mod_tlsmod_tls.c file for ProFTPD
1.2.x, and is not compiled by default. Installation instructions
are discussed here.
The most current version of mod_tls is distributed with the
ProFTPD source code.
This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (http://www.openssl.org/).
This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).
Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.
2002-09-01: Thanks to Peter 'Luna' Runestig <peter at
runestig.com> for his original mod_tls, upon which this version
is based. His module can be found here:
ftp://ftp.runestig.com/pub/proftpd-tls/
<VirtualHost>, <Global>
The TLSCACertificateFile directive configures one file where you
can assemble the certificates of Certification Authorities (CA) for your
clients. The CA certificates in the file are then used to verify client
certificates, if presented. Such a file is merely the concatenation of the
various PEM-encoded CA certificates, in order of preference. This directive
can be used in addition to, or as an alternative for,
TLSCACertificatePath.
Example:
TLSCACertificateFile /etc/ftpd/ca-bundle.pem
If neither TLSCACertificateFile nor
TLSCACertificatePath are specified, the following message will
appear in the TLSLog:
using default OpenSSL verification locations (see $SSL_CERT_DIR)This means that the
SSL_CERT_DIR environment variable, if set,
will be used to determine the location of a CA certificate directory, to be
used when verifying clients.
See also: TLSCACertificatePath
<VirtualHost>, <Global>
The TLSCACertificatePath directive sets the directory for the
certificates of Certification Authorities (CAs) for your clients. These are
used to verify the client certificates presented. This directive may be used
in addition to, or as alternative for, TLSCACertificateFile.
The files in the configured directory have to be PEM-encoded, and are accessed
through hash filenames. This means one cannot simply place the CA certificates
there: one also has to create symbolic links named hash-value.N. The
c_rehash utility that comes with OpenSSL can be used to create
the necessary symlinks.
Example:
TLSCACertificatePath /etc/ftpd/ca/
If neither TLSCACertificateFile nor
TLSCACertificatePath are specified, the following message will
appear in the TLSLog:
using default OpenSSL verification locations (see $SSL_CERT_DIR)This means that the
SSL_CERT_DIR environment variable, if set,
will be used to determine the location of a CA certificate directory, to be
used when verifying clients.
See also: TLSCACertificateFile
<VirtualHost>, <Global>
The TLSCARevocationFile directive configures one file that can
contain the Certificate Revocation Lists (CRL) of Certification Authorities
(CA) for your clients. These CRLs are used during the verification of client
certificates, if presented. Such a file is merely the concatenation of the
various PEM-encoded CRL files, in order of preference. This directive can be
used in addition to, or as an alternative for, TLSCARevocationPath.
Example:
TLSCARevocationFile /etc/ftpd/ca-crl-bundle.pem
See also: TLSCARevocationPath
<VirtualHost>, <Global>
The TLSCARevocationPath directive sets the directory for the
Certificate Revocation Lists (CRL) of Certification Authorities (CAs) for your
clients. These are used during the verification of client certificates, if
presented. This directive may be used in addition to, or as alternative for,
TLSCARevocationFile.
The files in the configured directory have to be PEM-encoded, and are accessed
through hash filenames. This means one cannot simply place the CRLs there:
one also has to create symbolic links named hash-value.N. The
c_rehash utility that comes with OpenSSL can be used to create
the necessary symlinks.
Example:
TLSCARevocationPath /etc/ftpd/crl/
See also: TLSCARevocationFile
<VirtualHost>, <Global>
The TLSCertificateChainFile directive sets the optional
all-in-one file where you can assemble the certificates of Certification
Authorities (CA) which form the certificate chain of the server certificate.
This starts with the issuing CA certificate of the server certificate and can
range up to the root CA certificate. Such a file is simply the concatenation
of the various PEM-encoded CA Certificate files in certificate chain order.
This server certificate chain is sent to the client, in addition to the
server's certificate.
If TLSCertificateChainFile is not used, and
TLSCACertificatePath is used, the certificate chain is built from
the certificates in that path. TLSCertificateChainFile should be
used as an alternative to TLSCACertificatePath for explicitly
constructing the server certificate chain. It is especially useful to avoid
conflicts with CA certificates when using client authentication. For although
placing a CA certificate of the server certificate chain into
the TLSCACertificatePath has the same effect for the certificate
chain construction, it has the side-effect that client certificates issued by
this same CA certificate are also accepted on client authentication. This
is usually not what one expects.
