{"id":52210,"date":"2019-11-03T00:00:00","date_gmt":"2019-11-02T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/v-openssh-dobavlena-podderzhka-universalnoj-dvuhfaktornoj-autentifikatsii"},"modified":"2020-02-18T13:59:53","modified_gmt":"2020-02-18T10:59:53","slug":"v-openssh-dobavlena-podderzhka-universalnoj-dvuhfaktornoj-autentifikatsii","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/v-openssh-dobavlena-podderzhka-universalnoj-dvuhfaktornoj-autentifikatsii","title":{"rendered":"OpenSSH has added support for universal two-factor authentication.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

In the OpenSSH codebase has added<\/a><\/noindex> experimental support for two-factor authentication using devices that support the protocol U2F<\/a><\/noindex>, developed by the FIDO<\/a><\/noindex>alliance. U2F enables the creation of inexpensive hardware tokens to confirm the physical presence of a user, interacting via USB, Bluetooth, or NFC. Such devices are promoted as a means for two-factor authentication on websites, are already supported by major browsers, and are produced by various manufacturers, including Yubico, Feitian, Thetis, and Kensington.<\/p>\n

To interact with devices that confirm user presence, OpenSSH has added a new key type \u2018sk-ecdsa-sha2-nistp256@openssh.com\u2019 (\u2018ecdsa-sk\u2019), which uses the ECDSA (Elliptic Curve Digital Signature Algorithm) with the NIST P-256 curve and SHA-256 hash. The procedures for interacting with tokens are implemented in an intermediary library that is loaded similarly to the library for supporting PKCS#11 and acts as a wrapper over the library. libfido2<\/a><\/noindex>, providing means for communication with tokens over USB (supports FIDO U2F\/CTAP 1 and FIDO 2.0\/CTAP 2 protocols). The intermediary library libsk-libfido2, prepared by OpenSSH developers, is included in the main libfido2 composition, as well as enabled<\/a><\/noindex> the HID driver for OpenBSD.<\/a><\/noindex> To authenticate and generate a key, it is necessary to specify the 'SecurityKeyProvider' parameter in the settings or set the environment variable SSH_SK_PROVIDER, indicating the path to the external library libsk-libfido2.so (export SSH_SK_PROVIDER=\/path\/to\/libsk-libfido2.so). There is an option to build OpenSSH with built-in support for the wrapper library (--with-security-key-builtin), in which case the 'SecurityKeyProvider=internal' parameter must be set.<\/p>\n

To enable U2F, you can use the latest codebase snapshot from repository<\/a><\/noindex> OpenSSH and the HEAD branch of the library libfido2<\/a><\/noindex>, which already includes the necessary layer for OpenSSH.
\nLibfido2 supports operation in OpenBSD, Linux, macOS, and Windows. <\/p>\n

To authenticate and generate a key, the SSH_SK_PROVIDER environment variable must be set, pointing to libsk-libfido2.so (export SSH_SK_PROVIDER=\/path\/to\/libsk-libfido2.so), or the library can be defined through the SecurityKeyProvider configuration. After that, run \u2018ssh-keygen -t ecdsa-sk\u2019 or, if the keys are already created and configured, connect to the server using \u2018ssh\u2019. When running ssh-keygen, the created key pair will be saved in \u2018~\/.ssh\/id_ecdsa_sk\u2019 and can be used similarly to other keys. <\/p>\n

The public key (id_ecdsa_sk.pub) should be copied to the server in the authorized_keys file. On the server side, only the digital signature is verified, while the interaction with tokens takes place on the client side (libsk-libfido2 does not need to be installed on the server, but the server must support the \u2018ecdsa-sk\u2019 key type). The generated private key (id_ecdsa_sk) is essentially a descriptor of the key, forming the actual key only in conjunction with a secret sequence stored on the U2F token side.<\/p>\n

If the id_ecdsa_sk key falls into the hands of an attacker, they will also need access to the hardware token for authentication, without which the private key stored in the id_ecdsa_sk file is useless. Additionally, by default, any operations with keys (both during generation and authentication) require local confirmation of the user's physical presence, for example, touching the sensor on the token, which complicates remote attacks on systems with the token connected. As an additional layer of protection during the ssh-keygen startup, a password can also be set for access to the key file. <\/p>\n

The U2F key can be added to the ssh-agent via \u2018ssh-add ~\/.ssh\/id_ecdsa_sk\u2019, but the ssh-agent must be built with support for \u2018ecdsa-sk\u2019 keys, and there must be a libsk-libfido2 layer present. The agent should be running on the system to which the token connects.
\nThe new \u2018ecdsa-sk\u2019 key type has been added because the OpenSSH ecdsa keys format differs from the U2F format for ECDSA signatures due to the presence of additional fields.<\/p>\n

<\/a><\/noindex><\/p>\n

Source: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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