SSL_CONF_cmd - OpenSSL Documentation

SSL_CONF_cmd - OpenSSL Documentation
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SSL_CONF_cmd
NAME
SSL_CONF_cmd_value_type, SSL_CONF_cmd - send configuration command
SYNOPSIS
#include

int SSL_CONF_cmd(SSL_CONF_CTX *cctx, const char *cmd, const char *value);
int SSL_CONF_cmd_value_type(SSL_CONF_CTX *cctx, const char *cmd);
DESCRIPTION
The function SSL_CONF_cmd() performs configuration operation
cmd
with optional parameter
value
on
ctx
. Its purpose is to simplify application configuration of
SSL_CTX
or
SSL
structures by providing a common framework for command line options or configuration files.
SSL_CONF_cmd_value_type() returns the type of value that
cmd
refers to.
SUPPORTED COMMAND LINE COMMANDS
Currently supported
cmd
names for command lines (i.e. when the flag
SSL_CONF_CMDLINE
is set) are listed below. Note: all
cmd
names are case sensitive. Unless otherwise stated commands can be used by both clients and servers and the
value
parameter is not used. The default prefix for command line commands is
and that is reflected below.
-sigalgs
This sets the supported signature algorithms for TLSv1.2 and TLSv1.3. For clients this value is used directly for the supported signature algorithms extension. For servers it is used to determine which signature algorithms to support.
The
value
argument should be a colon separated list of signature algorithms in order of decreasing preference of the form
algorithm+hash
or
signature_scheme
algorithm
is one of
RSA
DSA
or
ECDSA
and
hash
is a supported algorithm OID short name such as
SHA1
SHA224
SHA256
SHA384
of
SHA512
. Note: algorithm and hash names are case sensitive.
signature_scheme
is one of the signature schemes defined in TLSv1.3, specified using the IETF name, e.g.,
ecdsa_secp256r1_sha256
ed25519
, or
rsa_pss_pss_sha256
If this option is not set then all signature algorithms supported by the OpenSSL library are permissible.
Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by using
RSA
as the
algorithm
or by using one of the
rsa_pkcs1_*
identifiers) are ignored in TLSv1.3 and will not be negotiated.
-client_sigalgs
This sets the supported signature algorithms associated with client authentication for TLSv1.2 and TLSv1.3. For servers the value is used in the
signature_algorithms
field of a
CertificateRequest
message. For clients it is used to determine which signature algorithm to use with the client certificate. If a server does not request a certificate this option has no effect.
The syntax of
value
is identical to
-sigalgs
. If not set then the value set for
-sigalgs
will be used instead.
-groups
This sets the supported groups. For clients, the groups are sent using the supported groups extension. For servers, it is used to determine which group to use. This setting affects groups used for signatures (in TLSv1.2 and earlier) and key exchange. The first group listed will also be used for the
key_share
sent by a client in a TLSv1.3
ClientHello
The
value
argument is a colon separated list of groups. The group can be either the
NIST
name (e.g.
P-256
), some other commonly used name where applicable (e.g.
X25519
) or an OpenSSL OID name (e.g.
prime256v1
). Group names are case sensitive. The list should be in order of preference with the most preferred group first.
-curves
This is a synonym for the "-groups" command.
-named_curve
This sets the temporary curve used for ephemeral ECDH modes. Only used by servers
The
value
argument is a curve name or the special value
auto
which picks an appropriate curve based on client and server preferences. The curve can be either the
NIST
name (e.g.
P-256
) or an OpenSSL OID name (e.g.
prime256v1
). Curve names are case sensitive.
-cipher
Sets the TLSv1.2 and below ciphersuite list to
value
. This list will be combined with any configured TLSv1.3 ciphersuites. Note: syntax checking of
value
is currently not performed unless a
SSL
or
SSL_CTX
structure is associated with
cctx
-ciphersuites
Sets the available ciphersuites for TLSv1.3 to value. This is a simple colon (":") separated list of TLSv1.3 ciphersuite names in order of preference. This list will be combined any configured TLSv1.2 and below ciphersuites. See
ciphers(1)
for more information.
