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Secure Shell 125 Version 1.99 In January 2006, well after version 2.1 was established, RFC 4253 specified that an SSH server which supports both 2.0 and prior versions of SSH should identify its protoversion as 1.99. [12] This is not an actual version but a method to identify backward compatibility. OpenSSH and OSSH In 1999, developers wanting a free software version to be available went back to the older 1.2.12 release of the original SSH program, which was the last released under an open source license. Björn Grönvall's OSSH was subsequently developed from this codebase. Shortly thereafter, OpenBSD developers forked Grönvall's code and did extensive work on it, creating OpenSSH, which shipped with the 2.6 release of OpenBSD. From this version, a "portability" branch was formed to port OpenSSH to other operating systems. As of 2005, OpenSSH was the single most popular SSH implementation, coming by default in a large number of operating systems. OSSH meanwhile has become obsolete. [13] OpenSSH continued to be maintained and now supports both 1.x and 2.0 versions. Version 2.x "Secsh" was the official Internet Engineering Task Force's (IETF) name for the IETF working group responsible for version 2 of the SSH protocol. [14] In 2006, a revised version of the protocol, SSH-2, was adopted as a standard. This version is incompatible with SSH-1. SSH-2 features both security and feature improvements over SSH-1. Better security, for example, comes through Diffie-Hellman key exchange and strong integrity checking via message authentication codes. New features of SSH-2 include the ability to run any number of shell sessions over a single SSH connection. [15] Due to SSH-2's superiority and popularity over SSH-1, some implements such as Lsh [16] and Dropbear [17] , only support SSH-2 protocol. Vulnerabilities In November 2008, a vulnerability was discovered for all versions of SSH which allowed recovery of up to 32 bits of plaintext from a block of ciphertext that was encrypted using what was then the standard default encryption mode, CBC. [18] Internet standard documentation The following RFC publications by the IETF "secsh" working group document SSH-2 as a proposed Internet standard. • RFC 4250, The Secure Shell (SSH) Protocol Assigned Numbers • RFC 4251, The Secure Shell (SSH) Protocol Architecture • RFC 4252, The Secure Shell (SSH) Authentication Protocol • RFC 4253, The Secure Shell (SSH) Transport Layer Protocol • RFC 4254, The Secure Shell (SSH) Connection Protocol • RFC 4255, Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints • RFC 4256, Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) • RFC 4335, The Secure Shell (SSH) Session Channel Break Extension • RFC 4344, The Secure Shell (SSH) Transport Layer Encryption Modes • RFC 4345, Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol It was later modified and expanded by the following publications. • RFC 4419, Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol (March 2006) • RFC 4432, RSA Key Exchange for the Secure Shell (SSH) Transport Layer Protocol (March 2006)
Secure Shell 126 • RFC 4462, Generic Security Service Application Program Interface (GSS-API) Authentication and Key Exchange for the Secure Shell (SSH) Protocol (May 2006) • RFC 4716, The Secure Shell (SSH) Public Key File Format (November 2006) • RFC 5656, Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer (December 2009) Uses SSH is a protocol that can be used for many applications across many platforms including Unix, Microsoft Windows, Apple's Mac OS X, and Linux. Some of the applications below may require features that are only available or compatible with specific SSH clients or servers. For example, using the SSH protocol to implement a VPN is possible, but presently only with the OpenSSH server and client implementation. • For login to a shell on a remote host (replacing Telnet and rlogin) • For executing a single command on a remote host (replacing rsh) • Secure file transfer • In combination with rsync to back up, copy and mirror files efficiently and securely • For forwarding or tunneling a port (not to be confused with a VPN, which routes packets between different networks, or bridges two broadcast domains into one). • For using as a full-fledged encrypted VPN. Note that only OpenSSH server and client supports this feature. • For forwarding X from a remote host (possible through multiple intermediate hosts) Example of tunneling an X11 application over SSH: the user 'josh' has SSHed from the local machine 'foofighter' to the remote machine 'tengwar' to run xeyes. Logging into OpenWrt via SSH using PuTTY running on Windows. • For browsing the web through an encrypted proxy connection with SSH clients that support the SOCKS protocol. • For securely mounting a directory on a remote server as a filesystem on a local computer using SSHFS. • For automated remote monitoring and management of servers through one or more of the mechanisms discussed above. • For development on a mobile or embedded device that supports SSH. File transfer protocols using SSH There are multiple mechanisms for transferring files using the Secure Shell protocols. • Secure copy (SCP), which evolved from RCP protocol over SSH • SSH File Transfer Protocol (SFTP), a secure alternative to FTP (not to be confused with FTP over SSH) • Files transferred over shell protocol (a.k.a. FISH), released in 1998, which evolved from Unix shell commands over SSH
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IPsec 62 IPsec Internet Protocol Se
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Page 145 and 146: SHA-1 142 • Xiaoyun Wang, Yiqun L
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