часть .. третья вроде
соединение между компьютерами, используя unix shell ssh с запросом пароля и не спрашивая пароль, проверяя ключи.
обычно нужно для доступа к сайту или серверу vps , там и описание есть и примеры настройки.
чтобы расшифровать статью с непонятных слов на чужом языке ее надо скормить яндекс переводчику. А если срочно – отнести в бюро переводов за 5000р распечатав на 30 листах бумаги.
еще более правильно – выучить язык на котором разговаривают программисты. Чаще это русский и китайский уже, не только индийский вариант инглиш.. так во многих профессиях.
- с шифрованием доигрались – цепочкой операций теперь расшифровывается бухгалтерская книга у криптовалют.. а если – хакер смотрит на старую сидюшку года 2006 на которой шариковой ручкой подписано резольвер ша 256, она из за этого с третьего раза читается. надеюсь что как говорят наши заокеанские друзья конкуренты что фейк. (иначе первой крипте каюк или кранты)
причина изменения нескольких настроек – новые версии программ, и повышеная безопасность по большей части из за перестраховки. в третьем и четвертом абзаце не считая оглавление причина почему разные типы серверов например 2014 года и 2022 вроде бы linux а не связываются.
SSH keys

Reason: The intro and Background section ignore the server perspective. (Discuss in Talk:SSH keys) SSH keys can serve as a means of identifying yourself to an SSH server using public-key cryptography and challenge-response authentication. The major advantage of key-based authentication is that, in contrast to password authentication, it is not prone to brute-force attacks, and you do not expose valid credentials if the server has been compromised (see RFC 4251 9.4.4).
Furthermore, SSH key authentication can be more convenient than the more traditional password authentication. When used with a program known as an SSH agent, SSH keys can allow you to connect to a server, or multiple servers, without having to remember or enter your password for each system.
Key-based authentication is not without its drawbacks and may not be appropriate for all environments, but in many circumstances it can offer some strong advantages. A general understanding of how SSH keys work will help you decide how and when to use them to meet your needs.
This article assumes you already have a basic understanding of the Secure Shell protocol and have installed the openssh package.
Contents
better – install FreeBSD and read the .. manual.
FreeBSD Manual Pages
SSH-KEYGEN(1) FreeBSD General Commands Manual SSH-KEYGEN(1) NAME ssh-keygen -- OpenSSH authentication key utility SYNOPSIS ssh-keygen [-q] [-a rounds] [-b bits] [-C comment] [-f output_keyfile] [-m format] [-N new_passphrase] [-O option] [-t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa] [-w provider] [-Z cipher] ssh-keygen -p [-a rounds] [-f keyfile] [-m format] [-N new_passphrase] [-P old_passphrase] [-Z cipher] ssh-keygen -i [-f input_keyfile] [-m key_format] ssh-keygen -e [-f input_keyfile] [-m key_format] ssh-keygen -y [-f input_keyfile] ssh-keygen -c [-a rounds] [-C comment] [-f keyfile] [-P passphrase] ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile] ssh-keygen -B [-f input_keyfile] ssh-keygen -D pkcs11 ssh-keygen -F hostname [-lv] [-f known_hosts_file] ssh-keygen -H [-f known_hosts_file] ssh-keygen -K [-a rounds] [-w provider] ssh-keygen -R hostname [-f known_hosts_file] ssh-keygen -r hostname [-g] [-f input_keyfile] ssh-keygen -M generate [-O option] output_file ssh-keygen -M screen [-f input_file] [-O option] output_file ssh-keygen -I certificate_identity -s ca_key [-hU] [-D pkcs11_provider] [-n principals] [-O option] [-V validity_interval] [-z serial_number] file ... ssh-keygen -L [-f input_keyfile] ssh-keygen -A [-a rounds] [-f prefix_path] ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] file ... ssh-keygen -Q [-l] -f krl_file file ... ssh-keygen -Y find-principals [-O option] -s signature_file -f allowed_signers_file ssh-keygen -Y check-novalidate [-O option] -n namespace -s signature_file ssh-keygen -Y sign -f key_file -n namespace file ... ssh-keygen -Y verify [-O option] -f allowed_signers_file -I signer_identity -n namespace -s signature_file [-r revocation_file] DESCRIPTION ssh-keygen generates, manages and converts authentication keys for ssh(1). ssh-keygen can create keys for use by SSH protocol version 2. The type of key to be generated is specified with the -t option. If in- voked without any arguments, ssh-keygen will generate an RSA key. ssh-keygen is also used to generate groups for use in Diffie-Hellman group exchange (DH-GEX). See the MODULI GENERATION section for details. Finally, ssh-keygen can be used to generate and update Key Revocation Lists, and to test whether given keys have been revoked by one. See the KEY REVOCATION LISTS section for details. Normally each user wishing to use SSH with public key authentication runs this once to create the authentication key in ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519, ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa. Additionally, the system adminis- trator may use this to generate host keys, as seen in /etc/rc. Normally this program generates the key and asks for a file in which to store the private key. The public key is stored in a file with the same name but ".pub" appended. The program also asks for a passphrase. The passphrase may be empty to indicate no passphrase (host keys must have an empty passphrase), or it may be a string of arbitrary length. A passphrase is similar to a password, except it can be a phrase with a se- ries of words, punctuation, numbers, whitespace, or any string of charac- ters you want. Good passphrases are 10-30 characters long, are not sim- ple sentences or otherwise easily guessable (English prose has only 1-2 bits of entropy per character, and provides very bad passphrases), and contain a mix of upper and lowercase letters, numbers, and non-alphanu- meric characters. The passphrase can be changed later by using the -p option. There is no way to recover a lost passphrase. If the passphrase is lost or forgotten, a new key must be generated and the corresponding public key copied to other machines. ssh-keygen will by default write keys in an OpenSSH-specific format. This format is preferred as it offers better protection for keys at rest as well as allowing storage of key comments within the private key file itself. The key comment may be useful to help identify the key. The comment is initialized to "user@host" when the key is created, but can be changed using the -c option. It is still possible for ssh-keygen to write the previously-used PEM for- mat private keys using the -m flag. This may be used when generating new keys, and existing new-format keys may be converted using this option in conjunction with the -p (change passphrase) flag. After a key is generated, ssh-keygen will ask where the keys should be placed to be activated. The options are as follows: -A For each of the key types (rsa, dsa, ecdsa and ed25519) for which host keys do not exist, generate the host keys with the default key file path, an empty passphrase, default bits for the key type, and default comment. If -f has also been specified, its argument is used as a prefix to the default path for the result- ing host key files. This is used by /etc/rc to generate new host keys. -a rounds When saving a private key, this option specifies the number of KDF (key derivation function, currently bcrypt_pbkdf(3)) rounds used. Higher numbers result in slower passphrase verification and increased resistance to brute-force password cracking (should the keys be stolen). The default is 16 rounds. -B Show the bubblebabble digest of specified private or public key file. -b bits Specifies the number of bits in the key to create. For RSA keys, the minimum size is 1024 bits and the default is 3072 bits. Gen- erally, 3072 bits is considered sufficient. DSA keys must be ex- actly 1024 bits as specified by FIPS 186-2. For ECDSA keys, the -b flag determines the key length by selecting from one of three elliptic curve sizes: 256, 384 or 521 bits. Attempting to use bit lengths other than these three values for ECDSA keys will fail. ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length and the -b flag will be ignored. -C comment Provides a new comment. -c Requests changing the comment in the private and public key files. The program will prompt for the file containing the pri- vate keys, for the passphrase if the key has one, and for the new comment. -D pkcs11 Download the public keys provided by the PKCS#11 shared library pkcs11. When used in combination with -s, this option indicates that a CA key resides in a PKCS#11 token (see the CERTIFICATES section for details). -E fingerprint_hash Specifies the hash algorithm used when displaying key finger- prints. Valid options are: "md5" and "sha256". The default is "sha256". -e This option will read a private or public OpenSSH key file and print to stdout a public key in one of the formats specified by the -m option. The default export format is "RFC4716". This op- tion allows exporting OpenSSH keys for use by other programs, in- cluding several commercial SSH implementations. -F hostname | [hostname]:port Search for the specified hostname (with optional port number) in a known_hosts file, listing any occurrences found. This option is useful to find hashed host names or addresses and may also be used in conjunction with the -H option to print found keys in a hashed format. -f filename Specifies the filename of the key file. -g Use generic DNS format when printing fingerprint resource records using the -r command. -H Hash a known_hosts file. This replaces all hostnames and ad- dresses with hashed representations within the specified file; the original content is moved to a file with a .old suffix. These hashes may be used normally by ssh and sshd, but they do not reveal identifying information should the file's contents be disclosed. This option will not modify existing hashed hostnames and is therefore safe to use on files that mix hashed and non- hashed names. -h When signing a key, create a host certificate instead of a user certificate. Please see the CERTIFICATES section for details. -I certificate_identity Specify the key identity when signing a public key. Please see the CERTIFICATES section for details. -i This option will read an unencrypted private (or public) key file in the format specified by the -m option and print an OpenSSH compatible private (or public) key to stdout. This option allows importing keys from other software, including several commercial SSH implementations. The default import format is "RFC4716". -K Download resident keys from a FIDO authenticator. Public and private key files will be written to the current directory for each downloaded key. If multiple FIDO authenticators are at- tached, keys will be downloaded from the first touched authenti- cator. -k Generate a KRL file. In this mode, ssh-keygen will generate a KRL file at the location specified via the -f flag that revokes every key or certificate presented on the command line. Keys/certificates to be revoked may be specified by public key file or using the format described in the KEY REVOCATION LISTS section. -L Prints the contents of one or more certificates. -l Show fingerprint of specified public key file. For RSA and DSA keys ssh-keygen tries to find the matching public key file and prints its fingerprint. If combined with -v, a visual ASCII art representation of the key is supplied with the fingerprint. -M generate Generate candidate Diffie-Hellman Group Exchange (DH-GEX) parame- ters for eventual use by the `diffie-hellman-group-exchange-*' key exchange methods. The numbers generated by this operation must be further screened before use. See the MODULI GENERATION section for more information. -M screen Screen candidate parameters for Diffie-Hellman Group Exchange. This will accept a list of candidate numbers and test that they are safe (Sophie Germain) primes with acceptable group genera- tors. The results of this operation may be added to the /etc/moduli file. See the MODULI GENERATION section for more in- formation. -m key_format Specify a key format for key generation, the -i (import), -e (ex- port) conversion options, and the -p change passphrase operation. The latter may be used to convert between OpenSSH private key and PEM private key formats. The supported key formats are: "RFC4716" (RFC 4716/SSH2 public or private key), "PKCS8" (PKCS8 public or private key) or "PEM" (PEM public key). By default OpenSSH will write newly-generated private keys in its own for- mat, but when converting public keys for export the default for- mat is "RFC4716". Setting a format of "PEM" when generating or updating a supported private key type will cause the key to be stored in the legacy PEM private key format. -N new_passphrase Provides the new passphrase. -n principals Specify one or more principals (user or host names) to be in- cluded in a certificate when signing a key. Multiple principals may be specified, separated by commas. Please see the CERTIFICATES section for details. -O option Specify a key/value option. These are specific to the operation that ssh-keygen has been requested to perform. When signing certificates, one of the options listed in the CERTIFICATES section may be specified here. When performing moduli generation or screening, one of the op- tions listed in the MODULI GENERATION section may be specified. When generating a key that will be hosted on a FIDO authentica- tor, this flag may be used to specify key-specific options. Those supported at present are: application Override the default FIDO application/origin string of "ssh:". This may be useful when generating host or do- main-specific resident keys. The specified application string must begin with "ssh:". challenge=path Specifies a path to a challenge string that will be passed to the FIDO token during key generation. The challenge string may be used as part of an out-of-band protocol for key enrollment (a random challenge is used by default). device Explicitly specify a fido(4) device to use, rather than letting the token middleware select one. no-touch-required Indicate that the generated private key should not re- quire touch events (user presence) when making signa- tures. Note that sshd(8) will refuse such signatures by default, unless overridden via an authorized_keys option. resident Indicate that the key should be stored on the FIDO au- thenticator itself. Resident keys may be supported on FIDO2 tokens and typically require that a PIN be set on the token prior to generation. Resident keys may be loaded off the token using ssh-add(1). user A username to be associated with a resident key, overrid- ing the empty default username. Specifying a username may be useful when generating multiple resident keys for the same application name. verify-required Indicate that this private key should require user veri- fication for each signature. Not all FIDO tokens support this option. Currently PIN authentication is the only supported verification method, but other methods may be supported in the future. write-attestation=path May be used at key generation time to record the attesta- tion data returned from FIDO tokens during key genera- tion. Please note that this information is potentially sensitive. By default, this information is discarded. When performing signature-related options using the -Y flag, the following options are accepted: print-pubkey Print the full public key to standard output after signa- ture verification. verify-time=timestamp Specifies a time to use when validating signatures in- stead of the current time. The time may be specified as a date in YYYYMMDD format or a time in YYYYMMDDHHMM[SS] format. The -O option may be specified multiple times. -P passphrase Provides the (old) passphrase. -p Requests changing the passphrase of a private key file instead of creating a new private key. The program will prompt for the file containing the private key, for the old passphrase, and twice for the new passphrase. -Q Test whether keys have been revoked in a KRL. If the -l option is also specified then the contents of the KRL will be printed. -q Silence ssh-keygen. -R hostname | [hostname]:port Removes all keys belonging to the specified hostname (with op- tional port number) from a known_hosts file. This option is use- ful to delete hashed hosts (see the -H option above). -r hostname Print the SSHFP fingerprint resource record named hostname for the specified public key file. -s ca_key Certify (sign) a public key using the specified CA key. Please see the CERTIFICATES section for details. When generating a KRL, -s specifies a path to a CA public key file used to revoke certificates directly by key ID or serial number. See the KEY REVOCATION LISTS section for details. -t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa Specifies the type of key to create. The possible values are "dsa", "ecdsa", "ecdsa-sk", "ed25519", "ed25519-sk", or "rsa". This flag may also be used to specify the desired signature type when signing certificates using an RSA CA key. The available RSA signature variants are "ssh-rsa" (SHA1 signatures, not recom- mended), "rsa-sha2-256", and "rsa-sha2-512" (the default). -U When used in combination with -s, this option indicates that a CA key resides in a ssh-agent(1). See the CERTIFICATES section for more information. -u Update a KRL. When specified with -k, keys listed via the com- mand line are added to the existing KRL rather than a new KRL be- ing created. -V validity_interval Specify a validity interval when signing a certificate. A valid- ity interval may consist of a single time, indicating that the certificate is valid beginning now and expiring at that time, or may consist of two times separated by a colon to indicate an ex- plicit time interval. The start time may be specified as the string "always" to indi- cate the certificate has no specified start time, a date in YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format, a relative time (to the current time) consisting of a minus sign followed by an interval in the format described in the TIME FORMATS section of sshd_config(5). The end time may be specified as a YYYYMMDD date, a YYYYMMD- DHHMM[SS] time, a relative time starting with a plus character or the string "forever" to indicate that the certificate has no ex- piry date. For example: "+52w1d" (valid from now to 52 weeks and one day from now), "-4w:+4w" (valid from four weeks ago to four weeks from now), "20100101123000:20110101123000" (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011), "-1d:20110101" (valid from yesterday to midnight, January 1st, 2011), "-1m:forever" (valid from one minute ago and never expiring). -v Verbose mode. Causes ssh-keygen to print debugging messages about its progress. This is helpful for debugging moduli genera- tion. Multiple -v options increase the verbosity. The maximum is 3. -w provider Specifies a path to a library that will be used when creating FIDO authenticator-hosted keys, overriding the default of using the internal USB HID support. -Y find-principals Find the principal(s) associated with the public key of a signa- ture, provided using the -s flag in an authorized signers file provided using the -f flag. The format of the allowed signers file is documented in the ALLOWED SIGNERS section below. If one or more matching principals are found, they are returned on stan- dard output. -Y check-novalidate Checks that a signature generated using ssh-keygen -Y sign has a valid structure. This does not validate if a signature comes from an authorized signer. When testing a signature, ssh-keygen accepts a message on standard input and a signature namespace us- ing -n. A file containing the corresponding signature must also be supplied using the -s flag. Successful testing of the signa- ture is signalled by ssh-keygen returning a zero exit status. -Y sign Cryptographically sign a file or some data using a SSH key. When signing, ssh-keygen accepts zero or more files to sign on the command-line - if no files are specified then ssh-keygen will sign data presented on standard input. Signatures are written to the path of the input file with ".sig" appended, or to standard output if the message to be signed was read from standard input. The key used for signing is specified using the -f option and may refer to either a private key, or a public key with the private half available via ssh-agent(1). An additional signature name- space, used to prevent signature confusion across different do- mains of use (e.g. file signing vs email signing) must be pro- vided via the -n flag. Namespaces are arbitrary strings, and may include: "file" for file signing, "email" for email signing. For custom uses, it is recommended to use names following a NAME- SPACE@YOUR.DOMAIN pattern to generate unambiguous namespaces. -Y verify Request to verify a signature generated using ssh-keygen -Y sign as described above. When verifying a signature, ssh-keygen ac- cepts a message on standard input and a signature namespace using -n. A file containing the corresponding signature must also be supplied using the -s flag, along with the identity of the signer using -I and a list of allowed signers via the -f flag. The for- mat of the allowed signers file is documented in the ALLOWED SIGNERS section below. A file containing revoked keys can be passed using the -r flag. The revocation file may be a KRL or a one-per-line list of public keys. Successful verification by an authorized signer is signalled by ssh-keygen returning a zero exit status. -y This option will read a private OpenSSH format file and print an OpenSSH public key to stdout. -Z cipher Specifies the cipher to use for encryption when writing an OpenSSH-format private key file. The list of available ciphers may be obtained using "ssh -Q cipher". The default is "aes256-ctr". -z serial_number Specifies a serial number to be embedded in the certificate to distinguish this certificate from others from the same CA. If the serial_number is prefixed with a `+' character, then the se- rial number will be incremented for each certificate signed on a single command-line. The default serial number is zero. When generating a KRL, the -z flag is used to specify a KRL ver- sion number. MODULI GENERATION ssh-keygen may be used to generate groups for the Diffie-Hellman Group Exchange (DH-GEX) protocol. Generating these groups is a two-step process: first, candidate primes are generated using a fast, but memory intensive process. These candidate primes are then tested for suitabil- ity (a CPU-intensive process). Generation of primes is performed using the -M generate option. The de- sired length of the primes may be specified by the -O bits option. For example: # ssh-keygen -M generate -O bits=2048 moduli-2048.candidates By default, the search for primes begins at a random point in the desired length range. This may be overridden using the -O start option, which specifies a different start point (in hex). Once a set of candidates have been generated, they must be screened for suitability. This may be performed using the -M screen option. In this mode ssh-keygen will read candidates from standard input (or a file spec- ified using the -f option). For example: # ssh-keygen -M screen -f moduli-2048.candidates moduli-2048 By default, each candidate will be subjected to 100 primality tests. This may be overridden using the -O prime-tests option. The DH generator value will be chosen automatically for the prime under consideration. If a specific generator is desired, it may be requested using the -O generator