Identification and AuthenticationIdentification and Authentication

Lesson 11

Authentication & Access ControlsAuthentication & Access Controls

AuthenticationAuthentication

“Authentication is the process of determining whether information is trustworthy and genuine.”

Key question for computers and networks is how do you verify that the user is who they claim to be?

3 general methods to authenticateSomething you knowSomething you haveSomething about you/that you are

Denning likes to add a fourth – location Sandhu likes to add “what you do”, dynamic biometrics

Something you KnowSomething you Know

Most common technique for Authentication -- userids/password combination

Theoretically not a bad technique if chosen correctlyLength and size of character set have direct relationship on the strength of the chosen password

– For example, if lower case alphabet used: 1 character length = 26 possible passwords 2 character length = 26 x 26 = 676 possible passwords 3 character length = 26 x 26 x 26 = 17,576, and so on

– If upper and lower case alphabetic characters used 1 character length = 52 possible passwords 2 character length = 52 x 52 = 2704 possible passwords 3 character length = 52 x 52 x 52 = 140,608 possible passwords

Three Reasons Default accounts are left activeThree Reasons Default accounts are left active

The admin is not aware they exist or doesn’t know how to disable them.

The admin wants a “failsafe” mechanism (in case the vendor needs to access the system should a major problem occur)

The admin wants to make sure that he/she doesn’t get locked out

PasswordsPasswords The problem with passwords is that people don’t

always pick good ones.Passwords cracked from a sample set of 13,797

Number ofType of password Matches PercentageUser/account name 368 2.7%Common names 548 4.0%Female Names 161 1.2%Male Names 140 1.0%Phrases & Patterns 253 1.8%Dictionary word 1027 7.4%Machine names 132 1.0%Science fiction 59 0.4%

a total of 3340 passwords guessedFrom: Network and Internetwork Security by Stallings

PasswordsPasswords

Type of Password Percent

Dictionary Word 8% Length Percent

Common Names 4% 1 0.03%User/account name 3% 2 0.03%Phrases, patterns 2% 3 0.48%Male names 1% 4 1.36%Female Names 1% 5 2.30%Uncommon Names 1% 6 8.41%Machine names 1% 7 5.89%Place names 1% 8 5.65%King James Bible 1%

D.Klein “Foiling the Cracker: A Survey of, and Improvements to, Password Security”, 1990 USENIX UNIX Security Workshop

Passwords used in Morris WormPasswords used in Morris Worm

Experience from Eric Cole (Author of Hackers Beware)

Experience from Eric Cole (Author of Hackers Beware) “I started tracking statistics when I performed

security assessments and began to notice an interesting trend. Eighty percent of all the salespeople that I came in contact with had a password of either golf or bogey. If you know the user ID of a salesperson’s account and you want to get into his account, try these two passwords and your chances of success are very high.”

So you want to guess a passwordSo you want to guess a password If you know anything about the person you have a

chance to guess the password. One textbook used the following examples for a user “John”, try:

Sally (his wife)George (his child)Randoff (his wife’s maiden name)Tennis (John’s favorite sport)March9 (date of John’s, or his child’s or wife’s bday)Waterfall (a poster or some object seen in office)Alpha (the brand of computer John uses)

Rules for passwordsRules for passwords

Don’t pick an easy one to guessmix upper and lower case, add special characters and numbersat least 6 characters in length, 8 better, 10 even bettermaybe use pass-phrases instead of dictionary words

Don’t write it down Don’t reuse previous passwords (or just add a # to it) Change it on a regular basis (but not too often), 45 days. If you’re the sysadmin, run a password cracker periodically. If one-time passwords are possible, consider using them (they

have their own problems though)

An experience from Eric Cole, author Hackers BewareAn experience from Eric Cole, author Hackers Beware

“One common check was to look for passwords that were written down. Because most users wrote their password somewhere, just in case they forgot it, this turned into a battle to see how well the user could hide it and how well the reviewers would search to find it. The creative lengths users would go to always amazed me. Some users would hide their password in their rolodex under a certain name. One clever individual even wrote it on the bottom of his shoe… The key to remember is that users will get creative, but the creativity is limited, which means that if an attacker wants to find the password, he can.”

