**Claim** : IOTA is resistant to quantum computer based attacks

**Category** : Cryptocurrency

**Source** : IOTA’s Github

**My Stake** : Back claim (50 cred)

**My Argument/Evidence** :

IOTA uses Winternitz signatures unlike most other cryptocurrencies including Bitcoin which instead make use of ECDSA (Elliptic Curve Digital Signature Algorithm). ECDSA remains secure today because of the difficulty of solving the Discrete Logarithm Problem (DLP) by regular computers, which we will show below that quantum computers can solve in much faster time.

As evidence that IOTA uses Winternitz signatures, this blog post by IOTA explains how Winternitz signatures work.

In order to explain why Winternitz signatures are resistant to quantum computer attacks requires me to talk a little bit about quantum computers.

**Quantum computers**

A classical computer performs operations using classical bits where information is encoded as either 0 or 1. In contrast, a quantum computer can perform operations using quantum bits which allow the value of 0 or 1 simultaneously. As a result of the computer’s qubits existing in simultaneous states, a probabilistic approach to solving problems can be used allowing a certain set to be solved much faster than on traditional computers.

**How are quantum computers faster than regular computers?**

Time complexity theory helps us reason about how quantum computers can be faster than regular computers. The problems or computationally expensive tasks that computers solve can be broken into distinct classes as shown in the diagram below.

Problems that can be solved in P (polynomial time) are easy for current day computers to solve and are never used for cryptographic purposes. Problems that require NP (non-deterministic polynomial time) to solve are much harder, sometimes even impossible for current day computers to solve. The Discrete Logarithm Problem (DLP) is an example of a problem that can only be solved by traditional computers in NP time.

The real threat that quantum computers pose to existing DLP based cryptographic systems is that they use the nature of qubits with Shor’s Algorithm to solve the DLP in P time. This is represented as the BQP (bounded-error quantum polynomial time) category in the above diagram.

Further reading:

- https://www.youtube.com/watch?v=g_IaVepNDT4
- https://iota.stackexchange.com/a/207
- https://twitter.com/NNLokam/status/988441376311390209
- https://en.wikipedia.org/wiki/Shor's_algorithm
- https://en.bitcoin.it/wiki/Quantum_computing_and_Bitcoin
- https://iota.stackexchange.com/questions/584/whats-the-difference-between-a-private-key-and-a-seed
- https://en.wikipedia.org/wiki/BQP