Vssh 1 11 1 – Ssh Protocol Connectivity Tools

• Vssh 1 11 1 – Ssh Protocol Connectivity Tools Download
• Vssh 1 11 1 – Ssh Protocol Connectivity Tools Tool
• Vssh 1 11 1 – Ssh Protocol Connectivity Tools Free
• Vssh 1 11 1 – Ssh Protocol Connectivity Tools Pdf

1. With SSH, users can freely navigate the Internet, and system administrators can secure their networks or perform remote administration.Written for a wide, technical audience, SSH, The Secure Shell: The Definitive Guide covers several implementations of SSH for different operating systems and computing environments. Whether you're an individual.
2. If SSH isn't installed on your server. Install an SSH tool such as OpenSSH on the server you want to connect to using the sudo apt install openssh-server command. If your firewall is blocking your SSH connection. Disable the firewall rules blocking your SSH connection by changing the destination port's settings to ACCEPT.

Vssh 1 11 1 – Ssh Protocol Connectivity Tools Download

The SSH Connection Protocol has been designed to run on top of the SSH transport layer and user authentication protocols. It provides interactive login sessions, remote execution of commands, forwarded TCP/IP connections, and forwarded X11 connections. The service name for this protocol (after user authentication) is 'ssh. RFC 4254 SSH Connection Protocol January 2006 o The range of 0xFE000000 to 0xFEFFFFFF is to be used in conjunction with locally assigned channels. For example, if a channel is proposed with a 'channel type' of 'examplesession@example.com', but fails, then the response will contain either a 'reason code' assigned by the IANA (as listed above and in the range of 0x00000001 to 0xFDFFFFFF) or a.

Get OpenSSH v3.4p1 -- download it or get it in the latest AIX 5L Expansion Pack and Web Download Pack

Vssh 1 11 1 – Ssh Protocol Connectivity Tools Tool

What is Open Secure Shell?

Open Secure Shell (OpenSSH) is an open source version of the SSH protocol suite of network connectivity tools. The tools provide shell functions that are authenticated and encrypted. Best free audio editing program. A shell is a command language interpreter that reads input from a command line string, stdin or a file. Why use OpenSSH? When you're running over unsecure public networks like the Internet, you can use the SSH command suite instead of the unsecure commands telnet, ftp, and r-commands.

OpenSSH delivers code that communicates using SSH1 and SSH2 protocols. What's the difference? The SSH2 protocol is a rewrite of SSH1. SSH2 contains separate, layered protocols, but SSH1 is one large set of code. Million dollar mama. SSH2 supports both RSA & DSA keys, but SSH1 supports only RSA, and SSH2 uses a strong crypto integrity check, where SSH1 uses a CRC-32 check. The Internet Engineering Task Force (IETF) maintains the secure shell standards.

What's new?

OpenSSH has been updated to the 3.4p1 version of the open source code from openssh.org. You can download it from OpenSSH on AIX.

The primary new feature is user privilege separation, a security enhancement that prevents super user escalation risks by reducing the amount of code that runs with special privileges. User privilege separation is enabled by default in the OpenSSH server configuration file /etc/ssh/sshd_config:

The way it works is that a separate server process is created for each connection and when a request comes from a client, the ssh monitor process forks an unpriviledged child process that handles all of the requests from the client. If the client's request requires super user privileges the request is sent to the privileged monitor process. When you view the SSH processes started, you will see the sshd Keep it 1 7 9 download free. daemon for the monitor process and an unprivileged process owned by the client. For further detailed information about privilege separation, see the August 2002 article by Niels Provos, Preventing Privilege Escalation.

Since AIX 5.2 is a new release of the AIX operating system, a separate compilation of the OpenSSH source code was completed on this level of the operating system. The VRMF of the 5.2 level of code is 3.4.0.5200, to distinguish the install images from the 5.1 version. The new VRMF will also help if migrating from AIX 5.1 to AIX 5.2. OpenSSH is compiled using the C for AIX (cc) version 5.0 compiler. The VRMF of the installation images will closely match the open source code level, except for the 'F' (Fix level). The fix level will be increased each time a release is made that contains fixes between major open source releases. For example, if we change the 3.4p1 level of code to contain a patch from the 3.5 level of the open source code, the 'F' will be incremented (for example, 3.4.0.5201).