-cert
Attempts to use the file
value
as the certificate for the appropriate context. It currently uses SSL_CTX_use_certificate_chain_file() if an
SSL_CTX
structure is set or SSL_use_certificate_file() with filetype PEM if an
SSL
structure is set. This option is only supported if certificate operations are permitted.
-key
Attempts to use the file
value
as the private key for the appropriate context. This option is only supported if certificate operations are permitted. Note: if no
-key
option is set then a private key is not loaded unless the flag
SSL_CONF_FLAG_REQUIRE_PRIVATE
is set.
-dhparam
Attempts to use the file
value
as the set of temporary DH parameters for the appropriate context. This option is only supported if certificate operations are permitted.
-record_padding
Attempts to pad TLSv1.3 records so that they are a multiple of
value
in length on send. A
value
of 0 or 1 turns off padding. Otherwise, the
value
must be >1 or <=16384.
-no_renegotiation
Disables all attempts at renegotiation in TLSv1.2 and earlier, same as setting
SSL_OP_NO_RENEGOTIATION
-min_protocol
-max_protocol
Sets the minimum and maximum supported protocol. Currently supported protocol values are
SSLv3
TLSv1
TLSv1.1
TLSv1.2
TLSv1.3
for TLS;
DTLSv1
DTLSv1.2
for DTLS, and
None
for no limit. If either the lower or upper bound is not specified then only the other bound applies, if specified. If your application supports both TLS and DTLS you can specify any of these options twice, once with a bound for TLS and again with an appropriate bound for DTLS. To restrict the supported protocol versions use these commands rather than the deprecated alternative commands below.
-no_ssl3
-no_tls1
-no_tls1_1
-no_tls1_2
-no_tls1_3
Disables protocol support for SSLv3, TLSv1.0, TLSv1.1, TLSv1.2 or TLSv1.3 by setting the corresponding options
SSL_OP_NO_SSLv3
SSL_OP_NO_TLSv1
SSL_OP_NO_TLSv1_1
SSL_OP_NO_TLSv1_2
and
SSL_OP_NO_TLSv1_3
respectively. These options are deprecated, instead use
-min_protocol
and
-max_protocol
-bugs
Various bug workarounds are set, same as setting
SSL_OP_ALL
-comp
Enables support for SSL/TLS compression, same as clearing
SSL_OP_NO_COMPRESSION
. This command was introduced in OpenSSL 1.1.0. As of OpenSSL 1.1.0, compression is off by default.
-no_comp
Disables support for SSL/TLS compression, same as setting
SSL_OP_NO_COMPRESSION
. As of OpenSSL 1.1.0, compression is off by default.
-no_ticket
Disables support for session tickets, same as setting
SSL_OP_NO_TICKET
-serverpref
Use server and not client preference order when determining which cipher suite, signature algorithm or elliptic curve to use for an incoming connection. Equivalent to
SSL_OP_CIPHER_SERVER_PREFERENCE
. Only used by servers.
-prioritize_chacha
Prioritize ChaCha ciphers when the client has a ChaCha20 cipher at the top of its preference list. This usually indicates a client without AES hardware acceleration (e.g. mobile) is in use. Equivalent to
SSL_OP_PRIORITIZE_CHACHA
. Only used by servers. Requires
-serverpref
-no_resumption_on_reneg
set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. Only used by servers.
-legacyrenegotiation
permits the use of unsafe legacy renegotiation. Equivalent to setting
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
-legacy_server_connect
-no_legacy_server_connect
permits or prohibits the use of unsafe legacy renegotiation for OpenSSL clients only. Equivalent to setting or clearing
SSL_OP_LEGACY_SERVER_CONNECT
. Set by default.
-allow_no_dhe_kex
In TLSv1.3 allow a non-(ec)dhe based key exchange mode on resumption. This means that there will be no forward secrecy for the resumed session.
