<s>
Reproducible	B-Application
builds	I-Application
,	O
also	O
known	O
as	O
deterministic	B-Application
compilation	I-Application
,	O
is	O
a	O
process	O
of	O
compiling	B-Language
software	O
which	O
ensures	O
the	O
resulting	O
binary	O
code	O
can	O
be	O
reproduced	O
.	O
</s>
<s>
Source	O
code	O
compiled	B-Language
using	O
deterministic	B-Application
compilation	I-Application
will	O
always	O
output	O
the	O
same	O
binary	O
.	O
</s>
<s>
Reproducible	B-Application
builds	I-Application
can	O
act	O
as	O
part	O
of	O
a	O
chain	O
of	O
trust	O
;	O
the	O
source	O
code	O
can	O
be	O
signed	O
,	O
and	O
deterministic	B-Application
compilation	I-Application
can	O
prove	O
that	O
the	O
binary	O
was	O
compiled	B-Language
from	O
trusted	O
source	O
code	O
.	O
</s>
<s>
Verified	O
reproducible	B-Application
builds	I-Application
provide	O
a	O
strong	O
countermeasure	O
against	O
attacks	O
where	O
binaries	O
do	O
not	O
match	O
their	O
source	O
code	O
,	O
e.g.	O
,	O
because	O
an	O
attacker	O
has	O
inserted	O
malicious	O
code	O
into	O
a	O
binary	O
.	O
</s>
<s>
In	O
a	O
survey	O
of	O
17	O
experts	O
,	O
reproducible	B-Application
builds	I-Application
had	O
a	O
very	O
high	O
utility	O
rating	O
from	O
58.8	O
%	O
participants	O
,	O
but	O
also	O
a	O
high-cost	O
rating	O
from	O
70.6	O
%	O
.	O
</s>
<s>
For	O
the	O
compilation	B-Language
process	O
to	O
be	O
deterministic	O
,	O
the	O
input	O
to	O
the	O
compiler	B-Language
must	O
be	O
the	O
same	O
,	O
regardless	O
of	O
the	O
build	O
environment	O
used	O
.	O
</s>
<s>
This	O
typically	O
involves	O
normalizing	O
variables	O
that	O
may	O
change	O
,	O
such	O
as	O
order	O
of	O
input	O
files	O
,	O
timestamps	O
,	O
locales	B-Device
,	O
and	O
paths	B-Application
.	O
</s>
<s>
Additionally	O
,	O
the	O
compilers	B-Language
must	O
not	O
introduce	O
non-determinism	O
themselves	O
.	O
</s>
<s>
Build	B-Application
systems	I-Application
,	O
such	O
as	O
Bazel	B-Application
and	O
Gitian	O
,	O
can	O
be	O
used	O
to	O
automate	O
deterministic	O
build	O
processes	O
.	O
</s>
<s>
The	B-Application
GNU	I-Application
Project	I-Application
used	O
reproducible	B-Application
builds	I-Application
in	O
the	O
early	O
1990s	O
.	O
</s>
<s>
One	O
of	O
the	O
older	O
projects	O
to	O
promote	O
reproducible	B-Application
builds	I-Application
is	O
the	O
Bitcoin	B-Protocol
project	O
with	O
Gitian	O
.	O
</s>
<s>
Later	O
,	O
in	O
2013	O
,	O
the	O
Tor	B-Application
(	O
anonymity	O
network	O
)	O
project	O
started	O
using	O
Gitian	O
for	O
their	O
reproducible	B-Application
builds	I-Application
.	O
</s>
<s>
In	O
July	O
2013	O
on	O
the	O
Debian	O
project	O
started	O
implementing	O
reproducible	B-Application
builds	I-Application
across	O
its	O
entire	O
package	O
archive	O
.	O
</s>
<s>
In	O
November	O
2018	O
,	O
the	O
Reproducible	B-Application
Builds	I-Application
project	O
joined	O
the	O
Software	O
Freedom	O
Conservancy	O
.	O
</s>
<s>
F-droid	B-Application
uses	O
reproducible	B-Application
builds	I-Application
to	O
provide	O
a	O
guarantee	O
that	O
the	O
distributed	O
APKs	O
use	O
the	O
claimed	O
free	B-Application
source	I-Application
code	I-Application
.	O
</s>
<s>
The	O
Tails	B-Application
portable	O
operating	O
system	O
uses	O
reproducible	B-Application
builds	I-Application
and	O
explains	O
to	O
others	O
how	O
to	O
verify	O
their	O
distribution	O
.	O
</s>
<s>
NixOS	O
claims	O
100%	O
reproducible	B-Application
build	I-Application
in	O
June	O
2021	O
.	O
</s>
<s>
According	O
to	O
the	O
Reproducible	B-Application
Builds	I-Application
project	O
,	O
timestamps	O
are	O
"	O
the	O
biggest	O
source	O
of	O
reproducibility	O
issues	O
.	O
</s>
<s>
Many	O
build	B-Application
tools	I-Application
record	O
the	O
current	O
date	O
and	O
time	O
...	O
and	O
most	O
archive	O
formats	O
will	O
happily	O
record	O
modification	O
times	O
on	O
top	O
of	O
their	O
own	O
timestamps.	O
"	O
</s>
