Mini Project Report Cover Sheet SRM Institute of Science and Technology College of Engineering and Technology Department ese bh | Communication Engine Experiment based Project On Implementation of RC4 Cryptography Algorithm Rishabh Ghelani Nihaal Teenu C Abhinav Mishra i RA211100401000 | RA211100401002 | RA211100401003 Topic | Mar i 6 8 k Demonstratio | 15 ee \ 4 - n Document | 15 I 1s lon Preparation 2 ie Viva 10 ee 12 Total 40 ho 4e e BC REPORT VERIFICATION Date aslelas Staff Name Or. R-kumar / Dy. T- Ramu a Signature11.1 AIM Implementation of RC4 Encryption and Decryption Algorithms Using Python. 11.2 INTRODUCTION ‘The RC4 algorithm is a symmetric stream cipher used for encryption and decryption of data. It was developed by Ron Rivest in 1987 and was initially used for secure communication in the Intemet Engineering Task Force (IETF). The algorithm is known for its simplicity and speed and is widely used in various applications 11.3 SOFTWARE Python 3.8, Pycharm IDE 11.4RC4 ALGORITHM RC4 (Rivest Cipher 4) is a symmetric stream cipher algorithm that is widely used in various applications, such as secure socket layer (SSL), wireless network encryption, and Bluetooth. It operates on bytes of data and generates a stream of pseudo-random bytes, which are XOR-ed with the plaintext to produce the ciphertext, RC4 encryption and decryption is achieved by using a secret key of arbitrary length between 40 and 2048 bits. The RC4 algorithm consists of two main stages: key-scheduling and stream generation, In the key-scheduling stage, the algorithm creates a permutation of the 256-byte array, based on the secret key and an initialization vector (IV). The permutation is achieved by performing a series of swaps between elements of the array, depending on the key and IV. In the stream generation stage, the algorithm generates a pseudo-random stream of bytes by repeatedly swapping elements of the array and generating a byte from the array index, based on the current state of the algorithm, This stream is XOR-ed with the plaintext toproduce the ciphertext, and vice versa for decryption. Overall, RC4 is a simple, fast, and widely-used stream cipher that provides a g00d level of security for various applications. However, it is vulnerable to certain attacks, such as key recovery attacks and related key attacks, and. therefore should not be used as the sole security mechanism for critical applications. To encrypt a plaintext message using RC4, the pseudorandom stream is XORed with the plaintext to produce the ciphertext, To decrypt the ciphertext, the same pseudorandom stream is XORed with the ciphertext to recover the original plaintext. RCABLOCK DIAGRAM no Encrypted Tat ed 11.5 IMPLEMENTATION METHODOLOGY RC4 algorithm can be implemented using Python by following these stey 1. Define a function to perform the key-scheduling stage, which takes the secret key as input and generates the permutation of the 256-byte array. 2. Define a function to generate the pseudo-random stream of bytes, which takes the permutation array as input and generates a stream of bytes to XOR with the plaintext. 3. Define a function to perform the encryption, which takes the plaintext and secret key as input, and generates the ciphertext by XOR-ing the plaintext with the stream of bytes generated in step 2, 4, Define a function to perform the decryption, which takes the ciphertextand secret key as input, and generates the plaintext by XOR-ing the ciphertext with the same stream of bytes generated in step 2. 5, Test the encryption and decryption functions with sample plaintext and secret key, and verify that the output matches the expected ciphertext and plaintext, respectively. 11.6 RESULT AND DISCUSSION This Python script implements the RC4 stream cipher, comprising functions for key scheduling, key padding, stream generation, encryption, and decryption. The key scheduling function initializes the state array using the provided key, while the padding key function ensures the key is of the required length. The stream generation function produces a keystream based on the state array. Encryption XORs plaintext characters with keystream values, handling alphabetic and numeric characters differently. Decryption reverses the encryption process. The user interface prompts the user to choose between encryption and. decryption, then collects input text and keys accordingly, utilizing the appropriate functions to perform the selected operation and outputting the result. However, RC4 is deprecated due to its vulnerability to attacks, and it's advised to use modem encryption algorithms for secure communication. eT ‘ext= input("enter a plaintext: “) Keyrinput("Enter the key: ") cnerypeed ext = encrypt (texts Key) printc'cipher text ist", encrypted text) | euited =e 22 | TExr =. input( “Enter cipher text: “) | wer = input renter key! *) | decrypted. text = decrypt (TEXT, KEY) | princcbecrypted messages", decrypted text) else! print(‘Eeror in input ~ try again.") Enter 1 for Enerypt, or 2 for Decrypt: 2 Enter a plaintext: Abhinav Enter the key: COW Cipher text {21 Heleubg, Tabulation for Encryption S.No_| Plain text Keyword _| Cipher Text [1 ‘Abhinav ‘CCN Heloub 2 Nihaal ‘CCN. Ujluhm 3 Rishabh CCN Yjwbhes 4 Computer ‘CCN Ipaibupd 5 Networks ‘CCN UfxqvsveTabulation for Decryption S.No Cipher Text Keyword Plain Text [1 Heleubg CCN Abhinav 2___| Ujluhm CCN Nihaal 3 Yjwohes CCN Rishabh 4 Ipgibupd CCN Computer [5 Ufxqvsve CCN Networks 11.7 CONCLUSION ‘The RC4 algorithm is a widely used stream cipher for encryption and decryption of data, It is known for its simplicity and speed. In this report, we have explained the theory behind the RC4 algorithm, its implementation using Python and the software used, And the funetions that provides a convenient and easy-to-use interface for implementing the RC4 algorithm in Python. 11.8 REFERENCES 1. Data communications and networking I Behrouz A Forouzan 2. https://www youtube.com/watch?v=Pl-ySfSabv8 APPENDIX: Programme: import random def Key_Scheduling(key): key length = len(key) ifkey length > 256: raise ValueBrror("Key too long (max length = 256)") $= list(range(256))j=0 for iin range(256): j= (+ S[i] + key[i % key_length]) % 256 S[i], SEi] = SG), Sti) retum S def pad_key(key): padded_key = bytearray(256) key_len=len(key) if key_len> 256: padded_keyfkey_len: return padded_key def stream_generation(S): i=0 j=0 while True: i=(1+1) % 256 j= G+ Sli) % 256 _ Sli], Si]= SU) Sielif c.isupper(: ©= chr((ord(c) + Next(Keystream) - 65) % 26 + 65) elif c.isnumerie(): = str((int(c) + next(keystream)) % 10) encrypted _text += ¢ return encrypted_text def decrypt(ciphertext, key): key =pad_key(key) S=Key_Scheduling(key) keystream = stream_generation(S) decrypted_text =" for c in ciphertext: if c.isalpha(): if c.islower): c= chr((ord(c) - next(keystream) - 97) % 26 + 97) elif c.isupper(): c= chr((ord(c) - next(keystream) - 65) % 26 + 65) elif c.isnumeric(): ¢ = str((int(c) - next(keystream)) % 10) decrypted_text += return decrypted_text ed = input(‘Enter 1 for Encrypt, or 2 for Decrypt: ‘.upper() ifed="1': ‘text= input("Enter a plaintext: ") key=input("Enter the key: ") encrypted _text = encrypt(text, key) print("Cipher text is:", encrypted_text) elif ed = "2: TEXT = input("Enter cipher text: ") KEY = input("Enter k decrypted_text = decrypt(TEXT, KEY) ————_—print("Decrypted mMessage:", decrypted text) else: print(Error in input - ‘try again.)