# Presentation: 522270

## Secure Connections to NERSC Systems Using the Secure Shell (SSH)

**Jed Donnelley**
**http://www.nersc.gov/~jed**
**6/21/1999**

**Notes:**
Outline:
Why are people looking at PC clusters?
Why should NERSC be interested in PC clusters?
Who is doing PC clusters?
  Mention nersc/lbl/millennium/beowulf/sandia

Hardware/software issues
  hardware
  	processor
 	network
 software
 	operating system
	cluster software
	tools
Extreme Linux
Support issues (mention fnal)
What is NERSC doing?

## Using SSH to connect to Unix

_**Use**_**	****	****	****From:****	**_**Unix**_**	****	**_**PC/Mac**_
**Secure “Telnet”****	****	****ssh, slogin**
**X Windows****	****	****automatic      manually specified**
**Data Transfer****	****	****scp, ftp ****	****ftp**
**Authentication****	****	****ssh-keygen****	****Key generation                                                                                                                           ****	****	****	****	****	****	****    Wizard****	**
**DataFellows: ****	**http://www.datafellows.fi/

- June 2000

## Basic Facilities Offered by SSH

- 1.  **An encrypted channel for control (e.g. “Telnet”) communication.**
- 2.  Plumbing (aka forwarding, tunneling): multiplexing of IP forwarded communication across the encrypted channel.
**     **(e.g. for X Windows, FTP, POP email, etc.)
- 3.  Authentication: Public key authentication for users and servers.  Allows use of a single passphrase rather than multiple passwords.

- Local
- Host
- SSH
- Client

- Remote
- Host
- SSH
- Daemon

**Secure**
**Channel**

- June 2000

## Simplest form - a secure “Telnet”(“normal” case)

- mordor 1: ssh mcurie
- Host 'mcurie' added to the list of known hosts.
- Password:
-  ----------------------------------------------------------------------
-             * * *  W A R N I N G     W A R N I N G * * *
-                      U.S. GOVERNMENT COMPUTER
-        If not authorized to access this system, disconnect NOW.
-    YOU SHOULD HAVE NO EXPECTATION OF PRIVACY. By continuing, you
-    consent to your keystrokes and data content being monitored.
- ...
- Your terminal type is            vt100.
- Your current working directory is /u/mpccc/jed.
- %

- June 2000

## Simplest form - a secure “Telnet”(first time connecting to this host)

- mordor 6: **ssh www.nersc.gov**
- Host key not found from the list of known hosts.
- Are you sure you want to continue connecting (yes/no)? yes
- Host ’www.nersc.gov' added to the list of known hosts.
- Creating random seed file ~/.ssh/random_seed.  This may take a while.
- jed@www.nersc.gov’s **Password:**
- Last login: Wed Mar 10 11:07:08 1999 from gondor.nersc.gov
- No mail.
- Sun Microsystems Inc.   SunOS 5.6       Generic August 1997
- *****************************************************
- Welcome to the primary NERSC Web server.
- Please report any problems or concerns to consult@nersc.gov or x8600
- ******************************************************
**gondor.nersc.gov%**

- June 2000

## SSH “Telnet” - a PC/Mac Example

**Generally recommended**

- June 2000

## PC SSH - the Resulting Connection

**Note: If you set**
**$DISPLAY you will**
**break X forwarding.**
**You can, however,**
**specify a ****-display**
**option to ****xclock**

- June 2000

## Example: SSH from Unix

- % ssh killeen
- jed@killeen's password:
-  ----------------------------------------------------------------------
- ...
- Your current working directory is /u/ccc/jed.
- % printenv DISPLAY
-  killeen:36.0
- % xclock &
- [1] 16332
- %

- June 2000

## Advanced Facilities

- 1.  An encrypted channel for control (e.g. “Telnet”) communication.
- 2.  **Plumbing (aka forwarding, tunneling): multiplexing of forwarded IP communications across the encrypted channel. (e.g. for X Windows, FTP, POP email, etc.)**
- 3.  Authentication: Public key authentication for users and servers.**  **Allows use of a single passphrase rather than multiple passwords.

