What Is SSH (Secure Shell)?

  • SSH (Secure Shell) is a software package that enables secure system administration and file transfers over insecure networks, such as the Internet.
  • It is the protocol and standard for secure remote login, encrypted file transfers, and secure machine-to-machine automation.
  • SSH Communications Security is the company that invented the protocol and implemented the first open source version.
  • SSH keys are an an authentication credential for automation and single sign-on. They are extremely widely used in enterprises - in many organizations there are 10 times more keys than there are user names and passwords.
  • Key management is needed to audit, control, and monitor key-based access and to establish controlled provisioning and termination processes for keys. This is also required to comply with laws and regulations.
  • See also description of Secure Shell at Wikipedia.
  • ssh® is also a registered trademark of the inventors of the protocol.

Client/Server Software

Keys Used for Granting Access

Secure Shell uses keys for identifying hosts (these are called host keys) and for identifying users (these are called user keys).

The host keys are usually created automatically when the software is installed. However, managing and periodically changing host keys would be desirable.

User keys are used for public key authentication. A challenge with them is that OpenSSH allows self-provisioning key-based access in its legacy configuration and many organizations have massive numbers of unmanaged, unaudited keys on their systems granting privileged access to production servers. Proper key management solutions are needed to address this.

Management of the keys should be part of any identity and access management program. The security risks they pose are grave, and addressing them should be a top-5 cybersecurity priority for large enterprises.

History of the Protocol

Tatu Ylonen SSH program (Secure Shell) inventor

The protocol was developed by Tatu Ylonen in Spring 1995. It all started from a hacking incident in the Finnish university network. A password sniffer had been installed on a server connected directly to the backbone, and when it was discovered, it had thousands of usernames and passwords in its database, including several from Ylonen's company.

That incident triggered Ylonen to study cryptography and develop a solution he could use for remote login over the Internet safely. His friends proposed additional features, and three months later, in July 1995, Ylonen published the first version. Later he also designed the SSH File Transfer Protocol (SFTP).

Ylonen still works on topics related to Secure Shell (as well as broader cybersecurity topics); please follow his updates on Twitter as @tatuylonen.

The initial software was published as free open source software. That version eventually evolved into OpenSSH. It basically replaced the legacy remote login and file transfer tools telnet, rlogin, and ftp.

The rapid adoption of the protocol led to the standardization of the technology in the IETF - Internet Engineering Task Force.

Today, the protocol is used for managing more than half of world’s web servers. It is used extensively in practically every Unix or Linux computer, on-premise and in the cloud. Information security specialists and system administrators use it to configure, manage, maintain, and operate most firewalls, routers, switches, and servers in the millions of mission-critical networks and environments of our digital world. It is also embedded inside many file transfer and systems management solutions.

History and SSH Communications Security

At the end of 1995, Ylonen founded the company to provide commercial support for Secure Shell. From 1995 the company has been on the vanguard of the information security market, and released a number of leading products and solutions for information security.

The company has made countless contributions to the greater good with the security standardization efforts in the IETF. The IETF standards for PKI, Secure Shell, IPsec, and NAT Traversal (STUN, SIP, etc) are heavily influenced by the efforts of the company.

The company serves the most demanding customers in the public and private sectors. It has over 3000 customers ranging from finance & insurance to retail, industry, and healthcare, as well as to governmental organizations and militaries.

Today, the company is the clear market leader in management of access-granting keys and monitoring, control, and policy enforcement for Secure Shell.

The technologies and inventions of the company are deeply embedded and represented in today’s digital world. Telecommunications infrastructure, smartphones, tablets, and other portable computing devices use the NAT Traversal technology patented by the company. Certificate Management Protocol (CMP), co-authored by Tomi Kause and Tero Mononen, is widely used for managing digital certificates and trust in telecommunications networks (e.g., by Cisco).

Origin of the Protocol and Current Issues Around It, by Tatu Ylonen

Embedded content: https://www.youtube.com/watch?v=MbnMRi7664s