-strict
enables strict mode protocol handling. Equivalent to setting
SSL_CERT_FLAG_TLS_STRICT
-anti_replay
-no_anti_replay
Switches replay protection, on or off respectively. With replay protection on, OpenSSL will automatically detect if a session ticket has been used more than once, TLSv1.3 has been negotiated, and early data is enabled on the server. A full handshake is forced if a session ticket is used a second or subsequent time. Anti-Replay is on by default unless overridden by a configuration file and is only used by servers. Anti-replay measures are required for compliance with the TLSv1.3 specification. Some applications may be able to mitigate the replay risks in other ways and in such cases the built-in OpenSSL functionality is not required. Switching off anti-replay is equivalent to
SSL_OP_NO_ANTI_REPLAY
SUPPORTED CONFIGURATION FILE COMMANDS
Currently supported
cmd
names for configuration files (i.e. when the flag
SSL_CONF_FLAG_FILE
is set) are listed below. All configuration file
cmd
names are case insensitive so
signaturealgorithms
is recognised as well as
SignatureAlgorithms
. Unless otherwise stated the
value
names are also case insensitive.
Note: the command prefix (if set) alters the recognised
cmd
values.
CipherString
Sets the ciphersuite list for TLSv1.2 and below to
value
. This list will be combined with any configured TLSv1.3 ciphersuites. Note: syntax checking of
value
is currently not performed unless an
SSL
or
SSL_CTX
structure is associated with
cctx
Ciphersuites
Sets the available ciphersuites for TLSv1.3 to
value
. This is a simple colon (":") separated list of TLSv1.3 ciphersuite names in order of preference. This list will be combined any configured TLSv1.2 and below ciphersuites. See
ciphers(1)
for more information.
Certificate
Attempts to use the file
value
as the certificate for the appropriate context. It currently uses SSL_CTX_use_certificate_chain_file() if an
SSL_CTX
structure is set or SSL_use_certificate_file() with filetype PEM if an
SSL
structure is set. This option is only supported if certificate operations are permitted.
PrivateKey
Attempts to use the file
value
as the private key for the appropriate context. This option is only supported if certificate operations are permitted. Note: if no
PrivateKey
option is set then a private key is not loaded unless the
SSL_CONF_FLAG_REQUIRE_PRIVATE
is set.
ChainCAFile
ChainCAPath
VerifyCAFile
VerifyCAPath
These options indicate a file or directory used for building certificate chains or verifying certificate chains. These options are only supported if certificate operations are permitted.
RequestCAFile
This option indicates a file containing a set of certificates in PEM form. The subject names of the certificates are sent to the peer in the
certificate_authorities
extension for TLS 1.3 (in ClientHello or CertificateRequest) or in a certificate request for previous versions or TLS.
ServerInfoFile
Attempts to use the file
value
in the "serverinfo" extension using the function SSL_CTX_use_serverinfo_file.
DHParameters
Attempts to use the file
value
as the set of temporary DH parameters for the appropriate context. This option is only supported if certificate operations are permitted.
RecordPadding
Attempts to pad TLSv1.3 records so that they are a multiple of
value
in length on send. A
value
of 0 or 1 turns off padding. Otherwise, the
value
must be >1 or <=16384.
SignatureAlgorithms
This sets the supported signature algorithms for TLSv1.2 and TLSv1.3. For clients this value is used directly for the supported signature algorithms extension. For servers it is used to determine which signature algorithms to support.
The
value
argument should be a colon separated list of signature algorithms in order of decreasing preference of the form
algorithm+hash
or
signature_scheme
algorithm
is one of
RSA
DSA
or
ECDSA
and
hash
is a supported algorithm OID short name such as
SHA1
SHA224
SHA256
SHA384
of
SHA512
. Note: algorithm and hash names are case sensitive.
signature_scheme
is one of the signature schemes defined in TLSv1.3, specified using the IETF name, e.g.,
ecdsa_secp256r1_sha256
ed25519
, or
rsa_pss_pss_sha256
If this option is not set then all signature algorithms supported by the OpenSSL library are permissible.
Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by using
RSA
as the
algorithm
or by using one of the
rsa_pkcs1_*
identifiers) are ignored in TLSv1.3 and will not be negotiated.
