Published: 2020-04-08
... a Caesar cipher ... is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence. Wikipedia
I was signing up for a website that teaches the basics of cryptography and instead of a captcha they asked me to decrypt a four words than were encrypted with a Caeser Cipher.
So naturally I work a program to do it for me!
Once you know the byte representation of a few key letters the logic is very simple.
func shiftRight(words string, amount byte) string {
var output string
for _, v := range []byte(words) {
var b byte
switch v {
case 32: // Check for spaces
b = 32
case 90: // Change "Z" to "A"
b = 65
case 122: // Change "z" to "a"
b = 97
default:
b = v + amount
}
output = fmt.Sprintf("%s%s", output, string(b))
}
return output
}The logic is identical to shifting forward with only a few changes. Such as swapping cases 2 and 3 to look for the A's instead of the Z's. As well as changing the addition to subtraction.
func shiftLeft(words string, amount byte) string {
var output string
for _, v := range []byte(words) {
var b byte
switch v {
case 32: // Check for spaces
b = 32
case 65: // Change "A" to "Z"
b = 90
case 97: // Change "a" to "z"
b = 122
default:
b = v - amount
}
output = fmt.Sprintf("%s%s", output, string(b))
}
return output
}Running the above functions is as easy as assigning the function to a variable. Then passing in the string you want to encrypt or decrypt with the amount of shifting and printing the output.
func main() {
word := "J nbef b Dbftbs djqifs"
decrypted := shiftLeft(word, 1)
fmt.Println(decrypted)
}