The OpenSSH source code has been enhanced with National Language Support (NLS) enablement since the initial 2.9.9 release in April 2002. In the October 2002 release, the message catalog file openssh.cat has been translated into 35 languages. The message catalog files are packaged in installp format with a name like openssh.msg. where LANGUAGE_ABBREVIATION is the 4-character locale code for the country (for example, DE_DE is UTF German). The message catalog filesets are available from the AIX 5L Expansion Pack and Web Download Pack and come bundled in the .tar.Z file. When installing OpenSSH filesets on different locales, the installation software installp determines the correct version of the message catalog fileset to install and the translated message catalog file gets copied into /usr/lib/nls/msg/.

Additional fixes in this release

In the latest OpenSSH version 3.4p1 binaries, we included several patches specific for AIX from the openssh.org site. The patches are for the following fixes:

• password expiration enforced
• updated files /etc/security/login and failedlogin
• updated the unsuccessful login count
• LOGIN environment variable set
• streaming large amounts of data no longer hangs the session

AIX 5.2 enhancements

Since AIX 5.2 fully supports Pluggable Authentication Modules (PAM), OpenSSH 3.4.0.5200 has been compiled with PAM support. PAM is a framework where a system administrator can add or stack multiple different authentication modules by writing customized modules and configuring the system to use them. On AIX 5.2, the PAM framework consists of a library, pluggable modules and a configuration file. Because OpenSSH is compiled with PAM, the configuration file /etc/pam.conf will be created on the server at openssh.base.server package installation time. (In the future, /etc/pam.conf will be created at openssh.base.server installation time).

The default PAM module can be pam_aix, where pam_aix is provided by the base AIX operating system (automatically installed on AIX 5.2 in /usr/lib/security). The pam_aix module allows access to the AIX security services by providing access to AIX builtin functions such as the AIX pam_aix authentication() call. The /etc/pam.conf for OpenSSH will look like this:

Find free slot machines. The permissions on /etc/pam.conf will be 644.

Cryptographic applications depend on random numbers. If the random numbers are not highly random and are not protected during generation, the security of the encryption may be weakened.

OpenSSH on AIX 5.1 is compiled using the entropy gathering mechanism (random numbers) provided with the OpenSSH source code (ssh-rand-helper), as opposed to AIX 4.3.3 (AIX Linux Toolbox) which uses the PRNGD open source daemon (prngd-0.9.23-3.aix4.3.ppc.rpm package).

The AIX 5.2 base security provides new pseudo random number generator devices, /dev/random and /dev/urandomM, pseudo-device driver and configuration routines that select various hardware device interrupts to provide entropy. OpenSSH in AIX 5.2 is compiled to take advantage of the new device /dev/urandom. You will also need the latest OpenSSL version, openssl-0.9.6e-2.aix4.3.ppc.rpm (AIX Linux Toolbox), for OpenSSH to use the /dev/urandom device.

Where to get documentation

• The OpenSSH fileset includes man pages with openssh.man.en_US.
• On the web, openBSD provides very good man pages.
• For installation instructions on the different levels of AIX (AIX 4.3.3, AIX 5.1 and AIX 5.2), see the IBM redbook Managing AIX Server Farms. Chapter 4.2 provides details about software prerequisites and about how to manage the OpenSSH server and use the client commands.
• The AIX 5.2 Security Guide has information about AIX and PAM.

Packaging

Four installation packages contain the installp format of the code:

The installation packaging contains the scripts necessary to install the executables into the correct directories.

The following files are in the openssh.base.client fileset and are installed in /usr/bin:

The following files are in the openssh.base.server fileset and are installed in /usr/sbin:

The following configuration files are installed in /etc/ssh:

The packaging creates the sshd user, group, and /var/empty directory needed for server execution on 3.4p1 level of code. The packaging also enables the SRC control of the daemon, generates host keys and checks for the prerequisite of OpenSSL before installing.

