Fix race condition & allow operation cache to grow.

[thirdparty/openssl.git] / INSTALL.md

Build and Install
=================

This document describes installation on all supported operating
systems (the Unix/Linux family, including macOS), OpenVMS,
and Windows).

Table of Contents
=================

 - [Prerequisites](#prerequisites)
 - [Notational Conventions](#notational-conventions)
 - [Quick Installation Guide](#quick-installation-guide)
   - [Building OpenSSL](#building-openssl)
   - [Installing OpenSSL](#installing-openssl)
 - [Configuration Options](#configuration-options)
   - [API Level](#api-level)
   - [Cross Compile Prefix](#cross-compile-prefix)
   - [Build Type](#build-type)
   - [Directories](#directories)
   - [Compiler Warnings](#compiler-warnings)
   - [ZLib Flags](#zlib-flags)
   - [Seeding the Random Generator](#seeding-the-random-generator)
   - [Setting the FIPS HMAC key](#setting-the-FIPS-HMAC-key)
   - [Enable and Disable Features](#enable-and-disable-features)
   - [Displaying configuration data](#displaying-configuration-data)
 - [Installation Steps in Detail](#installation-steps-in-detail)
   - [Configure](#configure-openssl)
   - [Build](#build-openssl)
   - [Test](#test-openssl)
   - [Install](#install-openssl)
 - [Advanced Build Options](#advanced-build-options)
   - [Environment Variables](#environment-variables)
   - [Makefile Targets](#makefile-targets)
   - [Running Selected Tests](#running-selected-tests)
 - [Troubleshooting](#troubleshooting)
   - [Configuration Problems](#configuration-problems)
   - [Build Failures](#build-failures)
   - [Test Failures](#test-failures)
 - [Notes](#notes)
   - [Notes on multi-threading](#notes-on-multi-threading)
   - [Notes on shared libraries](#notes-on-shared-libraries)
   - [Notes on random number generation](#notes-on-random-number-generation)

Prerequisites
=============

To install OpenSSL, you will need:

 * A "make" implementation
 * Perl 5 with core modules (please read [NOTES-Perl.md](NOTES-Perl.md))
 * The Perl module `Text::Template` (please read [NOTES-PERL.md](NOTES-Perl.md))
 * an ANSI C compiler
 * a development environment in the form of development libraries and C
   header files
 * a supported operating system

For additional platform specific requirements, solutions to specific
issues and other details, please read one of these:

 * [NOTES-Unix.md](NOTES-Unix.md) - notes for Unix like systems
 * [NOTES-VMS.md](NOTES-VMS.md) - notes related to OpenVMS
 * [NOTES-Windows.txt](NOTES-Windows.txt) - notes related to the Windows platform
 * [NOTES-DJGPP.md](NOTES-DJGPP.md) - building for DOS with DJGPP
 * [NOTES-Android.md](NOTES-Android.md) - building for Android platforms (using NDK)
 * [NOTES-Valgrind.md](NOTES-Valgrind.md) - testing with Valgrind
 * [NOTES-Perl.m](NOTES-Perl.md) - some notes on Perl

Notational conventions
======================

Throughout this document, we use the following conventions.

Commands
--------

Any line starting with a dollar sign is a command line.

    $ command

The dollar sign indicates the shell prompt and is not to be entered as
part of the command.

Choices
-------

Several words in curly braces separated by pipe characters indicate a
**mandatory choice**, to be replaced with one of the given words.
For example, the line

    $ echo { WORD1 | WORD2 | WORD3 }

represents one of the following three commands

    $ echo WORD1
    - or -
    $ echo WORD2
    - or -
    $ echo WORD3

One or several words in square brackets separated by pipe characters
denote an **optional choice**.  It is similar to the mandatory choice,
but it can also be omitted entirely.

So the line

    $ echo [ WORD1 | WORD2 | WORD3 ]

represents one of the four commands

    $ echo WORD1
    - or -
    $ echo WORD2
    - or -
    $ echo WORD3
    - or -
    $ echo

Arguments
---------

**Mandatory arguments** are enclosed in double curly braces.
A simple example would be

    $ type {{ filename }}

which is to be understood to use the command `type` on some file name
determined by the user.

**Optional Arguments** are enclosed in double square brackets.

    [[ options ]]

Note that the notation assumes spaces around `{`, `}`, `[`, `]`, `{{`, `}}` and
`[[`, `]]`.  This is to differentiate from OpenVMS directory
specifications, which also use [ and ], but without spaces.

Quick Installation Guide
========================

If you just want to get OpenSSL installed without bothering too much
about the details, here is the short version of how to build and install
OpenSSL.  If any of the following steps fails, please consult the
[Installation in Detail](#installation-steps-in-detail) section below.

Building OpenSSL
----------------

Use the following commands to configure, build and test OpenSSL.
The testing is optional, but recommended if you intend to install
OpenSSL for production use.

### Unix / Linux / macOS

    $ ./Configure
    $ make
    $ make test

### OpenVMS

Use the following commands to build OpenSSL:

    $ perl Configure
    $ mms
    $ mms test

### Windows

If you are using Visual Studio, open a Developer Command Prompt and
issue the following commands to build OpenSSL.

    $ perl Configure
    $ nmake
    $ nmake test

As mentioned in the [Choices](#choices) section, you need to pick one
of the four Configure targets in the first command.

Most likely you will be using the `VC-WIN64A` target for 64bit Windows
binaries (AMD64) or `VC-WIN32` for 32bit Windows binaries (X86).
The other two options are `VC-WIN64I` (Intel IA64, Itanium) and
`VC-CE` (Windows CE) are rather uncommon nowadays.

Installing OpenSSL
------------------

The following commands will install OpenSSL to a default system location.

**Danger Zone:** even if you are impatient, please read the following two
paragraphs carefully before you install OpenSSL.

For security reasons the default system location is by default not writable
for unprivileged users.  So for the final installation step administrative
privileges are required.  The default system location and the procedure to
obtain administrative privileges depends on the operating system.
It is recommended to compile and test OpenSSL with normal user privileges
and use administrative privileges only for the final installation step.

On some platforms OpenSSL is preinstalled as part of the Operating System.
In this case it is highly recommended not to overwrite the system versions,
because other applications or libraries might depend on it.
To avoid breaking other applications, install your copy of OpenSSL to a
[different location](#installing-to-a-different-location) which is not in
the global search path for system libraries.

Finally, if you plan on using the FIPS module, you need to read the
[Post-installation Notes](#post-installation-notes) further down.

