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 filename 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 aborts the connection before sending or receiving any data.

       This option is independent of option CURLOPT_SSL_VERIFYPEER(3). If you turn off that option then the peer
       is still verified by public key.

       On mismatch, CURLE_SSL_PINNEDPUBKEYNOTMATCH is returned.

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

DEFAULT

       NULL

PROTOCOLS

       This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

       This option works only with the following TLS backends:  GnuTLS,  OpenSSL,  Schannel,  Secure  Transport,
       mbedTLS and wolfSSL

EXAMPLE

       int main(void)
       {
         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//YhKJKSzoTt2b5FP18fvpHo7fJYqQCjAa3HWY3"
                            "tvRMwE=;sha256//t62CeU2tQiqkexU74Gxa2eg7fRbEg"
                            "oChTociMee9wno=");
           */

           /* 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-----

HISTORY

       PEM/DER support
              7.39.0: OpenSSL, GnuTLS

              7.43.0: wolfSSL

              7.47.0: mbedTLS

              7.54.1: Secure Transport on macOS 10.7+/iOS 10+

              7.58.1: Schannel

       sha256 support
              7.44.0: OpenSSL, GnuTLS and wolfSSL

              7.47.0: mbedTLS

              7.54.1: Secure Transport on macOS 10.7+/iOS 10+

              7.58.1: Schannel

              Other SSL backends not supported.

AVAILABILITY

       Added in curl 7.39.0

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_CAINFO(3), CURLOPT_CAPATH(3), CURLOPT_SSL_VERIFYHOST(3), CURLOPT_SSL_VERIFYPEER(3)