Ah, someone who is more than a recreational mathematician ;-)

With circular functions, you have the truly periodic and the almost periodic. The truly periodic corresponds to a pure timbre, the simplest being a single pure tone (sine wave). If the ratio of at least one irregular component among the purely periodic ones, meet the number theory criteria of not being rational, not even algebraic eg square root of two, but is transcendental "pi/e/etc" ... then even after an infinite expansion of digits, the odd component will never align (harmonize). Such is the theory of almost-periodic functions, and how it becomes harder and harder to derive an accurate fourier analysis of the non-harmonics. Such is "percussive" sound, which can be partly harmonic (tympany) or nearly pure noise (true random number).

Consider not a true one time pad, but one that is arbitrarily close to a one time pad. Then the matter of being hard to decrypt is simply a parameter, that one can extend as necessary, as decryption gets better (an arms race). What if you have a key that isn't periodic (has a recurring depth), but is algebraic or even transcendental. In that case you can extend the key system indefinitely, without running into recurrence (which weakens the encryption). You can't as a practical matter use a true non-rational number, one approximates a non-rational number with a close enough rational number eg you use however many digits of "e" as necessary to meet the message size. The true key being incommensurable, while the practical key is a many digit rational approximation.

So what quantum computer can calculate the last digit of square root of two, or of "pi"? There is no free lunch on general problem solving, because of the "halting" problem. But specific classes of problems can be solved in closed form. We will have to wait to see, a practical demonstration that the multiplication of two large prime numbers is easy to factor or not. There are always surprises. To what extent is mathematics actually empirical not analytical?

I'm not a Mathematician. Not even a recreational one.

I think quantum computers will maybe be able a day to break a cryptosystem like this.

We will certainly discover new mathematical algorithms

**(Maybe it does already exist secret or top secret algorithms owned by some state actors)**.

But before ask if quantum computers will be able to do so a moment or another.

I think we must use a sufficient encryption process until the time the information we want to kept won't be necessary to be secret.

An info that must to be a secret indefinitely

**(For example an industrial secret that is the formula of a beverage. In this case encryption would be necessary even if the secret can be partially or fully discovered by reverse engineering with chemical analysis)** isn't the same as an info that must be a secret for one week as the fact a secret meeting will take place to reduce the risk of someone spying the meeting.

What was said in this meeting can be fully secret , partially secret or not secret.

If this meeting is about the secret project of companies for the next five years. Information must to be protected for the next five years.

If this meeting is about public and secret projects of companies for the next ten years. Information about public project can be released fully or partially released and info about secret projects must to be protected for the next ten years. The same for non-released info on public projects.

If this meeting is about public projects for the next two years. Information can be released fully or partially and non-released info must to be protected for the next two years.

Even if a project is public it doesn't means all details are public because some of these need to be secret in some situations.

If a project is secret. The public must not known its existence and therefore the content should not be known to the public.

Few secrets need to be kept indefinitely.

An industrial process can need to be a forever a secret but the fact a video game is being created don't need to be kept indefinitely as the game will be released unless the project is abandoned.

If this ciphertext and plain text is really from you ? I can't find it over Internet. I can suppose you're the author of this.

THE0RAIN0IN0SPAIN0FALLS0MAINLY0ON0THE0PLAIN

L5CRAGQIPVPVW9MTD827I6Q1ROVO0C8K51XJ416JXN0