---
name: "libressl-SSL_do_handshake"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-SSL_do_handshake"
---

# libressl-SSL\_do\_handshake(3)

perform a TLS/SSL handshake

## NAME

**SSL\_do\_handshake** – perform a TLS/SSL handshake

## SYNOPSIS

SSL Library (libssl, -lssl) libcrypto

**#include \<openssl/ssl.h\>**

*int*\

**SSL\_do\_handshake**(*SSL \*ssl*);

## DESCRIPTION

**SSL\_do\_handshake**() will wait for an SSL/TLS handshake to take place. If the connection is in client mode, the handshake will be started. The handshake routines may have to be explicitly set in advance using either SSL\_set\_connect\_state(3) or SSL\_set\_accept\_state(3).

The behaviour of **SSL\_do\_handshake**() depends on the underlying *BIO*.

If the underlying *BIO* is *blocking*, **SSL\_do\_handshake**() will only return once the handshake has been finished or an error occurred.

If the underlying *BIO* is *non-blocking*, **SSL\_do\_handshake**() will also return when the underlying *BIO* could not satisfy the needs of **SSL\_do\_handshake**() to continue the handshake. In this case a call to SSL\_get\_error(3) with the return value of **SSL\_do\_handshake**() will yield SSL\_ERROR\_WANT\_READ or SSL\_ERROR\_WANT\_WRITE. The calling process then must repeat the call after taking appropriate action to satisfy the needs of **SSL\_do\_handshake**(). The action depends on the underlying *BIO*. When using a non-blocking socket, nothing is to be done, but [select(2)](/select/2.md) can be used to check for the required condition. When using a buffering *BIO*, like a *BIO* pair, data must be written into or retrieved out of the *BIO* before being able to continue.

## RETURN VALUES

The following return values can occur:

- 0

  The TLS/SSL handshake was not successful but was shut down controlled and by the specifications of the TLS/SSL protocol. Call SSL\_get\_error(3) with the return value *ret* to find out the reason.

- 1

  The TLS/SSL handshake was successfully completed, and a TLS/SSL connection has been established.

- \<0

  The TLS/SSL handshake was not successful because either a fatal error occurred at the protocol level or a connection failure occurred. The shutdown was not clean. It can also occur if action is needed to continue the operation for non-blocking *BIO*s. Call SSL\_get\_error(3) with the return value *ret* to find out the reason.

## SEE ALSO

BIO\_new(3), [ssl(3)](/ssl/3.md), SSL\_accept(3), SSL\_connect(3), SSL\_get\_error(3), SSL\_set\_connect\_state(3)

## HISTORY

**SSL\_do\_handshake**() first appeared in SSLeay 0.8.0 and has been available since OpenBSD 2.4.