Updated: 2025/Nov/16

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SSL_get_handshake_rtt(3)            OpenSSL           SSL_get_handshake_rtt(3)


NAME
       SSL_get_handshake_rtt - get round trip time for SSL Handshake

SYNOPSIS
        #include <openssl/ssl.h>

        int SSL_get_handshake_rtt(const SSL *s, uint64_t *rtt);

DESCRIPTION
       SSL_get_handshake_rtt() retrieves the round-trip time (RTT) for ssl.

       This metric is represented in microseconds (us) as a uint64_t data
       type.

NOTES
       This metric is created by taking two timestamps during the handshake
       and providing the difference between these two times.

       When acting as the server, one timestamp is taken when the server is
       finished writing to the client. This is during the ServerFinished in
       TLS 1.3 and ServerHelloDone in TLS 1.2. The other timestamp is taken
       when the server is done reading the client's response. This is after
       the client has responded with ClientFinished.

       When acting as the client, one timestamp is taken when the client is
       finished writing the ClientHello and early data (if any). The other is
       taken when client is done reading the server's response. This is after
       ServerFinished in TLS 1.3 and after ServerHelloDone in TLS 1.2.

       In addition to network propagation delay and network stack overhead,
       this metric includes processing time on both endpoints, as this is
       based on TLS protocol-level messages and the TLS protocol is not
       designed to measure network timings. In some cases the processing time
       can be significant, especially when the processing includes asymmetric
       cryptographic operations.

RETURN VALUES
       Returns 1 if the TLS handshake RTT is successfully retrieved.  Returns
       0 if the TLS handshake RTT cannot be determined yet.  Returns -1 if,
       while retrieving the TLS handshake RTT, an error occurs.

HISTORY
       This function was added in OpenSSL 3.2.

COPYRIGHT
       Copyright 2023-2024 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

3.5.1                             2025-07-01          SSL_get_handshake_rtt(3)