### Unix / Linux / macOS

Depending on your distribution, you need to run the following command as
root user or prepend `sudo` to the command:

    $ make install

By default, OpenSSL will be installed to

    /usr/local

More precisely, the files will be installed into the  subdirectories

    /usr/local/bin
    /usr/local/lib
    /usr/local/include
    ...

depending on the file type, as it is custom on Unix-like operating systems.

### OpenVMS

Use the following command to install OpenSSL.

    $ mms install

By default, OpenSSL will be installed to

    SYS$COMMON:[OPENSSL-'version'...]

where 'version' is the OpenSSL version number with underscores instead
of periods.

### Windows

If you are using Visual Studio, open the Developer Command Prompt _elevated_
and issue the following command.

    $ nmake install

The easiest way to elevate the Command Prompt is to press and hold down
the both the `<CTRL>` and `<SHIFT>` key while clicking the menu item in the
task menu.

The default installation location is

    C:\Program Files\OpenSSL

for native binaries, or

    C:\Program Files (x86)\OpenSSL

for 32bit binaries on 64bit Windows (WOW64).

#### Installing to a different location

To install OpenSSL to a different location (for example into your home
directory for testing purposes) run `Configure` as shown in the following
examples.

On Unix:

    $ ./Configure --prefix=/opt/openssl --openssldir=/usr/local/ssl

On OpenVMS:

    $ perl Configure --prefix=PROGRAM:[INSTALLS] --openssldir=SYS$MANAGER:[OPENSSL]

Note: if you do add options to the configuration command, please make sure
you've read more than just this Quick Start, such as relevant `NOTES-*` files,
the options outline below, as configuration options may change the outcome
in otherwise unexpected ways.

Configuration Options
=====================

There are several options to `./Configure` to customize the build (note that
for Windows, the defaults for `--prefix` and `--openssldir` depend on what
configuration is used and what Windows implementation OpenSSL is built on.
More notes on this in [NOTES-Windows.txt](NOTES-Windows.txt):

API Level
---------

    --api=x.y[.z]

Build the OpenSSL libraries to support the API for the specified version.
If [no-deprecated](#no-deprecated) is also given, don't build with support
for deprecated APIs in or below the specified version number.  For example,
addding

    --api=1.1.0 no-deprecated

will remove support for all APIs that were deprecated in OpenSSL version
1.1.0 or below.  This is a rather specialized option for developers.
If you just intend to remove all deprecated APIs up to the current version
entirely, just specify [no-deprecated](#no-deprecated).
If `--api` isn't given, it defaults to the current (minor) OpenSSL version.

Cross Compile Prefix
--------------------

    --cross-compile-prefix=<PREFIX>

The `<PREFIX>` to include in front of commands for your toolchain.

It is likely to have to end with dash, e.g. `a-b-c-` would invoke GNU compiler
as `a-b-c-gcc`, etc.  Unfortunately cross-compiling is too case-specific to put
together one-size-fits-all instructions.  You might have to pass more flags or
set up environment variables to actually make it work.  Android and iOS cases
are discussed in corresponding `Configurations/15-*.conf` files.  But there are
cases when this option alone is sufficient.  For example to build the mingw64
target on Linux `--cross-compile-prefix=x86_64-w64-mingw32-` works.  Naturally
provided that mingw packages are installed.  Today Debian and Ubuntu users
have option to install a number of prepackaged cross-compilers along with
corresponding run-time and development packages for "alien" hardware.  To give
another example `--cross-compile-prefix=mipsel-linux-gnu-` suffices in such
case.

For cross compilation, you must [configure manually](#manual-configuration).
Also, note that `--openssldir` refers to target's file system, not one you are
building on.

Build Type
----------

    --debug

Build OpenSSL with debugging symbols and zero optimization level.

    --release

Build OpenSSL without debugging symbols.  This is the default.

Directories
-----------

### libdir

    --libdir=DIR

The name of the directory under the top of the installation directory tree
(see the `--prefix` option) where libraries will be installed.  By default
this is `lib/`. Note that on Windows only static libraries (`*.lib`) will
be stored in this location. Shared libraries (`*.dll`) will always be
installed to the `bin/` directory.

### openssldir

    --openssldir=DIR

Directory for OpenSSL configuration files, and also the default certificate
and key store.  Defaults are:

    Unix:           /usr/local/ssl
    Windows:        C:\Program Files\Common Files\SSL
    OpenVMS:        SYS$COMMON:[OPENSSL-COMMON]

For 32bit Windows applications on Windows 64bit (WOW64), always replace
`C:\Program Files` by `C:\Program Files (x86)`.

### prefix

    --prefix=DIR

The top of the installation directory tree.  Defaults are:

    Unix:           /usr/local
    Windows:        C:\Program Files\OpenSSL
    OpenVMS:        SYS$COMMON:[OPENSSL-'version']

Compiler Warnings
-----------------

    --strict-warnings

This is a developer flag that switches on various compiler options recommended
for OpenSSL development.  It only works when using gcc or clang as the compiler.
If you are developing a patch for OpenSSL then it is recommended that you use
this option where possible.

ZLib Flags
----------

### with-zlib-include

    --with-zlib-include=DIR

The directory for the location of the zlib include file.  This option is only
necessary if [zlib](#zlib) is used and the include file is not
already on the system include path.

### with-zlib-lib

    --with-zlib-lib=LIB

**On Unix**: this is the directory containing the zlib library.
If not provided the system library path will be used.

**On Windows:** this is the filename of the zlib library (with or
without a path).  This flag must be provided if the
[zlib-dynamic](#zlib-dynamic) option is not also used. If `zlib-dynamic` is used
then this flag is optional and defaults to `ZLIB1` if not provided.

**On VMS:** this is the filename of the zlib library (with or without a path).
This flag is optional and if not provided then `GNV$LIBZSHR`, `GNV$LIBZSHR32`
or `GNV$LIBZSHR64` is used by default depending on the pointer size chosen.

Seeding the Random Generator
----------------------------

    --with-rand-seed=seed1[,seed2,...]

A comma separated list of seeding methods which will be tried by OpenSSL
in order to obtain random input (a.k.a "entropy") for seeding its
cryptographically secure random number generator (CSPRNG).
The current seeding methods are:

### os

Use a trusted operating system entropy source.
This is the default method if such an entropy source exists.

### getrandom

Use the [getrandom(2)][man-getrandom] or equivalent system call.

