What's the difference between SSL, TLS, and HTTPS?

TLS is the new name for SSL. Namely, SSL protocol got to version 3.0; TLS 1.0 is "SSL 3.1". TLS versions currently defined include TLS 1.1 and 1.2. Each new version adds a few features and modifies some internal details. We sometimes say "SSL/TLS".

HTTPS is HTTP-within-SSL/TLS. SSL (TLS) establishes a secured, bidirectional tunnel for arbitrary binary data between two hosts. HTTP is a protocol for sending requests and receiving answers, each request and answer consisting of detailed headers and (possibly) some content. HTTP is meant to run over a bidirectional tunnel for arbitrary binary data; when that tunnel is an SSL/TLS connection, then the whole is called "HTTPS".

To explain the acronyms:

• "SSL" means "Secure Sockets Layer". This was coined by the inventors of the first versions of the protocol, Netscape (the company was later bought by AOL).
• "TLS" means "Transport Layer Security". The name was changed to avoid any legal issues with Netscape so that the protocol could be "open and free" (and published as a RFC). It also hints at the idea that the protocol works over any bidirectional stream of bytes, not just Internet-based sockets.
• "HTTPS" is supposed to mean "HyperText Transfer Protocol Secure", which is grammatically unsound. Nobody, except the terminally bored pedant, ever uses the translation; "HTTPS" is better thought of as "HTTP with an S that means SSL". Other protocol acronyms have been built the same way, e.g. SMTPS, IMAPS, FTPS... all of them being a bare protocol that "got secured" by running it within some SSL/TLS.

SSL and TLS are protocols that aim to provide privacy and data integrity between two parties (see RFC 2246), designed to run over a reliable communication protocol (typically TCP). Although the TLS specification doesn't talk about sockets, the design of SSL/TLS was done so that applications could use them almost like traditional TCP sockets, for example SSLSocket in Java extends Socket (there are small differences in terms of usability, though).

HTTPS is HTTP over SSL/TLS, where the SSL/TLS connection is established first, and then normal HTTP data is exchanged over this SSL/TLS connection. Whether you use SSL or TLS for this depends on the configuration of your browser and of the server (there usually is an option to allow SSLv2, SSLv3 or TLS 1.x). The details of how HTTP and SSL/TLS form HTTPS are in RFC 2818.

Regarding the difference between SSL and TLS, you may be interested in these two answers I wrote for these similar questions on StackOverflow and ServerFault:

• Difference between SSL & TLS [Stackoverflow]
• What are the exact protocol level differences between SSL and TLS? [Serverfault]

You could consider TLSv1.0 as SSLv3.1 (in fact that's what happens within the records exchanged). It's just easier to compare the TLSv1.0 with TLSv1.1 and TLSv1.2 because they've all been edited within IETF and follow more or less the same structure. SSLv3 being edited by a different institution (Netscape), it makes it a bit more difficult so spot the differences.

Here are a few differences, but I doubt I can list them all:

• In the ClientHello message (first message sent by the client, to initiate the handshake), the version is {3,0} for SSLv3, {3,1} for TLSv1.0 and {3,2} for TLSv1.1.
• The ClientKeyExchange differs.
• The MAC/HMAC differs (TLS uses HMAC whereas SSL uses an earlier version of HMAC).
• The key derivation differs.
• The client can send application data can be sent straight after sending the SSL/TLS Finished message in SSLv3. In TLSv1, it must wait for the server's Finished message.
• The list of cipher suites differ (and some of them have been renamed from SSL_* to TLS_*, keeping the same id number).
• There are also differences regarding the new re-negotiation extension.

Generally, the higher the version or SSL/TLS, the more secure it is, provided you choose your cipher suites properly too (higher versions of TLS also offer using cipher suites that are considered better). (SSLv2 is considered insecure.) In addition, SSL doesn't fall under the IETF scope. For example, the TLS renegotiation fix had to be retrofitted for SSLv3 (although SSL/TLS stacks had to be updated anyway).

You may also be interested in this answer:

• What happens on the wire when a TLS / LDAP or TLS / HTTP connection is set up?[Stackoverflow]

Note that some people oppose SSL and TLS as being the difference between "SSL/TLS upon connection" and "upgrade to TLS" (after some conversation using the application protocol). Despite some of these answers being relatively highly upvoted, this is incorrect. This mistake is propagated by the fact that certain applications, like Microsoft Outlook, offer two configuration options called "SSL" and "TLS" for SMTP/IMAP configuration when they really mean "SSL/TLS upon connection" and "upgrade to TLS". (The same goes for the JavaMail library, I think.)

The RFCs that talk about STARTTLS were written when TLS was already an official RFC, that's why they only talk about upgrading the connection to TLS. In practice, if you tweak the configuration of your mail client to force it to use SSLv3 instead of TLS (not something I would generally recommend), it's still likely to be able to upgrade to SSL/TLS using STARTTLS with an SSLv3 connection, simply because it's more about the mode of operation than the version of SSL/TLS and/or the cipher suites.

There is also a variant of HTTP where the upgrade to SSL/TLS is done within the HTTP protocol (similar to STARTTLS in LDAP/SMTP). This is described in RFC 2817. As far as I know, this is almost never used (and it's not what's used by https:// in browsers). The main relevant part of this RFC is the section about CONNECT for HTTP proxy servers (this is used by HTTP proxy servers to relay HTTPS connections).

SSL VS TLS

The terms SSL and TLS are often used interchangeably or in conjunction with each other (TLS/SSL), but one is in fact the predecessor of the other — SSL 3.0 served as the basis for TLS 1.0 which, as a result, is sometimes referred to as SSL 3.1.

Which is more Secure SSL or TLS

In terms of security they both are consider equally secured

The main difference is that, while SSL connections begin with security and proceed directly to secured communications, TLS connections first begin with an insecure “hello” to the server and only switch to secured communications after the handshake between the client and the server is successful. If the TLS handshake fails for any reason, the connection is never created.

(SSL and TLS vs HTTP)

HTTP protocol is used to request and recive the data and https in which the 's' is nothing but secure SSL which makes the http protocol request and receive activity encrypted so no middle man attacker can obtain the data easily.

If neither SSL nor TLS is used with HTTP

then your connection with the web server is unencrypted all the data will be sent in plaintext any middle man attacker can obtain and view that data.

so should go with SSL or TLS

well, both are same but TLS is more extensible and hoping to get more support in future and TLS is backward compatible.