Downloadable resources

Related topics

• Download the opensshi-aix package from OpenSSH on AIX.
• See the openBSD man pages.
• See Preventing Privilege Escalation, article by Niels Provos, August 2002.

OpenSSH uses the SSH protocol which connects over TCP. Normally, one SSH session per TCP connection is made, but multiple sessions can be multiplexed over a single TCP connection if planned that way. The current set of Secure Shell protocols is SSH2. It is a rewrite of the old, deprecated SSH1 protocol. It contains significant improvements in security, performance, and portability. The default is now SSH2 and SSH1 support has been removed from both the client and server.

The Secure Shell protocol is an open standard. As such, it is vendor-neutral and maintained by the Internet Engineering Task Force (IETF). The current protocol is described in RFC 4250 through RFC 4256 and standardized by the IETF secsh working group. The overall structure of SSH2 is described in RFC 4251, The Secure Shell (SSH) Protocol Architecture.

The SSH protocol is composed of three layers: the transport layer, the authentication layer, and the connection layer.

SSH-CONNECT – The connection layer runs over the user authentication protocol. It multiplexes many different concurrent encrypted channels into logical channels over the authenticated connection. It allows for tunneling of login sessions and TCP-forwarding. It provides a flow control service for these channels. Additionally, various channel-specific options can be negotiated. This layer manages the SSH session, session multiplexing, X11 forwarding, TCP forwarding, shell, remote program execution, invoking SFTP subsystem.

SSH-USERAUTH – The user authentication layer authenticates the client-side to the server. It uses the established connection and runs on top of the transport layer. It provides several mechanisms for user authentication. These include password authentication, public-key or host-based authentication mechanisms, challenge-response, pluggable authentication modules (PAM), Generic Security Services API (GSSAPI) and even dongles.

SSH-TRANS – The transport layer provides server authentication, confidentiality and data integrity over TCP. It does this through algorithm negotiation and a key exchange. The key exchange includes server authentication and results in a cryptographically secured connection: it provides integrity, confidentiality and optional compression. ^[1]

Among the differences between the current protocol, SSH2, and the deprecated SSH1 protocol, is that SSH2 uses host keys for authentication. Whereas SSH1 used both server and host keys to authenticate. There's not much which can be added about the protocols which is not already covered with more detail and authority in RFC 4251^[2].

SSH File Transfer Protocol (SFTP)[edit]

The SSH File Transfer Protocol (SFTP) is a binary protocol to provide secure file transfer, access and management.

SFTP was added by Markus Friedl on the server side in time for the 2.3.0 release of OpenSSH in November 2000. Damien Miller added support for SFTP to the client side in time for 2.5.0. Since then, many have added to both the client and the server.

SFTP is not FTPS[edit]

For basic file transfer, nothing more is needed than an account on the machine with the OpenSSH server. SFTP support is built into the OpenSSH server package. The SFTP protocol, in contrast to old FTP, has been designed from the ground up to be as secure as possible for both login and data transfer.

Vssh 1 11 1 – Ssh Protocol Connectivity Tools Free

Unless the use-case calls for publicly available, read-only, downloads, don't worry about trying to fiddle with FTP. It is the protocol FTP itself that is inherently insecure. It's great for read-only, public data transfer. The programs vsftpd and proftpd, for example, are secure insofar as the server software itself goes, although the protocol itself is still insecure. In other words the program itself is more or less fine and if you need to provide read-only, publicly available downloads then FTP maybe the right tool. Otherwise forget about FTP. Nearly always when users ask for 'FTP' they don't mean specifically the old file transfer protocol from 1971 as described in RFC 114, but a generic means of file transfer and there are many ways to solve that problem. This is especially true since the next part of their request is usually how to make it secure. The name 'FTP' is frequently mis-used generically to mean any file transfer utility, much the same way as the term 'Coke' is used in some of Southern United States to mean any carbonated soft drink, not just Coca-Cola. Consider SFTP or, for larger groups, even SSHFS, Samba or AFS. Screens 4 3 3 – access your computer remotely access. While old FTP succeeded very well in achieving its main goal to promote use of networked computers by allowing users at any host on the network to use the file system of any cooperating host, it cannot be made secure. There's nothing to be done about that, so it is past time to get over it.