[man-getrandom]: http://man7.org/linux/man-pages/man2/getrandom.2.html

### devrandom

Use the first device from the `DEVRANDOM` list which can be opened to read
random bytes.  The `DEVRANDOM` preprocessor constant expands to

    "/dev/urandom","/dev/random","/dev/srandom"

on most unix-ish operating systems.

### egd

Check for an entropy generating daemon.
This source is ignored by the FIPS provider.

### rdcpu

Use the `RDSEED` or `RDRAND` command if provided by the CPU.

### librandom

Use librandom (not implemented yet).
This source is ignored by the FIPS provider.

### none

Disable automatic seeding.  This is the default on some operating systems where
no suitable entropy source exists, or no support for it is implemented yet.
This option is ignored by the FIPS provider.

For more information, see the section [Notes on random number generation][rng]
at the end of this document.

[rng]: #notes-on-random-number-generation

Setting the FIPS HMAC key
-------------------------

    --fips-key=value

As part of its self-test validation, the FIPS module must verify itself
by performing a SHA-256 HMAC computation on itself. The default key is
the SHA256 value of "the holy handgrenade of antioch" and is sufficient
for meeting the FIPS requirements.

To change the key to a different value, use this flag. The value should
be a hex string no more than 64 characters.

Enable and Disable Features
---------------------------

Feature options always come in pairs, an option to enable feature
`xxxx`, and an option to disable it:

    [ enable-xxxx | no-xxxx ]

Whether a feature is enabled or disabled by default, depends on the feature.
In the following list, always the non-default variant is documented: if
feature `xxxx` is disabled by default then `enable-xxxx` is documented and
if feature `xxxx` is enabled by default then `no-xxxx` is documented.

### no-afalgeng

Don't build the AFALG engine.

This option will be forced on a platform that does not support AFALG.

### enable-ktls

Build with Kernel TLS support.

This option will enable the use of the Kernel TLS data-path, which can improve
performance and allow for the use of sendfile and splice system calls on
TLS sockets.  The Kernel may use TLS accelerators if any are available on the
system.  This option will be forced off on systems that do not support the
Kernel TLS data-path.

### enable-asan

Build with the Address sanitiser.

This is a developer option only.  It may not work on all platforms and should
never be used in production environments.  It will only work when used with
gcc or clang and should be used in conjunction with the [no-shared](#no-shared)
option.

### no-acvp_tests

Do not build support for Automated Cryptographic Validation Protocol (ACVP)
tests.

This is required for FIPS validation purposes. Certain ACVP tests require
access to algorithm internals that are not normally accessible.
Additional information related to ACVP can be found at
<https://github.com/usnistgov/ACVP>.

### no-asm

Do not use assembler code.

This should be viewed as debugging/troubleshooting option rather than for
production use.  On some platforms a small amount of assembler code may still
be used even with this option.

### no-async

Do not build support for async operations.

### no-autoalginit

Don't automatically load all supported ciphers and digests.

Typically OpenSSL will make available all of its supported ciphers and digests.
For a statically linked application this may be undesirable if small executable
size is an objective.  This only affects libcrypto.  Ciphers and digests will
have to be loaded manually using `EVP_add_cipher()` and `EVP_add_digest()`
if this option is used.  This option will force a non-shared build.

### no-autoerrinit

Don't automatically load all libcrypto/libssl error strings.

Typically OpenSSL will automatically load human readable error strings.  For a
statically linked application this may be undesirable if small executable size
is an objective.

### no-autoload-config

Don't automatically load the default `openssl.cnf` file.

Typically OpenSSL will automatically load a system config file which configures
default SSL options.

### enable-buildtest-c++

While testing, generate C++ buildtest files that simply check that the public
OpenSSL header files are usable standalone with C++.

Enabling this option demands extra care.  For any compiler flag given directly
as configuration option, you must ensure that it's valid for both the C and
the C++ compiler.  If not, the C++ build test will most likely break.  As an
alternative, you can use the language specific variables, `CFLAGS` and `CXXFLAGS`.

### no-bulk

Build only some minimal set of features.
This is a developer option used internally for CI build tests of the project.

### no-capieng

Don't build the CAPI engine.

This option will be forced if on a platform that does not support CAPI.

### no-cmp

Don't build support for Certificate Management Protocol (CMP)
and Certificate Request Message Format (CRMF).

### no-cms

Don't build support for Cryptographic Message Syntax (CMS).

### no-comp

Don't build support for SSL/TLS compression.

If this option is enabled (the default), then compression will only work if
the zlib or `zlib-dynamic` options are also chosen.

### enable-crypto-mdebug

This now only enables the `failed-malloc` feature.

### enable-crypto-mdebug-backtrace

This is a no-op; the project uses the compiler's address/leak sanitizer instead.

### no-ct

Don't build support for Certificate Transparency (CT).

### no-deprecated

Don't build with support for deprecated APIs up until and including the version
given with `--api` (or the current version, if `--api` wasn't specified).

### no-dgram

Don't build support for datagram based BIOs.

Selecting this option will also force the disabling of DTLS.

### no-dso

Don't build support for loading Dynamic Shared Objects (DSO)

### enable-devcryptoeng

Build the `/dev/crypto` engine.

This option is automatically selected on the BSD platform, in which case it can
be disabled with `no-devcryptoeng`.

### no-dynamic-engine

Don't build the dynamically loaded engines.

This only has an effect in a shared build.

### no-ec

Don't build support for Elliptic Curves.

### no-ec2m

Don't build support for binary Elliptic Curves

### enable-ec_nistp_64_gcc_128

Enable support for optimised implementations of some commonly used NIST
elliptic curves.

This option is only supported on platforms:

 - with little-endian storage of non-byte types
 - that tolerate misaligned memory references
 - where the compiler:
   - supports the non-standard type `__uint128_t`
   - defines the built-in macro `__SIZEOF_INT128__`

### enable-egd

Build support for gathering entropy from the Entropy Gathering Daemon (EGD).

### no-engine

Don't build support for loading engines.

### no-err

Don't compile in any error strings.

### enable-external-tests

Enable building of integration with external test suites.

This is a developer option and may not work on all platforms.  The following
external test suites are currently supported:

 - BoringSSL test suite
 - Python PYCA/Cryptography test suite
 - krb5 test suite

See the file [test/README-external.md](test/README-external.md)
for further details.

### no-filenames

Don't compile in filename and line number information (e.g.  for errors and
memory allocation).

### no-fips

Don't compile the FIPS provider

### no-fips-securitychecks

Don't perform FIPS module run-time checks related to enforcement of security
parameters such as minimum security strength of keys.