option. Valid generator values are 2, 3, and 5. Screened DH groups may be installed in /etc/moduli. It is important that this file contains moduli of a range of bit lengths. A number of options are available for moduli generation and screening via the -O flag: lines=number Exit after screening the specified number of lines while perform- ing DH candidate screening. start-line=line-number Start screening at the specified line number while performing DH candidate screening. checkpoint=filename Write the last line processed to the specified file while per- forming DH candidate screening. This will be used to skip lines in the input file that have already been processed if the job is restarted. memory=mbytes Specify the amount of memory to use (in megabytes) when generat- ing candidate moduli for DH-GEX. start=hex-value Specify start point (in hex) when generating candidate moduli for DH-GEX. generator=value Specify desired generator (in decimal) when testing candidate moduli for DH-GEX. CERTIFICATES ssh-keygen supports signing of keys to produce certificates that may be used for user or host authentication. Certificates consist of a public key, some identity information, zero or more principal (user or host) names and a set of options that are signed by a Certification Authority (CA) key. Clients or servers may then trust only the CA key and verify its signature on a certificate rather than trusting many user/host keys. Note that OpenSSH certificates are a different, and much simpler, format to the X.509 certificates used in ssl(8). ssh-keygen supports two types of certificates: user and host. User cer- tificates authenticate users to servers, whereas host certificates au- thenticate server hosts to users. To generate a user certificate: $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub The resultant certificate will be placed in /path/to/user_key-cert.pub. A host certificate requires the -h option: $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub The host certificate will be output to /path/to/host_key-cert.pub. It is possible to sign using a CA key stored in a PKCS#11 token by pro- viding the token library using -D and identifying the CA key by providing its public half as an argument to -s: $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub Similarly, it is possible for the CA key to be hosted in a ssh-agent(1). This is indicated by the -U flag and, again, the CA key must be identi- fied by its public half. $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub In all cases, key_id is a "key identifier" that is logged by the server when the certificate is used for authentication. Certificates may be limited to be valid for a set of principal (user/host) names. By default, generated certificates are valid for all users or hosts. To generate a certificate for a specified set of princi- pals: $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub Additional limitations on the validity and use of user certificates may be specified through certificate options. A certificate option may dis- able features of the SSH session, may be valid only when presented from particular source addresses or may force the use of a specific command. The options that are valid for user certificates are: clear Clear all enabled permissions. This is useful for clearing the default set of permissions so permissions may be added individu- ally. critical:name[=contents] extension:name[=contents] Includes an arbitrary certificate critical option or extension. The specified name should include a domain suffix, e.g. "name@example.com". If contents is specified then it is included as the contents of the extension/option encoded as a string, oth- erwise the extension/option is created with no contents (usually indicating a flag). Extensions may be ignored by a client or server that does not recognise them, whereas unknown critical op- tions will cause the certificate to be refused. force-command=command Forces the execution of command instead of any shell or command specified by the user when the certificate is used for authenti- cation. no-agent-forwarding Disable ssh-agent(1) forwarding (permitted by default). no-port-forwarding Disable port forwarding (permitted by default). no-pty Disable PTY allocation (permitted by default). no-user-rc Disable execution of ~/.ssh/rc by sshd(8) (permitted by default). no-x11-forwarding Disable X11 forwarding (permitted by default). permit-agent-forwarding Allows ssh-agent(1) forwarding. permit-port-forwarding Allows port forwarding. permit-pty Allows PTY allocation. permit-user-rc Allows execution of ~/.ssh/rc by sshd(8). permit-X11-forwarding Allows X11 forwarding. no-touch-required Do not require signatures made using this key include demonstra- tion of user presence (e.g. by having the user touch the authen- ticator). This option only makes sense for the FIDO authentica- tor algorithms ecdsa-sk and ed25519-sk. source-address=address_list Restrict the source addresses from which the certificate is con- sidered valid. The address_list is a comma-separated list of one or more address/netmask pairs in CIDR format. verify-required Require signatures made using this key indicate that the user was first verified. This option only makes sense for the FIDO au- thenticator algorithms ecdsa-sk and ed25519-sk. Currently PIN authentication is the only supported verification method, but other methods may be supported in the future. At present, no standard options are valid for host keys. Finally, certificates may be defined with a validity lifetime. The -V option allows specification of certificate start and end times. A cer- tificate that is presented at a time outside this range will not be con- sidered valid. By default, certificates are valid from the UNIX Epoch to the distant future. For certificates to be used for user or host authentication, the CA pub- lic key must be trusted by sshd(8) or ssh(1). Please refer to those man- ual pages for details. KEY REVOCATION LISTS ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs). These binary files specify keys or certificates to be revoked using a compact format, taking as little as one bit per certificate if they are being revoked by serial number. KRLs may be generated using the -k flag. This option reads one or more files from the command line and generates a new KRL. The files may ei- ther contain a KRL specification (see below) or public keys, listed one per line. Plain public keys are revoked by listing their hash or con- tents in the KRL and certificates revoked by serial number or key ID (if the serial is zero or not available). Revoking keys using a KRL specification offers explicit control over the types of record used to revoke keys and may be used to directly revoke certificates by serial number or key ID without having the complete orig- inal certificate on hand. A KRL specification consists of lines contain- ing one of the following directives followed by a colon and some direc- tive-specific information. serial: serial_number[-serial_number] Revokes a certificate with the specified serial number. Serial numbers are 64-bit values, not including zero and may be ex- pressed in decimal, hex or octal. If two serial numbers are specified separated by a hyphen, then the range of serial numbers including and between each is revoked. The CA key must have been specified on the ssh-keygen command line using the -s option. id: key_id Revokes a certificate with the specified key ID string. The CA key must have been specified on the ssh-keygen command line using the -s option. key: public_key Revokes the specified key. If a certificate is listed, then it is revoked as a plain public key. sha1: public_key Revokes the specified key by including its SHA1 hash in the KRL. sha256: public_key Revokes the specified key by including its SHA256 hash in the KRL. KRLs that revoke keys by SHA256 hash are not