Again, it is the protocol itself, FTP, which is the problem.^[3] With FTP, the data, passwords and user name are all sent back and forth unencrypted.^[4] Anyone on the client's subnet, the server's subnet or any subnet in between can 'sniff' the passwords and data when FTP is used. With extra effort it is possible to wrap FTP inside SSL or TLS, thus creating FTPS. However, tunneling FTP over SSL/TLS is complex to do and far from an optimum solution.

Unfortunately because of name confusion combined with the large number of posts and discussions created by complex, nit-picky tasks like wrapping FTP in SSL to provide FTPS, the wrong way still turns up commonly in web searches regarding file transfer. In contrast, easy, relatively painless solutions vanish because it is rarely necessary to post how to do those. Also, an easy solution can be summed up in very few lines and maybe a single answer. Thus, there is still a lot of talk online about 'securing' FTP and very little mention of using SFTP. It's a vicious cycle that this book hopes to help break: Difficult tasks mean lots of discussion and noise, lots of discussion and noise means strong web presence, strong web presence means high Google ranking.

SFTP tools are very common, but might be taken for granted and thus overlooked. SFTP tools are easy to use and more functional than old FTP clients. In fact a lot of improvements have been made in usability. There is no shortage of common, GUI-based SFTP clients to transfer files: Filezilla, Konqueror, Dolphin, Nautilus, Cyberduck, Fugu, and Fetch top the list but there are many more. Most are Free Software.Again, these SFTP clients are very easy to use. For example, in Konqueror, just type in the URL to the sftp server, where the server name or address is xx.yy.zz.aa.

If it is desirable to start with a particular directory, then that too can be specified.

One special client worth knowing about is sshfs. With sshfs as an SFTP client the other machine is accessible as an open folder on your machine's local file system. In that way any program you normally have to work with files, such as LibreOffice, Inkscape or Gimp can access the remote machine via that folder.

Background of FTP[edit]

FTP is from the 1970s. It's a well proven workhorse, but from an era when if you were on the net you were supposed to be there and if there was trouble it could usually be cleared up with a short phone call or an e-mail or two. It sends the login name, password and all of the data unencrypted for anyone to intercept. FTP clients can connect to the FTP server in either passive or active modes. Both active and passive modes for FTP^[5] use two ports, one for control and one for data. In FTP Active mode, after the client makes a connection to the FTP server it then allows an incoming connection to be initiated from the server to for data transfer. In FTP Passive mode, after the client makes a connection to the FTP server, the server then responds with information about a second port for data transfer and the client initiates the second connection. FTP is most relevant now as Anonymous FTP, which is still excellent for read-only downloads without login. FTP is still one way to go for transfering read-only data, as would be using the web (HTTP or HTTPS), or a P2P protocol like Bittorrent. So there are other options than FTP for offering read-only downloads. Preference is given lately to HTTPS for small files and Bittorrent for large files or large groups of files.

Using tcpdump to show FTP activity[edit]

An illustration of how the old protocol, FTP, is insecure can be had from the utility tcpdump. It can show what is going over the network during an Anonymous FTP session, or for that matter any FTP session. Look at the manual page for tcpdump for an explanation of the individual arguments, the usage example below displays the first FTP or FTP-Data packets going from the client to the server and vice versa.

What's new?

OpenSSH has been updated to the 3.4p1 version of the open source code from openssh.org. You can download it from OpenSSH on AIX.

The primary new feature is user privilege separation, a security enhancement that prevents super user escalation risks by reducing the amount of code that runs with special privileges. User privilege separation is enabled by default in the OpenSSH server configuration file /etc/ssh/sshd_config:

The way it works is that a separate server process is created for each connection and when a request comes from a client, the ssh monitor process forks an unpriviledged child process that handles all of the requests from the client. If the client's request requires super user privileges the request is sent to the privileged monitor process. When you view the SSH processes started, you will see the sshd Keep it 1 7 9 download free. daemon for the monitor process and an unprivileged process owned by the client. For further detailed information about privilege separation, see the August 2002 article by Niels Provos, Preventing Privilege Escalation.