### enable-fuzz-libfuzzer, enable-fuzz-afl

Build with support for fuzzing using either libfuzzer or AFL.

These are developer options only.  They may not work on all  platforms and
should never be used in production environments.

See the file [fuzz/README.md](fuzz/README.md) for further details.

### no-gost

Don't build support for GOST based ciphersuites.

Note that if this feature is enabled then GOST ciphersuites are only available
if the GOST algorithms are also available through loading an externally supplied
engine.

### no-legacy

Don't build the legacy provider.

Disabling this also disables the legacy algorithms: MD2 (already disabled by default).

### no-makedepend

Don't generate dependencies.

### no-module

Don't build any dynamically loadable engines.

This also implies `no-dynamic-engine`.

### no-multiblock

Don't build support for writing multiple records in one go in libssl

Note: this is a different capability to the pipelining functionality.

### no-nextprotoneg

Don't build support for the Next Protocol Negotiation (NPN) TLS extension.

### no-ocsp

Don't build support for Online Certificate Status Protocol (OCSP).

### no-padlockeng

Don't build the padlock engine.

### no-hw-padlock

As synonym for `no-padlockeng`.  Deprecated and should not be used.

### no-pic

Don't build with support for Position Independent Code.

### no-pinshared

Don't pin the shared libraries.

By default OpenSSL will attempt to stay in memory until the process exits.
This is so that libcrypto and libssl can be properly cleaned up automatically
via an `atexit()` handler.  The handler is registered by libcrypto and cleans
up both libraries.  On some platforms the `atexit()` handler will run on unload of
libcrypto (if it has been dynamically loaded) rather than at process exit.  This
option can be used to stop OpenSSL from attempting to stay in memory until the
process exits.  This could lead to crashes if either libcrypto or libssl have
already been unloaded at the point that the atexit handler is invoked, e.g.  on a
platform which calls `atexit()` on unload of the library, and libssl is unloaded
before libcrypto then a crash is likely to happen.  Applications can suppress
running of the `atexit()` handler at run time by using the
`OPENSSL_INIT_NO_ATEXIT` option to `OPENSSL_init_crypto()`.
See the man page for it for further details.

### no-posix-io

Don't use POSIX IO capabilities.

### no-psk

Don't build support for Pre-Shared Key based ciphersuites.

### no-rdrand

Don't use hardware RDRAND capabilities.

### no-rfc3779

Don't build support for RFC3779, "X.509 Extensions for IP Addresses and
AS Identifiers".

### sctp

Build support for Stream Control Transmission Protocol (SCTP).

### no-shared

Do not create shared libraries, only static ones.

See [Notes on shared libraries](#notes-on-shared-libraries) below.

### no-sock

Don't build support for socket BIOs.

### no-srp

Don't build support for Secure Remote Password (SRP) protocol or
SRP based ciphersuites.

### no-srtp

Don't build Secure Real-Time Transport Protocol (SRTP) support.

### no-sse2

Exclude SSE2 code paths from 32-bit x86 assembly modules.

Normally SSE2 extension is detected at run-time, but the decision whether or not
the machine code will be executed is taken solely on CPU capability vector.  This
means that if you happen to run OS kernel which does not support SSE2 extension
on Intel P4 processor, then your application might be exposed to "illegal
instruction" exception.  There might be a way to enable support in kernel, e.g.
FreeBSD kernel can be compiled with `CPU_ENABLE_SSE`, and there is a way to
disengage SSE2 code paths upon application start-up, but if you aim for wider
"audience" running such kernel, consider `no-sse2`.  Both the `386` and `no-asm`
options imply `no-sse2`.

### enable-ssl-trace

Build with the SSL Trace capabilities.

This adds the `-trace` option to `s_client` and `s_server`.

### no-static-engine

Don't build the statically linked engines.

This only has an impact when not built "shared".

### no-stdio

Don't use anything from the C header file `stdio.h` that makes use of the `FILE`
type.  Only libcrypto and libssl can be built in this way.  Using this option will
suppress building the command line applications.  Additionally, since the OpenSSL
tests also use the command line applications, the tests will also be skipped.

### no-tests

Don't build test programs or run any tests.

### no-threads

Don't build with support for multi-threaded applications.

### threads

Build with support for multi-threaded applications.  Most platforms will enable
this by default.  However, if on a platform where this is not the case then this
will usually require additional system-dependent options!

See [Notes on multi-threading](#notes-on-multi-threading) below.

### enable-trace

Build with support for the integrated tracing api.

See manual pages OSSL_trace_set_channel(3) and OSSL_trace_enabled(3) for details.

### no-ts

Don't build Time Stamping (TS) Authority support.

### enable-ubsan

Build with the Undefined Behaviour sanitiser (UBSAN).

This is a developer option only.  It may not work on all platforms and should
never be used in production environments.  It will only work when used with
gcc or clang and should be used in conjunction with the `-DPEDANTIC` option
(or the `--strict-warnings` option).

### no-ui-console

Don't build with the User Interface (UI) console method

The User Interface console method enables text based console prompts.

### enable-unit-test

Enable additional unit test APIs.

This should not typically be used in production deployments.

### no-uplink

Don't build support for UPLINK interface.

### enable-weak-ssl-ciphers

Build support for SSL/TLS ciphers that are considered "weak"

Enabling this includes for example the RC4 based ciphersuites.

### zlib

Build with support for zlib compression/decompression.

### zlib-dynamic

Like the zlib option, but has OpenSSL load the zlib library dynamically
when needed.

This is only supported on systems where loading of shared libraries is supported.

### 386

In 32-bit x86 builds, use the 80386 instruction set only in assembly modules

The default x86 code is more efficient, but requires at least an 486 processor.
Note: This doesn't affect compiler generated code, so this option needs to be
accompanied by a corresponding compiler-specific option.

### no-{protocol}

    no-{ssl|ssl3|tls|tls1|tls1_1|tls1_2|tls1_3|dtls|dtls1|dtls1_2}

Don't build support for negotiating the specified SSL/TLS protocol.

If `no-tls` is selected then all of `tls1`, `tls1_1`, `tls1_2` and `tls1_3`
are disabled.
Similarly `no-dtls` will disable `dtls1` and `dtls1_2`.  The `no-ssl` option is
synonymous with `no-ssl3`.  Note this only affects version negotiation.
OpenSSL will still provide the methods for applications to explicitly select
the individual protocol versions.

