NAME

       CURLOPT_PINNEDPUBLICKEY - pinned public key

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PINNEDPUBLICKEY,
                                 char *pinnedpubkey);

DESCRIPTION

       Pass  a  pointer to a null-terminated string as parameter. The string can be the file name
       of your pinned public key. The file format expected is "PEM" or  "DER".   The  string  can
       also be any number of base64 encoded sha256 hashes preceded by "sha256//" and separated by
       ";"

       When negotiating a TLS or SSL connection, the server sends a  certificate  indicating  its
       identity. A public key is extracted from this certificate and if it does not exactly match
       the public key provided to this option, curl will abort the connection before  sending  or
       receiving any data.

       On mismatch, CURLE_SSL_PINNEDPUBKEYNOTMATCH is returned.

       The application does not have to keep the string around after setting this option.

DEFAULT

       NULL

PROTOCOLS

       All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

EXAMPLE

       CURL *curl = curl_easy_init();
       if(curl) {
         curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
         curl_easy_setopt(curl, CURLOPT_PINNEDPUBLICKEY, "/etc/publickey.der");
         /* OR
         curl_easy_setopt(curl, CURLOPT_PINNEDPUBLICKEY, "sha256//YhKJKSzoTt2b5FP18fvpHo7fJYqQCjAa3HWY3tvRMwE=;sha256//t62CeU2tQiqkexU74Gxa2eg7fRbEgoChTociMee9wno=");
         */

         /* Perform the request */
         curl_easy_perform(curl);
       }

PUBLIC KEY EXTRACTION

       If  you  do  not  have  the  server's public key file you can extract it from the server's
       certificate.
       # retrieve the server's certificate if you do not already have it
       #
       # be sure to examine the certificate to see if it is what you expected
       #
       # Windows-specific:
       # - Use NUL instead of /dev/null.
       # - OpenSSL may wait for input instead of disconnecting. Hit enter.
       # - If you do not have sed, then just copy the certificate into a file:
       #   Lines from -----BEGIN CERTIFICATE----- to -----END CERTIFICATE-----.
       #
       openssl s_client -servername www.example.com -connect www.example.com:443 < /dev/null | sed -n "/-----BEGIN/,/-----END/p" > www.example.com.pem

       # extract public key in pem format from certificate
       openssl x509 -in www.example.com.pem -pubkey -noout > www.example.com.pubkey.pem

       # convert public key from pem to der
       openssl asn1parse -noout -inform pem -in www.example.com.pubkey.pem -out www.example.com.pubkey.der

       # sha256 hash and base64 encode der to string for use
       openssl dgst -sha256 -binary www.example.com.pubkey.der | openssl base64
       The public key in PEM format contains a header, base64 data and a footer:
       -----BEGIN PUBLIC KEY-----
       [BASE 64 DATA]

       -----END PUBLIC KEY-----

AVAILABILITY

       PEM/DER support:

         7.39.0: OpenSSL, GnuTLS

         7.39.0-7.48.0,7.58.1+: GSKit

         7.43.0: NSS and wolfSSL

         7.47.0: mbedtls

         7.54.1: SecureTransport on macOS 10.7+/iOS 10+

         7.58.1: SChannel

       sha256 support:

         7.44.0: OpenSSL, GnuTLS, NSS and wolfSSL

         7.47.0: mbedtls

         7.54.1: SecureTransport on macOS 10.7+/iOS 10+

         7.58.1: SChannel Windows XP SP3+

       Other SSL backends not supported.

RETURN VALUE

       Returns CURLE_OK if TLS enabled, CURLE_UNKNOWN_OPTION if not,  or  CURLE_OUT_OF_MEMORY  if
       there was insufficient heap space.

SEE ALSO

       CURLOPT_SSL_VERIFYPEER(3),          CURLOPT_SSL_VERIFYHOST(3),          CURLOPT_CAINFO(3),
       CURLOPT_CAPATH(3),