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