python program. Instructions are written within the quotation marks of how to define a function. def substitution(plainText, key):II II ||Returns encrypted string for the plainText using substitution encryption, whichis to substitute 'a'/'A' with the lower/upper case of key[0], and substitute'b'/'B' with the lower/upper case of key[1], and so on all the way to 'z'/'Z'.Leave all other non-alpha characters as it is in plainText.Your algorithm should be efficient so that it can run fairly quickly for verylarge strings.1. use replace() to convert each letter to its encrypted letter2. append encrypted letter to a list3. use ''.join(list_of_letters) to form the final string. Do not use + to dostring concatenation to form the encrypted string.II II ||return plainTextdef run():1. Prompt user for a key;2. Check if key is valid. If not, print an error message then return;if valid, prompt for a plain text to be encrypted with the valid key,3. Send the plain text and valid key to substitution function.4. Print out the encrypted message.II II||input("Enter a 26 letter key: ")keyif not isValidKey(key):print("Invalid key.")returnplainTextcipherText = substitution(plainText, key)print(f"Cipher Text: {cipherText}")input("Plain Text: ")returnif-_name_.__main__":run() • The run() function is implemented for you already that will get user to enter a key, call a function youimplemented to check the validity of the key and proceed to get plainText, encrypt with the key and print out thecipherText.• The isValidKey() function will check If the key is invalid (as by not containing 26 characters, containing anycharacter that is not an alphabetic character, or not containing each letter exactly once) and return False if it isnot valid and return True if it is valid.• Your substitution() function will generate a cipherText from plainText using a valid key. The cipherText is obtainedby replacing each alphabetical character in the plainText substituted for the corresponding character in theciphertext; non-alphabetical characters should be left unchanged. You should first implement the replace()function that do the substitution for one letter, and then map the replace() function to every letter in theplainText.• Your program must preserve case: capitalized letters must remain capitalized letters; lowercase letters mustremain lowercase letters.Here is your starter code in hw6.py:# Author: Yanling Wang yuw17@psu.edudef isValidKey(key):II II ||Returns True if key is a string that has 26 characters and each of the letter'a'/'A'-'z'/'Z' appeared once and only once in either lower case or upper case.Returns False otherwise.II II ||return Truedef replace(letter, key):II II ||Assume letter is a single characer string.Replace a single letter with its corresponding key, returns letter if it isnot in the alphabet 'a'-'z' or 'A'-'Z'II II ||return letter

Method- replace(letter, key): 1. If letter is not an alphabet 1. Return letter 2. If letter is…

def substitution(plainText, key): Returns encrypted string for the plainText using substitution encryption, which is to substitute 'a'/'A' with the lower/upper case of key[0], and substitute 'b'/'B' with the lower/upper case of key[1], and so on all the way to 'z'/'Z'. Leave all other non-alpha characters as it is in plainText. Your algorithm should be efficient so that it can run fairly quickly for very large strings. 1. use replace() to convert each letter to its encrypted letter 2. append encrypted letter to a list '.join(list_of_letters) to form the final string. Do not use + to do string concatenation to form the encrypted string. return plainText def run(): II II II 1. Prompt user for a key; 2. Check if key is valid. If not, print an error message then return; if valid, prompt for a plain text to be encrypted with the valid key, 3. Send the plain text and valid key to substitution function. 4. Print out the encrypted message. key = input("Enter a 26 letter key: ") if not isValidKey(key): print("Invalid key.") return plainText = input("Plain Text: ") cipherText = substitution(plainText, key) print(f"Cipher Text: {cipherText}") return if "-_main__": %3D _name__ run()

def substitution(plainText, key): Returns encrypted string for the plainText using substitution encryption, which is to substitute 'a'/'A' with the lower/upper case of key[0], and substitute 'b'/'B' with the lower/upper case of key[1], and so on all the way to 'z'/'Z'. Leave all other non-alpha characters as it is in plainText. Your algorithm should be efficient so that it can run fairly quickly for very large strings. 1. use replace() to convert each letter to its encrypted letter 2. append encrypted letter to a list '.join(list_of_letters) to form the final string. Do not use + to do string concatenation to form the encrypted string. return plainText def run(): II II II 1. Prompt user for a key; 2. Check if key is valid. If not, print an error message then return; if valid, prompt for a plain text to be encrypted with the valid key, 3. Send the plain text and valid key to substitution function. 4. Print out the encrypted message. key = input("Enter a 26 letter key: ") if not isValidKey(key): print("Invalid key.") return plainText = input("Plain Text: ") cipherText = substitution(plainText, key) print(f"Cipher Text: {cipherText}") return if "-_main__": %3D _name__ run()

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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