supported by OpenSSH versions prior to 7.9. hash: fingerprint Revokes a key using a fingerprint hash, as obtained from a sshd(8) authentication log message or the ssh-keygen -l flag. Only SHA256 fingerprints are supported here and resultant KRLs are not supported by OpenSSH versions prior to 7.9. KRLs may be updated using the -u flag in addition to -k. When this op- tion is specified, keys listed via the command line are merged into the KRL, adding to those already there. It is also possible, given a KRL, to test whether it revokes a particular key (or keys). The -Q flag will query an existing KRL, testing each key specified on the command line. If any key listed on the command line has been revoked (or an error encountered) then ssh-keygen will exit with a non-zero exit status. A zero exit status will only be returned if no key was revoked. ALLOWED SIGNERS When verifying signatures, ssh-keygen uses a simple list of identities and keys to determine whether a signature comes from an authorized source. This "allowed signers" file uses a format patterned after the AUTHORIZED_KEYS FILE FORMAT described in sshd(8). Each line of the file contains the following space-separated fields: principals, options, key- type, base64-encoded key. Empty lines and lines starting with a `#' are ignored as comments. The principals field is a pattern-list (see PATTERNS in ssh_config(5)) consisting of one or more comma-separated USER@DOMAIN identity patterns that are accepted for signing. When verifying, the identity presented via the -I option must match a principals pattern in order for the corre- sponding key to be considered acceptable for verification. The options (if present) consist of comma-separated option specifica- tions. No spaces are permitted, except within double quotes. The fol- lowing option specifications are supported (note that option keywords are case-insensitive): cert-authority Indicates that this key is accepted as a certificate authority (CA) and that certificates signed by this CA may be accepted for verification. namespaces=namespace-list Specifies a pattern-list of namespaces that are accepted for this key. If this option is present, the signature namespace embedded in the signature object and presented on the verification com- mand-line must match the specified list before the key will be considered acceptable. valid-after=timestamp Indicates that the key is valid for use at or after the specified timestamp, which may be a date in YYYYMMDD format or a time in YYYYMMDDHHMM[SS] format. valid-before=timestamp Indicates that the key is valid for use at or before the speci- fied timestamp. When verifying signatures made by certificates, the expected principal name must match both the principals pattern in the allowed signers file and the principals embedded in the certificate itself. An example allowed signers file: # Comments allowed at start of line user1@example.com,user2@example.com ssh-rsa AAAAX1... # A certificate authority, trusted for all principals in a domain. *@example.com cert-authority ssh-ed25519 AAAB4... # A key that is accepted only for file signing. user2@example.com namespaces="file" ssh-ed25519 AAA41... ENVIRONMENT SSH_SK_PROVIDER Specifies a path to a library that will be used when loading any FIDO authenticator-hosted keys, overriding the default of using the built-in USB HID support. FILES ~/.ssh/id_dsa ~/.ssh/id_ecdsa ~/.ssh/id_ecdsa_sk ~/.ssh/id_ed25519 ~/.ssh/id_ed25519_sk ~/.ssh/id_rsa Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, au- thenticator-hosted Ed25519 or RSA authentication identity of the user. This file should not be readable by anyone but the user. It is possible to specify a passphrase when generating the key; that passphrase will be used to encrypt the private part of this file using 128-bit AES. This file is not automatically accessed by ssh-keygen but it is offered as the default file for the pri- vate key. ssh(1) will read this file when a login attempt is made. ~/.ssh/id_dsa.pub ~/.ssh/id_ecdsa.pub ~/.ssh/id_ecdsa_sk.pub ~/.ssh/id_ed25519.pub ~/.ssh/id_ed25519_sk.pub ~/.ssh/id_rsa.pub Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, au- thenticator-hosted Ed25519 or RSA public key for authentication. The contents of this file should be added to ~/.ssh/authorized_keys on all machines where the user wishes to log in using public key authentication. There is no need to keep the contents of this file secret. /etc/moduli Contains Diffie-Hellman groups used for DH-GEX. The file format is described in moduli(5). SEE ALSO ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8) The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. AUTHORS OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added newer features and cre- ated OpenSSH. Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0. FreeBSD 13.0 August 11, 2021 FreeBSD 13.0
NAME | SYNOPSIS | DESCRIPTION | MODULI GENERATION | CERTIFICATES | KEY REVOCATION LISTS | ALLOWED SIGNERS | ENVIRONMENT | FILES | SEE ALSO | AUTHORS
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MODULI(5) FreeBSD File Formats Manual MODULI(5) NAME moduli -- Diffie-Hellman moduli DESCRIPTION The /etc/ssh/moduli file contains prime numbers and generators for use by sshd(8) in the Diffie-Hellman Group Exchange key exchange method. New moduli may be generated with ssh-keygen(1) using a two-step process. An initial candidate generation pass, using ssh-keygen -G, calculates numbers that are likely to be useful. A second primality testing pass, using ssh-keygen -T, provides a high degree of assurance that the numbers are prime and are safe for use in Diffie-Hellman operations by sshd(8). This moduli format is used as the output from each pass. The file consists of newline-separated records, one per modulus, contain- ing seven space-separated fields. These fields are as follows: timestamp The time that the modulus was last processed as YYYYM- MDDHHMMSS. type Decimal number specifying the internal structure of the prime modulus. Supported types are: 0 Unknown, not tested. 2 "Safe" prime; (p-1)/2 is also prime. 4 Sophie Germain; 2p+1 is also prime. Moduli candidates initially produced by ssh-keygen(1) are Sophie Germain primes (type 4). Further primality testing with ssh-keygen(1) produces safe prime moduli (type 2) that are ready for use in sshd(8). Other types are not used by OpenSSH. tests Decimal number indicating the type of primality tests that the number has been subjected to represented as a bitmask of the following values: 0x00 Not tested. 0x01 Composite number - not prime. 0x02 Sieve of Eratosthenes. 0x04 Probabilistic Miller-Rabin primality tests. The ssh-keygen(1) moduli candidate generation uses the Sieve of Eratosthenes (flag 0x02). Subsequent ssh-keygen(1) primality tests are Miller-Rabin tests (flag 0x04). trials Decimal number indicating the number of primality tri- als that have been performed on the modulus. size Decimal number indicating the size of the prime in bits. generator The recommended generator for use with this modulus (hexadecimal). modulus The modulus itself in hexadecimal. When performing Diffie-Hellman Group Exchange, sshd(8) first estimates the size of the modulus required to produce enough Diffie-Hellman output to sufficiently key the selected symmetric cipher. sshd(8) then randomly selects a modulus from /etc/ssh/moduli that best meets the size require- ment. SEE ALSO ssh-keygen(1), sshd(8) Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol, RFC 4419, 2006. FreeBSD 13.0 July 19, 2012 FreeBSD 13.0
NAME | DESCRIPTION | SEE ALSO
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How to Set Up SSH Keys on CentOS 8
Last Updated: Fri, Mar 13, 2020 CentOS Linux Guides System Admin
Introduction
This guide explains how to create SSH keys, add the public key to your CentOS 8 server, and configure sshd for passwordless login. The IP address 192.0.2.123 is an example.
