Encryption Schemes:
-
AES (Advanced Encryption Standard) is more secure than
DES or 3DES.
-
AES is a symmetric block cipher that can encrypt (encipher)
or decrypt (decipher) information
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AES is based on Rijndael algorithm
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PGP (Pretty Good Privacy) can use Diffie-Hellman or RSA
algorithms, but not AES or DES.
PGP (Pretty Good Privacy) : PGP certificates
differ from X.509 certificates in two ways:
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PGP certificates are issued (signed) by normal people
while the X.509 certificates must be issued by a professional
CA, and
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PGP implements a security fault tolerance mechanism,
called the Web of Trust. Here an individual is allowed to
sign and issue certificates to people they know
6.3 Explain the core concepts of
public key infrastructure
Three basic types of distributed trust models are:
Hierarchical trust model : Here one root
CA and one or more subordinate CAs will be present. The subordinate
CAs provide redundancy and load balancing. The root CA is usually
off-line. Here even if a subordinate CA is compromised, the
root CA can revoke the subordinate CA, thus providing redundancy.
Web of Trust : This is also called cross-certification
model. Here CAs form peer-to-peer relationship. This model is
difficult to manage as the number of CAs grow larger. This kind
of trust relationship may happen when different divisions of
a company has different CAs, and need to work together. Here
CAs must trust one another.
Bridge CA architecture : Bridge CA overcomes
the complexity involved with Web of Trust model. Here Bridge
CA act as the central co-ordinate point. All other CAs (known
as principals) must trust only the Bridge CA.
If the CA's
private key is compromised, certificates' private key is compromised,
certificates issued by that CA issued by that CA are affected.
This will lead to issuance of new certificates to all users,
and registration. These problems can be overcome by use of a
distributed trust model, in which multiple CAs are involved.
In public key infrastructure
-
A key is required to encode/decode a message, and the
security of a message depends on the security of key.
-
A cipher text is the encoded message, and
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A certificate is a digitally signed document by a trusted
authority.
Certificate Revocation List (CRL) : A certificate
revocation list (CRL) is a list of certificates, which have
been revoked, and are no longer valid. A digital certificate
is a credential issued by a trusted authority that binds you
(and individual or an organization) to an identity that can
be recognized and verified electronically by other agencies.
Locally issued digital certificates are valid only within an
organizations network (like intranet). Therefore, any secure
pages or digital signatures containing local registration will
not work on the Internet.
6.4 Implement PKI, certificate management
and associated components
Public Key Infrastructure (PKI) : It is
a framework for all of the entities involved in digital certificates-including
hardware, software, people, policies, and procedures to create,
store, distribute, and revoke digital certificates. PKI is essentially
digital certificate management.
Recovery agent : It is responsible for recovering
lost or damaged digital certificates
Certificate Revocation List (CRL) : A certificate
revocation list (CRL) is a list of certificates, which have
been revoked, and are no longer valid. A digital certificate
is a credential issued by a trusted authority that binds you
(and individual or an organization) to an identity that can
be recognized and verified electronically by other agencies.
Locally issued digital certificates are valid only within an
organizations network (like intranet). Therefore, any secure
pages or digital signatures containing local registration will
not work on the Internet.
Key escrow : Key escrow refers to a process
in which keys are managed by a third party, such as a trusted
CA. In key escrow, the private key is split and each half is
encrypted. The two halves are sent to the third party, which
stores each half in a separate location. A user can then retrieve
the two halves, combine them, and use this new copy of the private
key for decryption. Key escrow relieves the end user from the
worry of losing her private key. The drawback to this system
is that after the user has retrieved the two halves of the key
and combined them to create a copy of the key, that copy of
the key can be vulnerable to attacks.
Trust Models : A trust model refers to the
type of trusting relationship that can exist between individuals
or entities. In one type of trust model, direct trust, a relationship
exists between two individuals because one person knows the
other person.
A third-party trust refers to a situation in which two individuals
trust each other because each trusts a third party.
There are essentially three PKI trust models that use a CA.
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The hierarchical trust model assigns a single hierarchy
with one master CA called the root. This root signs all
digital certificate authorities with a single key.
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Distributed trust model has multiple CAs that sign digital
certificates. This essentially eliminates the limitations
of a hierarchical trust model; the loss of a CA's private
key would compromise only those digital certificates for
which it had signed, the workload of verifying and signing
digital certificates can be distributed, and there is no
competition regarding who can perform the functions of a
CA
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Bridge Trust Model The bridge trust model is similar
to the distributed trust model in that there is no single
CA that signs digital certificates. However, with the bridge
trust model there is one CA that acts as a "facilitator"
to interconnect all other Cas. This facilitator CA does
not issue digital certificates; instead, it acts as the
hub between hierarchical trust models and distributed trust
models.
