RFC 4217 defines FTP over SSL/TLS:
http://www.faqs.org/rfcs/rfc4217.htmlThe
mod_tls
module for proftpd
is an implementation
of RFC 4217.
RFC 2228 defines FTP Security Extensions, of which mod_tls
is one implementation. Another
such RFC 2228 implementation is the mod_gss
module, available
from SourceForge.
Example mod_tls
configuration:
<IfModule mod_tls.c> TLSEngine on TLSLog /var/ftpd/tls.log # Support both SSLv3 and TLSv1 TLSProtocol SSLv3 TLSv1 # Are clients required to use FTP over TLS when talking to this server? TLSRequired off # Server's certificate TLSRSACertificateFile /etc/ftpd/server.cert.pem TLSRSACertificateKeyFile /etc/ftpd/server.key.pem # CA the server trusts TLSCACertificateFile /etc/ftpd/root.cert.pem # Authenticate clients that want to use FTP over TLS? TLSVerifyClient off # Allow SSL/TLS renegotiations when the client requests them, but # do not force the renegotations. Some clients do not support # SSL/TLS renegotiations; when mod_tls forces a renegotiation, these # clients will close the data connection, or there will be a timeout # on an idle data connection. TLSRenegotiate required off </IfModule>
Debugging
There are a couple of tools available for debugging and analysing FTPS
traffic. One of the easiest to use is the s_client
application, part of OpenSSL.
The following examples assume that proftpd+mod_tls
is listening
on 127.0.0.1, port 21:
# openssl s_client -connect 127.0.0.1:21 -starttls ftp CONNECTED(00000003) depth=1 /CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington verify error:num=20:unable to get local issuer certificate verify return:0 --- Certificate chain 0 s:/CN=castaglia3-server/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington i:/CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington 1 s:/CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington i:/CN=castaglia3/C=US/ST=Washington/L=Seattle/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/emailAddress=tj@castaglia.org --- Server certificate -----BEGIN CERTIFICATE----- ... -----END CERTIFICATE----- subject=/CN=castaglia3-server/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington issuer=/CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington --- Acceptable client certificate CA names /CN=castaglia3-clientCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington /CN=castaglia3/C=US/ST=Washington/L=Seattle/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/emailAddress=tj@castaglia.org /CN=castaglia3-clientCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington /CN=castaglia3/C=US/ST=Washington/L=Seattle/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/emailAddress=tj@castaglia.org --- SSL handshake has read 3731 bytes and written 344 bytes --- New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA Server public key is 1024 bit Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 Cipher : DHE-RSA-AES256-SHA Session-ID: D1F2E7C001BCFE57D797F34BD1518BDCC6160106D56A238CC0F957337C093435 Session-ID-ctx: Master-Key: F8EE2812270E8FCD87D1B26F20546EF9BABAE40F36BC6F8DF45B0E2F089571E731EAFAEA5E61BCA7D9D204BE06F28B21 Key-Arg : None Start Time: 1232997620 Timeout : 300 (sec) Verify return code: 20 (unable to get local issuer certificate) --- 220 ProFTPD 1.3.2rc4 Server (TJ's FTPS Server) [127.0.0.1] quit 221 Goodbye. read:errno=0Note that the "verify error" message is not of particular concern for us, since we are not using
s_client
to verify the server's
certificate in this example.
The parts of the s_client
output which are of particular interest
are the highlighted "Certificate chain" and "Acceptable client certificate CA
names" sections.
The "Certificate chain" section shows the certificate chain/trust path, from
the server's certificate up through the root CA for that certificate. Note
that this assumes the certificates in the trust path are available on the
server. By default, OpenSSL constructs this certificate chain using the
server's certificate (configured using TLSRSACertificateFile
or
TLSDSACertificateFile
) and the trusted CA certificates configured
using TLSCACertificateFile
and/or
TLSCACertificatePath
. See the TLSCertificateChainFile
FAQ for more details on how to influence
the constructed certificate chain.
