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Preparing for Cryptographic Attacks
Cryptography Standards and Protocols
Key management and Key life cycle
Introduction of PKI
Trust models
PKI management
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Specific attacks on cryptographic systems can be divided
into three types:
 Attacking the key
 Attacking the algorithm
 Intercepting the transmission
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A birthday attack is an example of an attack targeted at the
key.
It isn’t an attack on the algorithm itself, just on the results.
If 25 people are in a room, there is some probability that
two of those people will have the same birthday.
The probability increases as additional people enter the
room.
It’s important to remember that probability doesn’t mean
that something will occur, only that it’s more likely to occur.
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Based on the premise that many common passwords are
used by lots of people.
If the key length is short, the resulting hash value will be
easier to guess.
Make sure your users use passwords and encryption keys
that are hard to guess. You may even want to consider a
random-password generating system.
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Mathematical attacks can be focused on the encryption
algorithm itself, the key mechanism, or any potential area
of weakness in the algorithm.
These attacks use mathematical modeling and statistical
analysis to determine how the system operates.
These types of attacks depend on intercepting large
amounts of data and methodically attempting to decrypt
the messages using one of the methods previously
described.
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Preparing for Cryptographic Attacks
Cryptography Standards and Protocols
Key management and Key life cycle
Introduction of PKI
Trust models
PKI management
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Public domain cryptography refers to the standards and
protocols that emerge from individual or corporate efforts
and are released to the general public for use
PGP and RSA are two common public cryptographic
initiatives.
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Developed by Phil Zimmerman
In 1991, he published the encryption system on the
Internet
PGP has become a de facto standard for e-mail
encryption.
PGP uses both symmetrical and asymmetrical encryption
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Rivest, Shamir, and Adleman
RSA has been very involved in developing Public-Key
Cryptography Standards (PKCS), and it maintains a list of
standards for PKCS
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Public-Key Cryptography Standards (PKCS) is a set of
voluntary standards created by RSA and security leaders.
Early members of this group included Apple, Microsoft,
DEC (now HP), Lotus, Sun, and MIT.
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The X.509 standard defines
 Certificate formats and fields for public keys
 The procedures that should be used to distribute public
keys.
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The X.509 version 2 certificate is still used as the primary
method of issuing Certificate Revocation List (CRL)
certificates.
The current version of X.509 certificates is version 3, and it
comes in two basic types:
 End-entity certificate
 The CA certificate is issued by one CA to another CA. The
second CA can, in turn, issue certificates to an end entity.
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X.509 certificate standard
 X.509 Version Number
 Subject
 Public Key!!!
 Issuer (CA that vouched for you)
 Serial Number
 Validity dates
 Certificate Usage
 Signature Algorithm
 Extensions
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Secure Sockets Layer (SSL):
 Establish a secure communication connection between two
TCP-based machines
 Uses the handshake method of establishing a session
 The number of steps is always between four and nine,
inclusive, based on who is doing the documentation
 http://support.microsoft.com:80/support/kb/articles/Q25
7/5/91.ASP
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Secure Sockets Layer (SSL):
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Transport Layer Security (TLS):
 Expands upon SSL
 TLS may replace SSL in the near future
 The TLS protocol is also referred to as SSL 3.1, but despite
its name, it doesn’t interoperate with SSL
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A messaging protocol used between PKI entities.
XML Key Management Specification (XKMS) is designed
to allow XML-based programs access to PKI services
CMP is expected to be an area of high growth as PKI
usage grows.
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S/MIME
A standard used for encrypting e-mail
Uses the PKCS #7 standard (Cryptographic Message
Syntax Standard) and is the most widely supported
standard used to secure e-mail communications.
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Provides encryption for credit card numbers that can be
transmitted over the Internet
Developed by Visa and MasterCard
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A tunneling protocol originally used on Unix systems
Now available for both Unix and Windows
SSH connections are established in two phases:
 The first phase is a secure channel to negotiate the channel
connection
 The second phase is a secure channel used to establish the
connection
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Hypertext Transport Protocol Secure (HTTPS) is the
secure version of HTTP
Uses SSL to secure the channel between the client and
server
Uses port 443 by default.
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Secure Hypertext Transport Protocol (S-HTTP) is HTTP
with message security (added by using RSA or a digital
certificate).
Whereas HTTPS creates a secure channel, S-HTTP
creates a secure message.
S-HTTP can use multiple protocols and mechanisms to
protect the message.
It also provides data integrity and authentication.
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Provides authentication and encryption across the Internet
Becoming a standard for encrypting virtual private network
(VPN) channels
One of the primary uses of IPSec is to create VPNs.
IPSec, in conjunction with Layer 2 Tunneling Protocol
(L2TP) or Layer 2 Forwarding (L2F), creates packets that
are difficult to read if intercepted by a third party.
IPSec works at layer 3 of the OSI model.
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Protocols used by IPSec at the bottom layer are
 Authentication Header (AH)
 Encapsulating Security Payload (ESP).
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Both can operate in either the transport or tunnel mode.