Password ManagementPassword Management

Password management issuesDefault accountsEasily guessed or cracked passwordsUnpassworded accountsShared accountsPassword agingPassword policy enforcementPassword auditing– Audit frequency– Control access to results

Cracking PasswordsCracking Passwords

Cracking PasswordsCracking Passwords

Step 1: Obtain the password fileNT: SAM file in %systemroot%\system32\config– Boot to alternate OS– Grab Backup SAM file from repair directory (rdisk run with /s

argument) %systemroot%\repair\SAM._ then expand it

expand sam._ sam

UNIX: /etc/passwd or /etc/shadow Step 2: download and run one of the cracking tools.

NT Password crackingNT Password cracking SAM file has two separately hashed versions of the password --

the LanMan version and the NT version. LanMan is the weak method and can easily be cracked. It

separates the password into two 7 character parts. Thus you really only have to crack two separate 7 character passwords instead of a 14 character password.

It also converts lower case characters to upper case. Because of poor hashing technique, for NT, a 10 character

password is actually potentially less secure than a 7 characterthe second half (last 3 characters) will quickly be cracked and then may provide clue for first part, ex: *******890

UNIX password crackingUNIX password cracking Generally harder than NT to crack. Unix passwords are stored in the form of a one-way hash function. One-way

hash functions are unique in cryptography because, unlike the other fundamental techniques of cryptography, they use no key at all. They work by encrypting two strings and comparing them to see if they're the same in encrypted form.

3 step process used by cracking programscreate file of possible passwords (dictionary file)Encrypt file of possible passwordsCompare results with encrypted form of passwords

Obvious why it is harder to guess if you don’t use simple words. Dictionary created must include combinations of words with various connectors, ...

One-Time PasswordsOne-Time Passwords

User given device that generates a password at certain time intervals (e.g. every minute)

The device is keyed with the server, so that both devices generate the same password at the same time.

If you want to log into the server, look at the display and type in the password you see.

Even if the password is sniffed, it was only good for the minute it was used.

QuestionnairesQuestionnaires

Another “something you know” method user is validated based on a series of questions

that an intruder is unlikely to know. Examples include:

name of pet, favorite teacher, favorite color…user may even be asked to write his/her own question

not likely to be used in high security situation, used as a secondary method frequently on the web.

Something you haveSomething you have May combine this method and userid/password Physical keys Magnetic cards

information stored on card, example is credit card Smart cards

more information stored, may be encrypted “calculators”

device that looks like (and may even function as) a calculator.Process may proceed as follows:

– user presents userid or name– system responds with challenge– challenge punched into calculator and returns response– user supplies response to system

Something about youSomething about you Biometrics

Voice prints

Fingerprint

Retinal Scan

Hand Geometry

Signature analysis

Problems with the 3 basic Authentication TechniquesProblems with the 3 basic Authentication Techniques

Something you know:people write things down, they choose poorly

Something you haverequires additional hardware ($)People lose them

Something about yourequires additional hardware ($$)things about you can change

Location-Based AuthenticationLocation-Based Authentication

Involves authenticating entities based on geodetic location (lat, long, alt).

Grounds cyberspace in the real world, aids in stopping spoofing attempts.

Uses GPS to compute and validate a location. Best suited for fixed sites -- wouldn’t work for portable

laptops. Expensive equipment, potential for DoS if GPS signal

jammed.May also be used offensively to track user’s location

“What you do”“What you do” Dynamic Biometrics – captures a dynamic process

rather than a static characteristic of a person.A person’s signature

– Concerned with more than just the shape or “look” of the signature.– Record the speed and acceleration of a person’s hand as they sign

their name on a special tablet

VoiceKeystroke Dynamics (typing behavior)

Just like a password, we need to avoid somebody capturing and playing back our signature, voice, or other similar data.

Access ControlsAccess Controls

“Access controls serve to enforce an authorization policy, which specifies what activity is allowed and who is allowed to initiate it.”

Governs not only activities by human actors but non-human actors as well.

Can apply to any media – print, tapes, networks, memory, . . .

Access modesAccess modes Read – allows entity to read the file or view the file’s

attributes Write – allows the entity to write to the file, which may

include creating, modifying, or appending to the file. Execute – the entity may load the file and run it. Delete – the entity may remove the file from the system. List – the entity may view the file’s attributes.

Protection TableProtection Table Illustrates what access controls are designed to do

File 1 File 2 File 3 Printer DiskUser 1 Read Write

WriteUser 2 Execute Read Write Read

WriteProg 1 Read Read

Write

• Protection Table seems like an easy solution to access control problem but . . .• Required table extremely large• Table generally sparsely populated

File PasswordsFile Passwords

In order to gain access to a file the user must present the system with the file’s password.

