cs 590/490 network security

CS 590/490 Network Security

Digital Certificate, CA (Certificate AuthorityRoot CA and chain of CA trust

Department of Computer ScienceSouthern Illinois University Edwardsville

Fall, 2007

Dr. Hiroshi FujinokiE-mail: [email protected]

Certificate/001

CS 590/490 Network SecurityDigital Certificate

• A set of information that securely identifies a host in a network

What is (Digital) Certificate?

• Certificate is a text (ASCII-coded) document file

• When you talk to a network host, you use a certificate of the host to confirm the identity of the host you talked to.

Your Host Another Host

You talked to this host“Are you there?”

Another host replies

“I’m here.”

• Masquerading• M-in-M

Certificateof this hostI see. It’s

you!

Certificate/002


• A set of information that securely identifies a host in a network

What is (Digital) Certificate?

• Certificate is a text (ASCII-coded) document file

• When you talk to a network host, you use a certificate of the host to confirm the identity of the host you talked to.

Your Host Another Host

You talked to this host“Are you there?”

Another host replies

“I’m here.”

• Masquerading• M-in-M

Certificateof this host

Certificateof your host

I see. It’syou!

I see. It’syou!

Certificate/003


secretkey

publickey

P1

publickey

serveryour host

S1

P1

Digital Certificate

• Expected procedure in the asymmetric public-key cryptography

Certificate/004


P1

serveryour host

S1

P1

S2

P2

• IP-Spoofing

• M-in-M

P2

You got a wrongpublic key

You believe you got thepublic key of this server

Digital Certificate

• What can happen to the asymmetric public-key cryptography

Certificate/005

Router

The actual format of a certificate is defined by ITUT X.509 Certificate Format


- Your name (or name of your organization)

What information is in a certificate?

- Network ID (IP address in the Internet) - Your e-mail address and URL (for your web site)

- Geographical location of your organization (or your host)

• Your public key

• Information about the CA who issued this certificate

• Information about you (or your organization)

• Digital signature by the CA who issued this certificate

Certificate/006

CertificateAuthority

CS 590/490 Network SecurityMerchant’shost (server)

Client’shost (browser)

CA creates a certificate for this merchant

S1

P1

Digital Certificate

S2

P2P2

HASH

CA encrypts this certificate using its PRIVATE key

Encrypt

CA issues (transmits) this certificates to the merchant

The merchant sends its certificate to you

HASH

Compare

P2

P1

Decrypt

(hash) digestof the server’scertificate

A client contacts this merchant for business

A

Digital Signatureof this CA

Extracted DigitalSignature of the CA

Re-Constructed DigitalSignature of the CA

Initiate the hybridencryption with

this server

Request for issuing a certificate for this merchant (must pay $$$)

P2P2P2

Certificate/007

Digital Certificate

Certificate: Data: Version: 3 (0x2) Serial Number: 7 (0x7) Signature Algorithm: md5WithRSAEncryption Issuer: C=JP, ST=Aichi-Ken, L=Nagoya, O=NIT, OU=TEST depth, CN=ailab second cert/[email protected] Validity Not Before: Sep 22 05:31:34 1998 GMT Not After : Sep 22 05:31:34 1999 GMT Subject: C=JP, ST=Aichi-Ken, O=nitech.ac.jp, OU=ailab, CN=test7.second/Email=7.second@mars Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (512 bit) Modulus (512 bit): 00:bd:06:2b:bc:35:55:0b:d7:c4:d6:09:a5:b7:5c: 57:2a:0a:e5:7d:8c:2e:ed:8f:df:c3:ca:37:63:bb: ae:b1:ac:94:54:40:da:7b:71:16:ff:e7:68:5e:00: 49:54:43:70:b7:a1:35:0a:e3:53:4d:4c:86:d2:90: e8:18:39:55:2b Exponent: 65537 (0x10001) X509v3 extensions: Netscape CA Revocation URL: .#http://www.cryptsoft.com/ca-crl.pem Netscape Comment: ..This is a comment Netscape Cert Type: ...@ Signature Algorithm: md5WithRSAEncryption e7:04:71:f0:9a:d5:da:5e:50:c5:13:20:97:8c:ff:69:fa:18: 2a:9d:b8:75:22:d7:f4:d5:87:4a:7c:c4:3a:7f:b7:72:0f:a3: f3:f4:82:60:8e:e0:f8:10:36:9f:d9:a8:c3:b2:83:50:3d:dd: 5c:b8:29:b7:79:49:03:13:6d:83

Declare the beginning of a certificate

ITU-T X.509 Version 3 certificate format

Unique Certificate Serial #

Which hash and encryption are used for the signature

Name of the CA who issued this certificate

Name of the server this certificate is issued to

This is the public-key information for the server!

