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

Source: Dev.to

Overview

Password storage is a critical security concern in .NET applications. Fast cryptographic hashes (e.g., SHA‑256) are unsuitable because attackers can compute billions of guesses per second using GPUs or ASICs. Password‑specific hashing algorithms are deliberately slow and incorporate a unique random salt for each password, making brute‑force and rainbow‑table attacks prohibitively expensive.

BCrypt

BCrypt was introduced in 1999 and is based on the Blowfish cipher. It uses a modified, expensive key schedule that repeats many times.

Technical Details

• Memory usage: Fixed low (~4 KB per hash) – not memory‑hard.
• Cost parameter: Single “work factor” (e.g., Cost = 13 → 2¹³ = 8 192 iterations).
• Performance: Purely CPU‑bound; modern GPUs can still compute many BCrypt hashes in parallel relatively cheaply.

Installation

dotnet add package BCrypt.Net-Next

Sample Code (C#)

using BCrypt.Net;

public static class PasswordHasher
{
    private const int WorkFactor = 13;

    public static string Hash(string password)
        => BCrypt.Net.BCrypt.HashPassword(password, WorkFactor);

    public static bool Verify(string password, string hash)
        => BCrypt.Net.BCrypt.Verify(password, hash);
}

Argon2

Argon2 won the Password Hashing Competition in 2015 and was designed from the ground up for password hashing.

Technical Details

• Memory‑hard: Forces attackers to allocate significant RAM per guess, dramatically raising the cost of large‑scale parallel attacks.
• Variants: Argon2d, Argon2i, Argon2id (recommended for passwords – hybrid approach).
• Configurable parameters:
  • Memory size (m) – typically 32 MB–128 MB+.
  • Iterations (t).
  • Parallelism (p).

Installation

dotnet add package Isopoh.Cryptography.Argon2

Sample Code (C#)

using Isopoh.Cryptography.Argon2;

public static class PasswordHasher
{
    public static string Hash(string password)
        => Argon2.Hash(password);

    public static bool Verify(string password, string hash)
        => Argon2.Verify(hash, password);
}

The library provides secure defaults and automatically handles salt generation and encoding.

Comparison

When to Use Which

Use BCrypt when:

• Maintaining legacy systems that already rely on BCrypt.
• Deploying on very low‑memory servers.
• Simplicity is a primary concern.

Use Argon2 when:

• Building new applications.
• Handling highly sensitive user data.
• Seeking the best protection against current and future hardware attacks.

Best Practices

• Benchmark on production hardware. Aim for a verification time of 400–800 ms per hash.
• Test memory consumption under concurrent load, especially for Argon2.
• Rehash passwords on the next successful login when switching algorithms.
• Combine password hashing with login rate limiting and, where possible, multi‑factor authentication (2FA).