Since AIX 5.2 is a new release of the AIX operating system, a separate compilation of the OpenSSH source code was completed on this level of the operating system. The VRMF of the 5.2 level of code is 3.4.0.5200, to distinguish the install images from the 5.1 version. The new VRMF will also help if migrating from AIX 5.1 to AIX 5.2. OpenSSH is compiled using the C for AIX (cc) version 5.0 compiler. The VRMF of the installation images will closely match the open source code level, except for the 'F' (Fix level). The fix level will be increased each time a release is made that contains fixes between major open source releases. For example, if we change the 3.4p1 level of code to contain a patch from the 3.5 level of the open source code, the 'F' will be incremented (for example, 3.4.0.5201).

The OpenSSH source code has been enhanced with National Language Support (NLS) enablement since the initial 2.9.9 release in April 2002. In the October 2002 release, the message catalog file openssh.cat has been translated into 35 languages. The message catalog files are packaged in installp format with a name like openssh.msg. where LANGUAGE_ABBREVIATION is the 4-character locale code for the country (for example, DE_DE is UTF German). The message catalog filesets are available from the AIX 5L Expansion Pack and Web Download Pack and come bundled in the .tar.Z file. When installing OpenSSH filesets on different locales, the installation software installp determines the correct version of the message catalog fileset to install and the translated message catalog file gets copied into /usr/lib/nls/msg/.

Additional fixes in this release

In the latest OpenSSH version 3.4p1 binaries, we included several patches specific for AIX from the openssh.org site. The patches are for the following fixes:

• password expiration enforced
• updated files /etc/security/login and failedlogin
• updated the unsuccessful login count
• LOGIN environment variable set
• streaming large amounts of data no longer hangs the session

AIX 5.2 enhancements

Since AIX 5.2 fully supports Pluggable Authentication Modules (PAM), OpenSSH 3.4.0.5200 has been compiled with PAM support. PAM is a framework where a system administrator can add or stack multiple different authentication modules by writing customized modules and configuring the system to use them. On AIX 5.2, the PAM framework consists of a library, pluggable modules and a configuration file. Because OpenSSH is compiled with PAM, the configuration file /etc/pam.conf will be created on the server at openssh.base.server package installation time. (In the future, /etc/pam.conf will be created at openssh.base.server installation time).

The default PAM module can be pam_aix, where pam_aix is provided by the base AIX operating system (automatically installed on AIX 5.2 in /usr/lib/security). The pam_aix module allows access to the AIX security services by providing access to AIX builtin functions such as the AIX pam_aix authentication() call. The /etc/pam.conf for OpenSSH will look like this:

Find free slot machines. The permissions on /etc/pam.conf will be 644.

Cryptographic applications depend on random numbers. If the random numbers are not highly random and are not protected during generation, the security of the encryption may be weakened.

OpenSSH on AIX 5.1 is compiled using the entropy gathering mechanism (random numbers) provided with the OpenSSH source code (ssh-rand-helper), as opposed to AIX 4.3.3 (AIX Linux Toolbox) which uses the PRNGD open source daemon (prngd-0.9.23-3.aix4.3.ppc.rpm package).

The AIX 5.2 base security provides new pseudo random number generator devices, /dev/random and /dev/urandomM, pseudo-device driver and configuration routines that select various hardware device interrupts to provide entropy. OpenSSH in AIX 5.2 is compiled to take advantage of the new device /dev/urandom. You will also need the latest OpenSSL version, openssl-0.9.6e-2.aix4.3.ppc.rpm (AIX Linux Toolbox), for OpenSSH to use the /dev/urandom device.

Where to get documentation

• The OpenSSH fileset includes man pages with openssh.man.en_US.
• On the web, openBSD provides very good man pages.
• For installation instructions on the different levels of AIX (AIX 4.3.3, AIX 5.1 and AIX 5.2), see the IBM redbook Managing AIX Server Farms. Chapter 4.2 provides details about software prerequisites and about how to manage the OpenSSH server and use the client commands.
• The AIX 5.2 Security Guide has information about AIX and PAM.

Packaging

Four installation packages contain the installp format of the code:

The installation packaging contains the scripts necessary to install the executables into the correct directories.