This is the digital signature signedby this CA (not by this server)

Encryption algorithm you need to usewhen you talk to this server


Certificate/008


CS 590/490 Network SecurityMerchant’shost (server)


S1

P1

S2

P2

CA issues (transmits) this certificates to the merchant

P1


P2P2P2

How can you be sure thatthis CA is a legitimate CA?

When (or how) did you getthe public-key of this CA?

Digital Certificate

If you are going to getthe public-key throughthe network, how you

are sure this key is fromthe CA?

Certificate/009



Merchant’shost (server)

S2

P2


P2P2P2

Digital Certificate

This is the certificatefor this merchant

Certificate forthis CA

CA’s use certificate to issue certificate to merchant

• Merchants confirm identify of the CA’s using the CA’s certificate when merchants request the CA’s to issue the merchant’s certificate!

Certificate/010




S2

P2

Certificate forthis CA Request for the certificate issued

to this CA

This CA sends its certificate to this merchant

P2P2P2


HASH

CompareDecrypt



P

We need the publickey for this decryption

S

P

Digital Certificate

You can (should) not getthe public-key from this CA

Certificate/011




S1

P1

S2

P2

Request for the certificate issued

to this CA

This CA sends its certificate to this merchant

P2P2P2


HASH

CompareDecrypt



AnotherCertificateAuthority

S3

P3

P3

P3

How can this merchantbe sure that P3 is from Y?

X

Y




CA X requests Y to issue a certificate for X!

Certificate forthis CA

Certificate/012

CertificateAuthorityCertificateAuthorityCertificateAuthority

R




Root CA

The CA who does not have the parent CA

Digital Certificate

(a) Your browser must have the pre-installed certificate of the root CA

(b) If your browser does not have the certificate of the root CA, you must make your own decision of you accept (trust) the certificate of not

S3

P3

S3S3S3

P3P3

P3P3

P4P4P4

P4P4P4

P5P5P5

P5P5P5

S6

P6

S6S6S6

P6P6P6

P6P6P6

P6P6P6

P3P3

X


Y


Z

S5

P5

S5S5

P5P5P5

S4

P4

S4S4

P4P4P4

Certificate/013

This implies that your browser (or your local host)does not have the pre-installed certificate for this site

and you have to decide if you trust this site or not


Certificate/014


Certificate/015

Pressing this “OK” means youdecided to trust this un-recognizedcertificate (because your browser

does not have any information for it)










Root CADigital Certificate

a chainof trust

Certificate/016

a new certificatearrives

find the CA who issuedthis new certificate

Do I have thepublic-key of

this CA?

NO

decrypt the encryptedsignature of this certificate

calculate themessage digest

of this certificate

the decryptedsignature anddigest match?

YES

check the validdate of the certificate

certificateeffective?

unsuccessfulauthentication

NO

extract the public-key for a merchant(or next lower CA)

YES

YES

NO

Start hybrid encryption

• If this is the certificate for a merchant

• This is the certificate for a CA

Decrypt the digitalsignature of the lowerCA using the public-key


Certificate/017

a new certificatearrives

find the CA who issuedthis new certificate

Do I have thepublic-key of

this CA?

YES

NO


YES

NO

Is this aroot CA?

NO

Request the certificate(public-key) of this CA

accept the public-keyin the certificate

(to the next slide)


Do you trust this certificate?

Certificate/018

NO

decrypt the encryptedsignature of this certificate

calculate themessage digest

of this certificate

the decryptedsignature anddigest match?

YES

check the validdate of the certificate

certificateeffective?

NO

extract the public-key for a merchant(or next lower CA)

YES

• If this is the certificate for a merchant

Start hybrid encryption

• This is the certificate for a CA

Decrypt the digitalsignature of the lowerCA using the public-key



The onlydifference

Certificate/019


Certificate/020

“issued to” and “issued by” are all same

“issued to” and “issued by” are different

For root CA’s

For non-root CA’s




S1

P1

P1

Digital Certificate

Pi

Pk

When (or how) did you getthe public-key of this CA?

If you are going to getthe public-key throughthe network, how you

are sure this key is fromthe CA?


Y

X


Z


PN

Root CAR

Certificate of X

Merchant’s certificate

PiPi

P1P1P1

Certificate/021

Your browser shouldhave the certificate forall the major root-CA’s

Digital Certificate

Certificate Authority (CA)

Public CA

Private CA

• The CA’s approved by the government

- Root CA’s

- The certificates of many of the root CA’s are pre-installed in client browsers

• CA’s certified by a root CA

• The CA’s that do not belong to either of the two categories in the above


Certificate/022

Digital Certificate

Internet




CA’s in the Internetshould be public CA’s

gatewayrouter

edge router

Client hostswithin a local

network domain

Application server

internalmasquerader


Your localnetwork domain


Certificate/023

cs 590/490 network security

Documents

network host

network securitycertificate023

network security merchants

network securityyour

cas certificate

network security ipspoofing

certificate information

network id ip address