doc/man1/openssl.pod

=pod

=head1 NAME

openssl - OpenSSL command line tool

=head1 SYNOPSIS

B<openssl>
I<command>
[ I<options> ... ]
[ I<parameters> ... ]

B<openssl>
B<list>
B<-standard-commands> |
B<-digest-commands> |
B<-cipher-commands> |
B<-cipher-algorithms> |
B<-digest-algorithms> |
B<-mac-algorithms> |
B<-public-key-algorithms>

B<openssl> B<no->I<XXX> [ I<options> ]

=head1 DESCRIPTION

OpenSSL is a cryptography toolkit implementing the Secure Sockets Layer (SSL
v2/v3) and Transport Layer Security (TLS v1) network protocols and related
cryptography standards required by them.

The B<openssl> program is a command line tool for using the various
cryptography functions of OpenSSL's B<crypto> library from the shell.
It can be used for

 o  Creation and management of private keys, public keys and parameters
 o  Public key cryptographic operations
 o  Creation of X.509 certificates, CSRs and CRLs
 o  Calculation of Message Digests and Message Authentication Codes
 o  Encryption and Decryption with Ciphers
 o  SSL/TLS Client and Server Tests
 o  Handling of S/MIME signed or encrypted mail
 o  Timestamp requests, generation and verification

=head1 COMMAND SUMMARY

The B<openssl> program provides a rich variety of commands (I<command> in
the L</SYNOPSIS> above).
Each command can have many options and argument parameters, shown above as
I<options> and I<parameters>.

Detailed documentation and use cases for most standard subcommands are available
(e.g., L<openssl-x509(1)>).

Many commands use an external configuration file for some or all of their
arguments and have a B<-config> option to specify that file.
The default name of the file is F<openssl.cnf> in the default certificate
storage area, which can be determined from the L<openssl-version(1)>
command.
The environment variable B<OPENSSL_CONF> can be used to specify
a different location of the file.
See L<openssl-env(7)>.

The list options B<-standard-commands>, B<-digest-commands>,
and B<-cipher-commands> output a list (one entry per line) of the names
of all standard commands, message digest commands, or cipher commands,
respectively, that are available.

The list parameters B<-cipher-algorithms>, B<-digest-algorithms>,
and B<-mac-algorithms> list all cipher, message digest, and message
authentication code names, one entry per line. Aliases are listed as:

 from => to

The list parameter B<-public-key-algorithms> lists all supported public
key algorithms.

The command B<no->I<XXX> tests whether a command of the
specified name is available.  If no command named I<XXX> exists, it
returns 0 (success) and prints B<no->I<XXX>; otherwise it returns 1
and prints I<XXX>.  In both cases, the output goes to B<stdout> and
nothing is printed to B<stderr>.  Additional command line arguments
are always ignored.  Since for each cipher there is a command of the
same name, this provides an easy way for shell scripts to test for the
availability of ciphers in the B<openssl> program.  (B<no->I<XXX> is
not able to detect pseudo-commands such as B<quit>,
B<list>, or B<no->I<XXX> itself.)

=head2 Standard Commands

=over 4

=item B<asn1parse>

Parse an ASN.1 sequence.

=item B<ca>

Certificate Authority (CA) Management.

=item B<ciphers>

Cipher Suite Description Determination.

=item B<cms>

CMS (Cryptographic Message Syntax) utility.

=item B<crl>

Certificate Revocation List (CRL) Management.

=item B<crl2pkcs7>

CRL to PKCS#7 Conversion.

=item B<dgst>

Message Digest calculation. MAC calculations are superseded by
L<openssl-mac(1)>.

=item B<dh>

Diffie-Hellman Parameter Management.
Obsoleted by L<openssl-dhparam(1)>.

=item B<dhparam>

Generation and Management of Diffie-Hellman Parameters. Superseded by
L<openssl-genpkey(1)> and L<openssl-pkeyparam(1)>.

=item B<dsa>

DSA Data Management.

=item B<dsaparam>

DSA Parameter Generation and Management. Superseded by
L<openssl-genpkey(1)> and L<openssl-pkeyparam(1)>.

=item B<ec>

EC (Elliptic curve) key processing.

=item B<ecparam>

EC parameter manipulation and generation.

=item B<enc>

Encryption, decryption, and encoding.

=item B<engine>

Engine (loadable module) information and manipulation.

=item B<errstr>

Error Number to Error String Conversion.