ClientSignatureAlgorithms
This sets the supported signature algorithms associated with client authentication for TLSv1.2 and TLSv1.3. For servers the value is used in the
signature_algorithms
field of a
CertificateRequest
message. For clients it is used to determine which signature algorithm to use with the client certificate. If a server does not request a certificate this option has no effect.
The syntax of
value
is identical to
SignatureAlgorithms
. If not set then the value set for
SignatureAlgorithms
will be used instead.
Groups
This sets the supported groups. For clients, the groups are sent using the supported groups extension. For servers, it is used to determine which group to use. This setting affects groups used for signatures (in TLSv1.2 and earlier) and key exchange. The first group listed will also be used for the
key_share
sent by a client in a TLSv1.3
ClientHello
The
value
argument is a colon separated list of groups. The group can be either the
NIST
name (e.g.
P-256
), some other commonly used name where applicable (e.g.
X25519
) or an OpenSSL OID name (e.g.
prime256v1
). Group names are case sensitive. The list should be in order of preference with the most preferred group first.
Curves
This is a synonym for the "Groups" command.
MinProtocol
This sets the minimum supported SSL, TLS or DTLS version.
Currently supported protocol values are
SSLv3
TLSv1
TLSv1.1
TLSv1.2
TLSv1.3
DTLSv1
and
DTLSv1.2
. The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds apply only to DTLS-based contexts. The command can be repeated with one instance setting a TLS bound, and the other setting a DTLS bound. The value
None
applies to both types of contexts and disables the limits.
MaxProtocol
This sets the maximum supported SSL, TLS or DTLS version.
Currently supported protocol values are
SSLv3
TLSv1
TLSv1.1
TLSv1.2
TLSv1.3
DTLSv1
and
DTLSv1.2
. The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds apply only to DTLS-based contexts. The command can be repeated with one instance setting a TLS bound, and the other setting a DTLS bound. The value
None
applies to both types of contexts and disables the limits.
Protocol
This can be used to enable or disable certain versions of the SSL, TLS or DTLS protocol.
The
value
argument is a comma separated list of supported protocols to enable or disable. If a protocol is preceded by
that version is disabled.
All protocol versions are enabled by default. You need to disable at least one protocol version for this setting have any effect. Only enabling some protocol versions does not disable the other protocol versions.
Currently supported protocol values are
SSLv3
TLSv1
TLSv1.1
TLSv1.2
TLSv1.3
DTLSv1
and
DTLSv1.2
. The special value
ALL
refers to all supported versions.
This can't enable protocols that are disabled using
MinProtocol
or
MaxProtocol
, but can disable protocols that are still allowed by them.
The
Protocol
command is fragile and deprecated; do not use it. Use
MinProtocol
and
MaxProtocol
instead. If you do use
Protocol
, make sure that the resulting range of enabled protocols has no "holes", e.g. if TLS 1.0 and TLS 1.2 are both enabled, make sure to also leave TLS 1.1 enabled.
Options
The
value
argument is a comma separated list of various flags to set. If a flag string is preceded
it is disabled. See the
SSL_CTX_set_options(3)
function for more details of individual options.
Each option is listed below. Where an operation is enabled by default the
-flag
syntax is needed to disable it.
SessionTicket
: session ticket support, enabled by default. Inverse of
SSL_OP_NO_TICKET
: that is
-SessionTicket
is the same as setting
SSL_OP_NO_TICKET
Compression
: SSL/TLS compression support, disabled by default. Inverse of
SSL_OP_NO_COMPRESSION
EmptyFragments
: use empty fragments as a countermeasure against a SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers. It is set by default. Inverse of
SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
Bugs
: enable various bug workarounds. Same as
SSL_OP_ALL
DHSingle
: enable single use DH keys, set by default. Inverse of
SSL_OP_DH_SINGLE
. Only used by servers.
ECDHSingle
: enable single use ECDH keys, set by default. Inverse of
SSL_OP_ECDH_SINGLE
. Only used by servers.
ServerPreference
: use server and not client preference order when determining which cipher suite, signature algorithm or elliptic curve to use for an incoming connection. Equivalent to
SSL_OP_CIPHER_SERVER_PREFERENCE
. Only used by servers.