Be careful: providing the certificate chain works only if you are using a single (either RSA or DSA) based server certificate. If you are using a coupled RSA+DSA certificate pair, this will work only if actually both certificates use the same certificate chain. Otherwise, clients will become confused.
Example:
TLSCertificateChainFile /etc/ftpd/client-ca-list.pem
<VirtualHost>, <Global>Default cipher list is "ALL:!ADH".
How to put together a cipher list parameter:
Key Exchange Algorithms:
"kRSA" RSA key exchange
"kDHr" Diffie-Hellman key exchange (key from RSA cert)
"kDHd" Diffie-Hellman key exchange (key from DSA cert)
"kEDH' Ephemeral Diffie-Hellman key exchange (temporary key)
Authentication Algorithm:
"aNULL" No authentication
"aRSA" RSA authentication
"aDSS" DSS authentication
"aDH" Diffie-Hellman authentication
Cipher Encoding Algorithm:
"eNULL" No encodiing
"DES" DES encoding
"3DES" Triple DES encoding
"RC4" RC4 encoding
"RC2" RC2 encoding
"IDEA" IDEA encoding
MAC Digest Algorithm:
"MD5" MD5 hash function
"SHA1" SHA1 hash function
"SHA" SHA hash function (should not be used)
Aliases:
"ALL" all ciphers
"SSLv2" all SSL version 2.0 ciphers (should not be used)
"SSLv3" all SSL version 3.0 ciphers
"EXP" all export ciphers (40-bit)
"EXPORT56" all export ciphers (56-bit)
"LOW" all low strength ciphers (no export)
"MEDIUM" all ciphers with 128-bit encryption
"HIGH" all ciphers using greater than 128-bit encryption
"RSA" all ciphers using RSA key exchange
"DH" all ciphers using Diffie-Hellman key exchange
"EDH" all ciphers using Ephemeral Diffie-Hellman key exchange
"ADH" all ciphers using Anonymous Diffie-Hellman key exchange
"DSS" all ciphers using DSS authentication
"NULL" all ciphers using no encryption
Each item in the list may include a prefix modifier:
"+" move cipher(s) to the current location in the list
"-" remove cipher(s) from the list (may be added again by a
subsequent list entry)
"!" kill cipher from the list (it may not be added again by a
subsequent list entry)
If no modifier is specified the entry is added to the list at the current position. "+" may also be used to combine tags to specify entries such as "RSA+RC4" describes all ciphers that use both RSA and RC4.
For example, all available ciphers not including ADH key exchange:
ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP
All algorithms including ADH and export but excluding patented algorithms:
HIGH:MEDIUM:LOW:EXPORT56:EXP:ADH:!kRSA:!aRSA:!RC4:!RC2:!IDEA
The OpenSSL command
openssl ciphers -v <list of ciphers>may be used to list all of the ciphers and the order described by a specific <list of ciphers>.
<VirtualHost>, <Global>
The TLSDHParamFile directive is used to configure a file that
mod_tls will use when engaging in a Diffie-Hellman key exchange.
Such a key exchange can be computationally intensive, in terms for parameter
generation; to help speed up the process, the parameters used may be generated
in advance, and stored in a file. The dhparam utility that comes
with OpenSSL may be used to generate an appropriate file for this directive.
The file parameter must be an absolute path.
<VirtualHost>, <Global>
The TLSDSACertificateFile directive points to the PEM-encoded
file containing the DSA certificate file for the server and optionally also
the corresponding DSA private key file.
If the contained private key is encrypted, the administrator will be prompted for the passphrase when the daemon starts up, and when the daemon is restarted.
Example:
TLSDSACertificateFile /etc/ftpd/server-dsa-cert.pem
<VirtualHost>, <Global>
The TLSDSACertificateKeyFile directive points to the PEM-encoded
private key file for the server. If the private key is not combined with the
certificate in the TLSDSACertificateFile, use this additional
directive to point to the file with the standalone private key. When
TLSDSACertificateFile is used and the file contains both the
certificate and the private key, this directive need not be used. However,
this practice is strongly discouraged. Instead we recommend you to separate
the certificate and the private key.
If the contained private key is encrypted, the administrator will be prompted for the passphrase when the daemon starts up, and when the daemon is restarted.