### no-{protocol}-method

    no-{ssl|ssl3|tls|tls1|tls1_1|tls1_2|tls1_3|dtls|dtls1|dtls1_2}-method

Analogous to `no-{protocol}` but in addition do not build the methods for
applications to explicitly select individual protocol versions.  Note that there
is no `no-tls1_3-method` option because there is no application method for
TLSv1.3.

Using individual protocol methods directly is deprecated.  Applications should
use `TLS_method()` instead.

### enable-{algorithm}

    enable-{md2|rc5}

Build with support for the specified algorithm.

### no-{algorithm}

    no-{aria|bf|blake2|camellia|cast|chacha|cmac|
        des|dh|dsa|ecdh|ecdsa|idea|md4|mdc2|ocb|
        poly1305|rc2|rc4|rmd160|scrypt|seed|
        siphash|siv|sm2|sm3|sm4|whirlpool}

Build without support for the specified algorithm.

The `ripemd` algorithm is deprecated and if used is synonymous with `rmd160`.

### Compiler-specific options

    -Dxxx, -Ixxx, -Wp, -lxxx, -Lxxx, -Wl, -rpath, -R, -framework, -static

These system specific options will be recognised and passed through to the
compiler to allow you to define preprocessor symbols, specify additional
libraries, library directories or other compiler options.  It might be worth
noting that some compilers generate code specifically for processor the
compiler currently executes on.  This is not necessarily what you might have
in mind, since it might be unsuitable for execution on other, typically older,
processor.  Consult your compiler documentation.

Take note of the [Environment Variables](#environment-variables) documentation
below and how these flags interact with those variables.

    -xxx, +xxx, /xxx

Additional options that are not otherwise recognised are passed through as
they are to the compiler as well.  Unix-style options beginning with a
`-` or `+` and Windows-style options beginning with a `/` are recognized.
Again, consult your compiler documentation.

If the option contains arguments separated by spaces, then the URL-style
notation `%20` can be used for the space character in order to avoid having
to quote the option.  For example, `-opt%20arg` gets expanded to `-opt arg`.
In fact, any ASCII character can be encoded as %xx using its hexadecimal
encoding.

Take note of the [Environment Variables](#environment-variables) documentation
below and how these flags interact with those variables.

### Environment Variables

    VAR=value

Assign the given value to the environment variable `VAR` for `Configure`.

These work just like normal environment variable assignments, but are supported
on all platforms and are confined to the configuration scripts only.
These assignments override the corresponding value in the inherited environment,
if there is one.

The following variables are used as "`make` variables" and can be used as an
alternative to giving preprocessor, compiler and linker options directly as
configuration.  The following variables are supported:

    AR              The static library archiver.
    ARFLAGS         Flags for the static library archiver.
    AS              The assembler compiler.
    ASFLAGS         Flags for the assembler compiler.
    CC              The C compiler.
    CFLAGS          Flags for the C compiler.
    CXX             The C++ compiler.
    CXXFLAGS        Flags for the C++ compiler.
    CPP             The C/C++ preprocessor.
    CPPFLAGS        Flags for the C/C++ preprocessor.
    CPPDEFINES      List of CPP macro definitions, separated
                    by a platform specific character (':' or
                    space for Unix, ';' for Windows, ',' for
                    VMS).  This can be used instead of using
                    -D (or what corresponds to that on your
                    compiler) in CPPFLAGS.
    CPPINCLUDES     List of CPP inclusion directories, separated
                    the same way as for CPPDEFINES.  This can
                    be used instead of -I (or what corresponds
                    to that on your compiler) in CPPFLAGS.
    HASHBANGPERL    Perl invocation to be inserted after '#!'
                    in public perl scripts (only relevant on
                    Unix).
    LD              The program linker (not used on Unix, $(CC)
                    is used there).
    LDFLAGS         Flags for the shared library, DSO and
                    program linker.
    LDLIBS          Extra libraries to use when linking.
                    Takes the form of a space separated list
                    of library specifications on Unix and
                    Windows, and as a comma separated list of
                    libraries on VMS.
    RANLIB          The library archive indexer.
    RC              The Windows resource compiler.
    RCFLAGS         Flags for the Windows resource compiler.
    RM              The command to remove files and directories.

These cannot be mixed with compiling/linking flags given on the command line.
In other words, something like this isn't permitted.

    $ ./Configure -DFOO CPPFLAGS=-DBAR -DCOOKIE

Backward compatibility note:

To be compatible with older configuration scripts, the environment variables
are ignored if compiling/linking flags are given on the command line, except
for the following:

    AR, CC, CXX, CROSS_COMPILE, HASHBANGPERL, PERL, RANLIB, RC, and WINDRES

For example, the following command will not see `-DBAR`:

    $ CPPFLAGS=-DBAR ./Configure -DCOOKIE

However, the following will see both set variables:

    $ CC=gcc CROSS_COMPILE=x86_64-w64-mingw32- ./Configure -DCOOKIE

If `CC` is set, it is advisable to also set `CXX` to ensure both the C and C++
compiler are in the same "family".  This becomes relevant with
`enable-external-tests` and `enable-buildtest-c++`.

### Reconfigure

    reconf
    reconfigure

Reconfigure from earlier data.

This fetches the previous command line options and environment from data
saved in `configdata.pm` and runs the configuration process again, using
these options and environment.  Note: NO other option is permitted together
with `reconf`.  Note: The original configuration saves away values for ALL
environment variables that were used, and if they weren't defined, they are
still saved away with information that they weren't originally defined.
This information takes precedence over environment variables that are
defined when reconfiguring.

Displaying configuration data
-----------------------------

The configuration script itself will say very little, and finishes by
creating `configdata.pm`.  This perl module can be loaded by other scripts
to find all the configuration data, and it can also be used as a script to
display all sorts of configuration data in a human readable form.

For more information, please do:

    $ ./configdata.pm --help                         # Unix

or

    $ perl configdata.pm --help                      # Windows and VMS

Installation Steps in Detail
============================

Configure OpenSSL
-----------------

### Automatic Configuration

On some platform a `config` script is available which attempts to guess
your operating system (and compiler, if necessary) and calls the `Configure`
Perl script with appropriate target based on its guess.  Further options can
be supplied to the `config` script, which will be passed on to the `Configure`
script.

#### Unix / Linux / macOS

    $ ./Configure [[ options ]]

#### OpenVMS

    $ perl Configure [[ options ]]

#### Windows

    $ perl Configure [[ options ]]

### Manual Configuration

OpenSSL knows about a range of different operating system, hardware and
compiler combinations.  To see the ones it knows about, run

    $ ./Configure LIST                               # Unix

or

    $ perl Configure LIST                            # All other platforms

For the remainder of this text, the Unix form will be used in all examples.
Please use the appropriate form for your platform.

