P); // gets the generated key
// Generating the secret key after the exchange
// of keys
ka = power(y, a, P); // Secret key for Alice
kb = power(x, b, P); // Secret key for Bob
printf("Secret key for the Alice is : %lld\n", ka);
printf("Secret Key for the Bob is : %lld\n", kb);
return 0;
}
```