Example:
TLSDSACertificateKeyFile /etc/ftpd/server-dsa-key.pem
<VirtualHost>, <Global>
The TLSEngine directive toggles the use of the SSL/TLS protocol
engine (e.g. mod_tls). This is usually used inside a
<VirtualHost> section to enable SSL/TLS sessions for a
particular virtual host. By default mod_tls is disabled for both
the main server and all configured virtual hosts.
<VirtualHost>, <Global>
The TLSLog directive is used to specify a log file for
mod_tls's reporting on a per-server basis. The file
parameter given must be the full path to the file to use for logging.
<VirtualHost>, <Global>
The TLSOptions directive is used to configure various optional
behavior of mod_tls.
Example:
TLSOptions iPAddressRequired StdEnvVars
The currently implemented options are:
AllowDotLogin
By default, mod_tls still requires that a user supply a
password for authentication, even if a valid client certificate is
presented. If this option is enabled, mod_tls will check
in the user's home directory for a .tlslogin file, which
should contain one or more PEM-encoded certificates. If the certificate
presented by the client, if any, matches a certificate in this
.tlslogin file, the user will be considered authenticated.
The server will still prompt for a password, and if the user's
.tlslogin does not exist, or does not contain the client's
certificate, then the server will fallback to using the password for
authentication.
AllowPerUser
This option affects how mod_tls evaluates any
TLSRequired directives. Usually mod_tls
will reject any FTP commands, when TLSRequired on or
TLSRequired ctrl is in effect, if the client has not
successfully negotiated a SSL/TLS handshake. The FTPS specification
requires that the SSL/TLS handshake occur, via the AUTH FTP command,
before the USER and PASS commands. This means that
mod_tls does not know the identity of the connecting client
when enforcing TLSRequired. If this AllowPerUser
is used, mod_tls will wait until after the PASS
command has been processed to enforce any TLSRequired
settings.
Important: if AllowPerUser is used, even if
TLSRequired on or TLSRequired ctrl are in
effect, it will be possible for the connecting client to send
usernames and passsword unprotected before mod_tls
rejects the connection. This results in a slightly weaker security
policy enforcement; please consider carefully if this tradeoff is
acceptable for your site.
ExportCertDataSets the following environment variables, if applicable. Note that doing so increases the memory size of the process quite a bit:
TLS_SERVER_CERT |
Server certificate, PEM-encoded |
TLS_CLIENT_CERT |
Client certificate, PEM-encoded |
TLS_CLIENT_CERT_CHAINn |
PEM-encoded certificates in client certificate chain |
NoCertRequestSome FTP clients are known to be buggy when handling a server's certificate request. This option causes the server not to include such a request during an SSL handshake.
StdEnvVars
Sets the following environment variables, if applicable. These environment
variables are then avaiable for use, such as in LogFormats.
Note that doing so increases the memory size of the process quite a bit:
FTPS |
Present if FTP over SSL/TLS is being used |
TLS_PROTOCOL |
SSL protocol version (e.g. SSLv3, TLSv1) |
TLS_SESSION_ID |
Hex-encoded SSL session ID |
TLS_CIPHER |
Cipher specification name |
TLS_CIPHER_EXPORT |
Present if cipher is an export cipher |
TLS_CIPHER_KEYSIZE_POSSIBLE |
Number of cipher bits possible |
TLS_CIPHER_KEYSIZE_USED |
Number of cipher bits used |
TLS_LIBRARY_VERSION |
OpenSSL version |
TLS_CLIENT_M_VERSION |
Client certificate version |
TLS_CLIENT_M_SERIAL |
Client certificate serial number |
TLS_CLIENT_S_DN |
Subject DN of client certificate |
TLS_CLIENT_S_DN_x509 |
Component of client certificate's Subject DN, where x509 is
a component of a X509 DN: C,CN,D,I,G,L,O,OU,S,ST,T,UID,Email |
TLS_CLIENT_I_DN |
Issuer DN of client certificate |
TLS_CLIENT_I_DN_x509 |
Component of client certificate's Issuer DN, where x509 is
a component of a X509 DN: C,CN,D,I,G,L,O,OU,S,ST,T,UID,Email |
TLS_CLIENT_V_START |
Start time of client certificate validity |
TLS_CLIENT_V_END |
End time of client certificate validity |
TLS_CLIENT_A_SIG |
Client certificate's signature algorithm |
TLS_CLIENT_A_KEY |
Client certificate's public key algorithm |
TLS_CLIENT_CERT
| Client certificate, PEM-encoded |
TLS_CLIENT_CERT_CHAINn |
PEM-encoded certificates in client certificate chain |
