BCrypt vs Argon2: Password Hashing in .NET – A Practical Deep Dive

I've worked with .NET for many years. One thing I never compromise on is password storage. Plain text or weak hashing is a disaster waiting to happen. In this post, I break down BCrypt and Argon2 with technical details, internal differences, clean code examples, and when to choose which. Why We Need Slow and Memory-Hard Hashing Normal cryptographic hashes (SHA-256, etc.) are designed to be fast. Attackers with GPUs or ASICs can try billions of password guesses per second. We need password-specific algorithms that are deliberately slow on purpose. They also generate a unique random salt for every password. This makes brute-force and rainbow table attacks extremely expensive. BCrypt – The Battle-Tested Classic BCrypt was created in 1999 based on the Blowfish cipher. It uses a modified expensive key schedule that repeats many times. Technical details: Fixed low memory usage (~4 KB per hash) Controlled by a single "cost" parameter (work factor) Cost = 13 means 2¹³ = 8,192 iterations Purely