sebven.com

What it is

This is a personal blog run by Sebastiaan Venendaal, an astronomy master's student from the University of Groningen in the Netherlands (username: Polymero). Its core content focuses on the cryptography side of CTF (Capture The Flag) competitions, and it's a niche personal site dedicated to creating cryptography challenges and sharing write-ups.

Core Features & Content

The site's content falls into two main categories: First, a wide range of original cryptography CTF challenges created by the author as a competition出题人, covering all major cryptography topics including RSA, Paillier homomorphic encryption, elliptic curve cryptography, and XOR encryption, with difficulty ranging from beginner to advanced. Second, complete write-ups for all challenges that clearly explain vulnerability discovery methods and step-by-step solution reasoning. On top of that, the site also features a dedicated curated beginner's guide to cryptography CTF that outlines the required foundational knowledge and tools, making it extremely friendly for new learners. All content is archived and searchable by competition and tags, so users can easily find what they need.

Pros, Cons & Who It's For

Pros: All content on the site is original practice-focused material, with strong professional credibility. It's 100% free, ad-free, and its clear beginner guidance lowers the barrier to entry for new learners.
Cons: As a personal blog, updates depend entirely on the author's personal schedule, so release frequency is inconsistent. The entire site is only available in English, and there is no built-in online practice environment — users need to set up a local working environment on their own to solve challenges.

It is ideal for CTF cryptography competitors, cybersecurity students, and beginners interested in learning cryptography.

Accessibility from China

This domain is currently directly accessible via the public internet, no proxy is required, and load speed is normal.