TLS_SERVER_M_VERSION |
Server certificate version |
TLS_SERVER_M_SERIAL |
Server certificate serial number |
TLS_SERVER_S_DN |
Subject DN of server certificate |
TLS_SERVER_S_DN_x509 |
Component of server certificate's Subject DN, where x509 is
a component of a X509 DN: C,CN,D,I,G,L,O,OU,S,ST,T,UID,Email |
TLS_SERVER_I_DN |
Issuer DN of server certificate |
TLS_SERVER_I_DN_x509 |
Component of server certificate's Issuer DN, where x509 is
a component of a X509 DN: C,CN,D,I,G,L,O,OU,S,ST,T,UID,Email |
TLS_SERVER_V_START |
Start time of server certificate validity |
TLS_SERVER_V_END |
End time of server certificate validity |
TLS_SERVER_A_SIG |
Server certificate's signature algorithm |
TLS_SERVER_A_KEY |
Server certificate's public key algorithm |
TLS_SERVER_CERT |
Server certificate, PEM-encoded |
dNSNameRequired
This option will cause mod_tls to perform checks on a client's
certificate once the SSL handshake has been completed: the client's
certificate will be searched for the subjectAltName X509v3
extension, and, in that extension, the dNSName value will
be looked up. Unless a dNSName value is present, and the
value matches the DNS name to which the client's IP address resolves,
the SSL session is closed. This check is only performed during
SSL handshakes on the control channel. Note that if
UseReverseDNS is off, this option is automatically
disabled.
iPAddressRequired
This option will cause mod_tls to perform checks on a client's
certificate once the SSL handshake has been completed: the client's
certificate will be searched for the subjectAltName X509v3
extension, and, in that extension, the iPAddress value will
be looked up. Unless an iPAddress value is present, and the
value matches the IP address of the client, the SSL session is closed.
This check is only performed during SSL handshakes on the control channel.
The TLSProtocol directive is used to configure the SSL/TLS
protocol versions that mod_tls should use when establishing
SSL/TLS sessions. Clients can then only connect using the configured
protocol.
Since the protocol version used by mod_tls is set only once,
when the daemon starts, the TLSProtocol directive is only allowed
in the "server config" context.
The allowed protocols are:
SSLv23 |
Compatibility mode, used to allow both SSLv3 and TLSv1 |
SSLv3 |
Allow only SSLv3 |
TLSv1 |
Allow only TLSv1 |
All use of SSLv2 is disabled. SSLv2 should not be used.
/.rnd<VirtualHost>, <Global>
The TLSRandomSeed directive configures the file that
mod_tls will use for seeding the PRNG. seed must be an
absolute path.
When the daemon shuts down, any random data left will be written out to the random seed file, so that that data may be used for seeding when the daemon is started again.
Example:
TLSRandomSeed /etc/ftpd/server.rnd
<VirtualHost>, <Global>
The TLSRenegotiate directive is used to configure when SSL
renegotiations are to occur. Renegotiations, and thus this directive, are
only supported by mod_tls if the version of OpenSSL installed
is 0.9.7 or greater.
If supported, renegotiations will occur on control channels that have been
established for four hours by default, and on data channels that have
transferred over one gigabyte of data by default. When renegotiations are
requested, the client is given a timeout of 30 seconds, by default, to perform
the renegotiation. To change the default control channel renegotiation
timeout, use ctrl followed by a number, greater than zero, in seconds.
Use data followed by a number, greater than zero, of kilobytes to
change the default data channel renegotiation threshhold. The timeout
parameter, followed by a positive number of seconds, is used to change the
length of time given to a client to complete a requested renegotiation, after
which the SSL session will be shutdown. By default, mod_tls
will require that the client comply with the requested renegotiation
within the TLSRenegotiate timeout. If, however, the client is
unwilling or unable to do so, and the daemon needs to support these clients,
set required to off. Doing so will cause renegotiations to
be requested, but not required.
By default, mod_tls will perform renegotiations if supported, on
the control channel after 4 hours, and on the data channel after one gigabyte
of transferred data. The default timeout for a renegotiation is 30 seconds.
Use none to disable all renegotiation requirements.
