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.\" ========================================================================
.\"
.IX Title "SSL_CTX_use_psk_identity_hint 3"
.TH SSL_CTX_use_psk_identity_hint 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
SSL_CTX_use_psk_identity_hint, SSL_use_psk_identity_hint,
SSL_CTX_set_psk_server_callback, SSL_set_psk_server_callback \- set PSK
identity hint to use
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
\&
\& int SSL_CTX_use_psk_identity_hint(SSL_CTX *ctx, const char *hint);
\& int SSL_use_psk_identity_hint(SSL *ssl, const char *hint);
\&
\& void SSL_CTX_set_psk_server_callback(SSL_CTX *ctx,
\&        unsigned int (*callback)(SSL *ssl, const char *identity,
\&        unsigned char *psk, int max_psk_len));
\& void SSL_set_psk_server_callback(SSL *ssl,
\&        unsigned int (*callback)(SSL *ssl, const char *identity,
\&        unsigned char *psk, int max_psk_len));
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBSSL_CTX_use_psk_identity_hint()\fR sets the given \fB\s-1NULL\s0\fR\-terminated \s-1PSK\s0
identity hint \fBhint\fR to \s-1SSL\s0 context object
\&\fBctx\fR. \fBSSL_use_psk_identity_hint()\fR sets the given \fB\s-1NULL\s0\fR\-terminated
\&\s-1PSK\s0 identity hint \fBhint\fR to \s-1SSL\s0 connection object \fBssl\fR. If \fBhint\fR
is \fB\s-1NULL\s0\fR the current hint from \fBctx\fR or \fBssl\fR is deleted.
.PP
In the case where \s-1PSK\s0 identity hint is \fB\s-1NULL\s0\fR, the server
does not send the ServerKeyExchange message to the client.
.PP
A server application must provide a callback function which is called
when the server receives the ClientKeyExchange message from the
client. The purpose of the callback function is to validate the
received \s-1PSK\s0 identity and to fetch the pre-shared key used during the
connection setup phase. The callback is set using functions
\&\fBSSL_CTX_set_psk_server_callback()\fR or
\&\fBSSL_set_psk_server_callback()\fR. The callback function is given the
connection in parameter \fBssl\fR, \fB\s-1NULL\s0\fR\-terminated \s-1PSK\s0 identity sent
by the client in parameter \fBidentity\fR, and a buffer \fBpsk\fR of length
\&\fBmax_psk_len\fR bytes where the pre-shared key is to be stored.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBSSL_CTX_use_psk_identity_hint()\fR and \fBSSL_use_psk_identity_hint()\fR return
1 on success, 0 otherwise.
.PP
Return values from the server callback are interpreted as follows:
.IP "0" 4
\&\s-1PSK\s0 identity was not found. An \*(L"unknown_psk_identity\*(R" alert message
will be sent and the connection setup fails.
.IP ">0" 4
.IX Item ">0"
\&\s-1PSK\s0 identity was found and the server callback has provided the \s-1PSK\s0
successfully in parameter \fBpsk\fR. Return value is the length of
\&\fBpsk\fR in bytes. It is an error to return a value greater than
\&\fBmax_psk_len\fR.
.Sp
If the \s-1PSK\s0 identity was not found but the callback instructs the
protocol to continue anyway, the callback must provide some random
data to \fBpsk\fR and return the length of the random data, so the
connection will fail with decryption_error before it will be finished
completely.