=item B<gendh>

Generation of Diffie-Hellman Parameters.
Obsoleted by L<openssl-dhparam(1)>.

=item B<gendsa>

Generation of DSA Private Key from Parameters. Superseded by
L<openssl-genpkey(1)> and L<openssl-pkey(1)>.

=item B<genpkey>

Generation of Private Key or Parameters.

=item B<genrsa>

Generation of RSA Private Key. Superseded by L<openssl-genpkey(1)>.

=item B<info>

Display diverse information built into the OpenSSL libraries.

=item B<kdf>

Key Derivation Functions.

=item B<mac>

Message Authentication Code Calculation.

=item B<nseq>

Create or examine a Netscape certificate sequence.

=item B<ocsp>

Online Certificate Status Protocol utility.

=item B<passwd>

Generation of hashed passwords.

=item B<pkcs12>

PKCS#12 Data Management.

=item B<pkcs7>

PKCS#7 Data Management.

=item B<pkcs8>

PKCS#8 format private key conversion tool.

=item B<pkey>

Public and private key management.

=item B<pkeyparam>

Public key algorithm parameter management.

=item B<pkeyutl>

Public key algorithm cryptographic operation utility.

=item B<prime>

Compute prime numbers.

=item B<rand>

Generate pseudo-random bytes.

=item B<rehash>

Create symbolic links to certificate and CRL files named by the hash values.

=item B<req>

PKCS#10 X.509 Certificate Signing Request (CSR) Management.

=item B<rsa>

RSA key management.

=item B<rsautl>

RSA utility for signing, verification, encryption, and decryption. Superseded
by  L<openssl-pkeyutl(1)>.

=item B<s_client>

This implements a generic SSL/TLS client which can establish a transparent
connection to a remote server speaking SSL/TLS. It's intended for testing
purposes only and provides only rudimentary interface functionality but
internally uses mostly all functionality of the OpenSSL B<ssl> library.

=item B<s_server>

This implements a generic SSL/TLS server which accepts connections from remote
clients speaking SSL/TLS. It's intended for testing purposes only and provides
only rudimentary interface functionality but internally uses mostly all
functionality of the OpenSSL B<ssl> library.  It provides both an own command
line oriented protocol for testing SSL functions and a simple HTTP response
facility to emulate an SSL/TLS-aware webserver.

=item B<s_time>

SSL Connection Timer.

=item B<sess_id>

SSL Session Data Management.

=item B<smime>

S/MIME mail processing.

=item B<speed>

Algorithm Speed Measurement.

=item B<spkac>

SPKAC printing and generating utility.

=item B<srp>

Maintain SRP password file.

=item B<storeutl>

Utility to list and display certificates, keys, CRLs, etc.

=item B<ts>

Time Stamping Authority tool (client/server).

=item B<verify>

X.509 Certificate Verification.

=item B<version>

OpenSSL Version Information.

=item B<x509>

X.509 Certificate Data Management.

=back

=head2 Message Digest Commands

=over 4

=item B<blake2b512>

BLAKE2b-512 Digest

=item B<blake2s256>

BLAKE2s-256 Digest

=item B<md2>

MD2 Digest

=item B<md4>

MD4 Digest

=item B<md5>

MD5 Digest

=item B<mdc2>

MDC2 Digest

=item B<rmd160>

RMD-160 Digest

=item B<sha1>

SHA-1 Digest

=item B<sha224>

SHA-2 224 Digest

=item B<sha256>

SHA-2 256 Digest

=item B<sha384>

SHA-2 384 Digest

=item B<sha512>

SHA-2 512 Digest

=item B<sha3-224>

SHA-3 224 Digest

=item B<sha3-256>

SHA-3 256 Digest

=item B<sha3-384>

SHA-3 384 Digest

=item B<sha3-512>

SHA-3 512 Digest

=item B<shake128>

SHA-3 SHAKE128 Digest

=item B<shake256>

SHA-3 SHAKE256 Digest

=item B<sm3>

SM3 Digest

=back

=head2 Encryption, Decryption, and Encoding Commands

The following aliases provide convenient access to the most used encodings
and ciphers.

Depending on how OpenSSL was configured and built, not all ciphers listed
here may be present. See L<openssl-enc(1)> for more information.

