API Reference#
argon2-cffi comes with an high-level API and uses the officially recommended low-memory Argon2 parameters that result in a verification time of 40–50ms on recent-ish hardware.
Warning
The current memory requirement is set to rather conservative 64 MB. However, in memory constrained environments such as Docker containers that can lead to problems. One possible non-obvious symptom are apparent freezes that are caused by swapping.
Please check Choosing Parameters for more details.
Unless you have any special needs, all you need to know is:
>>> from argon2 import PasswordHasher
>>> ph = PasswordHasher()
>>> hash = ph.hash("correct horse battery staple")
>>> hash
'$argon2id$v=19$m=65536,t=3,p=4$MIIRqgvgQbgj220jfp0MPA$YfwJSVjtjSU0zzV/P3S9nnQ/USre2wvJMjfCIjrTQbg'
>>> ph.verify(hash, "correct horse battery staple")
True
>>> ph.check_needs_rehash(hash)
False
>>> ph.verify(hash, "Tr0ub4dor&3")
Traceback (most recent call last):
...
argon2.exceptions.VerifyMismatchError: The password does not match the supplied hash
A login function could thus look like this:
import argon2
ph = argon2.PasswordHasher()
def login(db, user, password):
hash = db.get_password_hash_for_user(user)
# Verify password, raises exception if wrong.
ph.verify(hash, password)
# Now that we have the cleartext password,
# check the hash's parameters and if outdated,
# rehash the user's password in the database.
if ph.check_needs_rehash(hash):
db.set_password_hash_for_user(user, ph.hash(password))
While the PasswordHasher
class has the aspiration to be good to use out of the box, it has all the parametrization you’ll need:
- class argon2.PasswordHasher(time_cost: int = 3, memory_cost: int = 65536, parallelism: int = 4, hash_len: int = 32, salt_len: int = 16, encoding: str = 'utf-8', type: Type = Type.ID)#
High level class to hash passwords with sensible defaults.
Uses Argon2id by default and always uses a random salt for hashing. But it can verify any type of Argon2 as long as the hash is correctly encoded.
The reason for this being a class is both for convenience to carry parameters and to verify the parameters only once. Any unnecessary slowdown when hashing is a tangible advantage for a brute force attacker.
- Parameters:
time_cost (int) – Defines the amount of computation realized and therefore the execution time, given in number of iterations.
memory_cost (int) – Defines the memory usage, given in kibibytes.
parallelism (int) – Defines the number of parallel threads (changes the resulting hash value).
hash_len (int) – Length of the hash in bytes.
salt_len (int) – Length of random salt to be generated for each password.
encoding (str) – The Argon2 C library expects bytes. So if
hash()
orverify()
are passed astr
, it will be encoded using this encoding.type (Type) – Argon2 type to use. Only change for interoperability with legacy systems.
New in version 16.0.0.
Changed in version 18.2.0: Switch from Argon2i to Argon2id based on the recommendation by the current RFC draft. See also Choosing Parameters.
Changed in version 18.2.0: Changed default memory_cost to 100 MiB and default parallelism to 8.
Changed in version 18.2.0:
verify
now will determine the type of hash.Changed in version 18.3.0: The Argon2 type is configurable now.
New in version 21.2.0:
from_parameters()
Changed in version 21.2.0: Changed defaults to
argon2.profiles.RFC_9106_LOW_MEMORY
.- check_needs_rehash(hash: str) bool #
Check whether hash was created using the instance’s parameters.
Whenever your Argon2 parameters – or argon2-cffi’s defaults! – change, you should rehash your passwords at the next opportunity. The common approach is to do that whenever a user logs in, since that should be the only time when you have access to the cleartext password.
Therefore it’s best practice to check – and if necessary rehash – passwords after each successful authentication.
- Return type:
New in version 18.2.0.
- classmethod from_parameters(params: Parameters) PasswordHasher #
Construct a PasswordHasher from params.
New in version 21.2.0.
- hash(password: Union[str, bytes]) str #
Hash password and return an encoded hash.
- Parameters:
password (
bytes
orstr
) – Password to hash.- Raises:
argon2.exceptions.HashingError – If hashing fails.
- Return type:
- verify(hash: Union[str, bytes], password: Union[str, bytes]) Literal[True] #
Verify that password matches hash.
Warning
It is assumed that the caller is in full control of the hash. No other parsing than the determination of the hash type is done by argon2-cffi.
- Parameters:
hash (
bytes
orstr
) – An encoded hash as returned fromPasswordHasher.hash()
.password (
bytes
orstr
) – The password to verify.
- Raises:
argon2.exceptions.VerifyMismatchError – If verification fails because hash is not valid for password.
argon2.exceptions.VerificationError – If verification fails for other reasons.
argon2.exceptions.InvalidHash – If hash is so clearly invalid, that it couldn’t be passed to Argon2.
