Fix compile with current GnuTLS versions.

[tlsproxy/tlsproxy.git] / README

diff --git a/README b/README
index ebcb53fb201f0c111e20a2dc249d272e441f1f76..83b2442feaef4dbc2803127f947f38e6cbae3e65 100644 (file)
--- a/README
+++ b/README
@@ -11,8 +11,9 @@ tlsproxy is licensed under GPL 3 (or later).
 REQUIREMENTS
 ------------
 
+- C89 compiler
 - GnuTLS library including development headers
-- certtool (from by GnuTLS) to create TLS certificates
+- certtool (from GnuTLS) to create TLS certificates
 
 
 USAGE
@@ -23,7 +24,7 @@ This creates the following files:
 
 - `proxy-ca.pem`:      CA which is used for all connections to the client
 - `proxy-ca-key.pem`:  private key for the CA
-- `proxy-key.pem`:     private key for the server
+- `proxy-key.pem`:     private key for the proxy
 - `proxy-invalid.pem`: special certificate used for invalid pages
 
 Then import the CA file `proxy-ca.pem` in your browser so it can validate the
@@ -50,9 +51,49 @@ If an error occurs in the validation (missing `certificate-*.pem` files,
 fingerprint changed, etc.) it's logged by the proxy (stdout) and the special
 `proxy-invalid.pem` certificate is used to send a 500 error message to the
 client. The connection to the server is closed so there's no chance that any
-client data is sent to the (possible) evil server. The invalide certificate is
+client data is sent to the (possible) evil server. The invalid certificate is
 also easy to spot in the browser because it uses an invalid hostname
 ("invalid") and is self-signed.
 
 If an internal error occurs before the TLS connection can be established a 503
 Forwarding failure is sent to the client (unencrypted).
+
+
+-u option
+~~~~~~~~~
+
+The '-u' option passes through connections for hostnames with no stored
+certificate (i.e. `certificate-*-server.pem` is missing or unreadable). In
+this case the normal CA chain in your browser lets you validate the server
+certificate. If the server certificate changes you're _not_ informed!
+
+This option is useful if you often visit websites using HTTPS but you don't
+use critical information (e.g. no passwords, etc.) on these websites.
+
+For hostnames with a stored server certificate everything works as usual and a
+certificate change is detected.
+
+WARNING: The option might cause security problems if you're not careful:
+
+For example you normally visit https://example.org/ and store the server
+certificate in `certificate-example.org.server.pem`. Without '-u' everything
+is fine.
+
+But if you use '-u' and an attacker redirects you to e.g.
+https://www.example.org/ - leading .www - (or https://whatever.org/) (for
+example through a link on a different site) then the proxy just forwards the
+TLS connection (because it doesn't know the fingerprint for
+https://www.example.org/, that's how '-u' works) and you won't be aware that a
+different server certificate might be used!
+
+If you always verify the authentication of the connection this isn't a
+problem, but if you only check if it's a HTTPS connection then this attack is
+possible.
+
+
+KNOWN ISSUES
+------------
+
+- Firefox (at least Iceweasel 3.5.16 on Debian) fails to load the error page
+  sent with the "invalid" certificate once the certificate has been accepted.
+  As the user shouldn't accept the invalid certificate this is a minor issue.