The "Acceptable client certificate CA names" section contains the list of
CAs that can issue certificates that mod_tls
is willing to trust.
These CAs always come from the configured
TLSCACertificateFile
and/or TLSCACertificatePath
.
This list of acceptable client CAs is presented to the client whenever the
server is requesting the client's certificate (which is what
mod_tls
does by default). If you use:
TLSOptions NoCertRequestthen the server will not send this list of acceptable client CAs; using
s_client
in that case, you would see:
--- No client certificate CA names sent ---In case you're wondering, a list of CAs is sent to the client, rather than just a single CA, because this allows clients the ability to determine which certificate (as a client can have many) to use when talking to this particular server.
Another tool, slightly older, is ssldump
. This tool is more like ethereal
or
tcpdump
for any SSL/TLS traffic; it is deliberately modeled after
tcpdump
.
To use ssldump
for watching your FTPS traffic, you will need
the server key file (for decrypting), and possibly root privileges (for
listening on the network interface). Here is an example where
ssldump
is used to listen on the loopback interface
(lo0
), port 21:
# sudo ssldump -d -k server.pem -i lo0 port 21 New TCP connection #1: localhost(64148) <-> localhost(21) 0.0423 (0.0423) S>C --------------------------------------------------------------- 220 ProFTPD 1.3.2rc4 Server (TJ's FTPS Server) [127.0.0.1] --------------------------------------------------------------- 0.0427 (0.0004) C>S --------------------------------------------------------------- AUTH TLS --------------------------------------------------------------- 0.0430 (0.0002) S>C --------------------------------------------------------------- 234 AUTH TLS successful --------------------------------------------------------------- 1 1 0.0433 (0.0003) C>S SSLv2 compatible client hello Version 3.1 cipher suites Unknown value 0x39 Unknown value 0x38 Unknown value 0x35 TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA TLS_RSA_WITH_3DES_EDE_CBC_SHA SSL2_CK_3DES Unknown value 0x33 Unknown value 0x32 Unknown value 0x2f TLS_RSA_WITH_IDEA_CBC_SHA SSL2_CK_IDEA SSL2_CK_RC2 TLS_RSA_WITH_RC4_128_SHA TLS_RSA_WITH_RC4_128_MD5 SSL2_CK_RC4 TLS_DHE_RSA_WITH_DES_CBC_SHA TLS_DHE_DSS_WITH_DES_CBC_SHA TLS_RSA_WITH_DES_CBC_SHA SSL2_CK_DES TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA TLS_RSA_EXPORT_WITH_DES40_CBC_SHA TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 SSL2_CK_RC2_EXPORT40 TLS_RSA_EXPORT_WITH_RC4_40_MD5 SSL2_CK_RC4_EXPORT40 1 2 0.0658 (0.0225) S>C Handshake ServerHello Version 3.1 session_id[32]= 09 25 df 7a a8 e8 71 a2 9f 56 a6 7b dd 95 ac 67 7d 2e 81 b2 1c ca b4 5f 1e 95 13 47 01 28 20 19 cipherSuite Unknown value 0x39 compressionMethod NULL 1 3 0.0658 (0.0000) S>C Handshake Certificate 1 4 0.0658 (0.0000) S>C Handshake ServerKeyExchange 1 5 0.0658 (0.0000) S>C Handshake CertificateRequest certificate_types rsa_fixed_dh certificate_types dss_fixed_dh certificate_types rsa_sign certificate_types dss_sign