- Returns:
True
on success, raiseVerificationError
otherwise.- Return type:
Changed in version 16.1.0: Raise
VerifyMismatchError
on mismatches instead of its more generic superclass.New in version 18.2.0: Hash type agility.
If you don’t specify any parameters, the following constants are used:
- argon2.DEFAULT_RANDOM_SALT_LENGTH#
- argon2.DEFAULT_HASH_LENGTH#
- argon2.DEFAULT_TIME_COST#
- argon2.DEFAULT_MEMORY_COST#
- argon2.DEFAULT_PARALLELISM#
They are taken from argon2.profiles.RFC_9106_LOW_MEMORY
.
Profiles#
This module offers access to standardized parameters that you can load using
PasswordHasher.from_parameters()
. See the source code for
concrete values and Choosing Parameters for more information.
New in version 21.2.0.
You can try them out using the CLI interface. For example:
$ python -m argon2 --profile RFC_9106_HIGH_MEMORY
Running Argon2id 100 times with:
hash_len: 32 bytes
memory_cost: 2097152 KiB
parallelism: 4 threads
time_cost: 1 iterations
Measuring...
866.5ms per password verification
That should give you a feeling on how they perform in your environment.
- argon2.profiles.RFC_9106_HIGH_MEMORY#
Called “FIRST RECOMMENDED option” by RFC 9106.
Requires beefy 2 GiB, so be careful in memory-contrained systems.
New in version 21.2.0.
- argon2.profiles.RFC_9106_LOW_MEMORY#
Called “SECOND RECOMMENDED option” by RFC 9106.
The main difference is that it only takes 64 MiB of RAM.
The values from this profile are the default parameters used by
argon2.PasswordHasher
.New in version 21.2.0.
- argon2.profiles.PRE_21_2#
The default values that argon2-cffi used from 18.2.0 until 21.2.0.
Needs 100 MiB of RAM.
New in version 21.2.0.
- argon2.profiles.CHEAPEST#
This is the cheapest-possible profile.
Warning
This is only for testing purposes! Do not use in production!
New in version 21.2.0.
Exceptions#
- exception argon2.exceptions.VerificationError#
Verification failed.
You can find the original error message from Argon2 in
args[0]
.
- exception argon2.exceptions.VerifyMismatchError#
The secret does not match the hash.
Subclass of
argon2.exceptions.VerificationError
.New in version 16.1.0.
- exception argon2.exceptions.HashingError#
Raised if hashing failed.
You can find the original error message from Argon2 in
args[0]
.
- exception argon2.exceptions.InvalidHash#
Raised if the hash is invalid before passing it to Argon2.
New in version 18.2.0.
Utilities#
- argon2.extract_parameters(hash: str) Parameters #
Extract parameters from an encoded hash.
- Parameters:
params (str) – An encoded Argon2 hash string.
- Return type:
New in version 18.2.0.
Low Level#
Low-level functions if you want to build your own higher level abstractions.
Warning
This is a “Hazardous Materials” module. You should ONLY use it if you’re 100% absolutely sure that you know what you’re doing because this module is full of land mines, dragons, and dinosaurs with laser guns.
- class argon2.low_level.Type(value)#
Enum of Argon2 variants.
Please see Choosing Parameters on how to pick one.
- D = 0#
Argon2d is faster and uses data-depending memory access, which makes it less suitable for hashing secrets and more suitable for cryptocurrencies and applications with no threats from side-channel timing attacks.
- I = 1#
Argon2i uses data-independent memory access. Argon2i is slower as it makes more passes over the memory to protect from tradeoff attacks.
- ID = 2#
Argon2id is a hybrid of Argon2i and Argon2d, using a combination of data-depending and data-independent memory accesses, which gives some of Argon2i’s resistance to side-channel cache timing attacks and much of Argon2d’s resistance to GPU cracking attacks.
That makes it the preferred type for password hashing and password-based key derivation.
New in version 16.3.0.
- argon2.low_level.ARGON2_VERSION = 19#
The latest version of the Argon2 algorithm that is supported (and used by default).
New in version 16.1.0.
- argon2.low_level.hash_secret(secret: bytes, salt: bytes, time_cost: int, memory_cost: int, parallelism: int, hash_len: int, type: Type, version: int = 19) bytes #
Hash secret and return an encoded hash.
An encoded hash can be directly passed into
verify_secret()
as it contains all parameters and the salt.- Parameters:
For an explanation of the Argon2 parameters see
PasswordHasher
.- Return type:
- Raises:
argon2.exceptions.HashingError – If hashing fails.
New in version 16.0.0.
>>> import argon2
>>> argon2.low_level.hash_secret(
... b"secret", b"somesalt",
... time_cost=1, memory_cost=8, parallelism=1, hash_len=64, type=argon2.low_level.Type.D
... )
b'$argon2d$v=19$m=8,t=1,p=1$c29tZXNhbHQ$ba2qC75j0+JAunZZ/L0hZdQgCv+tOieBuKKXSrQiWm7nlkRcK+YqWr0i0m0WABJKelU8qHJp0SZzH0b1Z+ITvQ'
- argon2.low_level.verify_secret(hash: bytes, secret: bytes, type: Type) Literal[True] #
Verify whether secret is correct for hash of type.