Port 50 is used for ESP
Port 51 is used for AH.
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Point-to-Point Tunneling Protocol (PPTP)
 Encapsulation in a single point-to-point environment.
 PPTP encapsulates and encrypts Point-to-Point Protocol
(PPP) packets
 PPTP uses port 1723 and TCP for connections.
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Layer 2 Forwarding (L2F)
 Created by Cisco
 Creating tunnels primarily for dial-up connections.
 Shouldn’t be used over WANs.
 Provides authentication, but doesn’t provide encryption.
 L2F uses port 1701 and TCP for connections.
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Layer 2 Tunneling Protocol (L2TP)
L2TP is a hybrid of PPTP and L2F
Primarily a point-to-point protocol
Supports multiple network protocols so it can be used as a
bridge across many types of systems
 IPX, SNA, and IP
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L2TP doesn’t provide data security: The information isn’t
encrypted. (Security can be provided by protocols such as
IPSec.)
L2TP uses port 1701 and UDP for connections.
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Provides an encrypted and authenticated connection
between a wireless client and a server
WTLS is similar in function to TLS,
 Uses a lower bandwidth
 Less processing power
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It’s used to support wireless devices
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Preparing for Cryptographic Attacks
Cryptography Standards and Protocols
Key management and Key life cycle
Introduction of PKI
Trust models
PKI management
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Centralized versus decentralized key generation
Key storage and distribution
Key escrow
Key expiration
Key revocation
Key suspension
Key recovery and archival
Key renewal
Key destruction
Key usage
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Key length and the method used to create the key also
affect the security of the system in use.
The security of a key is measured by how difficult it is to
break the key
According to RSA, it would take 3 million years and a $10
million budget to break a key with a key length of 1,024
bits
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Centralized Key Generation
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Decentralized Key Generation
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Usually accomplished using a Key Distribution Center
(KDC), as used in Kerberos, or by using a Key Exchange
Algorithm (KEA), as in the case of PKI.
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Usually accomplished using a Key Distribution Center
(KDC), as used in Kerberos, or by using a Key Exchange
Algorithm (KEA), as in the case of PKI.
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A key escrow system stores keys for the purpose of law
enforcement access
Key escrow systems can also be a part of the key
recovery process
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A key expiration date identifies when a key is no longer
valid.
Normally, a key is date stamped; this means that it
becomes unusable after a specified date.
A new key or certificate is normally issued before the
expiration date.
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Keys are revoked when
 they are compromised
 the authentication process has malfunctioned
 people are transferred
 other security risks occur.
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Revoking a key keeps it from being misused.
A revoked key must be assumed to be invalid or possibly
compromised.
PKI use a CRL to perform a check on the status of
revoked keys
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A key suspension is a temporary situation.
If an employee were to take a leave of absence, the
employee’s key could be suspended until they came back
to work.
In a PKI system, a CRL would be checked to determine
the status of a certificate
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Key archiving
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Key recovery
 Current keys
 Previous Keys
 Archived keys
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Key renewal defines the process of enabling a key for use
after its scheduled expiration date.
A key would be reissued for a certain time in this situation.
This process is called a key rollover
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Key destruction is the process of destroying keys that
have become invalid.
Many symmetrically based encryption systems use a
dedicated device to carry the key for the encryption.
This key would be physically delivered to the site using the
encryption system.
Old keys would be recovered and destroyed.
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Preparing for Cryptographic Attacks
Cryptography Standards and Protocols
Key management and Key life cycle
Introduction of PKI
Trust models
PKI management
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Wouldn’t it be nice if some one we could distribute public
keys AND be assured that the public key we received was
the actual public key of the person we expect to talk to?
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PKIs are generally concerned with ensuring and
managing identity trust, specifically using “digital
certificates”.
Provides all the components necessary for users to be
able to communicate securely in a managed method.
Includes hardware, software, policies, services, algorithms
and protocols.
Enables C, and I of the CIA triad
Enables non-repudiation
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Confidentiality
 Confidentiality is the term used to prevent the disclosure of
information to unauthorized individuals or systems.
 Confidentiality is necessary (but not sufficient) for maintaining the
privacy of the people whose personal information a system holds.
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Integrity
 In information security, integrity means that data cannot be
modified without authorization.
 This is not the same thing as referential integrity in databases.
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Authenticity
 In computing, e-Business and information security it is necessary
to ensure that the data, transactions, communications or
documents (electronic or physical) are genuine. It is also important
for authenticity to validate that both parties involved are who they
claim they are.
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In a PKI you are given a digital certificate, which contains
your identity, and a key (public key) people can use to
encrypt data securely to you OR verify items that you have
digitally signed!
However we must have some way of ensuring that the
digital certificate has not been “faked” so we have a entity
called a Certificate Authority (CA) that digitally signs
your digital certificate, proving that the digital certificate is
really yours!
 It is important that users trust the CA, otherwise there is no
purpose!!! The entire PKI structure relies upon the fact that
the CA can be trusted! If the CA is comprimised the whole
PKI is useless.