=over 4

=item B<aes128>, B<aes-128-cbc>, B<aes-128-cfb>, B<aes-128-ctr>, B<aes-128-ecb>, B<aes-128-ofb>

AES-128 Cipher

=item B<aes192>, B<aes-192-cbc>, B<aes-192-cfb>, B<aes-192-ctr>, B<aes-192-ecb>, B<aes-192-ofb>

AES-192 Cipher

=item B<aes256>, B<aes-256-cbc>, B<aes-256-cfb>, B<aes-256-ctr>, B<aes-256-ecb>, B<aes-256-ofb>

AES-256 Cipher

=item B<aria128>, B<aria-128-cbc>, B<aria-128-cfb>, B<aria-128-ctr>, B<aria-128-ecb>, B<aria-128-ofb>

Aria-128 Cipher

=item B<aria192>, B<aria-192-cbc>, B<aria-192-cfb>, B<aria-192-ctr>, B<aria-192-ecb>, B<aria-192-ofb>

Aria-192 Cipher

=item B<aria256>, B<aria-256-cbc>, B<aria-256-cfb>, B<aria-256-ctr>, B<aria-256-ecb>, B<aria-256-ofb>

Aria-256 Cipher

=item B<base64>

Base64 Encoding

=item B<bf>, B<bf-cbc>, B<bf-cfb>, B<bf-ecb>, B<bf-ofb>

Blowfish Cipher

=item B<camellia128>, B<camellia-128-cbc>, B<camellia-128-cfb>, B<camellia-128-ctr>, B<camellia-128-ecb>, B<camellia-128-ofb>

Camellia-128 Cipher

=item B<camellia192>, B<camellia-192-cbc>, B<camellia-192-cfb>, B<camellia-192-ctr>, B<camellia-192-ecb>, B<camellia-192-ofb>

Camellia-192 Cipher

=item B<camellia256>, B<camellia-256-cbc>, B<camellia-256-cfb>, B<camellia-256-ctr>, B<camellia-256-ecb>, B<camellia-256-ofb>

Camellia-256 Cipher

=item B<cast>, B<cast-cbc>

CAST Cipher

=item B<cast5-cbc>, B<cast5-cfb>, B<cast5-ecb>, B<cast5-ofb>

CAST5 Cipher

=item B<chacha20>

Chacha20 Cipher

=item B<des>, B<des-cbc>, B<des-cfb>, B<des-ecb>, B<des-ede>, B<des-ede-cbc>, B<des-ede-cfb>, B<des-ede-ofb>, B<des-ofb>

DES Cipher

=item B<des3>, B<desx>, B<des-ede3>, B<des-ede3-cbc>, B<des-ede3-cfb>, B<des-ede3-ofb>

Triple-DES Cipher

=item B<idea>, B<idea-cbc>, B<idea-cfb>, B<idea-ecb>, B<idea-ofb>

IDEA Cipher

=item B<rc2>, B<rc2-cbc>, B<rc2-cfb>, B<rc2-ecb>, B<rc2-ofb>

RC2 Cipher

=item B<rc4>

RC4 Cipher

=item B<rc5>, B<rc5-cbc>, B<rc5-cfb>, B<rc5-ecb>, B<rc5-ofb>

RC5 Cipher

=item B<seed>, B<seed-cbc>, B<seed-cfb>, B<seed-ecb>, B<seed-ofb>

SEED Cipher

=item B<sm4>, B<sm4-cbc>, B<sm4-cfb>, B<sm4-ctr>, B<sm4-ecb>, B<sm4-ofb>

SM4 Cipher

=back

=head1 OPTIONS

Details of which options are available depend on the specific command.
This section describes some common options with common behavior.

=head2 Common Options

=over 4

=item B<-help>

Provides a terse summary of all options.
If an option takes an argument, the "type" of argument is also given.

=item B<-->

This terminates the list of options. It is mostly useful if any filename
parameters start with a minus sign:

 openssl verify [flags...] -- -cert1.pem...

=back

=head2 Format Options

Several OpenSSL commands can take input or generate output in a variety
of formats. The list of acceptable formats, and the default, is
described in each command documentation.  The list of formats is
described below. Both uppercase and lowercase are accepted.

=over 4

=item B<DER>

A binary format, encoded or parsed according to Distinguished Encoding Rules
(DER) of the ASN.1 data language.

=item B<ENGINE>

Used to specify that the cryptographic material is in an OpenSSL B<engine>.
An engine must be configured or specified using the B<-engine> option.
In addition, the B<-input> flag can be used to name a specific object in
the engine.
A password, such as the B<-passin> flag often must be specified as well.