Examples:
# Change renegotiations to occur on control channels after 1 hour
TLSRenegotiate ctrl 3600
# Change renegotiations to occur on data channels after 500 MB
TLSRenegotiate data 512000
# Change renegotiations so that they are not required, only requested
TLSRenegotiate required off
# Change only the timeout for renegotiations to be 5 minutes
TLSRenegotiate timeout 300
# Change all of the above renegotiation threshholds using one directive
TLSRenegotiate ctrl 3600 data 512000 required off timeout 300
# To disable renegotiations entirely
TLSRenegotiate none
<VirtualHost>, <Global>, <Anonymous>
The TLSRequired directive is used to define a basic security
policy, one that dictates whether the control channel, or data channel, or
both, of an FTP session must occur over SSL/TLS.
The on parameter enables SSL/TLS requirements on both control and data channels; off disables the requirements on both channels. Use ctrl and data to require SSL/TLS on either channel individually.
Example:
# Require SSL/TLS on the control channel, so that passwords are not sent # in the clear. TLSRequired ctrl # Require SSL/TLS on both channels. TLSRequired on
<VirtualHost>, <Global>
The TLSRSACertificateFile directive points to the PEM-encoded
file containing the RSA certificate file for the server and optionally also
the corresponding RSA private key file.
If the contained private key is encrypted, the administrator will be prompted for the passphrase when the daemon starts up, and when the daemon is restarted.
Example:
TLSRSACertificateFile /etc/ftpd/server-rsa-cert.pem
<VirtualHost>, <Global>
The TLSRSACertificateKeyFile directive points to the PEM-encoded
private key file for the server. If the private key is not combined with the
certificate in the TLSRSACertificateFile, use this additional
directive to point to the file with the standalone private key. When
TLSRSACertificateFile is used and the file contains both the
certificate and the private key, this directive need not be used. However,
this practice is strongly discouraged. Instead we recommend you to separate
the certificate and the private key.
If the contained private key is encrypted, the administrator will be prompted for the passphrase when the daemon starts up, and when the daemon is restarted.
Example:
TLSRSACertificateKeyFile /etc/ftpd/server-rsa-key.pem
<VirtualHost>, <Global>
The TLSTimeoutHandshake directive configures the maximum number
of seconds for mod_tls to accept an SSL/TLS handshake. If set to
zero, mod_tls will wait forever for a handshake to complete. The
default is 300 seconds (five minutes).
<VirtualHost>, <Global>
The TLSVerifyClient directive configures how mod_tls
handles certificates presented by clients. If off, the module
will accept the certificate and establish an SSL/TLS session, but will not
verify the certificate. If on, the module will verify a client's
certificate and, furthermore, will fail all SSL handshake attempts unless
the client presents a certificate when the server requests one. Note that the
server can be configured to not request a client certificate via
the TLSOptions directive's "NoCertRequest" parameter.
See also: TLSOptions
<VirtualHost>, <Global>
The TLSVerifyDepth directive sets how deeply mod_tls
should verify before deciding that the client does not have a valid
certificate. The depth actually is the maximum number of intermediate
certificate issuers, i.e. the number of CA certificates which are
allowed to be followed while verifying the client certificate. A depth of 0
means that only self-signed client certificates are accepted, a depth of 1
means the client certificate can be self-signed or has to be signed by a CA
which is directly known to the server (i.e. the CA's certificate is
under TLSCACertificatePath), etc.
Example:
TLSVerifyDepth 10
mod_ssl, concerning
certificates, OpenSSL usage, etc applies to this module as well:
http://www.modssl.org/docs/2.7/The OpenSSL documentation, and its FAQ, are recommended as well:
http://www.openssl.org/docs/
There is also a script, cert-tool, that can help in the creation
of certificates. See cert-tool --help for usage information:
http://www.castaglia.org/openssl/contrib/cert-tool
A copy of the Draft describing FTP over SSL/TLS is included with the source code for this module.
mod_tls module is distributed with ProFTPD. Simply follow
the normal steps for using third-party modules in proftpd:
./configure --with-modules=mod_tls make make installYou may need to specify the location of the OpenSSL header and library files in your
configure command, e.g.:
./configure --with-modules=mod_tls \
--with-includes=/usr/local/openssl/include \
--with-libraries=/usr/local/openssl
Author: $Author$
Last Updated: $Date$
© Copyright 2002-2003 TJ Saunders
All Rights Reserved