certificate_authority 30 81 b8 31 1c 30 1a 06 03 55 04 03 13 13 63 61 73 74 61 67 6c 69 61 33 2d 63 6c 69 65 6e 74 43 41 31 0b 30 09 06 03 55 04 06 13 02 55 53 31 1f 30 1d 06 09 2a 86 48 86 f7 0d 01 09 01 16 10 74 6a 40 63 61 73 74 61 67 6c 69 61 2e 6f 72 67 31 12 30 10 06 03 55 04 0a 13 09 43 61 73 74 61 67 6c 69 61 31 2b 30 29 06 03 55 04 0b 13 22 43 61 73 74 61 67 6c 69 61 20 52 65 73 65 61 72 63 68 20 61 6e 64 20 44 65 76 65 6c 6f 70 6d 65 6e 74 31 14 30 12 06 03 55 04 0b 13 0b 54 4a 20 53 61 75 6e 64 65 72 73 31 13 30 11 06 03 55 04 08 13 0a 57 61 73 68 69 6e 67 74 6f 6e certificate_authority 30 81 c1 31 13 30 11 06 03 55 04 03 13 0a 63 61 73 74 61 67 6c 69 61 33 31 0b 30 09 06 03 55 04 06 13 02 55 53 31 13 30 11 06 03 55 04 08 13 0a 57 61 73 68 69 6e 67 74 6f 6e 31 10 30 0e 06 03 55 04 07 13 07 53 65 61 74 74 6c 65 31 12 30 10 06 03 55 04 0a 13 09 43 61 73 74 61 67 6c 69 61 31 2b 30 29 06 03 55 04 0b 13 22 43 61 73 74 61 67 6c 69 61 20 52 65 73 65 61 72 63 68 20 61 6e 64 20 44 65 76 65 6c 6f 70 6d 65 6e 74 31 14 30 12 06 03 55 04 0b 13 0b 54 4a 20 53 61 75 6e 64 65 72 73 31 1f 30 1d 06 09 2a 86 48 86 f7 0d 01 09 01 16 10 74 6a 40 63 61 73 74 61 67 6c 69 61 2e 6f 72 67 certificate_authority 30 81 b8 31 1c 30 1a 06 03 55 04 03 13 13 63 61 73 74 61 67 6c 69 61 33 2d 63 6c 69 65 6e 74 43 41 31 0b 30 09 06 03 55 04 06 13 02 55 53 31 1f 30 1d 06 09 2a 86 48 86 f7 0d 01 09 01 16 10 74 6a 40 63 61 73 74 61 67 6c 69 61 2e 6f 72 67 31 12 30 10 06 03 55 04 0a 13 09 43 61 73 74 61 67 6c 69 61 31 2b 30 29 06 03 55 04 0b 13 22 43 61 73 74 61 67 6c 69 61 20 52 65 73 65 61 72 63 68 20 61 6e 64 20 44 65 76 65 6c 6f 70 6d 65 6e 74 31 14 30 12 06 03 55 04 0b 13 0b 54 4a 20 53 61 75 6e 64 65 72 73 31 13 30 11 06 03 55 04 08 13 0a 57 61 73 68 69 6e 67 74 6f 6e certificate_authority 30 81 c1 31 13 30 11 06 03 55 04 03 13 0a 63 61 73 74 61 67 6c 69 61 33 31 0b 30 09 06 03 55 04 06 13 02 55 53 31 13 30 11 06 03 55 04 08 13 0a 57 61 73 68 69 6e 67 74 6f 6e 31 10 30 0e 06 03 55 04 07 13 07 53 65 61 74 74 6c 65 31 12 30 10 06 03 55 04 0a 13 09 43 61 73 74 61 67 6c 69 61 31 2b 30 29 06 03 55 04 0b 13 22 43 61 73 74 61 67 6c 69 61 20 52 65 73 65 61 72 63 68 20 61 6e 64 20 44 65 76 65 6c 6f 70 6d 65 6e 74 31 14 30 12 06 03 55 04 0b 13 0b 54 4a 20 53 61 75 6e 64 65 72 73 31 1f 30 1d 06 09 2a 86 48 86 f7 0d 01 09 01 16 10 74 6a 40 63 61 73 74 61 67 6c 69 61 2e 6f 72 67 ServerHelloDone 1 6 0.1005 (0.0346) C>S Handshake Certificate 1 7 0.1005 (0.0000) C>S Handshake ClientKeyExchange 1 8 0.1005 (0.0000) C>S ChangeCipherSpec 1 9 0.1005 (0.0000) C>S Handshake 1 10 0.1164 (0.0159) S>C ChangeCipherSpec 1 11 0.1164 (0.0000) S>C Handshake 1 12 1.7856 (1.6692) C>S application_data 1 13 1.7856 (0.0000) C>S application_data 1 14 1.7861 (0.0004) S>C application_data 1 1.7866 (0.0004) S>C TCP FIN 1 15 1.7868 (0.0002) C>S Alert
As you can see, the level of granularity used by ssldump
is on
the level of each SSL/TLS packet; while useful in some cases, I suspect that
using openssl s_client
will provide most of the information you
will want in figuring out your certificate and verification issues.
