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https://github.com/moparisthebest/curl
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61 lines
3.0 KiB
Plaintext
61 lines
3.0 KiB
Plaintext
Peer SSL Certificate Verification
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=================================
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Since version 7.10, libcurl performs peer SSL certificate verification by
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default. This is done by installing a default CA cert bundle on 'make install'
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(or similar), that CA bundle package is used by default on operations against
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SSL servers.
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Alas, if you communicate with HTTPS servers using certificates that are signed
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by CAs present in the bundle, you will not notice any changed behavior and you
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will seamlessly get a higher security level on your SSL connections since you
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can be sure that the remote server really is the one it claims to be.
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If the remote server uses a self-signed certificate, if you don't install
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curl's CA cert bundle, if the server uses a certificate signed by a CA that
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isn't included in the bundle or if the remote host is an impostor
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impersonating your favorite site, and you want to transfer files from this
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server, do one of the following:
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1. Tell libcurl to *not* verify the peer. With libcurl you disable with with
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curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, FALSE);
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With the curl command line tool, you disable this with -k/--insecure.
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2. Get a CA certificate that can verify the remote server and use the proper
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option to point out this CA cert for verification when connecting. For
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libcurl hackers: curl_easy_setopt(curl, CURLOPT_CAPATH, capath);
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With the curl command line tool: --cacert [file]
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3. Add the CA cert for your server to the existing default CA cert bundle.
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The default path of the CA bundle installed with the curl package is:
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/usr/local/share/curl/curl-ca-bundle.crt, which can be changed by running
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configure with the --with-ca-bundle option pointing out the path of your
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choice.
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If you're using the curl command line tool, you can specify your own CA
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cert path by setting the environment variable CURL_CA_BUNDLE to the path
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of your choice.
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If you're using the curl command line tool on Windows, curl will search
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for a CA cert file named "curl-ca-bundle.crt" in these directories and in
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this order:
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1. application's directory
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2. current working directory
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3. Windows System directory (e.g. C:\windows\system32)
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4. Windows Directory (e.g. C:\windows)
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5. all directories along %PATH%
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Neglecting to use one of the above methods when dealing with a server using a
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certificate that isn't signed by one of the certificates in the installed CA
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cert bundle, will cause SSL to report an error ("certificate verify failed")
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during the handshake and SSL will then refuse further communication with that
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server.
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This procedure has been deemed The Right Thing even though it adds this extra
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trouble for some users, since it adds security to a majority of the SSL
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connections that previously weren't really secure. It turned out many people
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were using previous versions of curl/libcurl without realizing the need for
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the CA cert options to get truly secure SSL connections.
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