SSL_GET_VERSION(3)

NAME
SSL_client_version, SSL_get_version, SSL_is_dtls, SSL_is_tls, SSL_is_quic, SSL_CTX_is_quic, SSL_CTX_is_server, SSL_version - get the protocol information of a connection

SYNOPSIS
 #include <openssl/ssl.h>

 int SSL_client_version(const SSL *s);

 const char *SSL_get_version(const SSL *ssl);

 int SSL_is_dtls(const SSL *ssl);
 int SSL_is_tls(const SSL *ssl);
 int SSL_is_quic(const SSL *ssl);
 int SSL_CTX_is_quic(const SSL_CTX *ctx);
 int SSL_CTX_is_server(const SSL_CTX *ctx);

 int SSL_version(const SSL *s);

DESCRIPTION
For SSL, TLS and DTLS protocols SSL_client_version() returns the numeric protocol version advertised by the client in the legacy_version field of the ClientHello when initiating the connection. Note that, for TLS, this value will never indicate a version greater than TLSv1.2 even if TLSv1.3 is subsequently negotiated. For QUIC connections it returns OSSL_QUIC1_VERSION.

SSL_get_version() returns the name of the protocol used for the connection. SSL_version() returns the numeric protocol version used for the connection. They should only be called after the initial handshake has been completed. Prior to that the results returned from these functions may be unreliable.

SSL_is_dtls() returns 1 if the connection is using DTLS or 0 if not.

SSL_is_tls() returns 1 if the connection is using SSL/TLS or 0 if not.

SSL_is_quic() returns 1 if the connection is using QUIC or 0 if not.

SSL_CTX_is_quic() returns 1 if the ctx creates QUIC SSL objects or 0 if not.

SSL_CTX_is_server() returns 1 if the ctx uses a method that allows it to be a server (i.e. server-only or generic method) or 0 if not.

RETURN VALUES
SSL_get_version() returns one of the following strings:

SSLv3
    The connection uses the SSLv3 protocol.

TLSv1
    The connection uses the TLSv1.0 protocol.

TLSv1.1
    The connection uses the TLSv1.1 protocol.

TLSv1.2
    The connection uses the TLSv1.2 protocol.

TLSv1.3
    The connection uses the TLSv1.3 protocol.

DTLSv0.9
    The connection uses an obsolete pre-standardisation DTLS protocol

DTLSv1
    The connection uses the DTLSv1 protocol

DTLSv1.2
    The connection uses the DTLSv1.2 protocol

QUICv1
    The connection uses the QUICv1 protocol.

unknown
    This indicates an unknown protocol version.

SSL_version() and SSL_client_version() return an integer which could include any of the following:

SSL3_VERSION
    The connection uses the SSLv3 protocol.

TLS1_VERSION
    The connection uses the TLSv1.0 protocol.

TLS1_1_VERSION
    The connection uses the TLSv1.1 protocol.

TLS1_2_VERSION
    The connection uses the TLSv1.2 protocol.

TLS1_3_VERSION
    The connection uses the TLSv1.3 protocol (never returned for SSL_client_version()).

DTLS1_BAD_VER
    The connection uses an obsolete pre-standardisation DTLS protocol

DTLS1_VERSION
    The connection uses the DTLSv1 protocol

DTLS1_2_VERSION
    The connection uses the DTLSv1.2 protocol

OSSL_QUIC1_VERSION
    The connection uses the QUICv1 protocol.

SEE ALSO
ssl(7)

HISTORY
The SSL_is_dtls() function was added in OpenSSL 1.1.0. The SSL_is_tls() and SSL_is_quic() functions were added in OpenSSL 3.2.

The SSL_CTX_is_quic() and SSL_CTX_is_server() functions were added in OpenSSL 4.0

COPYRIGHT
Copyright 2001-2026 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>.