=item B<P12>

A DER-encoded file containing a PKCS#12 object.
It might be necessary to provide a decryption password to retrieve
the private key.

=item B<PEM>

A text format defined in IETF RFC 1421 and IETF RFC 7468. Briefly, this is
a block of base-64 encoding (defined in IETF RFC 4648), with specific
lines used to mark the start and end:

 Text before the BEGIN line is ignored.
 ----- BEGIN object-type -----
 OT43gQKBgQC/2OHZoko6iRlNOAQ/tMVFNq7fL81GivoQ9F1U0Qr+DH3ZfaH8eIkX
 xT0ToMPJUzWAn8pZv0snA0um6SIgvkCuxO84OkANCVbttzXImIsL7pFzfcwV/ERK
 UM6j0ZuSMFOCr/lGPAoOQU0fskidGEHi1/kW+suSr28TqsyYZpwBDQ==
 ----- END object-type -----
 Text after the END line is also ignored

The I<object-type> must match the type of object that is expected.
For example a C<BEGIN X509 CERTIFICATE> will not match if the command
is trying to read a private key. The types supported include:

 ANY PRIVATE KEY
 CERTIFICATE
 CERTIFICATE REQUEST
 CMS
 DH PARAMETERS
 DSA PARAMETERS
 DSA PUBLIC KEY
 EC PARAMETERS
 EC PRIVATE KEY
 ECDSA PUBLIC KEY
 ENCRYPTED PRIVATE KEY
 PARAMETERS
 PKCS #7 SIGNED DATA
 PKCS7
 PRIVATE KEY
 PUBLIC KEY
 RSA PRIVATE KEY
 SSL SESSION PARAMETERS
 TRUSTED CERTIFICATE
 X509 CRL
 X9.42 DH PARAMETERS

The following legacy I<object-type>'s are also supported for compatibility
with earlier releases:

 DSA PRIVATE KEY
 NEW CERTIFICATE REQUEST
 RSA PUBLIC KEY
 X509 CERTIFICATE

=item B<SMIME>

An S/MIME object as described in IETF RFC 8551.
Earlier versions were known as CMS and are compatible.
Note that the parsing is simple and might fail to parse some legal data.

=back

The options to specify the format are as follows. Refer to the individual
manpage to see which options are accepted.

=over 4

=item B<-inform> I<format>, B<-outform> I<format>

The format of the input or output streams.

=item B<-keyform> I<format>

Format of a private key input source.

=item B<-CRLform> I<format>

Format of a CRL input source.

=back

=head2 Pass Phrase Options

Several commands accept password arguments, typically using B<-passin>
and B<-passout> for input and output passwords respectively. These allow
the password to be obtained from a variety of sources. Both of these
options take a single argument whose format is described below. If no
password argument is given and a password is required then the user is
prompted to enter one: this will typically be read from the current
terminal with echoing turned off.

Note that character encoding may be relevant, please see
L<passphrase-encoding(7)>.

=over 4

=item B<pass:>I<password>

The actual password is I<password>. Since the password is visible
to utilities (like 'ps' under Unix) this form should only be used
where security is not important.

=item B<env:>I<var>

Obtain the password from the environment variable I<var>. Since
the environment of other processes is visible on certain platforms
(e.g. ps under certain Unix OSes) this option should be used with caution.

=item B<file:>I<pathname>

The first line of I<pathname> is the password. If the same I<pathname>
argument is supplied to B<-passin> and B<-passout> arguments then the first
line will be used for the input password and the next line for the output
password. I<pathname> need not refer to a regular file: it could for example
refer to a device or named pipe.

=item B<fd:>I<number>

Read the password from the file descriptor I<number>. This can be used to
send the data via a pipe for example.

=item B<stdin>

Read the password from standard input.

=back

=head2 Trusted Certificate Options

Part of validating a certificate includes verifying that the chain of CA's
can be traced up to an existing trusted root.  The following options specify
how to list the trusted roots, also known as trust anchors.  A collection
of trusted roots is called a I<trust store>.

Note that OpenSSL does not provide a default set of trust anchors.  Many
Linux distributions include a system default and configure OpenSSL to point
to that.  Mozilla maintains an influential trust store that can be found at
L<https://www.mozilla.org/en-US/about/governance/policies/security-group/certs/>.

=over 4

=item B<-CAfile> I<file>

Load the specified file which contains one or more PEM-format certificates
of CA's that are trusted.

