SSL vs TLS: what the difference actually is

SSL is the original name of the protocol that secures connections; TLS is the name it has carried since its revision as an open standard. In the SSL and TLS glossary they share one entry, because in everyday use they mean the same thing, and only TLS is actually in use.

The short answer

TLS replaced SSL. Every version called SSL is deprecated and refused by current browsers, so any HTTPS connection you make today runs TLS. The words are still used interchangeably, which is why certificates are sold as SSL certificates and settings are labelled SSL/TLS.

How SSL became TLS

SSL 2.0 and SSL 3.0 came first; SSL 3.0 is documented as historical in RFC 6101. The standard then moved to the IETF and was renamed TLS: TLS 1.0, 1.1 and 1.2 were revisions of the same line, and TLS 1.3 (RFC 8446) redesigned the handshake.

The old versions were retired as weaknesses were found. SSL 2.0 was prohibited, SSL 3.0 was deprecated in RFC 7568, and TLS 1.0 and 1.1 were deprecated in RFC 8996. What remains in use is TLS 1.2 and TLS 1.3.

SSL and TLS versions by year

What each current version changed is on TLS versions.

Why everyone still says "SSL certificate"

The name outlived the protocol. Certificates are sold as SSL certificates, libraries keep the word in their names, and configuration directives keep it for compatibility. None of that means the technology is outdated.

A certificate also has no protocol version. It binds a name to a key, and the same certificate works with whichever TLS version the two sides agree on. Asking for an "SSL certificate" and a "TLS certificate" gets you the same thing; see what a certificate contains. An app that pins a certificate checks the certificate's key, or the certificate itself, against a copy it carries.

What changed between TLS 1.2 and TLS 1.3

TLS 1.3 removed the options that caused most of the trouble in earlier versions, shortened the handshake to one round trip and encrypts more of it. What changed, whether TLS 1.2 is still safe and how to set the versions a server accepts are covered on TLS versions.

Where "SSL" still appears, and what it means there

The word stays in names that are too widely used to change. OpenSSL, LibreSSL and BoringSSL are TLS libraries. Server configuration keeps it in directive names: nginx writes the accepted versions as ssl_protocols TLSv1.2 TLSv1.3;, Apache as SSLProtocol -all +TLSv1.2 +TLSv1.3. In both, the directive name says SSL and the values say which TLS versions are allowed, and only the values matter.

Tools reporting an "SSL error" are reporting a TLS failure. The exact code tells you which check failed; see SSL errors.

What SSL/TLS means in mail settings

Mail clients often offer a choice labelled SSL/TLS or STARTTLS. Neither is about the protocol version. SSL/TLS means the connection is encrypted from the first byte on a dedicated port, such as 465 for submission or 993 for IMAP; STARTTLS means the client connects in plain text on the usual port and then upgrades. RFC 8314 recommends the first for mail submission and access.

Which versions a server should accept

TLS 1.2 and TLS 1.3, and nothing older. Turning on an old version because its label looks familiar is how a weak protocol stays reachable, so read version settings as the exact identifiers they are.

Check what a host actually agrees to rather than what its configuration file appears to say:

$ openssl s_client -connect example.com:443 -tls1_3
$ openssl s_client -connect example.com:443 -tls1_1

The first should complete; the second should be refused. How the protocol works step by step is on TLS.

FAQ

Related terms

The protocol is covered under TLS and forward secrecy; certificates under certificates, and the public record of their issuance under certificate transparency logs. The rest of the vocabulary is in this glossary.