- Local
- Host
- SSH
- Client

- Remote
- Host
- SSH
- Daemon

**Secure**
**Channel**

- June 2000

## SSH Plumbing: IP Forwarding(Tunneling)

- Local
- Host
- SSH
- Client

- Remote
- Host
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input**

- User
- Shell

- IP
- Fwd
- Client
- e.g. X,
- FTP

- IP
- Fwd
- Server

**Non-secure data channel**
**Note: Firewalls may affect this**
**Connection in different directions**

- June 2000

## SSH Port Forwarding: FTP example

- Local
- SSH
- Client

- Remote
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input/output**

**User**
**Shell**

- Port
- Fwd
- Client,
- FTP
- client

- Port
- Fwd
- Server,
- FTP
- demon

**S. port**

**D. port**

- FTP data connection
- Not secured

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## X Windows Forwarding - Automatic

**Not defaulted on PC**

- June 2000

## Configuration for Forwarded FTP

- June 2000

## FTP Data Transfer Configuration

**Note: Important for data connections**

**PC example: WS_FTP**

- June 2000

## When the Data Connection is Established

- June 2000

## When the Data Connection Fails

**Active/Passive mode failure indication**

- June 2000

## Very Similar on a Macintosh

**Mac example: “Fetch”**

**Connection dialog**

**Remote system file list**

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## FTP Tunneling under Unix

- Requires two windows on your local workstation
- In window 1, set up the forwarded port while making a “regular” ssh terminal connection:
**ssh -L *****forwarded_port*****:*****forwarded_host*****:*****host_port***** *****host***
**E.g.**
**% ftp -L 2000:killeen.nersc.gov:21 killeen.nersc.gov**
- SSH on your workstation listens for any outgoing connections using port 2000, and forwards them to port 21 on killeen; this is the FTP server port.
- In window 2:
**% ftp localhost 2000**
**% ftp myworkstation.lbl.gov 2000**
**% ftp 127.0.0.1 2000**
- When prompted to log in, supply password for remote system, e.g. killeen.
- The connection to your workstation on the forwarded port gets sent to port 21 on killeen, where it’s received by the FTP server.
- Only the CONTROL CONNECTION (user name and password) is protected by encryption.

- June 2000

## Secure Copy (scp) Client on Unix

- Syntax:
**scp [-aAqQprvBCL] [-S path-to-ssh] [-o ssh-options]**
**    ****[-P port] [-c cipher] [-i identity]**
**    ****[[user@]host1:]filename1 [[user@]host2:]filename2**
- Example:
**% scp test.file killeen.nersc.gov:new.file**
- jed@killeen.nersc.gov's password:** **
**test.file    | 0 KB |   0.0 kB/s | ETA: 00:00:00 |  99%**
**% **
- The entire session is protected by encryption.

- June 2000

## The Fly in the Ointment

- The fundamental operation of SSH is the terminal connection
**ftp** tunneling requires it, so any system that doesn’t allow a shell, won’t allow tunneling (e.g. HPSS)
**scp** seems to have a similar limitation, since it doesn’t work to HPSS, either
- Connecting to HPSS securely is something we’re working on. Right now it requires a two step process to do it securely, using an intermediate machine within NERSC, with the assumption that unsecured transfers between it and HPSS are safe.

- June 2000

## Firewalls

- There are many ways to set up firewalls, but they can be lumped into two categories:
- “statefull” - connections are remembered and this knowledge may be used in other connections; these are the easiest for users to deal with
- “stateless” - connections have no knowledge of other connections;

- June 2000

## SSH Port Forwarding: FTP Example

- Local
- SSH
- Client

- Remote
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input/output**

**User**
**Shell**

- Port
- Fwd
- Client,
- FTP
- Client

- Port
- Fwd
- Server,
- FTP
- Server

**S. port**

**D. port**

- FTP Data Connection
- Not secured

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## FTP - “Active” (Default) Mode

- Local
- Host
- FTP
- Client

-  Remote
- Host
- FTP
- Server

- Data Connection

- Control Connection

**Connect**

**Server Data**
**Connect**

**Port 21:**
**listen**

**“****PORT  <IP ADDR>, <client data>”**

**Client data:**
**          ****listen**

**“****STOR <‘filename’>”**

**“****filename”’s data  ---->**

- June 2000

## FTP - “Passive” Mode

- Local
- Host
- FTP
- Client

-  Remote
- Host
- FTP
- Server

- Data Connection

- Control Connection

**Connect**

**Client Data**
**Connect**

**Port 21:**
**listen**

**“****PORT  <IP ADDR>, <client data>”**

**Server data:**
**      ****listen**

**“****STOR <‘filename’>”**

**“****filename”’s data  ---->**

**“****PASV”**

- June 2000

## Firewall Consequences, Active Mode

- Local
- SSH
- Client

- Remote
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input/output**

**User**
**Shell**

**S. port**

**Dest. port**

- FTP data connection

- FTP
- Server

**Data. port**

**X**

**Port 22**

**Outgoing**
**connection: OK**

**Incoming**
**connection - blocked!**

- FTP
- Client

**Client data:**
**          ****listen**
**Never arrives**

- Fails:

