Public-key InfrastructurePublic-key Infrastructure

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CryptosystemsCryptosystems

Cryptosystems• Symmetric

• Asymmetric (public-key)

RSA• Public key: n=3233, e=17

• Private key: d=2753

• Let m=65Encryption: c = 6517 (mod 3233) = 2790Decryption: m = 27902753 (mod 3233) = 65

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Public-key InfrastructurePublic-key Infrastructure

Each person has his own public-private key pairPKI is• a set of hardware, software, people, policies, and procedures

• to create, manage, distribute, use, store, and revoke digital certificates

Then, we can do• Encryption

• Authentication

• Digital signature

• Bootstrapping secure communication protocols

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In God We TrustIn God We Trust

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Certificate – (1)Certificate – (1)

Alice:(1) Generate

Apub, Apriv

CA X:(3) Generate

Sig(Xpriv, Alice, Apub, T)

(2) Alice, Apub, ID proof

(4) Sig(Xpriv, Alice, Apub, T)

CertA,X=[Alice, Apub, Sig(Xpriv, Alice, Apub, T)]

NoteNote: CA does not know Apriv

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Certificate – (2)Certificate – (2)

Also called• Network Identity

A certificate is issued by a CA XA certificate of a user A consists:

• The name of the issuer CA X

• His/her public key Apub

• The signature Sig(Xpriv, A, Apub, T) by the CA X

• The expiration date

• ApplicationsEncryption / Signature

• …

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Root CARoot CA

Root CA (最高層認證中心 )• In Micro$oft:「根目錄授權憑證」• Root CA do not sign the certificates for users

Authorize CA to sign the certificates for users, instead.

• Root CA signs for itself. It is in the sky.

• To trust Root CA Install the certificate of Root CA via the secure channel

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Certificate and CACertificate and CA

Certificate Authority (CA)• “憑證授權” in Windows CHT version

• In X.509, it is itself a certificateThe data of CATo sign certificates for others

• Each CA contains a signature of Root CA.

To verify the validity of a certificate, check• the signature of Root CA in the certificate of CA

• the signature of CA in this certificate

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The Cost of CertificateThe Cost of Certificate

Tree structure of CA

Cost of certificate• VeriSign : NT $18,000 / per year / per host

• Myself : NT $0

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Secure communication protocolsSecure communication protocols

Security of transmitting DATA• Transmit session key first

Public-key cryptosystem

• Transmit DATA by session keySymmetric-key cryptosystem

Reference: http://www.imacat.idv.tw/tech/sslcerts.html

SSL & TLSSSL & TLS

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SSL/TLSSSL/TLS

SSL/TLS• Provide communication security over the Internet

Prevent eavesdropping and tampering

• Encrypt the segments over Transport Layer

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History – (1)History – (1)

SSL – developed by Netscape• SSL 1.0: never publicly released

• SSL 2.0: released in 1995A number of security flaws

• SSL 3.0: released in 1996A complete redesignNewer versions of SSL/TLS are based on SSL 3.0

TLS – IETF RFC• TLS 1.0(SSL 3.1): RFC 2246 in 1999.

Backward compatible to SSL 3.0CBC vulnerability discovered in 2002

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History – (2)History – (2)

TLS – IETF RFC• TLS 1.1(SSL 3.2): RFC 4346 in 2006

Prevent CBC attacks

• TLS 1.2(SSL 3.3): RFC 5246 in 2008Enhance security strength Introduce new cryptographic algorithms

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SSL/TLS NegotiationSSL/TLS Negotiation

(C) Request a secure connection, and present a list of supported ciphers and hash functions

(S) Select common cipher and hash function, and send back with server’s digital certificate

(C) Confirm the validity of the certificate(C) Encrypt a random number with server’s public

key, and send it to server(C/S) Generate session key(s) from the random

number

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SSL/TLS ApplicationsSSL/TLS Applications

Implemented on top of Transport Layer prototols• TCP

• UDP(DTLS)

Protect application-specific protocols• HTTP, FTP, SMTP, NNTP, …

• VPN(OpenVPN), SIP, VoIP

Activate SSL/TLS connection• Use a different port number (https/433, smtps/465)

• Use a protocol specific mechanism (STARTTLS)

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Support for Named-based Virtual ServersSupport for Named-based Virtual Servers

All virtual servers belong to the same domain• Wildcard certificate

• Add all virtual host names in subjectAltName

• DisadvantagesCertificate needs reissuing whenever adding a new virtual serverCannot support named-based virtual hosts for web service

Server Name Indication (SNI)• RFC 4366• http://wiki.apache.org/httpd/NameBasedSSLVHostsWithSNI

• The client browser must also support SNI

OpenSSL in FreeBSDOpenSSL in FreeBSD

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OpenSSLOpenSSL

http://www.openssl.org/In system

• /usr/src/crypto/openssl

In ports• security/openssl

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ports/Mk/bsd.openssl.mkports/Mk/bsd.openssl.mk

# WITH_OPENSSL_BASE=yes - Use the version in the base system.

# WITH_OPENSSL_PORT=yes - Use the port, even if base is up to date

# WITH_OPENSSL_BETA=yes - Use a snapshot of recent openssl

# WITH_OPENSSL_STABLE=yes - Use an older openssl version

……

# if no preference was set, check for an installed base version

# but give an installed port preference over it.

.if !defined(WITH_OPENSSL_BASE) && \

!defined(WITH_OPENSSL_BETA) && \

!defined(WITH_OPENSSL_PORT) && \

!defined(WITH_OPENSSL_STABLE) && \

!exists(${DESTDIR}/${LOCALBASE}/lib/libcrypto.so) && \

exists(${DESTDIR}/usr/include/openssl/opensslv.h)

WITH_OPENSSL_BASE=yes

.endif

Example: Apache SSL settingsExample: Apache SSL settings

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FlowFlow

Flow• Generate random seed

• Generate RootCAGenerate private key of RootCAFill the Request of Certificate.Sign the certificate itself.

