Some Encryption program in Python

Scuzz

Encryption program for a university module

Usage:

python joshcrypt.py [-h] [-e] [-d] keyword inputFile outputFile

Flags:

[-h] Help. This flag will generate help from the command line.
[-e] Encrypt. Use this flag to encrypt the inputFile.
[-d] Decrypt. Use this flag to decrypt the inputFile.

Arguments:

Keyword - The keyword used to encrypt the file.
inputFile - The Filename to save the encrypted/decrypted file as.

This program needs to be run from the command line; cmd.exe or any terminal emulator will suffice.
To start the encryption process a user must type:

python joshcrypt.py -e "keyword" "inputfile" "outputfile"

Keyword is the password used for the document.
Inputfile is the file that you want to be encrypted.
Outputfile is the file that you want the encrypted file to be saved as.

To start the decryption process a user must type:

python joshcrypt.py -d "keyword" "inputfile" "outputfile"

Keyword is the password used for the document.
Inputfile is the file that you want to be decrypted.
Outputfile is the file that you want the plain text file to be saved as.

# Requires Python 2.7 as Python 3.0+ contains bugs with the array.array() function.
import argparse
import array
import sys

# Opens file as a byte array.
def getBlock(fileName):
    f = open(fileName, "rb")
    blockArray = array.array('b', f.read())
    f.close
    return blockArray

# Converts bytes to string and writes it to a file.
def writeBlocks(blocks, fileName):
    f = open(fileName, "wb")
    string = blocks.tostring()
    f.write(blocks)
    f.close()

# Generates a key. 
# Converts the key into a byte array, creates another byte array of the key but reversed. 
# Xor the bytes together to generate the final key.
def genKey(key):
    a = array.array('b', key)
    b = a[::-1]
    for x in range(len(a)):
        a[x] = a[x] ^ b[x]
    return a

# Xor the bytes of the key with the bytes of the file.
# Loops through the key and adds the times it has looped to the end of the key
def encrypt(blocks, key):
    i = 0
    r = 0
    for block in range(len(blocks)):
        blocks[block] = blocks[block] ^ key[i]
        if i == len(key) - 1:
            i = 0
            r += 1
            key = genKey(key.tostring() + str(r))
        else:
            i += 1
    return blocks

def decrypt(blocks, key):
    i = 0
    r = 0
    for block in range(len(blocks)):
        blocks[block] = blocks[block] ^ key[i]
        if i == len(key) - 1:
            i = 0
            r += 1
            key = genKey(key.tostring() + str(r))
        else:
            i += 1
    return blocks

# Sets up the command line arguments
# Calls functions to encrypt the file.    
def main():
    parser = argparse.ArgumentParser(description="Encrypt and Decrypt a file.")
    parser.add_argument("-e", action = "store_true", default = False, dest = "edFlag", help = "Encrypt File")
    parser.add_argument("-d", action = "store_false", default = False, dest = "edFlag", help = "Decrypt File")
    parser.add_argument("keyword", action = "store", help = "Keyword used to encrypt or decrypt file")
    parser.add_argument("inputFile", action = "store", help = "Filename to be encrypted/decrypted")
    parser.add_argument("outputFile", action = "store", help = "Filename to save the encrypted/decrypted file as")
    args = parser.parse_args()
    
    if len(args.keyword) < 10 or len(args.keyword) > 40:
        print "Password needs to be greater than 10 characters and less than 40"
        sys.exit(1)

    if args.edFlag:
        print "ENCRYPTING"
        key = genKey(args.keyword)
        blocks = getBlock(args.inputFile)
        encrypted = encrypt(blocks, key)
        writeBlocks(encrypted, args.outputFile)
    else:
        print "DECRYPTING"
        key = genKey(args.keyword)
        blocks = getBlock(args.inputFile)
        decrypted = decrypt(blocks, key)
        writeBlocks(decrypted, args.outputFile)

if __name__ == '__main__':
    main()```

Some Encryption program in Python

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