Question: How do I generate the certificate files used
by
Question: Where can I find a list of clients that
support FTPS?
Note, though, that there are known issues with some FTPS clients:
Question: How come
The long answer is covered in Eric Rescorla's excellent book, "SSL and TLS". There tend to be two
different strategies used when adding new features to a protocol: separate
ports for protocol variants, or upward negotiation. Port 443 for HTTPS is an
example of the separate ports strategy. The drawback to the separate ports
approach is that there is a finite number of ports available, and so this
approach does not scale well. The benefit is that use of separate ports tends
to require smaller changes to client and server code. Upward negotiation
is more flexible, but requires that the protocol support some sort of feature
negotiation or extension discovery, allowing clients and servers to easily
agree to negotiate "upward" into a secure channel. The authors
of the FTPS Draft felt that upward negotiation was the more appropriate of
these two approaches for encrypting FTP channels.
Question: Can I require TLS on a per-user basis?
However, in 1.2.10rc2, the
Question: Why does
Note that the above happens only if the server requires that TLS be used on data
connections (e.g.
Question: How come
Question: Using
Unfortunately, this is a rather intractable--and known--issue. Earlier
versions of the Draft defining FTPS used to allow something known as
"implicit" FTPS, by which a client could contact a well-known port
(akin to port 443 for HTTPS; FTPS used port 990) and the server, simply
because the client contacted that certain port, would automatically encrypt
the session. This approach has several drawbacks (the reason why it was
removed from later versions of the Draft), but it did allow for simple
TCP proxying.
To attempt to deal with the above issue, the RFC for FTP over SSL/TLS
suggests using the
Note that in order to configure the
Question: Sometimes my encrypted transfers are slow.
Is there a way to speed them up?
Question: I can login using FTPS, but I cannot see
any directories. Why not?
You may also see the following appear in the
Question: Why would I see the following errors while attempting to build
I suspect that the reason this build option may be necessary is that OpenSSL
0.9.8 contained changes regarding how OpenSSL loads "engines", software modules
that talk to hardware devices that can do specialized cryptographic operations.
These changes involve being able to dynamically load the "engine" software
modules.
Question: Why would I see a "no shared cipher" error in the TLSLog when attempting to connect with my FTPS client?
The first is that there is indeed no ciphersuite in common between
Another possibility is a misconfiguration. If your
Question: My FTPS client sometimes times out after uploading/downloading more than 1 GB of data. When I turn off SSL/TLS, the upload/download works. Why?
Some FTPS clients, however, do not support server-initiated SSL/TLS
renegotations. When the server does try to force a renegotiation, the client
fails that new handshake, cannot upload/download any more data over the
protected channel, and the transfer will eventually time out. Alternatively,
the transfer could terminate strangely in the middle of the upload/download.
Note, however, that not all transfer issues will be caused
by SSL/TLS renegotiations. Bugs in firewalls and routers can also cause
these symptoms.
Should you suspect that you are having issues with your FTPS client because
of SSL/TLS renegotiations, you can configure
Question: My FTPS client has trouble connecting to
Now, one possible thing to try is to use the following in your
One user tried using both the Transmit and the Fetch applications for
the Mac; both state that they can handle FTP over SSL/TLS. Using both of
these applications, the user saw the above error. The user, when using
Transmit, saw the following error message appear from the client:
Question: When
Question: How can I configure
Compiling
Now, assuming you have compiled and installed your
In order for FIPS mode to be effective, OpenSSL must be told to run in FIPS
mode from the very beginning. The
Instead, you must use the -D command-line parameter when starting
For additional reading on OpenSSL and FIPS, see:
Question: Why do I see the following in my logs when
I start
This header/library version check was added recently, hence why older
Question: When should the
The long explanation requires an illustration. Let's say we have a CA hierarchy
that looks something like this:
Another way of asking the question thus is: "How to I send MyServerCA and
MyRootCA to the client without having them in my trusted CA locations"?
