Transcript Lecture 9: PKI Cont

PKI INFRASTRUCTURE
Digital Signatures
In the online world, how can one be sure that a
message is actually coming from the person
whom he or she thinks sent it? Similarly, how
can one be sure that a person cannot deny that he
or she sent a particular message?
Answer is a digital signature – electronic
equivalent of a personal signature that cannot be
forged.
They are based on public keys.
Used to authenticate the identity of the sender of
a message or a document.
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Also used to ensure that the original content of
an electronic message or document are
unchanged.
Added benefits to the online world is that, they
are portable, cannot be easily repudiated or
imitated, and can be time-stamped.
Scenario showing how digital signature works:
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(1)
Message with
contract
Message Digest
(2)
Sender applies
hash function
Digital Signature
(3)
Sender encrypts using
sender’s private key
Message with
digital
signature
(4)
Sender encrypts using
recipient’s public key
Digital envelope
(5) Sender e-mails to recipient
Digital envelope
(8) Recipient
applies hash
function
(1)
Message with
contract
(6) Recipient decrypts using recipient’s
private key
Digital Signature
(7) Recipient
Decrypts using sender’s public key
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New MD
(9) Compare for
match
Original MD
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1.
2.
3.
4.
The sender creates an email message in it.
Using a special software, a mathematical
computation called a hash function is applied to the
message, resulting in a small summary of the
message converted into a string of digits called a
message digest.
The sender uses his or her private key to encrypt the
hash. This is the sender’s digital signature. No one
can replicate it because it is based on the sender’s
private key.
The sender encrypts both the original message and
the digital signature with the recipients public key.
This is the digital envelope
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5.
6.
7.
8.
The sender emails the digital envelope to the
receiver.
Upon receipt, the receiver uses his or her private key
to decrypt the contents of the digital envelope. This
produces a copy of the message and the sender’s
digital signature.
The receiver uses the sender’s public key to decrypt
the digital signature, resulting in a copy of the
original message digest.
Using the same hash function employed in step 2,
the recipient then creates a MD from the decrypted
message.
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10.
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i.
ii.
The recipient compares this digest with the original
MD.
If the two digests match, then the recipient
concludes that the message is authentic.
From this scenario the following may be concluded:
The recipient has evidence that the sender sent the
email because the sender is the only one with access
to the private key.
The recipient knows the message has not been
tampered with because if it had then the two hashed
would not have matched.
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PKI INFRASTRUCTURE
The process of creating and verifying a digital
signature, accomplishes the essential effects desired
of a signature for many legal purposes:
Signee Authentication
If a public and a private key pair is associated with
an identified signee, the digital signature cannot be
forged, unless the signee loses control of his private
key.
Message Authentication
the digital signature also identifies the signed
message. Verification reveals any tampering, since
the comparison of the hash results shows whether
the message is the same as when signed.
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Affirmative Act
Creating a digital signature requires the signee to the
signee’s private key. This act can alert the signee to
the fact that the signee is consummating with legal
consequences
Assurance
Process of creating and verifying a digital signature
provide a high level of assurance that the digital
signature is genuinely the signee’s.
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PKI INFRASTRUCTURE
Digital Certificates and Certificate Authorities
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If one has to know someone’s public key to send
that person a message, where does the public key
come from and how can one be sure of the person’s
actual identity.
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A digital certificate will verify the holder of a
public/private key is who he or she claims to be.
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3rd parties called Certificate Authorities (CAs) issue
digital certificates.
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Certificates contain things like holder’s name,
validity period, public key information and a signed
hash of the certificate data. (i.e. hashes contents of
the certificate signed with the CA’s private key)
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Certificates are used to authenticate Web sites (site
certificates), individuals (personal certificates), and
software companies (software publisher certificates)
Well-known third party CA is VeriSign
(verisign.com). Issues three classes of certificates:
Class 1 verifies that an e-mail actually comes from
the user’s address.
Class 2 checks the user’s identity against a
commercial credit database.
Class 3 requires notarized documents
MSFT offer systems that enable companies to issue
their own private, in-house certificates.
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PKI INFRASTRUCTURE
Security Protocols for epayments
1. Secure Socket Layer
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Invented by Netscape to utilize standard certificates
for authentication and data encryption to ensure
privacy or confidentiality.
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SSL is between HTTP and TCP on a Web Server.
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It is a transport layer security protocol.
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Provides simple encrypted connection between the
client’s computer and merchant’s server over the
Internet.
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Provides authentication for the merchant’s server
with its digital certificate from a CA.
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This is a secured connection allowing cyber
shoppers to send payment information to e-tailor’s
web shop.
Reason for growth of SSL is that it provides a
secured
connection
with
encrypting
and
authenticating between two computers over the
Internet.
Provides a security handshake in which a client and
server computers exchange messages.
In these messages they agree upon, the level of
security to use when exchanging digital certificates.
The clients needs not to have a digital certificate, but
the server needs to have a valid certificate.
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2.
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ii.
SSL does not keep the credit card numbers after the
transaction is complete.
SET
A messaging protocol designed by VISA and
MasterCard for securing credit card transactions
over open networks.
In the SET protocol, the transaction has three
players – customer, merchant and merchant’s bank
It has three principle features:
All sensitive info sent within the three parties are
encrypted
All three parties are required to authenticate
themselves with certificates from SET CA
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iii.
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The merchant never sees the customer’s card
number in plaintext.
It is more secure than SSL
To implement SET, it requires SET POS client
software such as SET “electronic wallet”
implemented widely in the client’s web browser.
It is quite a challenge to make such a POS software
available to the Internet community
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ANY QUESTIONS …?
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