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diff --git a/docs/SSL-PROBLEMS b/docs/SSL-PROBLEMS new file mode 100644 index 00000000..36502672 --- /dev/null +++ b/docs/SSL-PROBLEMS @@ -0,0 +1,67 @@ + _ _ ____ _ + ___| | | | _ \| | + / __| | | | |_) | | + | (__| |_| | _ <| |___ + \___|\___/|_| \_\_____| + +SSL problems + + First, let's establish that we often refer to TLS and SSL interchangeably as + SSL here. The current protocol is called TLS, it was called SSL a long time + ago. + + There are several known reasons why a connection that involves SSL might + fail. This is a document that attempts to details the most common ones and + how to mitigate them. + +CA certs + + CA certs are used to digitally verify the server's certificate. You need a + "ca bundle" for this. See lots of more details on this in the SSLCERTS + document. + +CA bundle missing intermediate certificates + + When using said CA bundle to verify a server cert, you will experience + problems if your CA cert does not have the certificates for the + intermediates in the whole trust chain. + +SSL version + + Some broken servers fail to support the protocol negotiation properly that + SSL servers are supposed to handle. This may cause the connection to fail + completely. Sometimes you may need to explicitly select a SSL version to use + when connecting to make the connection succeed. + + An additional complication can be that modern SSL libraries sometimes are + built with support for older SSL and TLS versions disabled! + +SSL ciphers + + Clients give servers a list of ciphers to select from. If the list doesn't + include any ciphers the server wants/can use, the connection handshake + fails. + + curl has recently disabled the user of a whole bunch of seriously insecure + ciphers from its default set (slightly depending on SSL backend in use). + + You may have to explicitly provide an alternative list of ciphers for curl + to use to allow the server to use a WEAK cipher for you. + + Note that these weak ciphers are identified as flawed. For example, this + includes symmetric ciphers with less than 128 bit keys and RC4. + + References: + + https://tools.ietf.org/html/draft-popov-tls-prohibiting-rc4-01 + +Allow BEAST + + BEAST is the name of a TLS 1.0 attack that surfaced 2011. When adding means + to mitigate this attack, it turned out that some broken servers out there in + the wild didn't work properly with the BEAST mitigation in place. + + To make such broken servers work, the --ssl-allow-beast option was + introduced. Exactly as it sounds, it re-introduces the BEAST vulnerability + but on the other hand it allows curl to connect to that kind of strange + servers. |