The following files are in the openssh.base.client fileset and are installed in /usr/bin:

The following files are in the openssh.base.server fileset and are installed in /usr/sbin:

The following configuration files are installed in /etc/ssh:

The packaging creates the sshd user, group, and /var/empty directory needed for server execution on 3.4p1 level of code. The packaging also enables the SRC control of the daemon, generates host keys and checks for the prerequisite of OpenSSL before installing.

Downloadable resources

Related topics

• Download the opensshi-aix package from OpenSSH on AIX.
• See the openBSD man pages.
• See Preventing Privilege Escalation, article by Niels Provos, August 2002.

OpenSSH uses the SSH protocol which connects over TCP. Normally, one SSH session per TCP connection is made, but multiple sessions can be multiplexed over a single TCP connection if planned that way. The current set of Secure Shell protocols is SSH2. It is a rewrite of the old, deprecated SSH1 protocol. It contains significant improvements in security, performance, and portability. The default is now SSH2 and SSH1 support has been removed from both the client and server.

The Secure Shell protocol is an open standard. As such, it is vendor-neutral and maintained by the Internet Engineering Task Force (IETF). The current protocol is described in RFC 4250 through RFC 4256 and standardized by the IETF secsh working group. The overall structure of SSH2 is described in RFC 4251, The Secure Shell (SSH) Protocol Architecture.

The SSH protocol is composed of three layers: the transport layer, the authentication layer, and the connection layer.

SSH-CONNECT – The connection layer runs over the user authentication protocol. It multiplexes many different concurrent encrypted channels into logical channels over the authenticated connection. It allows for tunneling of login sessions and TCP-forwarding. It provides a flow control service for these channels. Additionally, various channel-specific options can be negotiated. This layer manages the SSH session, session multiplexing, X11 forwarding, TCP forwarding, shell, remote program execution, invoking SFTP subsystem.

SSH-USERAUTH – The user authentication layer authenticates the client-side to the server. It uses the established connection and runs on top of the transport layer. It provides several mechanisms for user authentication. These include password authentication, public-key or host-based authentication mechanisms, challenge-response, pluggable authentication modules (PAM), Generic Security Services API (GSSAPI) and even dongles.

SSH-TRANS – The transport layer provides server authentication, confidentiality and data integrity over TCP. It does this through algorithm negotiation and a key exchange. The key exchange includes server authentication and results in a cryptographically secured connection: it provides integrity, confidentiality and optional compression. ^[1]

Among the differences between the current protocol, SSH2, and the deprecated SSH1 protocol, is that SSH2 uses host keys for authentication. Whereas SSH1 used both server and host keys to authenticate. There's not much which can be added about the protocols which is not already covered with more detail and authority in RFC 4251^[2].

SSH File Transfer Protocol (SFTP)[edit]

The SSH File Transfer Protocol (SFTP) is a binary protocol to provide secure file transfer, access and management.

SFTP was added by Markus Friedl on the server side in time for the 2.3.0 release of OpenSSH in November 2000. Damien Miller added support for SFTP to the client side in time for 2.5.0. Since then, many have added to both the client and the server.

SFTP is not FTPS[edit]

For basic file transfer, nothing more is needed than an account on the machine with the OpenSSH server. SFTP support is built into the OpenSSH server package. The SFTP protocol, in contrast to old FTP, has been designed from the ground up to be as secure as possible for both login and data transfer.

Vssh 1 11 1 – Ssh Protocol Connectivity Tools Free

Unless the use-case calls for publicly available, read-only, downloads, don't worry about trying to fiddle with FTP. It is the protocol FTP itself that is inherently insecure. It's great for read-only, public data transfer. The programs vsftpd and proftpd, for example, are secure insofar as the server software itself goes, although the protocol itself is still insecure. In other words the program itself is more or less fine and if you need to provide read-only, publicly available downloads then FTP maybe the right tool. Otherwise forget about FTP. Nearly always when users ask for 'FTP' they don't mean specifically the old file transfer protocol from 1971 as described in RFC 114, but a generic means of file transfer and there are many ways to solve that problem. This is especially true since the next part of their request is usually how to make it secure. The name 'FTP' is frequently mis-used generically to mean any file transfer utility, much the same way as the term 'Coke' is used in some of Southern United States to mean any carbonated soft drink, not just Coca-Cola. Consider SFTP or, for larger groups, even SSHFS, Samba or AFS. Screens 4 3 3 – access your computer remotely access. While old FTP succeeded very well in achieving its main goal to promote use of networked computers by allowing users at any host on the network to use the file system of any cooperating host, it cannot be made secure. There's nothing to be done about that, so it is past time to get over it.

