side requirements for proper SSL support. It has checklist-style and is not
specific to fetchmail.
-In case of troubles, mail that other document to your ISP and have them check
-their server configuration against it.
+In case of troubles, mail the README.SSL-SERVER file to your ISP and
+have them check their server configuration against it.
Unfortunately, fetchmail confuses SSL/TLS protocol levels with whether
a service needs to use in-band negotiation (STLS/STARTTLS for POP3/IMAP4) or is
----------
For use of SSL or TLS with in-band negotiation on the regular service's port,
-i. e. with STLS or STARTTLS, use these command line options (in the rcfile,
-omit the leading "--"):
+i. e. with STLS or STARTTLS, use these command line options
--sslproto tls1 --sslcertck
+or these options in the rcfile (after the respective "user"... options)
+
+ sslproto tls1 sslcertck
+
+
For use of SSL or TLS on a separate port, if the whole TCP connection is
SSL-encrypted from the very beginning, use these command line options (in the
-rcfile, omit the leading "--"):
+rcfile, omit all leading "--"):
--ssl --sslproto ssl3 --sslcertck
+or these options in the rcfile (after the respective "user"... options)
+
+ ssl sslproto ssl3 sslcertck
+
Background and use (long version :-))
------------------
and the server in an encrypted form, so that eavesdropping should become
practically impossible.
-This works as following: the server has a key pair (a secret and a public key),
-and it sends the client it's public key. Messages encrypted with the public key
+This works as follows: the server has a key pair (a secret and a public key),
+and it sends the client its public key. Messages encrypted with the public key
can be decrypted using the private one and vice versa.
A symmetric session key (symmetric means that the same key is used for
However, so called man-in-the-middle attacks are still possible: in such
a setting, an attacker pretends to be the server, and thus can e.g. get your
-authentication information if you don't use a challenge based authentication
-mechanism (because he is thought to be the real server, fetchmail will try to
+authentication information if you do not use a challenge based authentication
+mechanism (because it is thought to be the real server, fetchmail will try to
authenticate against it by telling it your password).
-So, not only you need to prove your identity to the server, the server likewise
-needs to prove (authenticate) its identity to you.
+So, not only do you need to prove your identity to the server, the
+server likewise needs to prove (authenticate) its identity to you.
In the standard setting, the server has a certificate (the client can have
a certificate too to prove its identity, but this is not covered by this
document). This certificate contains the server's public key, some data about
Digital signatures can also be made using a key pair as described earlier.
To check this certificate, you should use the new option "sslcertck". When it
-is specified, the signature of server certificate is checked against local
+is specified, the signature of the server certificate is checked against local
trusted certificates to see whether the owner of one of the certificates has
signed that server certificate, and if so, whether the signature is valid.
So, if the server certificate is signed by a Certification Authority (CA),
certificates, and point fetchmail to it. Fetchmail will then accept
certificates signed by the owner of that certificate with the private key
belonging to the public key in the certificate.
-You can specify this path using the "sslcertpath" option if it's different from
-the one OpenSSL uses by default.
+You can specify this path using the "sslcertpath" option if it is
+different from the one OpenSSL uses by default.
The idea is that the CA only gives certificates to entities whose identity it
has checked and verified (and in this case, that the server name you specify
The certificate directory must be hashed in a way OpenSSL expects it: each time
you modify a file in that directory or add a file to it, you need to use the
"c_rehash" perl script that comes with OpenSSL (in the tools/ subdirectory, in
-case that it isn't installed). Additionally, you might need to convert the
+case that it is not installed). Additionally, you might need to convert the
certificates to different formats (the PEM format is expected and usually is
available, DER is another one; you can convert between both using the
openssl(1) utility's x509 sub-mode).
key that (hopefully) has few collisions and is hard to attack using a "birthday
attack", i.e. nobody can generate a second key that hashes to the same value of
the original key in reasonable time. So, if the fingerprint matches, you can be
-reasonable sure that you talk to the original server, because only that knows
-the secret key, and it is very hard to generate a matching secret key from the
-public key. If it doesn't, it might be an attack, but keep in mind that the
-server key may also have changed legitimately before panicking ;)
+reasonably sure that you are talking to the original server, because
+only that server knows the secret key, and it is very hard to generate a
+matching secret key from the public key. If the fingerprint does not
+match, there might be an attack, but, before panicking, keep in mind
+that the server key may also have changed legitimately.
Fetchmail will present the fingerprint to you in verbose mode. You can have
fetchmail check the fingerprint (using the "sslfingerprint" option, and giving
The fingerprints fetchmail uses are MD5 sums. You can generate them e.g. using
openssl(1)'s "x509 -fingerprint" command. The format is a hexadecimal string
-with a ":" separating two byes (i.e. a ":" every two hex "digits"). The
-match is case insensitive since release 6.3.10 (upper-case digits A to F
-were required up to and including release 6.3.9).
+with a ":" separating two bytes (i.e. a ":" between every two hex "digits"). The
+match is case insensitive since release 6.3.10 (upper-case digits A to F were
+required up to and including release 6.3.9).
*CAVEAT*: OpenSSL must be at least version 0.9.7 to be able to check CRLs.
projects / ~andy / fetchmail / blobdiff