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CAs are computer technology entities that issue/sign your
digital certificates, however they rely on an entity to
actually do a “background” check on you to prove you
really are you you say you are before the CA will “vouch”
for you. This “background” check entity is called an
Registration Authority (RA)
RA would take identifying information that proves I am who
I say I am such as
 Drivers license
 Passport
 Birth Certificate
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Once my identity is verified the RA will tell the CA to issue
and sign a digital certificate for me
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Once a digital certificate has been created and signed,
they are stored in a “Certificate repository” which can be
queried by users and applications in a PKI when someone
wants to communicate with a user.
These repositories are usually LDAP compliant
databases.
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Firefox – https://www.redhat.com
Click on the yellow lock at the bottom
In the pop-up click on “view certificate”
What version is it?
What’s the “Common Name”
Who is the Issuing Certificate Authority
When does the Certificate Expire
Why would a certificate expire?
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Now click on the details tab
What is this “Certificate Hierarchy” stuff?
Who Signed the cert for www.redhat.com
Who signed the cert for that CA?
This “vouching” for CAs is called a “certificate chain”
If someone signed for someone else… who signed for
them? When does this end? Let’s explore this…
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PKI implementations are usually a hierarchy, where one
CA signs another CAs certificate.
Parent - Child relationship
Top parent is called a root CA
All others are called subordinate CA
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Every CA should have a Certification Practice Statement
which outlines
 How the RA verifies identities
 How the Certificates are transferred
 How keys are secured
 What data is in a Digital Certificate
 How revocations are handled… etc
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Before using a 3rd party CA, you should understand and
be comfortable with CPS and the security controls they
use. If the CA does not handle things securely… there is
no point in using them.
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There are 3 main types of certificates
 End-entity certificates
Given to end users or servers or applications
 CA certificates
Given to CAs, can be signed by another CA or “self signed”
What does it mean to be self signed, what does it imply?
 Cross-certification certificates
When two companies want to trust each other, their root CAs
may issue a certificate to the root CAs for each other, allowing
a “peer to peer” trust model for CAs and allowing users in one
organization to trust users in another.
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A Certificate Practice Statement (CPS) is a detailed
statement the CA uses to issue certificates and implement
its policies of the CA.
If a CA is unwilling to provide this information to a user, the
CA itself may be untrustworthy, and the trustworthiness of
that CA’s users should be questioned.
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Some PKIs use multiple certificates, and as such multiple
public/private key pairs.
 One for digitally signing data
 One for encrypting data
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Why would we want to have two different keys? (Hint.
think key storage and non-repudiation)
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Preparing for Cryptographic Attacks
Cryptography Standards and Protocols
Key management and Key life cycle
Introduction of PKI
Trust models
PKI management
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Four main types of trust models are used with PKI:
 Hierarchical
 Bridge
 Mesh
 Hybrid
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PKI was designed to allow all of these trust models to be
created. They can be fairly granular from a control
perspective.
Granularity refers to the ability to manage individual
resources in the CA network.
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A root CA at the top provides all the information.
The intermediate CAs are next in the hierarchy, and they
only trust information provided by the root CA
The root CA also trusts intermediate CAs that are in their
level in the hierarchy and none that aren’t.
This arrangement allows a high level of control at all levels
of the hierarchical tree.
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Web of Trust is a PKI with no central hierarchy, it’s literally
a web. It’s like 6 degrees of separation.
 Bob vouches for Andy
 Sarah trusts Bob, so she trusts the identity of Andy
 Sara vouches for Bob
 Steve trusts Sara, therefore he trusts the identities of Bob,
and Andy via Sarah…
 PGP uses web of trust
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Verifing the signature of ClamAV
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Preparing for Cryptographic Attacks
Cryptography Standards and Protocols
Key management and Key life cycle
Introduction of PKI
Trust models
PKI management
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Certificates have a lifetime after which they expire. Why?
When a certificate expires you have to renew it. You don’t
have to go through the RA again. You just have to be able
to sign a message with your old private key.
When renewing you can use the old public/private key pair
or generate a new key pair. What is the advantage of
generating a new pair?
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Certificate revocation is the process of revoking a
certificate before it expires
Why?
 It was stolen
 An employee moved to a new company
 Someone has had their access revoked
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A certificate revocation is handled either through a
Certificate Revocation List (CRL) or by using the Online
Certificate Status Protocol (OCSP).
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Certificate Revocation List (CRL)
 Certificate serial number that have been revoked
 Reason for revocation
 Date of revocation
 The CRL is digitally signed by the CA
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Client software must check the CRL before trusting a
digital certificate
Once a certificate is revoked, it cannot be “un-revoked”
A certificate could be suspended, (or put on hold) this also
goes on the CRL, however a special “reason” of
suspended is used.
Suspended certificates MAY be un-suspended
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Online Certificate Status Protocol (OCSP)
 A client server model
 A client program actually queries a server to see if
someone’s certificate is valid.
 This way the client does not need to know how to find the
CRL for the given certificate Authority and doesn’t have to
actually search through the CRL.