Again, it is the protocol itself, FTP, which is the problem.^[3] With FTP, the data, passwords and user name are all sent back and forth unencrypted.^[4] Anyone on the client's subnet, the server's subnet or any subnet in between can 'sniff' the passwords and data when FTP is used. With extra effort it is possible to wrap FTP inside SSL or TLS, thus creating FTPS. However, tunneling FTP over SSL/TLS is complex to do and far from an optimum solution.

Unfortunately because of name confusion combined with the large number of posts and discussions created by complex, nit-picky tasks like wrapping FTP in SSL to provide FTPS, the wrong way still turns up commonly in web searches regarding file transfer. In contrast, easy, relatively painless solutions vanish because it is rarely necessary to post how to do those. Also, an easy solution can be summed up in very few lines and maybe a single answer. Thus, there is still a lot of talk online about 'securing' FTP and very little mention of using SFTP. It's a vicious cycle that this book hopes to help break: Difficult tasks mean lots of discussion and noise, lots of discussion and noise means strong web presence, strong web presence means high Google ranking.

SFTP tools are very common, but might be taken for granted and thus overlooked. SFTP tools are easy to use and more functional than old FTP clients. In fact a lot of improvements have been made in usability. There is no shortage of common, GUI-based SFTP clients to transfer files: Filezilla, Konqueror, Dolphin, Nautilus, Cyberduck, Fugu, and Fetch top the list but there are many more. Most are Free Software.Again, these SFTP clients are very easy to use. For example, in Konqueror, just type in the URL to the sftp server, where the server name or address is xx.yy.zz.aa.

If it is desirable to start with a particular directory, then that too can be specified.

One special client worth knowing about is sshfs. With sshfs as an SFTP client the other machine is accessible as an open folder on your machine's local file system. In that way any program you normally have to work with files, such as LibreOffice, Inkscape or Gimp can access the remote machine via that folder.

Background of FTP[edit]

FTP is from the 1970s. It's a well proven workhorse, but from an era when if you were on the net you were supposed to be there and if there was trouble it could usually be cleared up with a short phone call or an e-mail or two. It sends the login name, password and all of the data unencrypted for anyone to intercept. FTP clients can connect to the FTP server in either passive or active modes. Both active and passive modes for FTP^[5] use two ports, one for control and one for data. In FTP Active mode, after the client makes a connection to the FTP server it then allows an incoming connection to be initiated from the server to for data transfer. In FTP Passive mode, after the client makes a connection to the FTP server, the server then responds with information about a second port for data transfer and the client initiates the second connection. FTP is most relevant now as Anonymous FTP, which is still excellent for read-only downloads without login. FTP is still one way to go for transfering read-only data, as would be using the web (HTTP or HTTPS), or a P2P protocol like Bittorrent. So there are other options than FTP for offering read-only downloads. Preference is given lately to HTTPS for small files and Bittorrent for large files or large groups of files.

Using tcpdump to show FTP activity[edit]

An illustration of how the old protocol, FTP, is insecure can be had from the utility tcpdump. It can show what is going over the network during an Anonymous FTP session, or for that matter any FTP session. Look at the manual page for tcpdump for an explanation of the individual arguments, the usage example below displays the first FTP or FTP-Data packets going from the client to the server and vice versa.

The output below shows an excerpt from the output of tcpdump which captured packets between an FTP client and the FTP server, one line per packet. How to turn off auto lock on macbook pro.

As can be seen in lines 3 and 7, data such as text from the server is visible. In lines 1 and 5, text entered by the user is visible and in this case it includes the user name and password used to log in. Fortunately the session is Anonymous FTP, which is read-only and used for downloading. Anonymous FTP is a rather efficient way to publish material for download. For Anonymous FTP, the user name is always 'anonymous' and the password is the user's e-mail address and the server's data always read-only.