Pick a suitable name from the list that matches your system.  For most
operating systems there is a choice between using cc or gcc.
When you have identified your system (and if necessary compiler) use this
name as the argument to `Configure`.  For example, a `linux-elf` user would
run:

    $ ./Configure linux-elf [[ options ]]

### Creating your own Configuration

If your system isn't listed, you will have to create a configuration
file named `Configurations/{{ something }}.conf` and add the correct
configuration for your system.  See the available configs as examples
and read [Configurations/README.md](Configurations/README.md) and
[Configurations/README-design.md](Configurations/README-design.md)
for more information.

The generic configurations `cc` or `gcc` should usually work on 32 bit
Unix-like systems.

`Configure` creates a build file (`Makefile` on Unix, `makefile` on Windows
and `descrip.mms` on OpenVMS) from a suitable template in `Configurations/`,
and defines various macros in `include/openssl/configuration.h` (generated
from `include/openssl/configuration.h.in`.

### Out of Tree Builds

OpenSSL can be configured to build in a build directory separate from the
source code directory.  It's done by placing yourself in some other
directory and invoking the configuration commands from there.

#### Unix example

    $ mkdir /var/tmp/openssl-build
    $ cd /var/tmp/openssl-build
    $ /PATH/TO/OPENSSL/SOURCE/Configure [[ options ]]

#### OpenVMS example

    $ set default sys$login:
    $ create/dir [.tmp.openssl-build]
    $ set default [.tmp.openssl-build]
    $ perl D:[PATH.TO.OPENSSL.SOURCE]Configure [[ options ]]

#### Windows example

    $ C:
    $ mkdir \temp-openssl
    $ cd \temp-openssl
    $ perl d:\PATH\TO\OPENSSL\SOURCE\Configure [[ options ]]

Paths can be relative just as well as absolute.  `Configure` will do its best
to translate them to relative paths whenever possible.

Build OpenSSL
-------------

Build OpenSSL by running:

    $ make                                           # Unix
    $ mms                                            ! (or mmk) OpenVMS
    $ nmake                                          # Windows

This will build the OpenSSL libraries (`libcrypto.a` and `libssl.a` on
Unix, corresponding on other platforms) and the OpenSSL binary
(`openssl`).  The libraries will be built in the top-level directory,
and the binary will be in the `apps/` subdirectory.

If the build fails, take a look at the [Build Failures](#build-failures)
subsection of the [Troubleshooting](#troubleshooting) section.

Test OpenSSL
------------

After a successful build, and before installing, the libraries should
be tested.  Run:

    $ make test                                      # Unix
    $ mms test                                       ! OpenVMS
    $ nmake test                                     # Windows

**Warning:** you MUST run the tests from an unprivileged account (or disable
your privileges temporarily if your platform allows it).

See [test/README.md](test/README.md) for further details how run tests.

See [test/README-dev.md](test/README-dev.md) for guidelines on adding tests.

Install OpenSSL
---------------

If everything tests ok, install OpenSSL with

    $ make install                                   # Unix
    $ mms install                                    ! OpenVMS
    $ nmake install                                  # Windows

Note that in order to perform the install step above you need to have
appropriate permissions to write to the installation directory.

The above commands will install all the software components in this
directory tree under `<PREFIX>` (the directory given with `--prefix` or
its default):

### Unix / Linux / macOS

    bin/           Contains the openssl binary and a few other
                   utility scripts.
    include/openssl
                   Contains the header files needed if you want
                   to build your own programs that use libcrypto
                   or libssl.
    lib            Contains the OpenSSL library files.
    lib/engines    Contains the OpenSSL dynamically loadable engines.

    share/man/man1 Contains the OpenSSL command line man-pages.
    share/man/man3 Contains the OpenSSL library calls man-pages.
    share/man/man5 Contains the OpenSSL configuration format man-pages.
    share/man/man7 Contains the OpenSSL other misc man-pages.

    share/doc/openssl/html/man1
    share/doc/openssl/html/man3
    share/doc/openssl/html/man5
    share/doc/openssl/html/man7
                   Contains the HTML rendition of the man-pages.

### OpenVMS

'arch' is replaced with the architecture name, `Alpha` or `ia64`,
'sover' is replaced with the shared library version (`0101` for 1.1), and
'pz' is replaced with the pointer size OpenSSL was built with:

    [.EXE.'arch']  Contains the openssl binary.
    [.EXE]         Contains a few utility scripts.
    [.include.openssl]
                   Contains the header files needed if you want
                   to build your own programs that use libcrypto
                   or libssl.
    [.LIB.'arch']  Contains the OpenSSL library files.
    [.ENGINES'sover''pz'.'arch']
                   Contains the OpenSSL dynamically loadable engines.
    [.SYS$STARTUP] Contains startup, login and shutdown scripts.
                   These define appropriate logical names and
                   command symbols.
    [.SYSTEST]     Contains the installation verification procedure.
    [.HTML]        Contains the HTML rendition of the manual pages.

### Additional Directories

Additionally, install will add the following directories under
OPENSSLDIR (the directory given with `--openssldir` or its default)
for you convenience:

    certs          Initially empty, this is the default location
                   for certificate files.
    private        Initially empty, this is the default location
                   for private key files.
    misc           Various scripts.

The installation directory should be appropriately protected to ensure
unprivileged users cannot make changes to OpenSSL binaries or files, or
install engines.  If you already have a pre-installed version of OpenSSL as
part of your Operating System it is recommended that you do not overwrite
the system version and instead install to somewhere else.

Package builders who want to configure the library for standard locations,
but have the package installed somewhere else so that it can easily be
packaged, can use

    $ make DESTDIR=/tmp/package-root install         # Unix
    $ mms/macro="DESTDIR=TMP:[PACKAGE-ROOT]" install ! OpenVMS

The specified destination directory will be prepended to all installation
target paths.

Compatibility issues with previous OpenSSL versions
---------------------------------------------------

### COMPILING existing applications

Starting with version 1.1.0, OpenSSL hides a number of structures that were
previously open.  This includes all internal libssl structures and a number
of EVP types.  Accessor functions have been added to allow controlled access
to the structures' data.

This means that some software needs to be rewritten to adapt to the new ways
of doing things.  This often amounts to allocating an instance of a structure
explicitly where you could previously allocate them on the stack as automatic
variables, and using the provided accessor functions where you would previously
access a structure's field directly.