We might configure
We do want to be able to verify client certs issued by a different CA,
say, TheirClientCA. We configure TheirClientCA in
The client connects to
The solution here is to use
mod_tls
?
Answer: The mod_tls
module uses the
same certificate files as Apache's mod_ssl
. The
mod_ssl
documentation explains what the files are, how they
are used, and how to generate your own:
http://www.modssl.org/docs/2.7/ssl_faq.html
Answer: This page is a good FTPS resource:
http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html
including the list of FTPS clients. On a related note, there have been some
reports that Debian's ftp-ssl
client has a few bugs; using Peter
Runestig's ftp-tls
is known to work.
http://www.runestig.com/osp.html#NOTE1
mod_tls
does not support
"implicit" FTPS (i.e. automatically encrypting sessions on
port 990)?
Answer: The short answer is because the Draft no longer
specifies support for such a mode. Here is a description of why the alternatives
to the current mode (client-requested encryption using standard control
channel) are "bad".
Answer: Prior to ProFTPD 1.2.10rc2, no. The IETF
Draft specifying FTP over TLS requires that the TLS handshake occur
before the client sends the USER
command. This means that
the server does not know the name of the user that the client will be using
when the TLS session is established. It is possible that the client's
certificate, if one is even presented, may contain information the server may
use to map that certificate to a user, but such mapping is not currently
supported by mod_tls
. Note that this is also the reason the
TLSRequired
directive cannot appear in the
<Anonymous>
context: anonymous logins are based on the
USER
command.
mod_tls
module was modified to allow
such per-user TLS requirements. To do this, the AllowPerUser
parameter of the TLSOptions
directive is used. For example,
the following example mod_tls
configuration allows non-SSL
anonymous sessions, but requires SSL/TLS for all other sessions:
<IfModule mod_tls.c>
TLSEngine on
TLSRSACertificateFile ...
TLSCACertificateFile ...
TLSOptions AllowPerUser
TLSRequired on
<Anonymous ~ftp>
User ftp
Group ftp
UserAlias anonymous ftp
RequireValidShell off
# Note how TLSRequired is set to off here in the <Anonymous> context
TLSRequired off
</Anonymous>
</IfModule>
The modification also allows mod_ifsession
-based conditions, so
that one can have settings like:
<IfGroup trusted>
TLSRequired off
</IfGroup>
However, there is a risk involved in using the AllowPerUser
option: it causes mod_tls
not to enforce TLSRequired
until after the potentially sensitive USER and PASS commands have
been sent by the client. This allows clients, even when
TLSRequired on
or TLSRequired ctrl
are in effect,
to send the USER and PASS commands unencrypted. Depending on your
site's security needs, the ability to require SSL/TLS on a per-user basis
may or may not be worth the ability to require SSL/TLS for the USER and PASS
commands.
mod_tls
break FXP
transfers?
Answer: The Draft specifying FTP over SSL explicitly
omits site-to-site transfers. A TLS session is established between the client
and the server on the control channel and, to save on the expensive overhead of
TLS handshake, that session is reused for encrypting traffic on the data
channel. In a site-to-site transfer, the client opens two control
channels, one with each server, and then arranges for those servers to open a
data channel between themselves. However, since the servers have not
established a TLS session between themselves, that opening of the data channel
fails.
TLSRequired
is either on or
data), of if the client tells the server that the client will be
using TLS on the data connections (e.g. when it sends the
AUTH
command with an argument of TLS-P
). Without
these conditions, site-to-site transfers can occur normally, albeit unencrypted.
