Encryption and Decryption using Monoalphabetic Cipher Technique - System Security | Python3

a=input("Enter the msg: ")

pt=['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']

ct=['r','s','t','u','v','w','x','y','z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q']

d=[]

c=[]

for i in a:

    b=pt.index(i)

    d.append(ct[b])

str1 = ''.join(d)

print ("Encrypted Text: "+str1)

for j in d:

    b=ct.index(j)

    c.append(pt[b])

str2 = ''.join(c)

print ('Decrypted Text: '+str2)

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