The release of OpenSSH 9.5 has been published, providing an open implementation of the client and server for working with SSH 2.0 and SFTP protocols. <\/p>\n
Key Changes: <\/p>\n
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In ssh-keygen, key generation based on the Ed25519 digital signature, developed by Daniel Bernstein and standardized in RFC 8709, is enabled by default. Ed25519 keys have been supported since the release of OpenSSH 6.5 (2014) and are more convenient due to their small size. Moreover, Ed25519 digital signatures offer a higher level of security than ECDSA and DSA, demonstrating very high signature verification and creation speeds. The resistance to brute force attacks for Ed25519 is approximately 2^128 (on average, an attack on Ed25519 would require 2^140 bit operations), comparable to the strength of algorithms like NIST P-256 and RSA with a key size of 375 bytes or the 128-bit block cipher. Additionally, Ed25519 is immune to collision problems in hashes, is not sensitive to cache-timing attacks, and side-channel attacks.\n
The ssh utility has added protection against attacks from side channels that analyze the delays between keystrokes on a keyboard to recreate input. Such attacks are based on the fact that the delays between key presses during typing depend on the layout of keys on the keyboard (for example, the reaction time for typing the letter 'F' is faster than for typing 'Q' or 'X', as it requires less finger movement). SSH was vulnerable to these attacks because it sent information about the entered character in a separate packet immediately after each key press; thus, the delays between packet transmissions correlated with the delays between key presses.\n
To obscure the characteristics of interactive input in ssh traffic, data is sent not as it is typed but only at fixed intervals (default is 20 ms). Additionally, to confuse attackers, fake keystrokes are sent at random moments after sending real data. To configure this protection, the 'ObscureKeystrokeTiming' parameter has been added to ssh_config. <\/p>\n
Support for the SSH protocol extension 'ping@openssh.com' has been implemented in ssh and sshd, which adds a new type of messages SSH2_MSG_PING and SSH2_MSG_PONG for periodically sending packets at equal time intervals. This extension is necessary for the aforementioned protection against side channel attacks.\n
In sshd, it is allowed to override the Sybsystem directives through Match blocks.\n
In sshd, the handling of quotes in the Subsystem directive has been changed, which are now preserved for commands and arguments, potentially leading to compatibility issues with very rare configurations. <\/ul>\n