RSA algorithm in CIntroduction:The RSA algorithm is a highly quick encryption and decryption technique. It is utilized in numerous applications, including communication encryption and decryption. The algorithm is predicated on the notion that messages may be encrypted and decrypted if we are aware of both the public and private keys. In order to calculate n = pq, an RSA user generates the two huge prime numbers p and q. After that, the totient function is calculated (n) = (p  1)(q  1). They choose e as a public key by selecting it as a substantially prime integer to n and 1 e n. The private key, d, is calculated as follows: The process of encryption is as follows: Overall the characters. The process for decrypting all the characters is as follows: Example:Create a C program that will ask the user for two prime integers and then use the RSA technique to encrypt and decrypt a message. Solution for the problem:RSA Cryptography
Let's examine two samples of the RSA Algorithm in C.
Approach 1RSA Algorithm Using Simple ApproachThe RSA algorithm is used in this method. This kind of public key encryption makes use of two unique but connected keys, also known as asymmetric encryption and decryption technique. Additionally, knowing one key will not make it easier to understand how the other key protects itself. The RSA algorithm makes use of the fact that multiplying two large prime integers together yields a simple result. However, if you know only one of the original primes, you cannot fairly assume the other or the two original numbers from that product. Source Code Here is the C program's source code for implementing the RSA algorithm. On a Linux system, the C program is successfully compiled and executed. Also presented below is the output of the program. Cases of Runtime TestingIn this instance, we enter the two prime numbers "5" and "17", and then encrypt and decrypt a message using the RSA technique. Approach 2:Additional RSA Algorithm ProgrammingIn this method, we store some intermediate data in a temporary array that will be used later in the decrypt function. Methods applied int isPrime(int)  This function determines whether or not the number is a prime. int gcd(int, int)  The largest common divisor of two numbers is returned by this function. int totient(int, int)  The totient of an integer is returned by this function. int randome(int)  This function gives back a random integer that is smaller than the input. int private_key(int, int)  The private key is returned by this function. long pomod(long, long, long)  This function gives the number's modular exponentiation. char *encrypt(char *, long, long)  The message is encrypted using this feature. char *decrypt(char *, long, long)  The message is decrypted using this function. Example: Source Code Here is the C program's source code for implementing the RSA algorithm. On a Linux system, the C program is successfully compiled and executed. Also presented below is the output of the program. Output: Cases of Runtime TestingIn this instance, we enter the two prime numbers "5" and "13", and then encrypt and decrypt a message using the RSA technique. Program Description
Note: Given that the character set implementation in C is so limited, many characters are lost during the encryption and decryption processes, making Approach 2 (Additional program) an imperfect implementation for large values of n (p * q). As a result, as a workaround, all the intermediate calculations for this program should be performed on a long long int type array.Advantages and Disadvantages of RSA AlgorithmThere are various advantages and disadvantages of the RSA Algorithm. Some main advantages and disadvantages of the RSA Algorithm are as follows: Advantages:Security: The RSA algorithm is frequently utilized for secure data transfer, which is regarded as being exceptionally secure. Publickey cryptography: The RSA algorithm needs two separate keys for encryption and decryption because it is a publickey cryptography algorithm. Data is encrypted using the public key, and decrypted using the private key. Key conversation: A secret key can be exchanged between two parties securely using the RSA technique without actually sending the key over the network. Electronic signatures: A sender can sign a message using their private key and the recipient can verify the signature using the sender's public key when the RSA technique is used for digital signatures. Disadvantages:Poor processing rate: When working with huge amounts of data, the RSA algorithm is slower than alternative encryption techniques. Extralarge keys: Large key sizes are necessary for the RSA algorithm to be secure, which means that greater processing power and storage space are needed. Attacks through sidechannel are susceptible: The RSA technique is susceptible to sidechannel attacks, which allow an attacker to obtain the private key by using data that has been leaked through side channels such power usage, electromagnetic radiation, and timing analysis. Limited application in some cases: Due to its poor processing speed, the RSA algorithm is unsuitable for some applications, such as those that demand continuous encryption and decryption of substantial volumes of data.
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