- June 2000

## Firewall Consequences, Passive Mode

- Local
- SSH
- Client

- Remote
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input/output**

**User**
**Shell**

**S. port**

**Dest. port**

- FTP data connection

- FTP
- Server

**Data. Port:**
**  ****listen**

**Port 22**

**Outgoing**
**connection: OK**

**Outgoing**
**connection - OK!**

- FTP
- Client

**Client data:**
**       ****connect**

**“****PASV”**

- Succeeds:

- June 2000

## “Local” Connections, Local Host

- What is a “local” connection?
-     127.0.0.1  or mystation.lbl.gov or ?

- June 2000

## 127.0.0.1 as “Active” “Local Host”

- Local
- SSH
- Client

- Remote
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input/output**

**User**
**Shell**

**S. port**

- FTP data connection

**Port 22**

**Outgoing**
**connection - **
**Nobody home?**

- FTP
- Client

**Dest. port**

- FTP
- Server

- Fails:

**Client data:**
**          ****listen**
**Never arrives**

**Send**
**Data. port**

- June 2000

## <IP Addr> as “Active “Local Host”

- Local
- SSH
- Client

- Remote
- SSH
- Daemon

**Secure**
**Channel**

**User**
**Terminal**
**Input/output**

**User**
**Shell**

**S. port**

- FTP data connection
- to <IP Addr>
- OK

**Port 22**

- FTP
- Client

**Dest. port**

- FTP
- Server

**Client data:**
**          ****listen**
**          ****OK**

**Send**
**Data. port**

- Succeeds:

- June 2000

## SSH2

- The **SSH2** protocol is being standardized by the IETF and
- Will shortly become an official standard. The upcoming
- Internet standard is called **SECSH**. The SECSH working
- group at **IETF** is defining the SSH 2.x protocol. The goal of
- the working group is to define an IETF standards track
- protocol that will be used by future versions of SSH.

- June 2000

## F-Secure SSH Terminal

- F­Secure SSH Terminal provides the user with secure
**login connections** over untrusted networks. F­Secure
- SSH Terminal acts as a replacement for the **telnet** protocol.
- The Terminal uses the **cryptographic authentication**,
- automatic session encryption, and integrity protection
- methods that are defined by the SSH protocol. F­Secure
- SSH Terminal fully supports **VT100 terminal emulation**.

- June 2000

## F-Secure SSH Tunnel 

- F­Secure SSH Tunnel can be used to create **local proxy**
**servers** for remote **TCP**/IP services. The service can be one
- of the Internet protocols: pop, smtp (used by e-mail software),
- http (used by Web browsers), etc. or almost any other TCP/IP
- based service (e.g. a TCP/IP connection to an RDBMS server).
- The local proxy server created by the F­Secure SSH Tunnel
- listens for a socket on the desired port, **forwards** the request
- and data over the secure channel, and instructs the F­Secure
- SSH Server to make the connection to the specified service on
- the remote machine.

- June 2000

## SSH2 Protocol Considerations

- The SSH2 Server can be configured to spawn an SSH1 protocol handler.
- The SSH2 protocol is safer and the SSH2 client has more capability (**sftp**)
- Why not support SSH2?
- Cost?  ~2 person months (est. from Systems Group)
- Performance for SSH1 support?  Only a possible problem for very interactive applications.

- June 2000

## SSH1/SSH2 Compatibility - PCs

_**Font/color codes:**_
**!** - Works	                 	**!!!** - Works, compatibility
- O - Fails			*small italics* - untested
**!!** - Works, server fork            ***?*** - We don’t know

- June 2000

## Last Advanced Facility

- 1.  An encrypted channel for control (e.g. “Telnet”) communication.
- 2.  Plumbing: multiplexing of IP forwarded communication across the encrypted channel.
-      (e.g. for X Windows, FTP, POP email, etc.)
- 3.  **Authentication: Public key authentication for users and servers.  Allows use of a single passphrase rather than multiple passwords**.