=item B<-no-CAfile>

Do not load the default file of trusted certificates.

=item B<-CApath> I<dir>

Use the specified directory as a list of trust certificates. That is,
files should be named with the hash of the X.509 SubjectName of each
certificate. This is so that the library can extract the IssuerName,
hash it, and directly lookup the file to get the issuer certificate.
See L<openssl-rehash(1)> for information on creating this type of directory.

=item B<-no-CApath>

Do not use the default directory of trusted certificates.

=item B<-CAstore> I<uri>

Use I<uri> as a store of trusted CA certificates.  The URI may
indicate a single certificate, as well as a collection of them.
With URIs in the C<file:> scheme, this acts as B<-CAfile> or
B<-CApath>, depending on if the URI indicates a single file or
directory.
See L<ossl_store-file(7)> for more information on the C<file:> scheme.

These certificates are also used when building the server certificate
chain (for example with L<openssl-s_server(1)>) or client certificate
chain (for example with L<openssl-s_time(1)>).

=item B<-no-CAstore>

Do not use the default store.

=back

=head2 Random State Options

Prior to OpenSSL 3.0, it was common for applications to store information
about the state of the random-number generator in a file that was loaded
at startup and rewritten upon exit. On modern operating systems, this is
generally no longer necessary as OpenSSL will seed itself from the
appropriate CPU flags, device files, and so on. These flags are still
supported for special platforms or circumstances that might require them.

It is generally an error to use the same seed file more than once and
every use of B<-rand> should be paired with B<-writerand>.

=over 4

=item B<-rand> I<files>

A file or files containing random data used to seed the random number
generator.
Multiple files can be specified separated by an OS-dependent character.
The separator is C<;> for MS-Windows, C<,> for OpenVMS, and C<:> for
all others. Another way to specify multiple files is to repeat this flag
with different filenames.

=item B<-writerand> I<file>

Writes the seed data to the specified I<file> upon exit.
This file can be used in a subsequent command invocation.

=back

=head2 Extended Verification Options

Sometimes there may be more than one certificate chain leading to an
end-entity certificate.
This usually happens when a root or intermediate CA signs a certificate
for another a CA in other organization.
Another reason is when a CA might have intermediates that use two different
signature formats, such as a SHA-1 and a SHA-256 digest.

The following options can be used to provide data that will allow the
OpenSSL command to generate an alternative chain.

=over 4

=item B<-xchain_build>

Specify whether the application should build the certificate chain to be
provided to the server for the extra certificates via the B<-xkey>,
B<-xcert>, and B<-xchain> options.

=item B<-xkey> I<infile>, B<-xcert> I<infile>, B<-xchain>

Specify an extra certificate, private key and certificate chain. These behave
in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options.  When
specified, the callback returning the first valid chain will be in use by the
client.

=item B<-xcertform> B<DER>|B<PEM>, B<-xkeyform> B<DER>|B<PEM>

The input format for the extra certificate and key, respectively.
See L<openssl(1)/Format Options> for details.

=back

=head2 Name Format Options

OpenSSL provides fine-grain control over how the subject and issuer DN's are
displayed.
This is specified by using the B<-nameopt> option, which takes a
comma-separated list of options from the following set.
An option may be preceeded by a minus sign, C<->, to turn it off.
The default value is C<oneline>.
The first four are the most commonly used.

=over 4

=item B<compat>

Display the name using an old format from previous OpenSSL versions.

=item B<RFC2253>

Display the name using the format defined in RFC 2253.
It is equivalent to B<esc_2253>, B<esc_ctrl>, B<esc_msb>, B<utf8>,
B<dump_nostr>, B<dump_unknown>, B<dump_der>, B<sep_comma_plus>, B<dn_rev>
and B<sname>.

=item B<oneline>

Display the name in one line, using a format that is more readable
RFC 2253.
It is equivalent to B<esc_2253>, B<esc_ctrl>, B<esc_msb>, B<utf8>,
B<dump_nostr>, B<dump_der>, B<use_quote>, B<sep_comma_plus_space>,
B<space_eq> and B<sname> options.

=item B<multiline>

Display the name using multiple lines.
It is equivalent to B<esc_ctrl>, B<esc_msb>, B<sep_multiline>, B<space_eq>,
B<lname> and B<align>.

