CURLOPT_PINNEDPUBLICKEY(3)				     curl_easy_setopt options					CURLOPT_PINNEDPUBLICKEY(3)

NAME

       CURLOPT_PINNEDPUBLICKEY - set pinned public key

SYNOPSIS

       #include <curl/curl.h>

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

DESCRIPTION

       Pass  a	pointer  to  a	zero  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  cer-
       tificate  and if it does not exactly match the public key provided to this option, curl will abort the connection before sending or receiv-
       ing 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 don't 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 don't 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 and GSKit

	 7.43.0: NSS and wolfSSL/CyaSSL

	 7.47.0: mbedtls

	 7.49.0: PolarSSL

       sha256 support:

	 7.44.0: OpenSSL, GnuTLS, NSS and wolfSSL/CyaSSL

	 7.47.0: mbedtls

	 7.49.0: PolarSSL

       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),

libcurl 7.54.0							 December 21, 2016					CURLOPT_PINNEDPUBLICKEY(3)