- SSH
- client

- SSH
- Demon

**Secure**
**Channel**

- June 2000

## Background: Single Key Encryption

- _Single Key (traditional) Encryption_

- WE hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness -- That to secure these Rights, Governments are instituted among Men, deriving their just Powers from the Consent of the Governed, that whenever any Form of Government becomes destructive of these Ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its Foundation on such Principles, and organizing its Powers in such Form, as to them shall seem most likely to effect their Safety and Happiness...

- _Clear Text_

- _Shared Secret Key_
- oijh238ysoid93ww8u38

- _Encrypt using the_

- WE hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness -- That to secure these Rights, Governments are instituted among Men, deriving their just Powers from the Consent of the Governed, that whenever any Form of Government becomes destructive of these Ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its Foundation on such Principles, and organizing its Powers in such Form, as to them shall seem most likely to effect their Safety and Happiness...

- _Shared Secret Key_
- oijh238ysoid93ww8u38

- _Decrypt using the_

- ;lo4i50m;lkxiujermgldorjgmnkXjnboiu409u09u0ojfoe9u9jfdr9ue0ndlifbnod8rug039uy03updjo384h03ptr7q24opogmeojodijb0r96uy0984upownv9se8yp094imu[398jbndiuyfw8oy409umjh;pr9n0pdi6u048u98nlncvksh.vl.ksdjgo845yut9w4ytowihgoioseynonsilejh;o4u5b;obmjtho;ruh0596umbrijnmh9r8uhi5t09suv9w7tori83nytvowbj4;hmdrp/;okx;lkmnsoudgo8w746ty049umyowiemrhglidufhbnod9upo9w847y594oj hlrjntbloidhrngo9n87se5m9w4umj;yobe59u6h9osejmg;oeiuyp940uy;w94um5t98seynt9o84wu9o8rumj;oeijgpm9se8rumtp0m9w45muy9o8sreyG9pser8um04u50u5y4098uy40u0095uy04uli8ult9o4iu409upe95uy0ej0e9roijo98u08u09u0495uy09u049u09u...

- _Clear Text_

- _Cipher Text_

- Examples include DES, triple DES, Idea, Blowfish

- June 2000

## Public Key Encryption

- _Public Key (dual key) Encryption_

- WE hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness -- That to secure these Rights, Governments are instituted among Men, deriving their just Powers from the Consent of the Governed, that whenever any Form of Government becomes destructive of these Ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its Foundation on such Principles, and organizing its Powers in such Form, as to them shall seem most likely to effect their Safety and Happiness...

- _Clear Text_

- _Public Key_
- 80988989228302098770349850394803980837

- _Encrypt using the_

- WE hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness -- That to secure these Rights, Governments are instituted among Men, deriving their just Powers from the Consent of the Governed, that whenever any Form of Government becomes destructive of these Ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its Foundation on such Principles, and organizing its Powers in such Form, as to them shall seem most likely to effect their Safety and Happiness...

- _Private Key_
- 9837938798379783903

- _Decrypt using the_

- ;lo4i50m;lkxiujermgldorjgmnkXjnboiu409u09u0ojfoe9u9jfdr9ue0ndlifbnod8rug039uy03updjo384h03ptr7q24opogmeojodijb0r96uy0984upownv9se8yp094imu[398jbndiuyfw8oy409umjh;pr9n0pdi6u048u98nlncvksh.vl.ksdjgo845yut9w4ytowihgoioseynonsilejh;o4u5b;obmjtho;ruh0596umbrijnmh9r8uhi5t09suv9w7tori83nytvowbj4;hmdrp/;okx;lkmnsoudgo8w746ty049umyowiemrhglidufhbnod9upo9w847y594oj hlrjntbloidhrngo9n87se5m9w4umj;yobe59u6h9osejmg;oeiuyp940uy;w94um5t98seynt9o84wu9o8rumj;oeijgpm9se8rumtp0m9w45muy9o8sreyG9pser8um04u50u5y4098uy40u0095uy04uli8ult9o4iu409upe95uy0ej0e9roijo98u08u09u0495uy09u049u09u...

- _Clear Text_

- _Cipher Text_

- _Some Public key schemes have the useful feature:_
- _Pvt(Pub(Data) = Pub(Pvt(Data) = Data_
- _(E.g. RSA)_

- June 2000

## RSA Public Key Generation

- Pick two prime numbers, p and q, and compute n = pq.
- Next, choose d < n such that d is relatively prime to p-1 and q-1.
- Now, find e such that d*e -1 is divisible by (p-1)(q-1) .
- The number n iscalled the modulus and the key pairs are (d, n)
- and (e, n).
- For example, if you pick p = 23 and q = 29, then n = 667.
- Choose d = 53, giving e = 93.
- The key pairs are then (53, 667) and (93, 667).