PrioritizeChaCha
: prioritizes ChaCha ciphers when the client has a ChaCha20 cipher at the top of its preference list. This usually indicates a mobile client is in use. Equivalent to
SSL_OP_PRIORITIZE_CHACHA
. Only used by servers.
NoResumptionOnRenegotiation
: set
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
flag. Only used by servers.
NoRenegotiation
: disables all attempts at renegotiation in TLSv1.2 and earlier, same as setting
SSL_OP_NO_RENEGOTIATION
UnsafeLegacyRenegotiation
: permits the use of unsafe legacy renegotiation. Equivalent to
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
UnsafeLegacyServerConnect
: permits the use of unsafe legacy renegotiation for OpenSSL clients only. Equivalent to
SSL_OP_LEGACY_SERVER_CONNECT
. Set by default.
EncryptThenMac
: use encrypt-then-mac extension, enabled by default. Inverse of
SSL_OP_NO_ENCRYPT_THEN_MAC
: that is,
-EncryptThenMac
is the same as setting
SSL_OP_NO_ENCRYPT_THEN_MAC
AllowNoDHEKEX
: In TLSv1.3 allow a non-(ec)dhe based key exchange mode on resumption. This means that there will be no forward secrecy for the resumed session. Equivalent to
SSL_OP_ALLOW_NO_DHE_KEX
MiddleboxCompat
: If set then dummy Change Cipher Spec (CCS) messages are sent in TLSv1.3. This has the effect of making TLSv1.3 look more like TLSv1.2 so that middleboxes that do not understand TLSv1.3 will not drop the connection. This option is set by default. A future version of OpenSSL may not set this by default. Equivalent to
SSL_OP_ENABLE_MIDDLEBOX_COMPAT
AntiReplay
: If set then OpenSSL will automatically detect if a session ticket has been used more than once, TLSv1.3 has been negotiated, and early data is enabled on the server. A full handshake is forced if a session ticket is used a second or subsequent time. This option is set by default and is only used by servers. Anti-replay measures are required to comply with the TLSv1.3 specification. Some applications may be able to mitigate the replay risks in other ways and in such cases the built-in OpenSSL functionality is not required. Disabling anti-replay is equivalent to setting
SSL_OP_NO_ANTI_REPLAY
VerifyMode
The
value
argument is a comma separated list of flags to set.
Peer
enables peer verification: for clients only.
Request
requests but does not require a certificate from the client. Servers only.
Require
requests and requires a certificate from the client: an error occurs if the client does not present a certificate. Servers only.
Once
requests a certificate from a client only on the initial connection: not when renegotiating. Servers only.
RequestPostHandshake
configures the connection to support requests but does not require a certificate from the client post-handshake. A certificate will not be requested during the initial handshake. The server application must provide a mechanism to request a certificate post-handshake. Servers only. TLSv1.3 only.
RequiresPostHandshake
configures the connection to support requests and requires a certificate from the client post-handshake: an error occurs if the client does not present a certificate. A certificate will not be requested during the initial handshake. The server application must provide a mechanism to request a certificate post-handshake. Servers only. TLSv1.3 only.
ClientCAFile
ClientCAPath
A file or directory of certificates in PEM format whose names are used as the set of acceptable names for client CAs. Servers only. This option is only supported if certificate operations are permitted.
SUPPORTED COMMAND TYPES
The function SSL_CONF_cmd_value_type() currently returns one of the following types:
SSL_CONF_TYPE_UNKNOWN
The
cmd
string is unrecognised, this return value can be use to flag syntax errors.
SSL_CONF_TYPE_STRING
The value is a string without any specific structure.
SSL_CONF_TYPE_FILE
The value is a filename.
SSL_CONF_TYPE_DIR
The value is a directory name.
SSL_CONF_TYPE_NONE
The value string is not used e.g. a command line option which doesn't take an argument.
NOTES
The order of operations is significant. This can be used to set either defaults or values which cannot be overridden. For example if an application calls:
SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
SSL_CONF_cmd(ctx, userparam, uservalue);
it will disable SSLv3 support by default but the user can override it. If however the call sequence is:
SSL_CONF_cmd(ctx, userparam, uservalue);
SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
SSLv3 is
always
disabled and attempt to override this by the user are ignored.
