implement Signed-By option for sources.list

Limits which key(s) can be used to sign a repository. Not immensely useful
from a security perspective all by itself, but if the user has
additional measures in place to confine a repository (like pinning) an
attacker who gets the key for such a repository is limited to its
potential and can't use the key to sign its attacks for an other (maybe
less limited) repository… (yes, this is as weak as it sounds, but having
the capability might come in handy for implementing other stuff later).

1 files changed, 12 insertions, 12 deletions

diff --git a/doc/sources.list.5.xml b/doc/sources.list.5.xml
index aded8ecef..12a7773f5 100644
--- a/doc/sources.list.5.xml
+++ b/doc/sources.list.5.xml
@@ -232,18 +232,18 @@ deb-src [ option1=value1 option2=value2 ] uri suite [component1] [component2] [.
        anomalies.
 
        <itemizedlist>
-	  <listitem><para><option>Trusted</option> (<option>trusted</option>)
-		is a tri-state value which defaults to APT deciding if a source
-		is considered trusted or if warnings should be raised before e.g.
-		packages are installed from this source. This option can be used
-		to override this decision either with the value <literal>yes</literal>,
-		which lets APT consider this source always as a trusted source
-		even if it has no or fails authentication checks by disabling parts
-		of &apt-secure; and should therefore only be used in a local and trusted
-		context (if at all) as otherwise security is breached. The opposite
-		can be achieved with the value no, which causes the source to be handled
-		as untrusted even if the authentication checks passed successfully.
-		The default value can't be set explicitly.
+	  <listitem><para><option>Signed-By</option> (<option>signed-by</option>)
+		is either an absolute path to a keyring file (has to be
+		accessible and readable for the <literal>_apt</literal> user,
+		so ensure everyone has read-permissions on the file) or a
+		fingerprint of a key in either the
+		<filename>trusted.gpg</filename> keyring or in one of the
+		keyrings in the <filename>trusted.gpg.d/</filename> directory
+		(see <command>apt-key fingerprint</command>). If the option is
+		set only the key(s) in this keyring or only the key with this
+		fingerprint is used for the &apt-secure; verification of this
+		repository. Otherwise all keys in the trusted keyrings are
+		considered valid signers for this repository.
 	  </para></listitem>
 
 	  <listitem><para><option>Check-Valid-Until</option> (<option>check-valid-until</option>)