# Quantum Computers Are Not a Threat to 128-bit Symmetric Keys

DevFeed: [Quantum Computers Are Not a Threat to 128-bit Symmetric Keys](<https://devfeed.tech/articles/quantum-computers-are-not-a-threat-to-128-bit-symmetric-keys-20691.md>)

Original publisher: [Read original article](<https://words.filippo.io/128-bits/>)

Author: Filippo Valsorda

Published: 2026-04-20T15:21:12Z

Content type: article

Language: en

Sources: [Filippo Valsorda](<https://devfeed.tech/sources/filippo-valsorda.md>)

Topics: [Post-Quantum](<https://devfeed.tech/topics/post-quantum.md>), [Cryptography](<https://devfeed.tech/topics/cryptography.md>), [Algorithms, Complexity](<https://devfeed.tech/topics/algorithms-complexity.md>), [Security](<https://devfeed.tech/topics/security.md>)

Tags: [algorithm](<https://devfeed.tech/tags/algorithm.md>), [algorithms](<https://devfeed.tech/tags/algorithms.md>), [cryptography](<https://devfeed.tech/tags/cryptography.md>), [post-quantum](<https://devfeed.tech/tags/post-quantum.md>), [quantum](<https://devfeed.tech/tags/quantum.md>), [quantum-algorithms](<https://devfeed.tech/tags/quantum-algorithms.md>), [security](<https://devfeed.tech/tags/security.md>)

## AI overview

The article argues that quantum computers do not require larger symmetric key sizes during the post-quantum transition. It explains why Grover's algorithm does not reduce the practical security of AES-128 and SHA-256 enough to justify replacing 128-bit symmetric keys, while asymmetric cryptography remains affected by Shor's algorithm.

## Source excerpt

There is no need to update symmetric key sizes as part of the post-quantum transition, due to the details of how Grover's algorithm scales. Most authorities agree.