- June 2000

## RSA Public Key Encryption

- The "**public key**" is the pair (p*q, e)
- The “**private key**” is the pair (p*q, d)
**Plain text** T must be a number between 0 and n-1 = p*q-1.
- The **encryption** function is encrypt(T) = (T^e) mod p*q = C
- The **decryption** function is decrypt(C) = (C^d) mod p*q
- decrypt(encrypt(T)) = encrypt(decrypt(T) = T

- June 2000

## Server Key Discussion

- SSH
- client

- SSH
- Demon

**Secure**
**Channel**

**User**
**Terminal**
**Input**

- User
- Shell

- IP
- Fwd
- Client
- e.g. X
- FTP

- IP
- Fwd
- Server

**Server:**
**Private Key**
**Public Key**

- June 2000

## Example Output for a New Host

- % ssh killeen
**Host key not found from the list of known hosts.**
**Are you sure you want to continue connecting (yes/no)? **yes
**Host 'killeen' added to the list of known hosts.**
- jed@killeen's password:
-  ----------------------------------------------------------------------
- ...
- Your current working directory is /u/ccc/jed.
- %

- June 2000

## ~<username>/.ssh/known_hosts

- Example entry in jed/.ssh/known_hosts:
- killeen 1024 37 705325930642807236155564174058288088509433716307985164803840
- 4543720554999191917517478645773148302567656570907357366598312001346457953433
- 8113231393286414542817887873620249521301011281291251294893172579641922785486
- 2900150139148456014559802540031948689674063297709082139734061659587439275589
- 32541915106864908137

- June 2000

## User (Client) Key Discussion

- SSH
- client

- SSH
- Demon

**Secure**
**Channel**

**User**
**Terminal**
**Input**

- User
- Shell

- IP
- Fwd
- Client
- e.g. X
- FTP

- IP
- Fwd
- Server

**Server:**
**Private Key**
**Public Key**

**Client:**
**Private Key**
**Public Key**

- June 2000

## Example Key Generation, Unix

- gondor.nersc.gov% ssh-keygen
- Initializing random number generator...
- Generating p:  ...................................++ (distance 524)
- Generating q:  ........................++ (distance 280)
- Computing the keys...
- Testing the keys...
- Key generation complete.
- Enter file in which to save the key (/u/ccc/jed/.ssh/identity):
- Enter passphrase:
- Enter the same passphrase again:
- Your identification has been saved in /u/ccc/jed/.ssh/identity.
- Your public key is:
- 1024 37 141065829193088583535393787336236519596422356561555617621686481111309766411198772661982321105598609309699536285550930419740866537251689728318439216288854655452937112522267785457094285051527541171601963234454922870814357588148505347811819557940284482322861085587046666885623959789222189095197602745618669956589 jed@gondor.nersc.gov
- Your public key has been saved in /u/ccc/jed/.ssh/identity.pub
- gondor.nersc.gov%

- June 2000

## ~<username>/.ssh/authorized_keys

- Copied from **<source>:****~<username>/.ssh/identity.pub**
- Example entry in **<destination>:~jed/.ssh/authorized_keys**:
- 1024 37 141065829193088583535393787336236519596422356561555617621686481111309766
- 4111987726619823211055986093096995362855509304197408665372516897283184392162888
- 5465545293711252226778545709428505152754117160196323445492287081435758814850534
- 7811819557940284482322861085587046666885623959789222189095197602745618669956589 jed@gondor.nersc.gov

- June 2000

## Client Authentication Using RSA

- June 2000

## For Unix, ssh-agent, ssh-add

- gondor.nersc.gov% ssh-agent csh
- gondor.nersc.gov% ssh-add
- Need passphrase for /u/ccc/jed/.ssh/identity (jed@gondor.nersc.gov).
- Enter passphrase:
- Identity added: /u/ccc/jed/.ssh/identity (jed@gondor.nersc.gov)
- gondor.nersc.gov% ssh mcurie
-  ----------------------------------------------------------------------
-             * * *  W A R N I N G     W A R N I N G * * *
- ...
- gondor.nersc.gov% scp test.file mcurie:ssh.file
- gondor.nersc.gov%  printenv
- SSH_AUTH_SOCK=/tmp/ssh-jed/agent-socket-19174
- SSH_AGENT_PID=19175
- gondor.nersc.gov%

- June 2000