- Parameters:
hash (bytes) – An encoded Argon2 hash as returned by
hash_secret()
.secret (bytes) – The secret to verify whether it matches the one in hash.
type (Type) – Type for hash.
- Raises:
argon2.exceptions.VerifyMismatchError – If verification fails because hash is not valid for secret of type.
argon2.exceptions.VerificationError – If verification fails for other reasons.
- Returns:
True
on success, raiseVerificationError
otherwise.- Return type:
New in version 16.0.0.
Changed in version 16.1.0: Raise
VerifyMismatchError
on mismatches instead of its more generic superclass.
The raw hash can also be computed:
- argon2.low_level.hash_secret_raw(secret: bytes, salt: bytes, time_cost: int, memory_cost: int, parallelism: int, hash_len: int, type: Type, version: int = 19) bytes #
Hash password and return a raw hash.
This function takes the same parameters as
hash_secret()
.New in version 16.0.0.
>>> argon2.low_level.hash_secret_raw(
... b"secret", b"somesalt",
... time_cost=1, memory_cost=8, parallelism=1, hash_len=8, type=argon2.low_level.Type.D
... )
b'\xe4n\xf5\xc8|\xa3>\x1d'
The super low-level argon2_core()
function is exposed too if you need access to very specific options:
- argon2.low_level.core(context: Any, type: int) int #
Direct binding to the
argon2_ctx
function.Warning
This is a strictly advanced function working on raw C data structures. Both Argon2’s and argon2-cffi’s higher-level bindings do a lot of sanity checks and housekeeping work that you are now responsible for (e.g. clearing buffers). The structure of the context object can, has, and will change with any release!
Use at your own peril; argon2-cffi does not use this binding itself.
- Parameters:
- Return type:
- Returns:
An Argon2 error code. Can be transformed into a string using
error_to_str()
.
New in version 16.0.0.
In order to use core()
, you need access to argon2-cffi’s FFI objects.
Therefore it is OK to use argon2.low_level.ffi
and argon2.low_level.lib
when working with it:
>>> from argon2.low_level import ARGON2_VERSION, Type, core, ffi, lib
>>> pwd = b"secret"
>>> salt = b"12345678"
>>> hash_len = 8
>>> # Make sure you keep FFI objects alive until *after* the core call!
>>> cout = ffi.new("uint8_t[]", hash_len)
>>> cpwd = ffi.new("uint8_t[]", pwd)
>>> csalt = ffi.new("uint8_t[]", salt)
>>> ctx = ffi.new(
... "argon2_context *", dict(
... version=ARGON2_VERSION,
... out=cout, outlen=hash_len,
... pwd=cpwd, pwdlen=len(pwd),
... salt=csalt, saltlen=len(salt),
... secret=ffi.NULL, secretlen=0,
... ad=ffi.NULL, adlen=0,
... t_cost=1,
... m_cost=8,
... lanes=1, threads=1,
... allocate_cbk=ffi.NULL, free_cbk=ffi.NULL,
... flags=lib.ARGON2_DEFAULT_FLAGS,
... )
... )
>>> ctx
<cdata 'struct Argon2_Context *' owning 120 bytes>
>>> core(ctx, Type.D.value)
0
>>> out = bytes(ffi.buffer(ctx.out, ctx.outlen))
>>> out
b'\xb4\xe2HjO\x14d\x9b'
>>> out == argon2.low_level.hash_secret_raw(pwd, salt, 1, 8, 1, 8, Type.D)
True
All constants and types on argon2.low_level.lib
are guaranteed to stay as long they are not altered by Argon2 itself.
Deprecated APIs#
These APIs are from the first release of argon2-cffi and proved to live in an unfortunate mid-level. On one hand they have defaults and check parameters but on the other hand they only consume byte strings.
Therefore the decision has been made to replace them by a high-level (argon2.PasswordHasher
) and a low-level (argon2.low_level
) solution.
There are no immediate plans to remove them though.
- argon2.hash_password(password: bytes, salt: Optional[bytes] = None, time_cost: int = 3, memory_cost: int = 65536, parallelism: int = 4, hash_len: int = 32, type: Type = Type.I) bytes #
Legacy alias for
hash_secret()
with default parameters.Deprecated since version 16.0.0: Use
argon2.PasswordHasher
for passwords.
- argon2.hash_password_raw(password: bytes, salt: Optional[bytes] = None, time_cost: int = 3, memory_cost: int = 65536, parallelism: int = 4, hash_len: int = 32, type: Type = Type.I) bytes #
Legacy alias for
hash_secret_raw()
with default parameters.Deprecated since version 16.0.0: Use
argon2.PasswordHasher
for passwords.