By checking the return code of SSL_CONF_cmd() it is possible to query if a given
cmd
is recognised, this is useful if SSL_CONF_cmd() values are mixed with additional application specific operations.
For example an application might call SSL_CONF_cmd() and if it returns -2 (unrecognised command) continue with processing of application specific commands.
Applications can also use SSL_CONF_cmd() to process command lines though the utility function SSL_CONF_cmd_argv() is normally used instead. One way to do this is to set the prefix to an appropriate value using SSL_CONF_CTX_set1_prefix(), pass the current argument to
cmd
and the following argument to
value
(which may be NULL).
In this case if the return value is positive then it is used to skip that number of arguments as they have been processed by SSL_CONF_cmd(). If -2 is returned then
cmd
is not recognised and application specific arguments can be checked instead. If -3 is returned a required argument is missing and an error is indicated. If 0 is returned some other error occurred and this can be reported back to the user.
The function SSL_CONF_cmd_value_type() can be used by applications to check for the existence of a command or to perform additional syntax checking or translation of the command value. For example if the return value is
SSL_CONF_TYPE_FILE
an application could translate a relative pathname to an absolute pathname.
RETURN VALUES
SSL_CONF_cmd() returns 1 if the value of
cmd
is recognised and
value
is
NOT
used and 2 if both
cmd
and
value
are used. In other words it returns the number of arguments processed. This is useful when processing command lines.
A return value of -2 means
cmd
is not recognised.
A return value of -3 means
cmd
is recognised and the command requires a value but
value
is NULL.
A return code of 0 indicates that both
cmd
and
value
are valid but an error occurred attempting to perform the operation: for example due to an error in the syntax of
value
in this case the error queue may provide additional information.
EXAMPLES
Set supported signature algorithms:
SSL_CONF_cmd(ctx, "SignatureAlgorithms", "ECDSA+SHA256:RSA+SHA256:DSA+SHA256");
There are various ways to select the supported protocols.
This set the minimum protocol version to TLSv1, and so disables SSLv3. This is the recommended way to disable protocols.
SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1");
The following also disables SSLv3:
SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
The following will first enable all protocols, and then disable SSLv3. If no protocol versions were disabled before this has the same effect as "-SSLv3", but if some versions were disables this will re-enable them before disabling SSLv3.
SSL_CONF_cmd(ctx, "Protocol", "ALL,-SSLv3");
Only enable TLSv1.2:
SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1.2");
SSL_CONF_cmd(ctx, "MaxProtocol", "TLSv1.2");
This also only enables TLSv1.2:
SSL_CONF_cmd(ctx, "Protocol", "-ALL,TLSv1.2");
Disable TLS session tickets:
SSL_CONF_cmd(ctx, "Options", "-SessionTicket");
Enable compression:
SSL_CONF_cmd(ctx, "Options", "Compression");
Set supported curves to P-256, P-384:
SSL_CONF_cmd(ctx, "Curves", "P-256:P-384");
SEE ALSO
SSL_CONF_CTX_new(3)
SSL_CONF_CTX_set_flags(3)
SSL_CONF_CTX_set1_prefix(3)
SSL_CONF_CTX_set_ssl_ctx(3)
SSL_CONF_cmd_argv(3)
SSL_CTX_set_options(3)
HISTORY
The SSL_CONF_cmd() function was added in OpenSSL 1.0.2.
The
SSL_OP_NO_SSL2
option doesn't have effect since 1.1.0, but the macro is retained for backwards compatibility.
The
SSL_CONF_TYPE_NONE
was added in OpenSSL 1.1.0. In earlier versions of OpenSSL passing a command which didn't take an argument would return
SSL_CONF_TYPE_UNKNOWN
MinProtocol
and
MaxProtocol
where added in OpenSSL 1.1.0.
AllowNoDHEKEX
and
PrioritizeChaCha
were added in OpenSSL 1.1.1.
Copyright 2012-2022 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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