1. Create an SSH key pair
Create an SSH key pair on your computer with ssh-keygen.
$ ssh-keygen
After running this command, you should see the following prompt:
Output Generating public/private rsa key pair. Enter file in which to save the key (/your_home/.ssh/id_rsa):
Press ENTER to save this SSH key pair into the ./ssh subdirectory of your home directory, or specify an alternate path if you want.
After this you should see the following output:
Output Your identification has been saved in ~/.ssh/id_rsa. Your public key has been saved in ~/.ssh/id_rsa.pub. The key fingerprint is: your_fingerprint_key username@remote_host The key's randomart image is: +--[ RSA 2048]----+ | ..o | | E o= . | | o. o | | .. | | ..S | | o o. | | =o.+. | |. =++.. | |o=++. | +-----------------+
You have created a public and private key pair. To view your public key:
$ cat ~/.ssh/id_rsa.pub
You will see a very long string that starts with ssh-rsa.
2. Add SSH key to CentOS server
SSH to the server and create the .ssh directory, if it doesn’t already exist:
$ mkdir -p ~/.ssh
Add the public key from step 1 to ~/.ssh/authorized_keys. Replace public_key with the contents of id_rsa.pub from step 1.
$ echo public_key >> ~/.ssh/authorized_keys
Log out of the server, then log back in:
$ ssh root@192.0.2.123
You will be prompted for your server root password.
3. Disable Password Authentication
Your SSH key-based authentication is configured, but password authentication is still active. To change this you need to make some changes to the file sshd_config which is located in /etc/ssh directory. You can open that file with this command:
sudo vi /etc/ssh/sshd_config
In the file, you need to find and change several lines Permit Root Login should be set to yes
... PermitRootLogin yes ...
Password Authentication should be set to no
... PasswordAuthentication no ...
Challenge-Response Authentication should be set to no
... ChallengeResponseAuthentication no ...
Using of Password Authentication Method (PAM) should be set to yes
... UsePAM yes ...
After making these changes, press ESC and then :WQ. For this change to take effect, restart the sshd service:
sudo systemctl restart sshd.service
Before closing your terminal, open a new terminal window and run this command
ssh root@192.0.2.123
You should connect to the server without a password. SSH-based authentication is successfully configured and password authentication is disabled.
по – русски
Описание параметров файла конфигурации sshd config
sshd config это файл конфигурации SSH-сервера openssh-server.
Обычное местоположение файла /etc/ssh/sshd_config, но может быть указано и другое в параметрах запуска программы.
Описание параметров
Port ПОРТ порт на котором создаётся сервера, по умолчанию 22
ListenAddress АДРЕС указание адреса на котором создаётся сервер, по умолчанию сервер принимает подключения на всех сетевых интерфейсах. Возможные варианты ListenAddress :: ListenAddress 0.0.0.0 - создание на всех IP4 адресах ListenAddress 192.168.0.1 - создание только на одном сетевом интерфёйсе ListenAddress 192.168.10.0:48675 - создание только на одном сетевом интерфейсе вместе с портом
Protocol 2 указание версии протокола SSH, по умолчанию 2 Внимание! Первая версия протокола SSH небезопасна!
HostKey /etc/ssh/ssh_host_rsa_key HostKey /etc/ssh/ssh_host_dsa_key (для версии протокола 2) указание названия файлов RSA/DSA ключей и их расположение.
UsePrivilegeSeparation yes установка разделения привилегий. Если указано yes - то сначала создаётся непривилегированный дочерний процесс для входящего сетевого трафика. После успешной авторизации запускается другой процесс с привилегиями вошедшего пользователя. Основная цель разделения привилегий - предотвращение превышения прав доступа.
KeyRegenerationInterval 3600 (для версии протокола 1) установка временного ключа
ServerKeyBits 768 (для версии протокола 1) установка длины ключа
SyslogFacility AUTH установка типа событий для записи в журнал (/var/log/auth.log) Доступны следующие значения: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7, где AUTH - авторизация на сервере
LogLevel INFO установка детализации событий для записи в журнал (/var/log/auth.log), по умолчанию INFO Доступны следующие события: SILENT, QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, DEBUG3.
LoginGraceTime 120 установка времени разрыва соединения в секундах, если пользователь не осущствит авторизацию, по умолчанию 120 сек
PermitRootLogin without-password установка разрешения для авторизации суперпользователя Доступны следующие значения: yes - вход суперпользователю разрешён, параметр по умолчанию no - вход суперпользователю запрещён without-password - авторизация суперпользователя по паролю отключена (но возможна по открытому ключу) forced-commands-only - вход суперпользователю по открытому ключу разрешён, но только для выполнения команды (указанному в AuthorizedKeysFile ?!)
