Argon2idEdit

Argon2id is a password-hashing function that belongs to the Argon2 family. It is designed to securely derive a fixed-length key from a user’s password in a way that makes brute-force attacks expensive in terms of both time and memory. The “id” variant is a hybrid that blends data-independent and data-dependent memory access patterns, a design choice intended to balance resistance to side-channel leakage with robustness against GPU-accelerated cracking. In practice, Argon2id is widely used in modern password-storage schemes and is supported by a growing ecosystem of libraries and frameworks.

Argon2 as a family was selected through the Password Hashing Competition Password Hashing Competition and has since become a reference point for modern password storage. The family includes several variants, among them Argon2i, Argon2d, and Argon2id. Argon2id, in particular, is often recommended as the default choice for password hashing because it aims to combine strong security properties with practical performance characteristics. For many developers, Argon2id represents a robust baseline for protecting credentials in a range of applications—from small services to large-scale systems. Argon2 Argon2i Argon2d Password hashing memory-hard function BLAKE2 PHC libsodium Go (programming language) PHP password_hash PASSWORD_ARGON2ID

Design and operation

What it is and how it works

Argon2id is a memory-hard function designed to be parameterizable. It operates on a fixed-size block of memory and a series of transformation steps that mix the input password, a cryptographic salt, and several algorithmic parameters to produce a derived key of configurable length. The memory-hard property is intended to force attackers to allocate significant memory resources, which helps to deter inexpensive parallel cracking on GPUs or custom hardware. See also memory-hard function.
The internal cryptographic primitive in Argon2 is based on a secure hash function framework (the implementation uses a construction derived from BLAKE2). The algorithm fills a memory array with blocks, performing multiple passes to produce the final derived key. This process is parameterizable to control the resource cost of hashing a password.

The Argon2 variants

Argon2i (data-independent) emphasizes constant-time-like behavior with respect to password-dependent data, which helps resist timing- and cache-related side-channel information leakage. It trades some performance in certain scenarios for stronger resistance against side-channel leakage.
Argon2d (data-dependent) uses memory accesses that depend on the password data. This can provide strong resistance against certain offline cracking strategies but may be more vulnerable to side-channel observations in some environments.
Argon2id is the hybrid variant that uses data-independent memory access for part of the computation (often the initial phase) and data-dependent access for the remainder. The intent is to capture the resilience against side-channel leakage from Argon2i while retaining the strong defense against offline GPU-based attackers typical of Argon2d. For many deployments, Argon2id provides a practical balance of security properties and performance. See also Argon2i Argon2d.

Parameters and configuration

Key knobs control the cost and behavior of Argon2id: - Memory cost (M): the amount of RAM the algorithm uses during hashing. Higher M increases resistance to parallel attacks but requires more hardware resources. See memory-hard function. - Time cost (t): the number of independent iterations over the memory. Higher t increases computational work for each password guess. - Parallelism (p): the number of parallel lanes that the algorithm can use, enabling multi-core CPUs to speed up hashing without compromising security. - Salt: a unique value per password that prevents precomputed attacks and ensures identical passwords hash differently. See salt. - Output length: the length of the derived key, which should be chosen to align with the intended use (e.g., storage of password hashes with sufficient entropy). See hash function. - Versioning and updates: implementations may support different parameters or version identifiers to facilitate upgrades over time. See password hashing.

Security considerations and practical deployment

Side-channel resistance: Argon2id’s design explicitly aims to mitigate side-channel leakage by incorporating data-independent memory access in the early steps, reducing information leaked through timing and cache behavior in some environments. See side-channel attack.
Memory-hardness: The memory-hard property makes it hard to accelerate password cracking using specialized hardware that lacks large memory, which is a central reason Argon2id is favored for password storage in modern systems. See memory-hard function.
GPU and ASIC resistance: While no password-hashing scheme is completely resistant to well-funded attackers, Argon2id is structured to raise the cost of parallel brute-force attempts relative to older schemes such as bcrypt or early scrypt configurations. See GPU ASIC.
Comparison with earlier schemes: Argon2id generally provides stronger security guarantees and more flexible tuning than older approaches, while offering comparable or better real-world performance when configured properly. See bcrypt scrypt.

Adoption, interoperability, and usage

Libraries and language ecosystems: Argon2id is supported by a broad range of cryptographic libraries and language ecosystems, including those used in web backends and systems programming. This broad support helps standardize secure password storage practices across platforms. See libsodium.
Default and recommended practice: In many modern frameworks and libraries, Argon2id is recommended as the default password-hashing scheme due to its balanced security properties and configurability. See password hashing.
Practical considerations for deployment:
- Choose memory and time parameters that reflect the hardware you expect your authentication servers to encounter, aiming for a workable balance between security and latency.
- Use unique salts for every password and store the resulting hash along with the parameters used for hashing, so updates can be performed without reworking existing credentials. See salt hashing.
Real-world usage: Argon2id has become a go-to option for secure password storage in modern systems, and it is commonly integrated in frameworks and services that handle credential storage and authentication.