Some APIs have changed as well.  However, older APIs have been preserved when
possible.

Post-installation Notes
-----------------------

With the default OpenSSL installation comes a FIPS provider module, which
needs some post-installation attention, without which it will not be usable.
This involves using the following command:

    $ openssl fipsinstall

See the openssl-fipsinstall(1) manual for details and examples.

Advanced Build Options
======================

Environment Variables
---------------------

A number of environment variables can be used to provide additional control
over the build process.  Typically these should be defined prior to running
`Configure`.  Not all environment variables are relevant to all platforms.

    AR
                   The name of the ar executable to use.

    BUILDFILE
                   Use a different build file name than the platform default
                   ("Makefile" on Unix-like platforms, "makefile" on native Windows,
                   "descrip.mms" on OpenVMS).  This requires that there is a
                   corresponding build file template.
                   See [Configurations/README.md](Configurations/README.md)
                   for further information.

    CC
                   The compiler to use. Configure will attempt to pick a default
                   compiler for your platform but this choice can be overridden
                   using this variable. Set it to the compiler executable you wish
                   to use, e.g. gcc or clang.

    CROSS_COMPILE
                   This environment variable has the same meaning as for the
                   "--cross-compile-prefix" Configure flag described above. If both
                   are set then the Configure flag takes precedence.

    NM
                   The name of the nm executable to use.

    OPENSSL_LOCAL_CONFIG_DIR
                   OpenSSL comes with a database of information about how it
                   should be built on different platforms as well as build file
                   templates for those platforms. The database is comprised of
                   ".conf" files in the Configurations directory.  The build
                   file templates reside there as well as ".tmpl" files. See the
                   file [Configurations/README.md](Configurations/README.md)
                   for further information about the format of ".conf" files
                   as well as information on the ".tmpl" files.
                   In addition to the standard ".conf" and ".tmpl" files, it is
                   possible to create your own ".conf" and ".tmpl" files and
                   store them locally, outside the OpenSSL source tree.
                   This environment variable can be set to the directory where
                   these files are held and will be considered by Configure
                   before it looks in the standard directories.

    PERL
                   The name of the Perl executable to use when building OpenSSL.
                   Only needed if builing should use a different Perl executable
                   than what is used to run the Configure script.

    HASHBANGPERL
                   The command string for the Perl executable to insert in the
                   #! line of perl scripts that will be publicly installed.
                   Default: /usr/bin/env perl
                   Note: the value of this variable is added to the same scripts
                   on all platforms, but it's only relevant on Unix-like platforms.

    RC
                   The name of the rc executable to use. The default will be as
                   defined for the target platform in the ".conf" file. If not
                   defined then "windres" will be used. The WINDRES environment
                   variable is synonymous to this. If both are defined then RC
                   takes precedence.

    RANLIB
                   The name of the ranlib executable to use.

    WINDRES
                   See RC.

Makefile Targets
----------------

The `Configure` script generates a Makefile in a format relevant to the specific
platform.  The Makefiles provide a number of targets that can be used.  Not all
targets may be available on all platforms.  Only the most common targets are
described here.  Examine the Makefiles themselves for the full list.

    all
                   The target to build all the software components and
                   documentation.

    build_sw
                   Build all the software components.
                   THIS IS THE DEFAULT TARGET.

    build_docs
                   Build all documentation components.

    clean
                   Remove all build artefacts and return the directory to a "clean"
                   state.

    depend
                   Rebuild the dependencies in the Makefiles. This is a legacy
                   option that no longer needs to be used since OpenSSL 1.1.0.

    install
                   Install all OpenSSL components.

    install_sw
                   Only install the OpenSSL software components.

    install_docs
                   Only install the OpenSSL documentation components.

    install_man_docs
                   Only install the OpenSSL man pages (Unix only).

    install_html_docs
                   Only install the OpenSSL HTML documentation.

    install_fips
                   Install the FIPS provider module configuration file.

    list-tests
                   Prints a list of all the self test names.

    test
                   Build and run the OpenSSL self tests.

    uninstall
                   Uninstall all OpenSSL components.

    reconfigure
    reconf
                   Re-run the configuration process, as exactly as the last time
                   as possible.

    update
                   This is a developer option. If you are developing a patch for
                   OpenSSL you may need to use this if you want to update
                   automatically generated files; add new error codes or add new
                   (or change the visibility of) public API functions. (Unix only).

Running Selected Tests
----------------------

You can specify a set of tests to be performed
using the `make` variable `TESTS`.

See the section [Running Selected Tests of
test/README.md](test/README.md#running-selected-tests).

Troubleshooting
===============

Configuration Problems
----------------------

### Selecting the correct target

The `./Configure` script tries hard to guess your operating system, but in some
cases it does not succeed. You will see a message like the following:

    $ ./Configure
    Operating system: x86-whatever-minix
    This system (minix) is not supported. See file INSTALL.md for details.

Even if the automatic target selection by the `./Configure` script fails,
chances are that you still might find a suitable target in the `Configurations`
directory, which you can supply to the `./Configure` command,
possibly after some adjustment.

The `Configurations/` directory contains a lot of examples of such targets.
The main configuration file is [10-main.conf], which contains all targets that
are officially supported by the OpenSSL team. Other configuration files contain
targets contributed by other OpenSSL users. The list of targets can be found in
a Perl list `my %targets = ( ... )`.

    my %targets = (
    ...
    "target-name" => {
        inherit_from     => [ "base-target" ],
        CC               => "...",
        cflags           => add("..."),
        asm_arch         => '...',
        perlasm_scheme   => "...",
    },
    ...
    )

If you call `./Configure` without arguments, it will give you a list of all
known targets. Using `grep`, you can lookup the target definition in the
`Configurations/` directory. For example the `android-x86_64` can be found in
[Configurations/15-android.conf](Configurations/15-android.conf).

The directory contains two README files, which explain the general syntax and
design of the configuration files.

 - [Configurations/README.md](Configurations/README.md)
 - [Configurations/README-design.md](Configurations/README-design.md)

If you need further help, try to search the [openssl-users] mailing list
or the [GitHub Issues] for existing solutions. If you don't find anything,
you can [raise an issue] to ask a question yourself.

More about our support resources can be found in the [SUPPORT] file.

