SQRL or Secure, Quick, Reliable Login (pronounced "squirrel" /ˈskwɝl/ en (help·info)) (formerly Secure QR Login) is a draft open standard for secure website login and authentication. The software solution typically uses a QR code, which provides authentication, where a user identifies anonymously rather than providing a user ID and password. This method is thought to be impervious to a brute force password attack or data breach. It shifts the burden of security away from the party requesting the authentication and closer to the operating system Implementation of what is possible on the hardware, as well as to the user. SQRL was proposed by Steve Gibson of Gibson Research Corporation in October 2013 as a way to simplify the process of Authentication protocol , without revealing any information about the transaction to a third party.
The protocol is an answer to a problem of identity fragmentation. It improves on protocols such as OAuth and OpenID by not requiring a third party to broker the transaction. Additionally, it provides a standard that can be freely used to simplify the login processes available to password manager applications such as LastPass.
Example use case
For the protocol to be used on a website, two components are necessary: an implementation, that is part of the Web service to which the implementation authenticates, which displays a QR code or specially crafted URL according to the specifications of the protocol, and a browser plugin or a mobile application, which can read this code in order to provide secure authentication.
The SQRL client uses "one-way" functions (so called, because they are difficult or impossible to reverse, leaving brute-force attack as the only method of solution) and the user's single master password to decrypt a secret master key, then, in combination with the site name (comprising the domain name and optionally an additional sub-site identifier: "example.com", "example.edu/chessclub"), generates a (sub-)site-specific public/private key pair. It signs the transaction tokens with the private key and gives the public key to the site, so it can verify the encrypted data.
There are no "shared secrets" which a compromise of the site could expose to allow attacks on accounts at other sites. The only thing a successful attacker could get, the public key, would be limited to verifying signatures that are only used at the same site. Even though the user unlocks the master key with a single password, it never leaves the SQRL client; the individual sites do not receive any information from the SQRL process that could be used at any other site.
The acronym SQRL was coined by Steve Gibson and the protocol drafted, discussed and analyzed in-depth, by himself and a community of Internet security enthusiasts on the news.grc.com newsgroups and during his weekly podcast, Security Now!, on October 2, 2013. Within two days of the airing of this podcast, both the W3C and Google expressed interest in working on the standard.
Steve Gibson states that SQRL is "open and free as it should be", and that the solution is "unencumbered by patents". While SQRL brought a lot of attention to QR code based authentication mechanisms, the suggested protocol is said to have been patented earlier and is not generally available for royalty free use. But Gibson says "What those guys are doing as described in that patent  is completely different from the way SQRL operates, so there would be no conflict between SQRL and their patent. Superficially, anything that uses a 2D code for authentication seems "similar"... and superficially all such solutions are. But the details matter, and the way SQRL operates is entirely different in the details."
- "Details about phishing defenses and limitations". grc.com. 2013-12-06. Retrieved 2013-12-06.
- "Security Now! #425 SQRL Q&A #176 (Transcript)". 2013-10-09. Retrieved 2013-10-16.
- "SQRL / Gibson Research". grc.com. Retrieved 2014-05-12.
- "SQRL is not really new". Mike Beiter. October 4, 2013. Retrieved 2014-05-12.
- Method and system for authenticating a user by means of a mobile device US 20100070759 A1