StrictModes yes установка проверки у пользователя прав на владение пользовательскими файлами и домашним каталогом перед разращением входа
AllowUsers user1 user2 ... установка разрешения доступа к серверу по протоколу SSH только для перечисленных пользователей. Значениями этого параметра могут выступать имена пользователей (не UID!), отделённые друг от друга пробелами. Допускается использование записи вида user@host, что означает разрешёние доступа пользователю user с компьютера host. Причём пользователь и компьютер проверяются отдельно, то естть доступ может быть разрешён только определенным пользователям с определенных компьютеров.
DenyUsers user1 user2 ... установка запрета доступа к серверу по протоколу SSH для перечисленных пользователей. Правила формирования имён такие же как у AllowUsers
AllowGroups user1 user2 ... установка разрешения доступа к серверу по протоколу SSH только для перечисленных групп пользователей.
DenyGroups user1 user2 ... установка запрета доступа к серверу по протоколу SSH для перечисленных групп пользователей.
RSAAuthentication yes установка типа аутентификации RSA
PubkeyAuthentication yes включение аутентификации по открытому ключу
AuthorizedKeysFile .ssh/authorized_keys указание имени файла, в котором содержатся публичные ключи, используемые для аутентификации пользователей по открытому ключу. В записи могут присутствовать записи в форме %T, которые заменяются в момент установки соединения, например %% заменяется на %, %h означает домашний каталог пользователя,а %u – имя пользователя. По умолчанию ".ssh/authorized_keys .ssh/authorized_keys2".
IgnoreRhosts yes установка игнорирования параметров пользователя из файлов ~/.rhosts and ~/.shosts (параметр для совместимости с программой rhosts)
RhostsRSAAuthentication no включение поддержки аутентификации RSA для rhosts. Для работы этого параметра ключи узла должны быть присоединены в /etc/ssh_known_hosts (параметр для совместимости с программой rhosts)
HostbasedAuthentication no включение поддержки аутентификации Hostbased для rhosts. (параметр для совместимости с программой rhosts)
IgnoreUserKnownHosts yes установка игнорирования пользовательскому ~/.ssh/known_hosts для RhostsRSAAuthentication (параметр для совместимости с программой rhosts)
PermitEmptyPasswords no установка разрешения входа с пустым паролем.
ChallengeResponseAuthentication no включение PAM интерфейса при авторизации. Если задано значение yes, то для всех типов аутентификации помимо обработки модуля сессии и аккаунта PAM, будет использоваться аутентификация на основе запроса-ответа (ChallengeResponseAuthentication и PasswordAuthentication).
PasswordAuthentication yes включение авторизации по паролю. Альтернатива аутентификации по ключу хоста.
Параметры, отвечающие за аутентификацию Kerberos #KerberosAuthentication no #KerberosGetAFSToken no #KerberosOrLocalPasswd yes #KerberosTicketCleanup yes
Параметры, отвечающие за аутентификацию GSSAPI #GSSAPIAuthentication no #GSSAPICleanupCredentials yes
X11Forwarding yes установка разрешения перенаправления портов X-системы через ssh-туннель Будет работать, если на сервере установлен XServer.
X11DisplayOffset 10 установка смещения дисплеев X11 при пробросе портов X-системы через ssh туннель Будет работать, если на сервере включён X11Forwarding
PrintMotd no включение вывода при создании ssh-сессии информационного сообщения из файла /etc/motd.
PrintLastLog yes включение добавления к сообщению, установленному параметром PrintMotd, информации о том, когда в последний раз и с какого компьютера осуществлялся вход на сервер.
TCPKeepAlive yes включение поддержания соединения со стороны сервера. Внимание! возможно безопасней будет реализация данной функции вручную с помощью параметров ClientAliveCountMax и ClientAliveInterval, как указано ниже.
ClientAliveCountMax 3 установка количества запросов, которое ssh-сервер отправляет ssh-клиентам через определённые промежутки времени. Как только установленное значение запросов достигнуто, а клиент так и не ответил, соединение разрывается. Если этого делать, то сессии на сервере будут длиться бесконечно, отбирая его ресурсы.
ClientAliveInterval 20 установка интервала отправки запросов ClientAliveCountMax в секундах.
UseLogin no установка использования login для интерактивных сессий, значение по умолчанию no.
MaxStartups start:rate:full установка количества неавторизованных подключений к серверу ssh, по умолчанию значение данного параметра 10. Длительность такого подключения определяется параметром LoginGraceTime. Формат записи может быть представлен виде start:rate:full, где start – это уже имеющееся количество неавторизованных подключений, rate – процент вероятности отклонения попытки подключения, full – максимальное количество неавторизованных соединений. Например запись в виде MaxStartups 2:30:7 устанавливает что, если уже имеется 2 неавторизованных подключения, то следующее подключение будет отклонено с вероятностью 30%, а если количество неавторизованных подключений достигнет 7, то все последующие попытки подключения будут отвергнуты.
Banner /etc/issue.net установка местоположения файла-баннера, который будет выведен на экран, при попытке подключиться к серверу sshd. В Debian по умолчанию параметр имеет значение /etc/motd.tail.
DebianBanner no включение в строку ответа sshd при обращению к серверу по протоколу TELNET или при сканировании nmap информации об операционной системе.
AcceptEnv LANG LC_* установка переменных окружения, которые будут переданы клиенту
Subsystem sftp /usr/lib/openssh/sftp-server включение внешней подсистемы (например, FTP). В качестве параметров передаются имя подсистемы и команда, которая будет выполнена при запросе подсистемы. Команда sftp-server, реализует протокол передачи файлов через SSH - SFTP.
UsePAM yes установка разрешений на запуск sshd. Например если параметр UsePAM включён, то запустить sshd можно будет только от имени root.
