secure connections to nersc systems using the secure shell (ssh) jed donnelley jed 6/21/1999

Secure Connections to NERSC Systems

Using the Secure Shell (SSH)

Jed Donnelley

http://www.nersc.gov/~jed

6/21/1999

June 2000Secure Connections to NERSC Systems

Using the Secure Shell (SSH) 2

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/



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.

LocalHostSSH

Client

RemoteHostSSH

Daemon

Secure

Channel



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.

%



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.

[email protected]’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 [email protected] or x8600

******************************************************

gondor.nersc.gov%



SSH “Telnet” - a PC/Mac Example

Generally recommended



PC SSH - the Resulting Connection

Note: If you set

$DISPLAY you will

break X forwarding.

You can, however,

specify a -display

option to xclock



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

%



Advanced Facilities


2. Plumbing (aka forwarding, tunneling): multiplexing of forwarded IP communications across the encrypted channel. (e.g. for X Windows, FTP, POP email, etc.)


LocalHostSSH

Client

RemoteHostSSH

Daemon

Secure

Channel



SSH Plumbing: IP Forwarding(Tunneling)

LocalHostSSH

Client

RemoteHostSSH

Daemon

Secure

Channel

User

Terminal

InputUserShell

IPFwd

Cliente.g. X,FTP

IPFwd

ServerNon-secure data channelNote: Firewalls may affect thisConnection in different directions



SSH Port Forwarding: FTP example

LocalSSH

Client

RemoteSSH

Daemon

Secure

Channel

User

Terminal

Input/outputUserShell

PortFwd

Client,FTP

client

PortFwd

Server,FTP

demon

S. port

D. port

FTP data connection

Not secured



X Windows Forwarding - Automatic

Not defaulted on PC



Configuration for Forwarded FTP



FTP Data Transfer Configuration

Note: Important for data connections

PC example: WS_FTP



When the Data Connection is Established



When the Data Connection Fails

Active/Passive mode failure indication



Very Similar on a Macintosh

Mac example: “Fetch”

Connection dialog Remote system file list



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 hostE.g.% ftp -L 2000:killeen.nersc.gov:21 killeen.nersc.govSSH 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 2000When 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.



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

[email protected]'s password:

test.file | 0 KB | 0.0 kB/s | ETA: 00:00:00 | 99%

%

The entire session is protected by encryption.



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.



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;



SSH Port Forwarding: FTP Example

LocalSSH

Client

RemoteSSH

Daemon

Secure

Channel

User

Terminal


PortFwd

Client,FTP

Client

PortFwd

Server,FTP

Server

S. port

D. port

FTP Data Connection

Not secured



FTP - “Active” (Default) Mode

LocalHostFTP

Client

RemoteHostFTP

ServerData Connection

Control ConnectionConnect

Server Data

Connect

Port 21:

listen

“PORT <IP ADDR>, <client data>”

Client data:

listen

“STOR <‘filename’>”

“filename”’s data ---->



FTP - “Passive” Mode

LocalHostFTP

Client

RemoteHostFTP

ServerData Connection

Control ConnectionConnect

Client Data

Connect

Port 21:

listen

“PORT <IP ADDR>, <client data>”

Server data:

listen

“STOR <‘filename’>”

“filename”’s data ---->

“PASV”



Firewall Consequences, Active Mode

LocalSSH

Client

RemoteSSH

Daemon

Secure

Channel

User

Terminal


S. port

Dest. port

FTP data connectionFTPServer

Data. portX

Port 22

Outgoingconnection: OK

Incomingconnection - blocked!

FTPClient

Client data:

listen

Never arrives

Fails:



Firewall Consequences, Passive Mode

LocalSSH

Client

RemoteSSH

Daemon

Secure

Channel

User

Terminal


S. port

Dest. port

FTP data connectionFTPServer

Data. Port:

listen

Port 22

Outgoingconnection: OK

Outgoingconnection - OK!

FTPClient

Client data:

connect

“PASV”

Succeeds:



“Local” Connections, Local Host

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



127.0.0.1 as “Active” “Local Host”

LocalSSH

Client

RemoteSSH

Daemon

Secure

Channel

User

Terminal


S. port

FTP data connection

Port 22

Outgoingconnection - Nobody home?

FTPClient

Dest. port

FTPServer

Fails:

Client data:

listen

Never arrives

Send

Data. port



<IP Addr> as “Active “Local Host”

LocalSSH

Client

RemoteSSH

Daemon

Secure

Channel

User

Terminal


S. port

FTP data connection

to <IP Addr>

OK

Port 22

FTPClient

Dest. port

FTPServer

Client data:

listen

OK

Send

Data. port

Succeeds:



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.



F-Secure SSH Terminal

F Secure SSH Terminal provides the user with secure

login connections over untrusted networks. F Secure

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. F Secure

SSH Terminal fully supports VT100 terminal emulation.



F-Secure SSH Tunnel

F Secure 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 F Secure SSH Tunnel

listens for a socket on the desired port, forwards the request

and data over the secure channel, and instructs the F Secure

SSH Server to make the connection to the specified service on

the remote machine.



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.



SSH1/SSH2 Compatibility - PCs

Windows Macintosh Unix Client

Server SSH1 SSH2 SFTP SSH1 SSH2 SFTP SSH1 SSH2 SCP SFTP

SSH1D ! O O ! O O ! !!! ! O

SSH2D !! ! ! !! ! ! !! ! ? !

Font/color codes:

! - Works !!! - Works, compatibilityO - Fails small italics - untested!! - Works, server fork ? - We don’t know



Last Advanced Facility


2. Plumbing: multiplexing of IP forwarded communication across the encrypted channel.

(e.g. for X Windows, FTP, POP email, etc.)


SSHclient

SSHDemon

Secure

Channel



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


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 TextCipher Text

Examples include DES, triple DES, Idea, Blowfish



Public Key Encryption

Public Key (dual key) Encryption


Clear Text

Public Key80988989228302098770349850394803980837

Encrypt using the


Private Key9837938798379783903

Decrypt using the

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

Clear TextCipher Text

Some Public key schemes have the useful feature:Pvt(Pub(Data) = Pub(Pvt(Data) = Data

(E.g. RSA)



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).



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



Server Key Discussion

SSHclient

SSHDemon

Secure

Channel

User

Terminal

InputUserShell

IPFwd

Cliente.g. XFTP

IPFwd

Server

Server:

Private Key

Public Key



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.

%



~<username>/.ssh/known_hosts

Example entry in jed/.ssh/known_hosts:

killeen 1024 37 705325930642807236155564174058288088509433716307985164803840

4543720554999191917517478645773148302567656570907357366598312001346457953433

8113231393286414542817887873620249521301011281291251294893172579641922785486

2900150139148456014559802540031948689674063297709082139734061659587439275589

32541915106864908137



User (Client) Key Discussion

SSHclient

SSHDemon

Secure

Channel

User

Terminal

InputUserShell

IPFwd

Cliente.g. XFTP

IPFwd

Server

Server:

Private Key

Public Key

Client:

Private Key

Public Key



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 [email protected]

Your public key has been saved in /u/ccc/jed/.ssh/identity.pub

gondor.nersc.gov%



~<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 [email protected]



Client Authentication Using RSA



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 ([email protected]).

Enter passphrase:

Identity added: /u/ccc/jed/.ssh/identity ([email protected])

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%

secure connections to nersc systems using the secure shell (ssh) jed donnelley jed 6/21/1999

Documents

secure connections

ssh telnet

ssh killeen

pc ssh

nersc systems

unixpcmac secure telnetssh

ssh mcurie host mcurie

xclock slide