• Generate certificate of Web ServerGenerate private key of Web ServerFill the Request of certificateSign the certificate using RootCA

• Modify apache configuration restart apache

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Generate random seedGenerate random seed

Generate num pseudo-random bytes• % openssl rand -out rnd-file num

Protect the psuedo-random file• % chmod go-rwx rnd-file

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Generate private key of RootCAGenerate private key of RootCA

Generate public-private key pairs• % openssl genrsa -des3 -rand rnd-file

-out rootca-key-file num

Note: phrase are asked (something like password)

Protect the private key• % chmod go-rwx rootca-key-file

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Fill the Request of CertificateFill the Request of Certificate

Generate the request of certificate• % openssl req -new -key rootca-key-file

-out rootca-req-file

Enter pass phrase for rootca-key-file:

Country Name (2 letter code) [AU]:TWState or Province Name (full name) [Some-State]:TaiwanLocality Name (eg, city) []:HsinChuOrganization Name (eg, company) [Internet Widgits Pty Ltd]:NCTUOrganizational Unit Name (eg, section) []:CSCommon Name (eg, YOUR name) []:nasa.cs.nctu.edu.twEmail Address []:liuyh@cs.nctu.edu.tw

A challenge password []: (No need ， Enter please)An optional company name []: (Enter please)

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Sign the certificate itselfSign the certificate itself

Sign the certificate of RootCA• % openssl x509 -req -days num -sha1

-extfile path_of_openssl.cnf -extensions v3_ca -signkey rootca-key-file -in rootca-req-file -out rootca-crt-file

Delete the request file (Optional)• % rm -f rootca-req-file

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Generate private key of Web ServerGenerate private key of Web Server

Generate the public-private key pair• % openssl genrsa -out host-key-file num

Protect the private key• % chmod go-rwx host-key-file

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Fill the Request of CertificateFill the Request of Certificate

Generate the request of certificate• % openssl req -new -key host-key-file -out host-req-file

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Sign the certificate using RootCASign the certificate using RootCA

Tramsmit host-req-file to Root CASing the certificate by RootCA

• % openssl x509 -req -days num -sha1 -extfile path_of_openssl.cnf -extensions v3_ca -CA rootca-crt-file -CAkey rootca-key-file -CAserial rootca-srl-file -CAcreateserial -in host-req-file -out host-crt-file

Remove the request file in RootCA and Web ServerTransmit host-crt-file back to Web Server

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Certificate AuthorityCertificate Authority

• Include etc/apache22/extra/httpd-ssl.conf#### SSL Virtual Host Context##<VirtualHost _default_:443># General setup for the virtual hostDocumentRoot /home/wwwadm/data<Directory “/home/wwwadm/data"> Options Indexes FollowSymLinks AllowOverride All Order allow,deny Allow from all</Directory>ServerName nasa.cs.nctu.edu.tw:443ServerAdmin liuyh@nasa.cs.nctu.edu.twErrorLog /var/log/httpd/nasa.cs-error.logCustomLog /var/log/httpd/nasa.cs-access.log common

SSLEngine onSSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:!SSLv2:+EXP:+eNULLSSLCertificateFile /etc/ssl/nasa/nasa.crt.pemSSLCertificateKeyFile /etc/ssl/nasa/private/nasa.key.pem

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View the content of Certificate – (1)View the content of Certificate – (1)

% vim host-crt-file

-----BEGIN CERTIFICATE-----MIIE0DCCA7igAwIBAgIJAL5UBzbv+hl1MA0GCSqGSIb3DQEBBQUAMIGgMQswCQYDVQQGEwJUVzEPMA0GA1UECBMGVGFpd2FuMRAwDgYDVQQHEwdIc2luQ2h1MQ0wCwYDVQQKEwROQ1RVMQswCQYDVQQLEwJBTTEiMCAGA1UEAxMZZXZpbGJpZzUubWF0aC5u……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-----END CERTIFICATE-----

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View the content of Certificate – (2)View the content of Certificate – (2)

% openssl x509 -text -in host-crt-file

Certificate: Data: ...... Signature Algorithm: sha1WithRSAEncryption Issuer: C=TW, ST=Taiwan, L=HsinChu, O=NCTU, OU=CS, CN=../emailAddress=.. Validity ... Subject: C=TW, ST=Taiwan, L=HsinChu, O=NCTU, OU=CS, CN=../emailAddress=. Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (2048 bit) Modulus (2048 bit): ...... Exponent: 65537 (0x10001) X509v3 extensions: ...... Signature Algorithm: sha1WithRSAEncryption 8b:90:d6:da:f4:b4:a9:09:33:a1:ed:6b:37:87:5f:16:48:a4: ...... e0:b2:25:a5-----BEGIN CERTIFICATE-----MIIE0DCCA7igAwIBAgIJAL5UBzbv+hl1MA0GCSqGSIb3DQEBBQUAMIGgMQswCQYD......ELgGQXpVrFPSzZG0PyAr5rxtOI8E7yl7jl2pu7yXk9jgsiWl-----END CERTIFICATE-----

AppendixAppendix

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PGP – Pretty Good PrivacyPGP – Pretty Good Privacy

security/gnupg• GNU’s Privacy Guard

Public-key system• Encryption

• Signature

• Use with mutthttp://www.gnupg.org/documentation/howtos.html#Mutt-GnuP

Ghttp://wiki.mutt.org/?MuttGuide/UseGPG

Ref: http://security.nknu.edu.tw/textbook/chap15.pdf