The most secure cipher ever?
Right now, cryptography is still a developing science. Different types of ciphers are still being tried and tested, and while many are far too complicated for me to cover in detail, hardly any cipher that we use is completely indecipherable.
Except for one. And it’s not even that new. The one-time pad cipher, as it is called, was initially devised in 1882, and it began to see use after the First World War. It makes use of a one-time pad, a sequence of randomly chosen letters which must be at least as long as the message itself. Then, the alphabet positions of a letter in the original text and a matching letter in the one-time pad are added using modular addition(a topic we previously covered) are added to create a letter in the ciphertext. A different pad is used for every message, and no pad can be used more than once.
So we have a key that is completely random, at least as long as the plaintext, never reused, and kept completely secret. If all these conditions are met, then the cipher will be completely indecipherable by anyone who doesn’t know the key. So why isn’t this cipher used more often? Why isn’t this cipher universally used? Why does cryptography still exist as a field?
The main reason, which you may have already figured out, is how unreasonable it is. All the factors which make it unbreakable also make it a logistical nightmare to coordinate. If you want to send a message to someone using a onetime pad cipher, you have to be sure they’re using the exact same pad as you, and that you both have a large supply of pads(if you run out, you can’t just make more, because then your recipient won’t be able to decrypt it), and you can’t coordinate any of this while writing the message because then hostiles could just intercept that communication line, and be able to decrypt the actual message.
This inefficiency is why onetime pads are rarely used in communication, and most people nowadays use other, more subtle methods, which I’ll cover in later posts. However, some very important and high-profile communications make use of one-time pads, for example, the phone line between the American and Russian presidents.
