Update README.md

Project/Team_4/RC4 Implementation and Cryptanalysis/RC4_final.py

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+from flask import Flask, render_template, request
+
+app = Flask(__name__)
+# app.config.from_object(__name__)
+
+#This code is used to encrypt messages using RC4(Rivest Cipher 4).
+
+"""This function is used to perform xor between two binary strings. We use this this function rather
+than using ^ operator because the leading zeroes would be discarded and the size of the output could
+be altered which produces wrong outputs."""
+def xor_b(b1, b2):
+    result = ''
+    for bit1, bit2 in zip(b1, b2):
+        if bit1==bit2:
+            result +='0'
+        else:
+            result +='1'
+
+    return result
+
+# This function is used to change the binary string to hexadecimal string and returns the hexadecimal string.
+
+def toHex(bin):
+    vals = [bin[i:i + 8] for i in range(0, len(bin), 8)]
+    vals = [chr(int(i,2)) for i in vals]
+    text = ''.join(i for i in vals)
+    hex = text.encode("utf-8").hex()
+    return hex
+
+#This function is used to change the hexadecimal string to binary string and returns the binary string.
+
+def fromHex(hex):
+    byte_string = bytes.fromhex(hex)            
+    result = byte_string.decode('utf-8')
+    m = ''.join([format(ord(j),'08b') for j in result])
+    return m
+
+"""This function is used for scheduling the key from the input key to a scheduled key array of length
+256. In RC4, the following algorithm is used for key scheduling.This function returns the scheduled 
+key list."""
+
+def key_schedule(key):
+    S = list(range(256))
+    T = list()
+
+    for i in range(len(S)):
+        T.append(ord(key[i%len(key)]))
+
+    j = 0
+    for i in range(256):
+        j = (j + S[i] + T[i]) % 256
+
+        S[i],S[j] = S[j],S[i]
+
+    return S
+"""This function is used for generating the keystream from the scheduled key and length of the
+message. In RC4, the following algorithm is used to generate the keystream which is used for encryption
+and decryption."""
+
+def generate_keystream(S,message):
+    i,j = 0,0
+    p = []
+    l = len(message)
+    while(l>0):
+        i = (i+1) % 256
+        j = (j+S[i]) % 256
+        S[i],S[j] = S[j],S[i]
+        k = S[(S[i]+S[j]) % 256]
+        p.append(k)
+        l -= 1
+    return p
+
+"""This function is used to encrypt the message using the key, changes the message and key
+into binary strings and performs XOR for the two binary strings and returns the result in
+hexadecimal string.
+"""
+
+def encrypt(key,m):
+    m = str(m)
+    S = key_schedule(list(key))
+    k = generate_keystream(S,m)
+
+    kf = ''.join([format(i,'08b') for i in k])
+    m = ''.join([format(ord(j),'08b') for j in m])
+
+
+    ct = xor_b(kf,m)
+
+    return toHex(ct)
+
+"""This function is used to decrypt the ciphertext using the key, changes the ciphertext from hexadecimal
+string to binary string and key into binary string and performs XOR for the two binary strings and returns
+the result in ASCII.
+"""
+
+def decrypt(key,c):
+
+    S = key_schedule(list(key))
+    try:
+        c = fromHex(c)
+    except ValueError as e:
+        return str(e)
+    k = generate_keystream(S,c)    
+    kf = ''.join([format(i,'08b') for i in k])
+
+    pt = xor_b(kf,c)
+
+    vals = [pt[i:i + 8] for i in range(0, len(pt), 8)]
+    vals = [chr(int(i,2)) for i in vals]
+    dec_m = ''.join(i for i in vals)
+    return str(dec_m)
+
+@app.route('/')
+def welcome():
+    return render_template('RC4.html')
+
+@app.route('/', methods=['POST'])
+def result():
+    var_1 = request.form['var_1']
+    var_2 = request.form['var_2']
+    if(var_1 == '' or var_2 == ''):
+            k = f"Cannot be Implemented"
+            entry = "Nothing_to_do!!"
+            return render_template('RC4.html',k = k,entry = entry)
+    operation = request.form.get("operation")
+    if(operation == 'Encrypt' or operation == 'encrypt'):
+        result = encrypt(var_2,var_1)
+    elif(operation == 'Decrypt' or operation == 'decrypt'):
+        for i in var_1:
+            if i not in "0123456789abcdef":
+                k = f"Ciphertext not in valid hexadecimal form."
+                entry = "Not_Valid."
+                return render_template('RC4.html',k = k,entry = entry)
+        result = decrypt(var_2,var_1)
+        if "non-hexadecimal number found in fromhex()" in result:
+            k = "Non-hexadecimal is not allowed"
+            entry = "Not_Valid."
+            return render_template('RC4.html',k = k,entry = entry)
+
+    else:
+        k = "Invalid operation"
+        entry = "Not_Valid."
+        return render_template('RC4.html',k = k,entry = entry)
+    entry = result
+    return render_template('RC4.html', entry=entry)
+
+
+if __name__ == '__main__':
+    app.run(debug=True)