Documentation

EncryptDecrypt with RC5 in Nim

This code is written in Nim, a statically typed programming language that offers features similar to Python but with a syntax that is more reminiscent of C. The code implements basic file encryption and decryption using the RC5 encryption algorithm, which is a symmetric-key block cipher. Let's break down the code step by step:

Imports

import nimcrypto, os, strutils, sequtils

• nimcrypto: A library that provides cryptographic functions, including the RC5 cipher.
• os: A module that provides OS-related functions, such as file reading/writing.
• strutils: Contains utility functions for string manipulation.
• sequtils: Provides utility functions for working with sequences.

Encryption Function

proc encryptFile(inputFile: string, outputFile: string, key: string) =

• This defines a procedure named encryptFile which takes three parameters: the path to the input file, the path to the output file, and the encryption key.

Inside encryptFile:

1. Read Input File:

   let inputData = readFile(inputFile, fmRead)

   • Reads the content of inputFile and stores it in inputData as a sequence of bytes.

2. Convert Key to Bytes:

   let keyBytes = key.toSeq.map(cast[byte])

   • Converts the string key to a sequence of bytes.

3. Create RC5 Cipher:

   var cipher = newRC5(keyBytes)

   • Initializes a new RC5 cipher instance using the byte representation of the key.

4. Encrypt Data:

   let encryptedData = cipher.encrypt(inputData)

   • Encrypts the inputData using the RC5 cipher.

5. Write Encrypted Data to Output File:

   writeFile(outputFile, encryptedData, fmWrite)

   • Writes the encrypted data to outputFile.

Decryption Function

proc decryptFile(inputFile: string, outputFile: string, key: string) =

• This procedure is similar to encryptFile but is used to decrypt an encrypted file.

Inside decryptFile:

1. Read Encrypted File:

   let encryptedData = readFile(inputFile, fmRead)

   • Reads the content of the inputFile (which contains the encrypted data).

2. Convert Key to Bytes:

   • Similar to the encryption function, it converts the key to bytes.

3. Create RC5 Cipher:

   • Initializes a new RC5 cipher instance using the byte representation of the key.

4. Decrypt Data:

   let decryptedData = cipher.decrypt(encryptedData)

   • Decrypts the encryptedData using the RC5 cipher.

5. Write Decrypted Data to Output File:

   writeFile(outputFile, decryptedData, fmWrite)

   • Writes the decrypted data to outputFile.

Main Procedure

proc main() =

• This is the entry point of the program.

Inside main:

1. Define File Paths and Key:

   let inputFile = "example.txt"
   let encryptedFile = "encrypted.bin"
   let decryptedFile = "decrypted.txt"
   let key = "mysecretkey"

   • Sets the names of the input, output (encrypted), and output (decrypted) files, as well as the secret key used for encryption and decryption.

2. Encrypt the File:

   encryptFile(inputFile, encryptedFile, key)
   echo "File encrypted successfully."

   • Calls the encryptFile function, then prints a success message.

3. Decrypt the File:

   decryptFile(encryptedFile, decryptedFile, key)
   echo "File decrypted successfully."

   • Calls the decryptFile function, then prints a success message.

Run the Main Procedure

main()

• This line calls the main() procedure to execute the program.

Summary

The code provides a simple way to encrypt and decrypt files using the RC5 algorithm. The user specifies an input file, an output file for the encrypted data, and a key for the encryption process. The program reads the input file, encrypts its contents, and then allows for the encrypted file to be decrypted back to its original form using the same key.