Encrypted site-to-site transfers are not supported.
mod_tls
does not support
SSLv2?
Answer: Various defects have been found in the SSLv2
protocol. Some legacy sites need to support SSLv2 for their HTTP traffic, in
spite of its flaws. Use of FTP over TLS is fairly new, however, and there is
not much "legacy" in that regard; it was felt that, as
mod_tls
aims to provide strong cryptographic security, supporting
a known bad protocol is a Bad Idea.
mod_tls
, FTP sessions
through my firewall now no longer work. What's going on?
Answer: The short answer is that FTPS and firewalls
(and devices performing NAT) do not interact well. The control connection
happens on a well-known port, and has no issues; it is the data connection
that poses problems for FTP-aware firewalls. In a non-FTPS session, the
firewall can inspect the FTP server's responses on the control connection to a
client's PASV
or PORT
command, and thus know which
on which ports/addresses the data connection will be established. In an FTPS
session, though, those control connection messages are encrypted (that is the
point of using FTPS, right?), and so the FTP-aware firewall cannot peek.
Hence, it cannot know which on which ports the data connection will be
established. For firewalls that are configured to always allow a certain
range of ports (such as might be configured using the PassivePorts
directive), FTPS should function without issue.
CCC
FTP command (Clear Command Channel). The CCC
command makes an encrypted control channel
revert back to an unencrypted channel. This helps to solve data connection
problems in situations where network equipment (such as firewalls, routers,
NAT) peek at the control channel in order to open ports. By sending the
CCC
command and unecrypting the control channel, the network
equipment can once again peek at the commands (i.e. PORT
and EPRT
) in the control channel. Since the CCC command must
come after the client has logged in, the USER
and
PASS
commands on the control channel will still be protected by
SSL/TLS.
mod_tls
module to allow use of
the CCC
command by clients, the following must appear in your
proftpd.conf
:
TLSRequired auth+data
See the TLSRequired
description for more details.
Answer: There have been reports that increasing the
tunable buffer size (using the --enable-buffer-size
option
of the configure
script) to 8192 increases transfer speeds, most
notably on very high speed networks. Increasing the buffer size does not
appear to affect normal FTP transfers (in fact, it may benefit them as well,
depending on the client).
Answer: You have most likely configured
mod_tls
to require SSL/TLS protection for data transfers as
well as control commands, by using:
TLSRequired on
However, if your FTPS client does not expect to handle encrypted data
transfers (and directory listings count as data transfers, as they are
sent over a data channel), you may see your client appear to hang, waiting
for data it can read. Make sure your client is prepared to handle the
security requirements you have configured on the server.
TLSLog
on occasion:
PROT: unwilling to accept security parameter (C), declining
The PROT
FTP command is used to set the protection level to
be used for data transfers. Some clients send a PROT
command
with a security parameter of C
, meaning "Clear",
which effectively tells the server not to protect data transfers. The
mod_tls
module will refuse the C
security parameter
if, like above, there is "TLSRequired on" in your
proftpd.conf
. This case also indicates a disagreement between
the client's security expectations and the security policy you have configured
on the server.
proftpd
with mod_tls
?
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x35): In function `dlfcn_load': : undefined reference to `dlopen'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x95): In function `dlfcn_load': : undefined reference to `dlclose'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0xbc): In function `dlfcn_load': : undefined reference to `dlerror'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x147): In function `dlfcn_bind_var': : undefined reference to `dlsym'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x172): In function `dlfcn_bind_var': : undefined reference to `dlerror'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x237): In function `dlfcn_bind_func': : undefined reference to `dlsym'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x262): In function `dlfcn_bind_func': : undefined reference to `dlerror'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x50b): In function `dlfcn_unload': : undefined reference to `dlclose'
collect2: ld returned 1 exit status
make: *** [proftpd] Error 1
Answer:
Add -ldl
to your configure command, for example:
make clean
./configure LDFLAGS=-ldl ...
make
This tells the proftpd
build system to add libdl
,
an OS-specific library for handling dynamically loaded code, to the list
of libraries used when linking proftpd
. On some systems, the
functions in the libdl
library are part of libc
, and
are not in a separate library.
