Solution:
Because you're dealing with .lower()-case letters, it's right to know that their ASCII range is [97-122].
A proper way to do the shifting circular would be to represent each letter with the range [0-25], which is done by ord(ch) - 97, and then include the key, then modulo the result with 26 so it becomes (ord(ch) - 97 + key)%26, we'll then have a result in range [0-25], including 97 will then obtain it's ASCII code:
def main():
print("This program can encode and decode Caesar Ciphers")
inputText = input("Please enter a string of plaintext:").lower()
inputValue = int(input("Please enter the value of the key:")) # use int(), don't eval unless you read more about it
inputEorD = input("Please enter e (to encrypt) or d (to decrypt) ")
codedMessage = ""
if inputEorD == "e":
for ch in inputText:
codedMessage += chr((ord(ch) - 97 + inputValue)%26 + 97)
elif inputEorD =="d":
codedMessage += chr((ord(ch) - 97 - inputValue)%26 + 97)
else:
print("You did not enter E/D! Try again!!")
print("The text inputed:", inputText, ".Is:", inputEorD, ".By the key of",inputValue, ".To make the message", codedMessage)
main()
Program that accepts a Text (string) and Shift value( integer) and returns the encrypted text.
// A C++ program to illustrate Caesar Cipher Technique
#include <iostream>
using namespace std;
// This function receives text and shift and
// returns the encrypted text
string encrypt(string text, int s)
{
string result = "";
// traverse text
for (int i=0;i<text.length();i++)
{
// apply transformation to each character
// Encrypt Uppercase letters
if (isupper(text[i]))
result += char(int(text[i]+s-65)%26 +65);
// Encrypt Lowercase letters
else
result += char(int(text[i]+s-97)%26 +97);
}
// Return the resulting string
return result;
}
// Driver program to test the above function
int main()
{
string text="ATTACKATONCE";
int s = 4;
cout << "Text : " << text;
cout << "\nShift: " << s;
cout << "\nCipher: " << encrypt(text, s);
return 0;
}
In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the easiest and most broadly known encryption techniques. It is a type of substitution cipher in which every letter in the plaintext is replaced by a letter few fixed number of positions down the alphabet. Example given- with a left shift of 3, D would be replaced by A, E would become B, and so on. The process is named after Julius Caesar, who employed it in his private conformation.
Python Code:
#https://gist.github.com/nchitalov/2f2b03e5cf1e19da1525
def caesar_encrypt(realText, step):
outText = []
cryptText = []
uppercase = ['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']
lowercase = ['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']
for eachLetter in realText:
if eachLetter in uppercase:
index = uppercase.index(eachLetter)
crypting = (index + step) % 26
cryptText.append(crypting)
newLetter = uppercase[crypting]
outText.append(newLetter)
elif eachLetter in lowercase:
index = lowercase.index(eachLetter)
crypting = (index + step) % 26
cryptText.append(crypting)
newLetter = lowercase[crypting]
outText.append(newLetter)
return outText
code = caesar_encrypt('abc', 2)
print()
print(code)
print()
Program for Caesar Cipher in Python
def encrypt(string, shift):
cipher = ''
for char in string:
if char == ' ':
cipher = cipher + char
elif char.isupper():
cipher = cipher + chr((ord(char) + shift - 65) % 26 + 65)
else:
cipher = cipher + chr((ord(char) + shift - 97) % 26 + 97)
return cipher
text = input("enter string: ")
s = int(input("enter shift number: "))
print("original string: ", text)
print("after encryption: ", encrypt(text, s))
