Public Key Distribution

A Presentation on
Public Key Distribution

Topics to be covered by
 Public key cryptography
 Public key announcement
 Trusted center and Controlled trusted center
 Certification Authority
 X.509
 Public key Infrastructures

Public Key Distribution
 Diffie - Hellman (1976) proposed the “public file”
concept
 Universally accessible
 No unauthorized modification

Public Key Cryptography
 In public key cryptography, everyone has access to
everyone’s public key.
 Public key are available to everyone.

Ways of Public Key Distribution:
 Public Announcement
 Trusted center
 Controlled trusted center
 Certification Authority
 Public key Infrastructures

Public Announcement
 Each person /user can announce or broadcast their public key to
the world.
 No authenticity : It is not a secure way.

Trusted Center
 It has a directory and the directory can be publicly
advertised by the trusted center
 User can keep the private key, and deliver the
public key for insertion into the directory.
 The center can also respond to any inquiry about a
public key

Controlled Trusted Center
 Controls are added on the distribution of the
public keys to achieve a higher level of security.
 The public key announcement can include a
timestamp.
 Trusted center can be signed by an authority to
prevent interception and modification of the
response.

Fig: Controlled trusted center

Certification Authority
 Certification Authority(CA) which is a federal or
state organization that binds a public key to an entity
and issues a certificate.
 CA must verify the entity requesting a new
certificate.
 CA’s own certificate is signed by a higher-level CA.
Root CA’s certificate is self-signed and its name is
“well- known”.

X.509
 CA has solved the problem of public –key fraud
but it has created a side-effect. To remove this
side-effect, ITU has designed a protocol called
X.509.
 X.509 uses a well known protocol called ASN.1.

Public-Key Infrastructures (PKI)
 A public key infrastructures a set of roles, policies
and procedures needed to create, manage,
distribute, use, store digital certificates and
manage public-key encryption.
 It is a hierarchical structure.

Summary:
 Distribution of public keys.
 X.509 authentication.
 A hierarchical system (PKI) to answer queries
about key certification.

Public Key Distribution

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Public Key Distribution