How Quantum Computers Break Encryption
The Bernstein-Vazirani Circuit
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Modern asymmetric encryption builds upon the assumption that it is practically impossible to find the prime factors of very large numbers.
Accordingly, the outcry was great when Peter Shor presented his algorithm that allows a quantum computer to factorize a large number efficiently. Of course, we all want to understand how this algorithm works. But unfortunately, it is not exactly beginner-friendly.
Fortunately, we don’t need to master factorization to understand how quantum computers break encryption. Instead, we can first use a more straightforward example to understand it conceptually.
Suppose we have a three-character binary message (e.g., 000, 001, 010, 011, etc.) that we want to encrypt and a three-character binary secret — the password, if you will.
We encrypt the message by calculating modulo two of the inner product of the message and the secret key.
The inner product is formed by multiplying the digits at each position and summing the results.
Finally, modulo denotes the remainder of the division of two numbers. So if we…