Jan 10 17:15:18 mod_tls/2.1.1[2212]: TLS/TLS-C requested, starting TLS handshake
Jan 10 17:15:18 mod_tls/2.1.1[2212]: unable to accept TLS connection:
(1) error:1408A0C1:SSL routines:SSL3_GET_CLIENT_HELLO:no shared cipher
Jan 10 17:15:18 mod_tls/2.1.1[2212]: TLS/TLS-C negotiation failed on control channel
Answer:
There are two reasons this might happen.
mod_tls
and your FTPS client. The SSL/TLS ciphersuites used by
mod_tls
are configured using the TLSCipherSuite
directive. If you have a complex or restrictive TLSCipherSuite
configured, that could be the culprit. Try relaxing (or removing outright)
your TLSCipherSuite
, or try to configure your FTPS client to use
the same SSL/TLS ciphersuites.
TLSCACertificateFile
and TLSRSACertificateFile
directives are in the "server config" context of the
proftpd.conf
file, and you have
<VirtualHost>
sections in your proftpd.conf
,
then you might see the "no shared cipher" error. The easiest
thing is to move those TLSCACertificateFile
and
TLSRSACertificateFile
directives into a <Global>
section in your proftpd.conf
, so that they apply to all
vhosts configured. The virtual hosting howto
describes this in more detail.
Answer:
The culprit behind this is most likely SSL/TLS renegotiations. By default,
mod_tls
uses SSL/TLS renegotiations to periodically update the
session key which protects the data being transferred; see the
TLSRenegotiate
documentation for more details, particularly the time-based and
bytes-based limits at which renegotations are forced.
mod_tls
to
accept renegotiations if the client requests one, but not to otherwise force
them:
TLSRenegotiate required off
proftpd
using SSL/TLS, with the following error appearing in the TLSLog
:
Sep 17 11:03:46 mod_tls/2.1.2[9628]: TLS/TLS-C requested, starting TLS handshake
Sep 17 11:03:46 mod_tls/2.1.2[9628]: unable to accept TLS connection: received EOF that violates protocol
Sep 17 11:03:46 mod_tls/2.1.2[9628]: TLS/TLS-C negotiation failed on control channel
Is this a bug in mod_tls
, in the client, or something else?
Answer: There might be several different causes for
this error. It could be a bug in the OpenSSL library, in mod_tls
,
in the FTPS client, or it could be a transient network issue.
proftpd.conf
file:
TLSOptions NoCertRequest
This option tells the OpenSSL library to not include a message requesting
the client's certificate in the SSL/TLS handshake messages. Some older
SSL implementations seem to have trouble with this certificate request message,
and react badly. This includes some Windows FTP clients, as well as some
FTP clients for the Mac.
Server said:
AUTH TLS successful
error:00000000:lib(0):func(0):reason(0)
And when using Fetch, the error message displayed by that client was:
SSL Error -9844
Server responded: "AUTH TLS successful"
In both causes, using "TLSOptions NoCertRequest" appeared to make
those clients happy.
proftpd
starts up, I am
prompted to enter the passphrases for my certificates. How can I get the
daemon to start without having to enter passphrases?
Answer: You can either remove the passphrase from
the certificate key file (as mentioned in the Apache mod_ssl
FAQ), or you can use the TLSPassPhraseProvider
directive to configure
a program will which provide the passphrases to proftpd
automatically.
mod_tls
to
use OpenSSL in FIPS mode?
Answer: Using OpenSSL in FIPS mode requires quite
a few steps. First, you would configure proftpd
to use the
mod_tls
module as normal, assuming your OpenSSL installation
has been compiled with FIPS support:
./configure --with-modules=mod_tls ...
proftpd
requires the following, for FIPS support
to work properly:
make CC=/path/to/openssl/bin/fipsld FIPSLD_CC=gcc
The FIPSLD_CC
variable should point to your normal C compiler,
e.g. gcc
. The use of this fipsld
program
is mandatory. The FIPS standard requires that the linking process
happen a very specific way, involving verification of calculated and expected
checksums of compiled code, etc. The OpenSSL packages with FIPS
support supply this fipsld
program which will link the compiled
code according to the FIPS specifications. If you do not use
fipsld
, then attempts to use OpenSSL in FIPS mode will fail.
