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Cryptography. Digital security domain. Digital signature. Problems in digital signatures. Firewall. An open network

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Information security technology

Teemupekka Virtanen

Helsinki University of Technology

Telecommunication Software and

Multimedia Laboratory

teemupekka.virtanen@hut.fi

Content

• 1. Information security technology in general

– What, why, content • 2. Preventive systems

– Cryptography, Firewall, VPN, • Access control

– access control, authentication, authorization, key management, PKI

• 3. Detection Systems – IDS

• 4. Malicious content prevention Virus protection content filtering

Corporate Security

Physical Security

• Security domains

• Prevent outsiders from intruding – Fences, walls

• Authenticate the insiders – Keys, access control • Alarms

– Intrusion detection • Prevent intrusion

– Guards

Traditional security domain

Tamper resistant devices

• Tamper resistant devices combined physical security with information related services. • E.g. smartcards are desiged to store secret

information which never come out • The device authenticate user itself and can

make some operation on behalf of authorized user

• Good: excellent storage for secret keys and other information

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Cryptography

• Passive methods to prevent

unauthorized access to the content

• Can also prevent unathorized

modification of the content

• Non-repudiation

Digital security domain

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Digital signature

• In asymetric cryptography there are always two different keys binded together so that

– text encrypted with one key can be decrypted with other key and only with that

– one can’t find out what is the other key • If a text can be decrypted with a key we

know that the text is encrypted with another key of the pair

• If we know that another key is owned by a certain person we know that only him has been able to encrypt the message

Problems in digital signatures

• Signature is something that connects a

person to a document and states that

the person accepts the document

– If one put the name on the paper to show that he has seen a document it is not a signature

• In electronic environment a user have

no control what happens

– It can’t be a signature

Firewall

• There are several possible definitions. My definition is:

– A policy how information is allowed to flow between two domains and device(s) which are required to put that policy into use

• The first and often the only defence line against an intruder

• Often dedicated devices which have special features to define policies and rise security level

• Requires constant administration and monitoring

• Not a buy and forget –box

(3)

A protected network

VPN

• A trusted connection between secure

areas

• A cryptographically protected channel

• Good: one solution for all the

applications

• Bad: is the other site really secure

enough

A channel between protected

networks

Several protection layers

Access control

• Traditionally a method to decide if somebody has a permission to enter restricted zone

• Consists several areas – Identification - who is who – Authentication – who is going to enter – Authorization – does one have permission to

enter this area

– Auditing – collect information who has entered a certain zone

Authentication

• Connects identity to a subject • Can based on

– Something one has: the one time pad, the key, the device, ...

– Something one knows: the password, the answer, the protocol

– Something one is: the fingerprint, the voice, the eye, the signature, the face

• Several methods can be combined: – A device which requires a password – an id-card with correct face

(4)

Authorization

• Decides if the subject has permission

to certain object

• Access control based (ACL):

– -rw-r---- tpv users file.txt

• Capabilities based:

– tpv: file.txt(rw)

• In multilevel systems there are more

information in security labels

Key management

• Probably the weakest point of cryptography • In symmetric methods the same key has to

be distributed to all authorized persons and nobody else

• In asymmetric methods everyone needs only one pair of keys and the key management is easier

– secure creation of keys, initial distribution, secure strore of secret keys, secure publishing of public keys

PKI

• Public key infrastucture

• Method for digital signature

• Method to negotiate symmetric key

for encryption

• Certificates to create trust

• Method to revokate a certificate

Residual information

• A computer is used normally three years and during that time there have been several confidental files

• How to remove these files permanently when discarding a computer?

• There are also communicators and handheld computers which are gate to systems and strorages of information

Intrusion detection systems

• Systems which detect attempts to intrude • Server based IDS systems monitor one

server

• Network based systems monitor traffic in the network

• Try to find out known attacks – The database must be updated

• There must be some active response for alarms

Virus protection methods

• Traditional scanner

– Scans files and tried to find fingerprints – Databases mus be updated regularly • Heuristic scanner

– Tries to find typical elements of virus • Firewall type virus protection

– Removes all executables and Office-macros • Activity analyzer

– Notices if there are too many same attachments and puts them in hold

(5)

Virus protection

• In firewall

– Scans all the attachments, www-pages and FTP-transfers

– Good in prevention and in maintainability – Slow if there is lot of trafic

• In mail-server

– Scans all the attachments

– Almost all the viruses spread with mail – Efficient

• In file server – Scans all the files • In workstations

– Scans all the files

Content filtering

• ”Information firewall” which includes a policy and methods to put the policy in use • May block

– certain adresses: www.playboy.com,

www.enemy.com – certain filetypes *.mp3

– documents with certain strings: ”Secret”, ”project-X”

• Several protocols: HTTP, FTP, SMTP,... • Can open documents, zip-files, ...

Example of content filtering

ht tp:// ano n.fre e.anonymizer.com/http ://www.iltalehti.fi Con tent filterin g

pro xy F irew all

http:

ht tp: ht tp:

htt p://w ww.iltaleht i.fi

Co nten t filt erin g pro xy Firewall

h ttp:

http: http: music.mp 3

Problems with content

filtering

• Practical

– Requires plenty of maintenance and updates – Prevents often authorized work

• Ethical

– Who is allowed to decide acceptable content – For what reason

• Theoretical

– Is content filtering a method to decide what is acceptable: everything which is possible is also allowed

Centralized management

• Personal computer is not personal any more • Centralized user administration

• Centralized software distribution • Software inventory

• Spying users?

• Good: easier administration, support and asset management

• Bad: single point of failure, loss of confidence

Availability

• Availability is often more crucial

property than confidentiality

• Confidentiality and availability are

almost always conflicting properties

• Availability prevents loss of

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Backup systems

• Backup is the basic protection method against losing information

• It can be done by every user with servers, floppy disks, CD-Rs, ...

• In the bigger systems the increased capacity is a problem

– There might be tens of tapes in a carousel – There are not hours enough in a day to transfer

all the information to the tapes • It is difficult to store only changed

information in a database system where everything is just a big file

RAID

• Several hard disks in one system

looking as an one hard disk

• RAID-1 several hard disks with the

same data

• RAID-2-5 several hard disks, data is

distributed to several disks and

equipped with checksums

HA-systems

• High availability systems are systems

which have duplicated components

• HA systems use standard components

and are therefore much cheaper than

real fault tolerant systems

• In some case it is also possible to

balance load between components

HA-system structure

Network

Synchronization network

Server A Server B RAID storage system

Conclusion

• There are several technical methods to provide security

• Every improvements one can buy are very cheap. If security could be improved by just bying a box everything would be in excellent condition

• All the methods have side effects

References

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