Detailed Explanation of Simple Encryption Algorithms

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The expansion part is to create a program that can both encrypt and decrypt, while utilizing custom functions. The idea is as follows:

The program is divided into four modules: character conversion, encryption, decryption, and main function call, which can be realized through four custom functions change(), encrypt(), decrypt(), main().

1. Custom character conversion function change(), this function converts the input string code into a lowercase letter string between a-z.

2. Custom encryption function encrypt(), encrypts based on the input plaintext string code and key key, generating ciphertext code_new.

3. Custom decryption function decrypt(), decrypts based on the input ciphertext string code and key key, generating plaintext code_new.

4. Custom main function main(). Running main(), allows for encryption and decryption selection through 1 and 2.

[Program Segment]

def change(code,key):
    code=code.lower()
    m=ord(code)
    if m >=97 and m<=122:
        m =97+((m-97)+key)%26
    return chr(m)
def encrypt(code,key):
    code_new=""
    for s in code:
        code_new+=change(s,key)
    print(code_new)
    return code_new
def decrypt(code,key):
    code_new=""
    for s in code:
        m=ord(s)-key
        if m<97:
            m=m+26
        code_new+=chr(m)
    print(code_new)
    return code_new
def main():
    print("Please select number 1 or 2:")
    print("1: Encrypt")
    print("2: Decrypt")
    select =input()
    if select =="1":
        code =input("Please enter the string to encrypt:")
        key =int(input("Please enter the shift number:"))
        encrypt(code,key)
    elif select =="2":
        code =input("Please enter the string to decrypt:")
        key =int(input("Please enter the shift number:"))
        decrypt(code,key)
    else:
        print("Input error, please try again!")
if __name__=='__main__':
    main()

Simple

XOR

The plaintext refers to the original information that has not been encrypted, while the ciphertext refers to the information that has been encrypted. The steps of a certain encryption algorithm are as follows:

I. Remove spaces from the plaintext;

II. Append lowercase letters in alphabetical order at the end of the string to make its length a multiple of k (1<k<=26);

III. Rearrange the string into k groups, extracting elements from the same position in each group and concatenating them to form the ciphertext.

For example: k=3, s=”i am okay”, the encryption process is shown in the figure.

Please answer the following questions:

(1) In the figure, the plaintext is ▲ (Single choice, fill in the letter).

A.i am okay

B.iamokay

C.iamokayab

D.ioyakamab

(2) If s=”today”, k=4, according to the question, after the letter padding step, the new string content is ▲ (Single choice, fill in the letter).

A.todaya

B.todayab

C.todayabc

(3) Define the following append function. The function’s purpose is to remove spaces from the string according to step I, append letters according to step II, making its length a multiple of k, and return the new string after padding. Please fill in the appropriate code in the underlined part.

def append(s,k):
    st=space(s) # The space function removes spaces from the string s and returns the string without spaces
    n=len(st)
    i=ord("a")
    while n%k!=0:
        st+=chr(i)
        i+=1
        __________
    return st

The code to fill in the underlined part is ▲ (Single choice, fill in the letter: A.n-=1/B.n+=1)

(4) Define the following function place. The function’s function is to rearrange the string according to step III to form a new string, generating ciphertext. Please fill in the appropriate code in the underlined part.

def place(news,k):
    n=len(news)
    m=n//k
    i,j=0,0
    ct=""
    while i<m:
        if j<n:
            ct=__①__
            j=j+m
        else:
            i+=1
            __②__
    return ct
# Main program
s=input("Please enter plaintext:")
k=int(input("Please enter k:"))
news=append(s,k)
print("Ciphertext is:",place(news,k))