GSoC 2019 Final Report: Incorporating the memory-hard Argon2 hashing scheme into NetBSD


January 12, 2020 posted by Jason High

Introduction

We successfully incorporated the Argon2 reference implementation into NetBSD/amd64 for our 2019 Google Summer of Coding project. We introduced our project here and provided some hints on how to select parameters here. For our final report, we will provide an overview of what changes were made to complete the project.

Incorporating the Argon2 Reference Implementation

The Argon2 reference implementation, available here, is available under both the Creative Commons CC0 1.0 and the Apache Public License 2.0. To import the reference implementation into src/external, we chose to use the Apache 2.0 license for this project.

During our initial phase 1, we focused on building the libargon2 library and integrating the functionality into the existing password management framework via libcrypt. Toward this end, we imported the reference implementation and created the "glue" to incorporate the changes into /usr/src/external/apache. The reference implementation is found in

m2$ ls /usr/src/external/apache2/argon2                                                                                    
Makefile dist     lib      usr.bin
The Argon2 reference implementation provides both a library and a binary. We build the libargon2 library to support libcrypt integration, and the argon2(1) binary to provide a userland command-line tool for evaluation. To build the code, we add MKARGON2 to bsd.own.mk
_MKVARS.yes= \
	...
        MKARGON2 \
	...
and add the following conditional build to /usr/src/external/apache2/Makefile
.if (defined(MKARGON2) && ${MKARGON2} != "no")
SUBDIR+= argon2
.endif
After successfully building and installation, we have the following new files and symlinks
/usr/bin/argon2
/usr/lib/libargon2.a
/usr/lib/libargon2.so
/usr/lib/libargon2.so.1
/usr/lib/libargon2.so.1.0
To incorporate Argon2 into the password management framework of NetBSD, we focused on libcrypt. In /usr/src/lib/libcrypt/Makefile, we first check for MKARGON2
.if (defined(MKARGON2) && ${MKARGON2} != "no")
HAVE_ARGON2=1
.endif
If HAVE_ARGON2 is defined and enabled, we append the following to the build flags
.if defined(HAVE_ARGON2)
SRCS+=          crypt-argon2.c
CFLAGS+=        -DHAVE_ARGON2 -I../../external/apache2/argon2/dist/phc-winner
-argon2/include/
LDADD+=         -largon2 
.endif
As hinted above, our most significant addition to libcrypt is the file crypt-argon2.c. This file pulls in the functionality of libargon2 into libcrypt. Changes were also made to pw_gensalt.c to allow for parameter parsing and salt generation.

Having completed the backend support, we pull Argon2 into userland tools, such as pwhash(1), in the same way as above

.if ( defined(MKARGON2) && ${MKARGON2} != "no" )
CPPFLAGS+=      -DHAVE_ARGON2
.endif
Once built, we can specify Argon2 using the '-A' command-line argument to pwhash(1), followed by the Argon2 variant name, and any of the parameterized values specified in argon2(1). See our first blog post for more details. As an example, to generate an argon2id encoding of the password password using default parameters, we can use the following
m2# pwhash -A argon2id password
$argon2id$v=19$m=4096,t=3,p=1$.SJJCiU575MDnA8s$+pjT4JsF2eLNQuLPEyhRA5LCFG
QWAKsksIPl5ewTWNY
To simplify Argon2 password management, we can utilize passwd.conf(5) to apply Argon2 to a specified user or all users. The same parameters are accepted as for argon2(1). For example, to specify argon2i with non-default parameters for user 'testuser', you can use the following in your passwd.conf
m1# grep -A1 testuser /etc/passwd.conf 
testuser:
        localcipher = argon2i,t=6,m=4096,p=1
With the above configuration in place, we are able to support standard password management. For example
m1# passwd testuser
Changing password for testuser.
New Password:
Retype New Password:

m1# grep testuser /etc/master.passwd  
testuser:$argon2i$v=19$m=4096,t=6,p=1$PDd65qr6JU0Pfnpr$8YOMYcwINuKHoxIV8Q0FJHG+
RP82xtmAuGep26brilU:1001:100::0:0::/home/testuser:/sbin/nologin

Testing

The argon2(1) binary allows us to easily validate parameters and encoding. This is most useful during performance testing, see here. With argon2(1), we can specify our parameterized values and evaluate both the resulting encoding and timing.
m2# echo -n password|argon2 somesalt -id -p 3 -m 8
Type:           Argon2id
Iterations:     3
Memory:         256 KiB
Parallelism:    3
Hash:           97f773f68715d27272490d3d2e74a2a9b06a5bca759b71eab7c02be8a453bfb9
Encoded:        $argon2id$v=19$m=256,t=3,p=3$c29tZXNhbHQ$l/dz9ocV0nJySQ09LnSiqb
BqW8p1m3Hqt8Ar6KRTv7k
0.000 seconds
Verification ok
We provide one approach to evaluating Argon2 parameter tuning in our second post. In addition to manual testing, we also provide some ATF tests for pwhash, for both hashing and verification. These tests are focus on encoding correctness, matching known encodings to test results during execution.
/usr/src/tests/usr.bin/argon2

tp: t_argon2_v10_hash
tp: t_argon2_v10_verify
tp: t_argon2_v13_hash
tp: t_argon2_v13_verify


cd /usr/src/tests/usr.bin/argon2
atf-run

info: atf.version, Automated Testing Framework 0.20 (atf-0.20)
info: tests.root, /usr/src/tests/usr.bin/argon2

..

tc-so:Executing command [ /bin/sh -c echo -n password | \
argon2 somesalt -v 13 -t 2 -m 8 -p 1 -r ]
tc-end: 1567497383.571791, argon2_v13_t2_m8_p1, passed

...

Conclusion

We have successfully integrated Argon2 into NetBSD using the native build framework. We have extended existing functionality to support local password management using Argon2 encoding. We are able to tune Argon2 so that we can achieve reasonable performance on NetBSD. In this final post, we summarize the work done to incorporate the reference implementation into NetBSD and how to use it. We hope you can use the work completed during this project. Thank you for the opportunity to participate in the Google Summer of Code 2019 and the NetBSD project!

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