COMP 208/214/215/216 – Lecture 10

ImplementationIssues Security

Database and system Security• Authentication• Privacy• Integrity• Audits and control

• Commonly based on shared secret

• Passwords are typically– Stored in hashed form– Used as part of challenge

handshake response– Should be encrypted before

transmitting over the network

Authentication

Password hashing• One way function• Hash(“secret”)= A13FCB34DF• Now the password cannot be read plain from dbase

table• Salt, helps to protect against pre-computed “rainbow”

table, (salt is random bits stored with hash)• Rainbow table

– “cat” ABCEF– “fred” 24ABFC– “password” 4BAF12

• Now to attack a particular hash seen on the network one would need to use all different salt combinations

SSL/TLS/https• SSL

– Secure sockets layer, developed by Netscape for secure connection between browsers and web servers

• TLS– IETF standard, based on SSL

• https– This means http (hyper text transfer

protocol transfer securely over TLS)

slide 6 Internet Security

Asymmetric Key

Encryption Decryption

Key 123 Key ABC

Hi MumPlaintext Hi MumHi MumHi MumHi MumHi MumHi MumGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCGH BVCH BVCGH BVCGH BVCGH BVCGH BVCGH BVCHi MumHi MumHi MumHi MumHi MumHi MumHi Mum Plaintext

Cipher text

Different Keys used for Encryption and Decryption

slide 7Internet Security

Digital Signature• Example Signature

Dear Bank M anager,I would like to transfer $1,000,000from the company account to mypersonal accountthank youJohn Tayloraccount manager

</signature>2344553AD1EF9896454343343434674785BE0E85CD </signature>

em ail to: Bank M anager@ Bank.Comfrom : JohnTaylor@ com pany.comsubject: Transfer of funds

slide 8Internet Security

Digital Signature• Transmission Operation

I would liketo transfer$1,000,000Thank you.

HashFunction

Hash ResultE12D4378BA980C1214390

SigningFunction

I would liketo transfer$1,000,000Thank you.

<sig>34E02B2BC8D746A21B4285C87E64BA29<sig>Digital

signature

Sender’sprivate key

slide 9Internet Security

Digital SignatureDigital Signature

Reception Operation

HashFunction

Hash ResultE12D4378BA980C1214390

Decrypt

I would liketo transfer$1,000,000Thank you.

<sig>34E02B2BC8D746A21B4285C87E64BA29<sig>

Sender’spublic key

Hash valuesthe same?

reject

accept

slide 10Internet Security

Secure Hash Functions• h = H(M)• Where h = hash value H = hash function M = message• Special properties of hash function• Different h value for different messages (random

distribution)• Impossible (very difficult to generate message

with given hash value)• Very difficult to generate two messages with

same hash value i.e. two message M1, M2 where H(M1)=H(M2)

slide 11Internet Security

PKI Public Key Infrastructure• Services defined

– Key/identity binding– Key distribution– Key integrity– Key revocation

PKI Public Key Infrastructure

• When you connect to web server, using TLS• Web server sends certificate containing

– Organisation’s identity– Organisation’s public key– Digital Signature of certification authority

• The certificate is validated and then the public key and the private key held at the server is used to– Authenticate the server– Help establish encryption keys between client and

server

Limitations of https

• Only secures data transmission over the Internet, so is just secure transport

• Does not– Secure data in database– Provide user authentication– Provide security for relayed messages

(example for email security)

Database Encryption options• Database encryption functions (backend)

– e.g. MySQL AES_Encrypt– Drawbacks… technology specific, change dbase needs re-write– Puts extra load on database server– Needs secure connections between middleware and backend

• Middleware encryption (application layer)– Easier to port– Easier to integrate hardware support for encryption

• Client side – True end to end security– Relies on client side key management which is hard to keep

secure, v.complex– Clients have to be attacked 1 by 1 makes large scale attacks

difficult

Authentication and authorization• Authentication

– Who are you?

• Authorization– What can you do?

Authentication

• Challenge handshake response– Server sends long random number as

challenge (nonce)– Client responds with nonce encrypted

with private key

• Commonly used in– ISP access as part of PPP

Authorization

• Run all code through standard API• For each user/table have

– Read/write/insert/delete permissions

• Can be done at– MySQL level (poor granularity, need

different MySQL creds. For each user role)

– Application layer (better flexibility, more coding)

Security policy

• Gives the organization– A fixed set of rules to secure

• Passwords, data base access• Backups and data integrity

• Policy– Can be analysed and amended to look

for weaknesses– Guards against adhoc security

decisions

Security policy examples• Password strength• Procedures for password retrieval (email, post or

phone)• Media

– Document, USB stick shredding and destruction– Removal from site– Bringing on to site

• Backups– Encryption

• Firewall – Configuration policy

Bell–LaPadula security model• Each user is given security clearance (top secret,

secret, public)– All documents they develop are automatically set at that

clearance

• Each user can– Must not read any document above their clearance (no

read up)– Must not write any document below their clearance (no

write down)

• Trusted subjects– Are allowed to write down, to lower the clearance

of secured information

Summary

• To secure your system you need to– Secure the network transport– Secure all persistent data– Have a proper security policy– Protect against physical failure