If you have the package for the OpenSSH server already installed, no further configuration of the server is needed to start using SFTP for file transfers. Though comparatively speaking, FTPS is significantly more secure than FTP. If you want remote remote login access, then both FTP and FTPS should be avoided. A very large reason to avoid both is to save work.

On FTPS[edit]

FTPS is FTP tunneled over SSL or TLS. A goal of FTP was to encourage the use of remote computers which, along with the web, has succeeded. A goal of FTPS was to secure logins and transfers, and it was a necessary step in securing file transfers with the legacy protocol. However, since SFTP is so much easier to deploy and most systems now include both graphical and text-based SFTP clients, FTPS can really be considered deprecated for most occasions.

Some good background material can be found in the Request for Comments (RFCs) for FTP and FTPS. There, SFTP and even HTTPS are better matches and largely supercede FTPS. See the section on Client Applications for an idea of the SFTP clients available.

Privilege Separation[edit]

Privilege separation is when a process is divided into sub-processes, each of which have just enough access to just the right services to do their part of the job. An underlying principle is that of least privilege, which is where each process has exactly enough privileges to accomplish a task, neither more nor less. The goal of privilege separation is to compartmentalize any corruption and prevent a corrupt process from accessing other parts of the system. Privilege separation is applied in OpenSSH by using several levels of access, some higher some lower, to run sshd(8) and its subsystems and components. The SSH server ➊ starts out with a privileged process ➋ which then creates an unprivileged process ➌ to work with the network traffic. Once the user has authenticated, another unprivileged process is created ➍ with the privileges of that authenticated user. See the 'Sequence Diagram for OpenSSH Privilege Separation'. As seen in the diagram, a total of four processes get run to create an SSH session. One process, the server, remains and listens for new connections and spawn new child processes.

After the initial connection while waiting for password authentication from user 'fred', a privileged monitor process supervises an unprivileged process by user 'sshd' which handles the contact with the remote user's client.

Then after authentication is completed and a session established for user 'fred', a new privieged monitor process is created to supervise the process running as user 'fred'. At that point the other process running as user 'sshd' has gone away.

Privilege separation has been the default in OpenSSH since version 3.3^[6] Since version 5.9, privilege separation further applies mandatory restrictions on which system calls the privilege separated child can perform. The intent is to prevent a compromised privilege separated child from being used to attack other hosts either by opening sockets and proxying or by probing local kernel attack surface. ^[7] Since version 6.1, this sandboxing has been the default.

References[edit]

Vssh 1 11 1 – Ssh Protocol Connectivity Tools Pdf

1. ↑'OpenSSH Manual Pages'. OpenSSH. http://www.openssh.com/manual.html. Retrieved 2011-02-17.
2. ↑'RFC 4251: The Secure Shell (SSH) Protocol Architecture'. 2006-01. http://tools.ietf.org/html/rfc4251. Retrieved 2013-10-31.
3. ↑'Why You Need To Stop Using FTP'. JDPFu.com. 2011-07-10. http://blog.jdpfu.com/2011/07/10/why-you-need-to-stop-using-ftp. Retrieved 2012-01-09.
4. ↑Manolis Tzanidakis (2011-09-09). 'Stop Using FTP! How to Transfer Files Securely'. Wazi. http://olex.openlogic.com/wazi/2011/stop-using-ftp-how-to-transfer-files-securely/. Retrieved 2012-01-09.
5. ↑Jay Ribak (2002). 'Active FTP vs. Passive FTP, a Definitive Explanation'. Slacksite.com. http://slacksite.com/other/ftp.html. Retrieved 2020-03-20.
6. ↑Nils Provos (2003). 'Privilege Separated OpenSSH'. University of Michigan. http://www.citi.umich.edu/u/provos/ssh/privsep.html. Retrieved 2011-02-17.
7. ↑'OpenSSH 5.9 Release Notes'. OpenSSH. 2011-09-06. http://www.openssh.com/txt/release-5.9. Retrieved 2012-11-17.