### Configuration Errors

If the `./Configure` or `./Configure` command fails with an error message,
read the error message carefully and try to figure out whether you made
a mistake (e.g., by providing a wrong option), or whether the script is
working incorrectly. If you think you encountered a bug, please
[raise an issue] on GitHub to file a bug report.

Along with a short description of the bug, please provide the complete
configure command line and the relevant output including the error message.

Note: To make the output readable, pleace add a 'code fence' (three backquotes
` ``` ` on a separate line) before and after your output:

     ```
     ./Configure [your arguments...]

     [output...]

     ```

Build Failures
--------------

If the build fails, look carefully at the output. Try to locate and understand
the error message. It might be that the compiler is already telling you
exactly what you need to do to fix your problem.

There may be reasons for the failure that aren't problems in OpenSSL itself,
for example if the compiler reports missing standard or third party headers.

If the build succeeded previously, but fails after a source or configuration
change, it might be helpful to clean the build tree before attempting another
build.  Use this command:

    $ make clean                                     # Unix
    $ mms clean                                      ! (or mmk) OpenVMS
    $ nmake clean                                    # Windows

Assembler error messages can sometimes be sidestepped by using the
`no-asm` configuration option.

Compiling parts of OpenSSL with gcc and others with the system compiler will
result in unresolved symbols on some systems.

If you are still having problems, try to search the [openssl-users] mailing
list or the [GitHub Issues] for existing solutions. If you think you
encountered an OpenSSL bug, please [raise an issue] to file a bug report.
Please take the time to review the existing issues first; maybe the bug was
already reported or has already been fixed.

Test Failures
-------------

If some tests fail, look at the output.  There may be reasons for the failure
that isn't a problem in OpenSSL itself (like an OS malfunction or a Perl issue).

You may want increased verbosity, that can be accomplished as described in
section [Test Failures of test/README.md](test/README.md#test-failures).

You may also want to selectively specify which test(s) to perform. This can be
done using the `make` variable `TESTS` as described in section [Running
Selected Tests of test/README.md](test/README.md#running-selected-tests).

If you find a problem with OpenSSL itself, try removing any
compiler optimization flags from the `CFLAGS` line in the Makefile and
run `make clean; make` or corresponding.

To report a bug please open an issue on GitHub, at
<https://github.com/openssl/openssl/issues>.

Notes
=====

Notes on multi-threading
------------------------

For some systems, the OpenSSL `Configure` script knows what compiler options
are needed to generate a library that is suitable for multi-threaded
applications.  On these systems, support for multi-threading is enabled
by default; use the `no-threads` option to disable (this should never be
necessary).

On other systems, to enable support for multi-threading, you will have
to specify at least two options: `threads`, and a system-dependent option.
(The latter is `-D_REENTRANT` on various systems.)  The default in this
case, obviously, is not to include support for multi-threading (but
you can still use `no-threads` to suppress an annoying warning message
from the `Configure` script.)

OpenSSL provides built-in support for two threading models: pthreads (found on
most UNIX/Linux systems), and Windows threads.  No other threading models are
supported.  If your platform does not provide pthreads or Windows threads then
you should use `Configure` with the `no-threads` option.

Notes on shared libraries
-------------------------

For most systems the OpenSSL `Configure` script knows what is needed to
build shared libraries for libcrypto and libssl.  On these systems
the shared libraries will be created by default.  This can be suppressed and
only static libraries created by using the `no-shared` option.  On systems
where OpenSSL does not know how to build shared libraries the `no-shared`
option will be forced and only static libraries will be created.

Shared libraries are named a little differently on different platforms.
One way or another, they all have the major OpenSSL version number as
part of the file name, i.e.  for OpenSSL 1.1.x, `1.1` is somehow part of
the name.

On most POSIX platforms, shared libraries are named `libcrypto.so.1.1`
and `libssl.so.1.1`.

on Cygwin, shared libraries are named `cygcrypto-1.1.dll` and `cygssl-1.1.dll`
with import libraries `libcrypto.dll.a` and `libssl.dll.a`.

On Windows build with MSVC or using MingW, shared libraries are named
`libcrypto-1_1.dll` and `libssl-1_1.dll` for 32-bit Windows,
`libcrypto-1_1-x64.dll` and `libssl-1_1-x64.dll` for 64-bit x86_64 Windows,
and `libcrypto-1_1-ia64.dll` and `libssl-1_1-ia64.dll` for IA64 Windows.
With MSVC, the import libraries are named `libcrypto.lib` and `libssl.lib`,
while with MingW, they are named `libcrypto.dll.a` and `libssl.dll.a`.

On VMS, shareable images (VMS speak for shared libraries) are named
`ossl$libcrypto0101_shr.exe` and `ossl$libssl0101_shr.exe`.  However, when
OpenSSL is specifically built for 32-bit pointers, the shareable images
are named `ossl$libcrypto0101_shr32.exe` and `ossl$libssl0101_shr32.exe`
instead, and when built for 64-bit pointers, they are named
`ossl$libcrypto0101_shr64.exe` and `ossl$libssl0101_shr64.exe`.

Notes on random number generation
---------------------------------

Availability of cryptographically secure random numbers is required for
secret key generation.  OpenSSL provides several options to seed the
internal CSPRNG.  If not properly seeded, the internal CSPRNG will refuse
to deliver random bytes and a "PRNG not seeded error" will occur.

The seeding method can be configured using the `--with-rand-seed` option,
which can be used to specify a comma separated list of seed methods.
However, in most cases OpenSSL will choose a suitable default method,
so it is not necessary to explicitly provide this option.  Note also
that not all methods are available on all platforms.  The FIPS provider will
silently ignore seed sources that were not validated.

I) On operating systems which provide a suitable randomness source (in
form  of a system call or system device), OpenSSL will use the optimal
available  method to seed the CSPRNG from the operating system's
randomness sources.  This corresponds to the option `--with-rand-seed=os`.

II) On systems without such a suitable randomness source, automatic seeding
and reseeding is disabled (`--with-rand-seed=none`) and it may be necessary
to install additional support software to obtain a random seed and reseed
the CSPRNG manually.  Please check out the manual pages for `RAND_add()`,
`RAND_bytes()`, `RAND_egd()`, and the FAQ for more information.

<!-- Links  -->

[openssl-users]:
    <https://mta.openssl.org/mailman/listinfo/openssl-users>

[SUPPORT]:
    ./SUPPORT.md

[GitHub Issues]:
    <https://github.com/openssl/openssl/issues>

[raise an issue]:
    <https://github.com/openssl/openssl/issues/new/choose>

[10-main.conf]:
    Configurations/10-main.conf