The "Choosing parameters" guide references "the Argon2 draft guidelines" and walks users through a time-first tuning process:
Decide how much time each call should take.
The Argon2 draft guidelines recommend 500 milliseconds (0.5 seconds).
RFC 9106 (2021)1 inverts this: maximize memory first, then set iterations.
If a uniformly safe option that is not tailored to your application or hardware is acceptable, select Argon2id with t=1 iteration, p=4 lanes, m=2 GiB [...]. This is the FIRST RECOMMENDED option.
If much less memory is available, a uniformly safe option is Argon2id with t=3 iterations, p=4 lanes, m=64 MiB [...]. This is the SECOND RECOMMENDED option.
Current defaults vs. recommendations
| Source |
t_cost |
m_cost (memory) |
parallelism |
| argon2_elixir |
3 |
16 (64 MiB) |
4 |
| RFC 9106 first |
1 |
21 (2 GiB) |
4 |
| RFC 9106 second |
3 |
16 (64 MiB) |
4 |
The current defaults match the RFC's second, memory-constrained recommendation. They also exceed the OWASP minimum recommendations2. For reference, Python's argon2-cffi3 also defaults to the RFC 9106 low-memory profile (since v21.2.0) but explicitly documents both profiles and exposes them as RFC_9106_HIGH_MEMORY / RFC_9106_LOW_MEMORY.
Suggested changes
-
Update docs to reference RFC 9106 instead of "the Argon2 draft guidelines" and recommend a memory-first tuning approach. Also mention first and second recommendation in the docs.
-
Note the Out of Memory risk for high m_cost values: each concurrent hash allocates memory in native C space with no built-in concurrency limit.
-
Optionally expose RFC 9106 profiles (like argon2-cffi does) so users can easily opt into the high-memory configuration.
References
The "Choosing parameters" guide references "the Argon2 draft guidelines" and walks users through a time-first tuning process:
RFC 9106 (2021)1 inverts this: maximize memory first, then set iterations.
Current defaults vs. recommendations
t_costm_cost(memory)parallelismThe current defaults match the RFC's second, memory-constrained recommendation. They also exceed the OWASP minimum recommendations2. For reference, Python's argon2-cffi3 also defaults to the RFC 9106 low-memory profile (since v21.2.0) but explicitly documents both profiles and exposes them as
RFC_9106_HIGH_MEMORY/RFC_9106_LOW_MEMORY.Suggested changes
Update docs to reference RFC 9106 instead of "the Argon2 draft guidelines" and recommend a memory-first tuning approach. Also mention first and second recommendation in the docs.
Note the Out of Memory risk for high
m_costvalues: each concurrent hash allocates memory in native C space with no built-in concurrency limit.Optionally expose RFC 9106 profiles (like argon2-cffi does) so users can easily opt into the high-memory configuration.
References
Footnotes
RFC 9106 §4 ↩
OWASP minimum recommendations ↩
argon2-cffi parameters ↩