Initial assignment can be accomplished by sysadmin or creator of file.

In order to control the type of access granted to the file, multiple passwords for each file may be necessary.

Method is easy to implement and understand.

File passwords - problemsFile passwords - problems Since users will have to remember different passwords for each

file it will mean LOTS of passwords to remember (or write down!). No easy way to keep track of who has access to the password for

a file. Passwords distributed manually which leaves no automated audit trail.Hard to control.

Revocation easy to do (change a password), problem is doing it without affecting all of the other users.

Files (programs) that require access to other files requires that all passwords be identified before program is executed or execution has to be interrupted to wait for a user to enter the required password.

Capabilities Based Access ControlsCapabilities Based Access Controls Divides the protection table by rows. Associated with each entity is a list of the objects

the user may access along with its permissions.

Object PermissionsFile 1 Read, Write, ListFile 3 Read, ListPrinter Write

Object PermissionsFile 1 Read, ListFile 2 Read, Execute, ListPrinter Write

User 1 User 2

Capabilities based access controlsCapabilities based access controls

The system must maintain a list for each subject. A single object may be accessible to all or a large number

of subjects and will thus have its access information repeated many times.

Thus, tremendous overhead Revoking access to a file is cumbersome since it must be

changed in a number of places. Hard to answer the question “which subjects have access

to this object?”

Access Control Lists (ACL)Access Control Lists (ACL) Divides protection table by columns. Instead of maintaining a separate list for each

subject, ACLs are created for each object.

User 1 ExecuteUser 2 Read, Write, ListUser 4 Read, ListProgram 1 Write

User 1 ReadUser 2 ReadUser 3 Read, Execute, ListProgram 1 Write

File 1 Disk 1

Access Control ListsAccess Control Lists Can easily answer question “which subjects

have access to a specific object?”This is the more frequently asked question.Hard to answer “which objects does a specific subject have access to?”

Access to a file can easily be revoked. Storage space is saved.

Generally more objects than subjects

Modified ACLModified ACL Divide users into groups.

Smith.Sales Read, Execute*.Sales ReadJones.Personnel Read, Execute, List*.* List

File 1

• Requires much less room• Can also use this concept to easily

restrict access by including “no access” entries which can be extended to restrict access to specific dates or times.

ACL with access restrictionsACL with access restrictions

Smith.Sales Read, Execute 0800-1800Smith.Sales Read localJones.Personnel Read, Execute, List*.* List

File 1

ACL with multiple individual user access restrictions based on time and location.

NT Access Control Lists (ACL)NT Access Control Lists (ACL)

All securable objects are assigned a security descriptor when created.

Descriptor controls who has what access to the objectConsists of

– Owner SID: The owner’s security ID– Group SID: The security ID fo the primary group.– Discretionary Access Control List (DACL): specifies who has what

access to the object.– System Access Control List (SACL): Specifies which operations by

which users should be logged in the security audit log.

NT ACLsNT ACLs

The access control list is made up of an ACL header and 0 or more access control entry (ACE) structures. An ACL with 0 ACEs is called a nullACL and indicates that no user has access to the object.

File Object

SecurityDescriptor

Objectheader Allow

DAVECRead data

AllowTEAMA

Read dataWrite Data

AllowEveryone

File Execute

ACE ACE ACE

Access Control List

Protection BitsProtection Bits A modification of ACLs. Protection bits are attached to each file but instead of providing a

complete list of all users they specify permissions for specific classes. Sometimes referred to as “permission bits”. Example classes: Owner, Group, World

File 1 r,w,x, , , r, ,x, , , , , x, , ,File 2 r, ,x,d, , r, ,x, , , , , , , ,

Protection BitsProtection Bits

Owner

R W E D L

Group

R W E D L

World

R W E D L

Generalized Example

Owner

R W E

Group

R W E

World

R W E

UNIX Example

UNIX Example: R W E, R, , E, , , E 1 1 1 1 0 1 0 0 1

7 5 1Thus, permission set for this object can be contained in 9 bits

Nondiscretionary controlsNondiscretionary controls Discretionary Access Controls are controls

implemented at the discretion or option of the user/owner (e.g. protection bits)

Nondiscretionary Access Controls are controls that are determined by a central authority in the organization and can be based on the individual’s role or job.

Role-based Access Controls: tied to the particular role the user performsTask-based Access Controls: tied to a particular assignment or responsibility

SummarySummary

What is the Importance and Significance of this material?

How does this topic fit into the subject of “Voice and Data Security”?