=item B<esc_2253>

Escape the "special" characters in a field, as required by RFC 2253.
That is, any of the characters C<,+"E<lt>E<gt>;>, C<#> at the beginning of
a string and leading or trailing spaces.

=item B<esc_2254>

Escape the "special" characters in a field as required by RFC 2254 in a field.
That is, the B<NUL> character and and of C<()*>.

=item B<esc_ctrl>

Escape non-printable ASCII characters, codes less than 0x20 (space)
or greater than 0x7F (DELETE). They are displayed using RFC 2253 C<\XX>
notation where B<XX> are the two hex digits representing the character value.

=item B<esc_msb>

Escape any characters with the most significant bit set, that is with
values larger than 127, as described in B<esc_ctrl>.

=item B<use_quote>

Escapes some characters by surrounding the entire string with quotation
marks, C<">.
Without this option, individual special characters are preceeded with
a backslash character, C<\>.

=item B<utf8>

Convert all strings to UTF-8 format first as required by RFC 2253.
If the output device is UTF-8 compatible, then using this option (and
not setting B<esc_msb>) may give the correct display of multibyte
characters.
If this option is not set, then multibyte characters larger than 0xFF
will be output as C<\UXXXX> for 16 bits or C<\WXXXXXXXX> for 32 bits.
In addition, any UTF8Strings will be converted to their character form first.

=item B<ignore_type>

This option does not attempt to interpret multibyte characters in any
way. That is, the content octets are merely dumped as though one octet
represents each character. This is useful for diagnostic purposes but
will result in rather odd looking output.

=item B<show_type>

Display the type of the ASN1 character string before the value,
such as C<BMPSTRING: Hello World>.

=item B<dump_der>

Any fields that would be output in hex format are displayed using
the DER encoding of the field.
If not set, just the content octets are displayed.
Either way, the B<#XXXX...> format of RFC 2253 is used.

=item B<dump_nostr>

Dump non-character strings, such as ASN.1 B<OCTET STRING>.
If this option is not set, then non character string types will be displayed
as though each content octet represents a single character.

=item B<dump_all>

Dump all fields. When this used with B<dump_der>, this allows the
DER encoding of the structure to be unambiguously determined.

=item B<dump_unknown>

Dump any field whose OID is not recognised by OpenSSL.

=item B<sep_comma_plus>, B<sep_comma_plus_space>, B<sep_semi_plus_space>,
B<sep_multiline>

Specify the field separators. The first word is used between the
Relative Distinguished Names (RDNs) and the second is between
multiple Attribute Value Assertions (AVAs). Multiple AVAs are
very rare and their use is discouraged.
The options ending in "space" additionally place a space after the separator to make it more readable.
The B<sep_multiline> starts each field on its own line, and uses "plus space"
for the AVA separator.
It also indents the fields by four characters.
The default value is B<sep_comma_plus_space>.

=item B<dn_rev>

Reverse the fields of the DN as required by RFC 2253.
This also reverses the order of multiple AVAs in a field, but this is
permissible as there is no ordering on values.

=item B<nofname>, B<sname>, B<lname>, B<oid>

Specify how the field name is displayed.
B<nofname> does not display the field at all.
B<sname> uses the "short name" form (CN for commonName for example).
B<lname> uses the long form.
B<oid> represents the OID in numerical form and is useful for
diagnostic purpose.

=item B<align>

Align field values for a more readable output. Only usable with
B<sep_multiline>.

=item B<space_eq>

Places spaces round the equal sign, C<=>, character which follows the field
name.

=back

=head2 TLS Version Options

Several commands use SSL, TLS, or DTLS. By default, the commands use TLS and
clients will offer the lowest and highest protocol version they support,
and servers will pick the highest version that the client offers that is also
supported by the server.

The options below can be used to limit which protocol versions are used,
and whether TCP (SSL and TLS) or UDP (DTLS) is used.
Note that not all protocols and flags may be available, depending on how
OpenSSL was built.

=over 4

=item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-tls1_3>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>

These options require or disable the use of the specified SSL or TLS protocols.
When a specific TLS version is required, only that version will be offered or
accepted.
Only one specific protocol can be given and it cannot be combined with any of
the B<no_> options.

=item B<-dtls>, B<-dtls1>, B<-dtls1_2>

These options specify to use DTLS instead of DLTS.
With B<-dtls>, clients will negotiate any supported DTLS protocol version.
Use the B<-dtls1> or B<-dtls1_2> options to support only DTLS1.0 or DTLS1.2,
respectively.