пример
# $OpenBSD: sshd_config,v 1.103 2018/04/09 20:41:22 tj Exp $ # This is the sshd server system-wide configuration file. See # sshd_config(5) for more information. # This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin # The strategy used for options in the default sshd_config shipped with # OpenSSH is to specify options with their default value where # possible, but leave them commented. Uncommented options override the # default value. Include /etc/ssh/sshd_config.d/*.conf #Port 22 #AddressFamily any #ListenAddress 0.0.0.0 #ListenAddress :: #HostKey /etc/ssh/ssh_host_rsa_key #HostKey /etc/ssh/ssh_host_ecdsa_key #HostKey /etc/ssh/ssh_host_ed25519_key # Ciphers and keying #RekeyLimit default none # Logging #SyslogFacility AUTH #LogLevel INFO # Authentication: #LoginGraceTime 2m PermitRootLogin yes # do not check file permission ## StrictModes ############################################# # # # Указывает должен ли sshd проверить режимы доступа и # # владения пользовательских папок и файлов перед тем, как # # дать пользователю войти. Обычно это объясняется тем, что # # новички часто делают свои файлы доступными для записи # # всем подряд.По умолчанию - “yes”. # # # StrictModes no # Sep 5 23:45:33 belosnezhka sshd[981]: Server listening on 0.0.0.0 port 22. #Sep 5 23:45:48 belosnezhka sshd[1384]: Authentication refused: bad ownership or modes for directory /root #Sep 5 23:45:53 belosnezhka sshd[1384]: Connection closed by authenticating user root 83.167.105.127 port 41556 [preauth] # включать только если права на каталог root или другого пользователя не 700 или его использует несколько пользователей например служба почты postfix. есть риск взлома или просмотра данных. #StrictModes yes #MaxAuthTries 6 #MaxSessions 10 #PubkeyAuthentication yes # Expect .ssh/authorized_keys2 to be disregarded by default in future. #AuthorizedKeysFile .ssh/authorized_keys .ssh/authorized_keys2 #AuthorizedPrincipalsFile none #AuthorizedKeysCommand none #AuthorizedKeysCommandUser nobody # For this to work you will also need host keys in /etc/ssh/ssh_known_hosts #HostbasedAuthentication no # Change to yes if you don't trust ~/.ssh/known_hosts for # HostbasedAuthentication #IgnoreUserKnownHosts no # Don't read the user's ~/.rhosts and ~/.shosts files #IgnoreRhosts yes # To disable tunneled clear text passwords, change to no here! #PasswordAuthentication yes #PermitEmptyPasswords no # Change to yes to enable challenge-response passwords (beware issues with # some PAM modules and threads) ChallengeResponseAuthentication no # Kerberos options #KerberosAuthentication no #KerberosOrLocalPasswd yes #KerberosTicketCleanup yes #KerberosGetAFSToken no # GSSAPI options #GSSAPIAuthentication no #GSSAPICleanupCredentials yes #GSSAPIStrictAcceptorCheck yes #GSSAPIKeyExchange no # Set this to 'yes' to enable PAM authentication, account processing, # and session processing. If this is enabled, PAM authentication will # be allowed through the ChallengeResponseAuthentication and # PasswordAuthentication. Depending on your PAM configuration, # PAM authentication via ChallengeResponseAuthentication may bypass # the setting of "PermitRootLogin without-password". # If you just want the PAM account and session checks to run without # PAM authentication, then enable this but set PasswordAuthentication # and ChallengeResponseAuthentication to 'no'. UsePAM yes #AllowAgentForwarding yes #AllowTcpForwarding yes #GatewayPorts no X11Forwarding yes #X11DisplayOffset 10 #X11UseLocalhost yes #PermitTTY yes PrintMotd no #PrintLastLog yes #TCPKeepAlive yes #PermitUserEnvironment no #Compression delayed #ClientAliveInterval 0 #ClientAliveCountMax 3 #UseDNS no #PidFile /var/run/sshd.pid #MaxStartups 10:30:100 #PermitTunnel no #ChrootDirectory none #VersionAddendum none # no default banner path #Banner none # Allow client to pass locale environment variables AcceptEnv LANG LC_* # override default of no subsystems Subsystem sftp /usr/lib/openssh/sftp-server # Example of overriding settings on a per-user basis #Match User anoncvs # X11Forwarding no # AllowTcpForwarding no # PermitTTY no # ForceCommand cvs server
смотрим журнал secure – это прошло соединение по открытому ключу. Лучше пароль не набирать так как интернет открытый, подключился кто к провайдеру и слушает весь трафик, а пароли идут открытым текстом. Для этого и придумали ключи.
Sep 6 11:10:08 belosnezhka sshd[6439]: Accepted publickey for www from 83.167.105.127 port 41610 ssh2: RSA SHA256:4tcF6xa9ZbMpvRYrTYaj2pUtUjq6n9jLSX9thL7jWVs
Sep 6 11:10:08 belosnezhka sshd[6439]: pam_unix(sshd:session): session opened for user www by (uid=0)
Sep 6 11:10:11 belosnezhka sshd[6441]: Received disconnect from 83.167.105.127 port 41610:11: disconnected by user
(chmod 500 /root ; chown root:root * ; chmod 700 .ssh ; chmod 644 known_hosts ; chmod 644 id_rsa.pub ; chmod 600 .ssh/authorized_keys ; chmod 600 id_rsa; )
UsePAM yes установка разрешений на запуск sshd. Например если параметр UsePAM включён, то запустить sshd можно будет только от имени root. * не совсем так все прописано в файле pam.d sshd #%PAM-1.0 auth<--> required<--->pam_sepermit.so auth include password-auth account required pam_nologin.so account include password-auth password include password-auth # pam_selinux.so close should be the first session rule session required pam_selinux.so close session required pam_loginuid.so # pam_selinux.so open should only be followed by sessions to be executed in the user context session required pam_selinux.so open env_params session required pam_namespace.so session optional pam_keyinit.so force revoke session include password-auth session include postlogin # Used with polkit to reauthorize users in remote sessions -session optional pam_reauthorize.so prepare system-auth #%PAM-1.0 # This file is auto-generated. # User changes will be destroyed the next time authselect is run. auth required pam_env.so auth required pam_faildelay.so delay=2000000 auth sufficient pam_unix.so nullok try_first_pass auth requisite pam_succeed_if.so uid >= 1000 quiet_success auth required pam_deny.so account required pam_unix.so account sufficient pam_localuser.so account sufficient pam_succeed_if.so uid < 1000 quiet account required pam_permit.so password requisite pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type= password sufficient pam_unix.so sha512 shadow nullok try_first_pass use_authtok password required pam_deny.so session optional pam_keyinit.so revoke session required pam_limits.so -session optional pam_systemd.so session [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid session required pam_unix.so
read more (learn Russian) http://mydebianblog.blogspot.com/2006/12/ssh.html