For example, you would see the following if starting a proftpd
daemon which has not been linked using fipsld
while requesting
use of FIPS:
- mod_tls/2.1.2: unable to use FIPS mode: (unknown)
- Fatal: unable to load module 'mod_tls.c': Operation not permitted
proftpd
properly, e.g.:
make CC=/path/to/openssl/bin/fipsld FIPSLD_CC=gcc
make CC=/path/to/openssl/bin/fipsld FIPSLD_CC=gcc install
you will now be ready to start proftpd
.
mod_tls
module initializes the
OpenSSL library when the mod_tls
module is loaded, before the
proftpd.conf
file is parsed. Thus the requesting of FIPS mode
cannot be done via a setting in proftpd.conf
. (Annoying,
I know.)
proftpd
(see the docs for the <IfDefine>
and
Define
directives) to define a specific variable, which the
mod_tls
module will look for. Specifically, you will need to
start proftpd
like thus:
/path/to/proftpd -DTLS_USE_FIPS ...
This will define the TLS_USE_FIPS
variable; this tells
mod_tls
to initialize OpenSSL using FIPS mode. When this works,
you will see the following when proftpd
starts up:
- mod_tls/2.1.2: FIPS mode enabled
http://www.openssl.org/docs/fips/SecurityPolicy-1.1.1.pdf
http://www.openssl.org/docs/fips/UserGuide-1.1.1.pdf
proftpd
using mod_tls
?
- mod_tls/2.2: compiled using OpenSSL version 'OpenSSL 0.9.7i 14 Oct 2005'
headers, but linked to OpenSSL version 'OpenSSL 0.9.7l 28 Sep 2006' library
Answer: That message is a warning, not an error. It
is telling you that the OpenSSL headers on your system don't match the OpenSSL
library version. In most cases, this is not a problem. However, there
can be inexplicable errors if the difference in header versus library versions
is too large.
proftpd
releases do not log the warning.
TLSCertificateChainFile
directive be used?
Answer: Short answer: only in very specific
arrangements of CA hierarchies. Most of the time, you probably do not need
it.
MyRootCA TheirRootCA
| |
MyServerCA TheirClientCA
| |
+------+------+ +------+------+
| | | | | |
certA certB certC cert1 cert2 cert3
mod_tls
to have "certA" as the server's
certificate, via TLSRSACertificateFile
. The "certA" certificate
is issued by MyServerCA. And let's assume that we do not want to verify
any client certificates issued by MyServerCA.
mod_tls
using
TLSCACertificateFile
or TLSCACertificatePath
.
mod_tls
, and starts the SSL/TLS handshake.
mod_tls
sends its "certA" certificate, along with any certs that
may be needed on the client for verifying the server's certificate. (This
is what appears in the "Certificate chain" output from s_client
;
see SSL/TLS debugging above). Perhaps the client
does not have MyServerCA present in the client certificate store. So we need
to tell mod_tls
to send the MyServerCA and MyRootCA certs, along
with "certA". We could place the MyServerCA and MyRootCA certs in
TLSCACertificatePath
, but then any client certs issued by
MyServerCA would be trusted as well (and that's not what we want for this
example).
TLSCertificateChainFile
to supply the
MyServerCA and MyRootCA certs, as part of the server cert chain. The
configured TLSCertificateChainFile
would contain the PEM-formatted
MyServerCA and MyRootCA public certs. And although the
TLSCertificateChainFile
states that the certs contained in the
file should be in certificate chain order, this is not strictly necessary; the
OpenSSL library will adjust the ordering as appropriate.
Last Updated: $Date: 2009/01/26 20:57:07 $