=back

=head2 Engine Options

=over 4

=item B<-engine> I<id>

Use the engine identified by I<id> and use all the methods it
implements (algorithms, key storage, etc.), unless specified otherwise in
the command-specific documentation or it is configured to do so, as described
in L<config(5)/Engine Configuration Module>.

=back

=head1 ENVIRONMENT

The OpenSSL library can be take some configuration parameters from the
environment.  Some of these variables are listed below.  For information
about specific commands, see L<openssl-engine(1)>, L<openssl-provider(1)>,
L<openssl-rehash(1)>, and L<tsget(1)>.

For information about the use of environment variables in configuration,
see L<config(5)/ENVIRONMENT>.

For information about querying or specifying CPU architecture flags, see
L<OPENSSL_ia32cap(3)>, and L<OPENSSL_s390xcap(3)>.

For information about all environment variables used by the OpenSSL libraries,
see L<openssl-env(7)>.

=over 4

=item B<OPENSSL_TRACE=>I<name>[,...]

Enable tracing output of OpenSSL library, by name.
This output will only make sense if you know OpenSSL internals well.
Also, it might not give you any output at all, depending on how
OpenSSL was built.

The value is a comma separated list of names, with the following
available:

=over 4

=item B<TRACE>

The tracing functionality.

=item B<TLS>

General SSL/TLS.

=item B<TLS_CIPHER>

SSL/TLS cipher.

=item B<ENGINE_CONF>

ENGINE configuration.

=item B<ENGINE_TABLE>

The function that is used by RSA, DSA (etc) code to select registered
ENGINEs, cache defaults and functional references (etc), will generate
debugging summaries.

=item B<ENGINE_REF_COUNT>

Reference counts in the ENGINE structure will be monitored with a line
of generated for each change.

=item B<PKCS5V2>

PKCS#5 v2 keygen.

=item B<PKCS12_KEYGEN>

PKCS#12 key generation.

=item B<PKCS12_DECRYPT>

PKCS#12 decryption.

=item B<X509V3_POLICY>

Generates the complete policy tree at various point during X.509 v3
policy evaluation.

=item B<BN_CTX>

BIGNUM context.

=back

=back

=head1 SEE ALSO

L<openssl-asn1parse(1)>,
L<openssl-ca(1)>,
L<openssl-ciphers(1)>,
L<openssl-cms(1)>,
L<openssl-crl(1)>,
L<openssl-crl2pkcs7(1)>,
L<openssl-dgst(1)>,
L<openssl-dhparam(1)>,
L<openssl-dsa(1)>,
L<openssl-dsaparam(1)>,
L<openssl-ec(1)>,
L<openssl-ecparam(1)>,
L<openssl-enc(1)>,
L<openssl-engine(1)>,
L<openssl-errstr(1)>,
L<openssl-gendsa(1)>,
L<openssl-genpkey(1)>,
L<openssl-genrsa(1)>,
L<openssl-kdf(1)>,
L<openssl-mac(1)>,
L<openssl-nseq(1)>,
L<openssl-ocsp(1)>,
L<openssl-passwd(1)>,
L<openssl-pkcs12(1)>,
L<openssl-pkcs7(1)>,
L<openssl-pkcs8(1)>,
L<openssl-pkey(1)>,
L<openssl-pkeyparam(1)>,
L<openssl-pkeyutl(1)>,
L<openssl-prime(1)>,
L<openssl-rand(1)>,
L<openssl-rehash(1)>,
L<openssl-req(1)>,
L<openssl-rsa(1)>,
L<openssl-rsautl(1)>,
L<openssl-s_client(1)>,
L<openssl-s_server(1)>,
L<openssl-s_time(1)>,
L<openssl-sess_id(1)>,
L<openssl-smime(1)>,
L<openssl-speed(1)>,
L<openssl-spkac(1)>,
L<openssl-srp(1)>,
L<openssl-storeutl(1)>,
L<openssl-ts(1)>,
L<openssl-verify(1)>,
L<openssl-version(1)>,
L<openssl-x509(1)>,
L<config(5)>,
L<crypto(7)>,
L<openssl-env(7)>.
L<ssl(7)>,
L<x509v3_config(5)>


=head1 HISTORY

The B<list> -I<XXX>B<-algorithms> options were added in OpenSSL 1.0.0;
For notes on the availability of other commands, see their individual
manual pages.

=head1 COPYRIGHT

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut