The password hash Argon2, winner of PHC

This is the reference C implementation of Argon2, the password-hashing function that won the Password Hashing Competition (PHC).

You should use Argon2 whenever you need to hash passwords for credential storage, key derivation, or other applications.

There are two main versions of Argon2, Argon2i and Argon2d. Argon2i is the safest against side-channel attacks, while Argon2d provides the highest resistance against GPU cracking attacks.

Argon2i and Argon2d are parametrized by

  • A time cost, which defines the amount of computation realized and therefore the execution time, given in number of iterations
  • A memory cost, which defines the memory usage, given in kibibytes
  • A parallelism degree, which defines the number of parallel threads

The Argon2 document gives detailed specs and design rationale.

Please report bugs as issues on this repository.


make builds the executable argon2, the static library libargon2.a, and the shared library (or libargon2.dylib on OSX). Make sure to run make test to verify that your build produces valid results.

Command-line utility

argon2 is a command-line utility to test specific Argon2 instances on your system. To show usage instructions, run ./argon2 without arguments as

Usage:  ./argon2 salt [-d] [-t iterations] [-m memory] [-p parallelism]
Password is read from stdin
salt The salt to use, at most 16 characters
-d Use Argon2d instead of Argon2i (which is the default)
-t N Sets the number of iterations to N (default = 3)
-m N Sets the memory usage of 2^N KiB (default 12)
-p N Sets parallelism to N threads (default 1)

For example, to hash “password” using “somesalt” as a salt and doing 2 iterations, consuming 64 MiB, and using four parallel threads:

$ echo -n "password" | ./argon2 somesalt -t 2 -m 16 -p 4
Type: Argon2i
Iterations: 2
Memory: 65536 KiB
Parallelism: 4
Hash: 4162f32384d8f4790bd994cb73c83a4a29f076165ec18af3cfdcf10a8d1b9066
Encoded: $argon2i$m=65536,t=2,p=4$c29tZXNhbHQAAAAAAAAAAA$QWLzI4TY9HkL2ZTLc8g6SinwdhZewYrzz9zxCo0bkGY
0.271 seconds
Verification ok


libargon2 provides an API to both low-level and high-level functions for using Argon2.

The example program below hashes the string “password” with Argon2i using the high-level API and then using the low-level API. While the high-level API only takes input/output buffers and the two cost parameters, the low-level API additionally takes parallelism parameters and several others, as defined in src/argon2.h.

Here the time cost t_cost is set to 2 iterations, the memory cost m_cost is set to 216 kibibytes (64 mebibytes), and parallelism is set to 1 (single-thread).

Compile for example as gcc test.c libargon2.a -Isrc -o test, if the program below is named test.c and placed in the project’s root directory.

#include "argon2.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define HASHLEN 32
#define SALTLEN 16
#define PWD "password"

int main(void)
uint8_t hash1[HASHLEN];
uint8_t hash2[HASHLEN];

uint8_t salt[SALTLEN];
memset( salt, 0x00, SALTLEN );

uint8_t *pwd = (uint8_t *)strdup(PWD);
uint32_t pwdlen = strlen((char *)pwd);

uint32_t t_cost = 2; // 1-pass computation
uint32_t m_cost = (1<<16); // 64 mebibytes memory usage
uint32_t parallelism = 1; // number of threads and lanes

// high-level API
argon2i_hash_raw(t_cost, m_cost, parallelism, pwd, pwdlen, salt, SALTLEN, hash1, HASHLEN);

// low-level API
uint32_t lanes = parallelism;
uint32_t threads = parallelism;
argon2_context context = {
hash2, HASHLEN,
pwd, pwdlen,
salt, SALTLEN,
NULL, 0, /* secret data */
NULL, 0, /* associated data */
t_cost, m_cost, parallelism, parallelism,
NULL, NULL, /* custom memory allocation / deallocation functions */
ARGON2_DEFAULT_FLAGS /* by default the password is zeroed on exit */
argon2i( &context );

for( int i=0; i<HASHLEN; ++i ) printf( "%02x", hash1[i] ); printf( "\n" );
if (memcmp(hash1, hash2, HASHLEN)) {
for( int i=0; i<HASHLEN; ++i ) printf( "%02x", hash2[i] ); printf( "\n" );
else printf("ok\n");

return 0;

To use Argon2d instead of Argon2i call argon2d_hash instead of argon2i_hash using the high-level API, and argon2d instead of argon2i using the low-level API.

To produce the crypt-like encoding rather than the raw hash, call argon2i_hash_encoded for Argon2i and argon2d_hash_encoded for Argon2d.

See src/argon2.h for API detais.

Note: in this example the salt is set to the all-0x00 string for the sake of simplicity, but in your application you should use a random salt.


make bench creates the executable bench, which measures the execution time of various Argon2 instances:

$ ./bench
Argon2d 1 iterations 1 MiB 1 threads: 5.91 cpb 5.91 Mcycles
Argon2i 1 iterations 1 MiB 1 threads: 4.64 cpb 4.64 Mcycles
0.0041 seconds

Argon2d 1 iterations 1 MiB 2 threads: 2.76 cpb 2.76 Mcycles
Argon2i 1 iterations 1 MiB 2 threads: 2.87 cpb 2.87 Mcycles
0.0038 seconds

Argon2d 1 iterations 1 MiB 4 threads: 3.25 cpb 3.25 Mcycles
Argon2i 1 iterations 1 MiB 4 threads: 3.57 cpb 3.57 Mcycles
0.0048 seconds


Argon2d 1 iterations 4096 MiB 2 threads: 2.15 cpb 8788.08 Mcycles
Argon2i 1 iterations 4096 MiB 2 threads: 2.15 cpb 8821.59 Mcycles
13.0112 seconds

Argon2d 1 iterations 4096 MiB 4 threads: 1.79 cpb 7343.72 Mcycles
Argon2i 1 iterations 4096 MiB 4 threads: 2.72 cpb 11124.86 Mcycles
19.3974 seconds



Bindings are available for the following languages (make sure to read their documentation):

Intellectual property

Except for the components listed below, the Argon2 code in this repository is copyright (c) 2015 Daniel Dinu, Dmitry Khovratovich (main authors), Jean-Philippe Aumasson and Samuel Neves, and under CC0 license.

The string encoding routines in src/encoding.c are copyright (c) 2015 Thomas Pornin, and under CC0 license.

The BLAKE2 code in src/blake2/ is copyright (c) Samuel Neves, 2013–2015, and under CC0 license.

All licenses are therefore GPL-compatible.

January 7, 2016 at 09:31PM
 via Hacker News

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