E-mail SecurityUsing Certified Electronic mail (CEM)

Team Members

Pankaj Bhambhani (200901047) (pankajb64@gmail.com)

Pratik Kumar (200901239) (pratik.kumar.bharat@gmail.com)

Dipesh Shah (200901094) (dipesh1005@gmail.com)

Jignesh Kakadiya (200901201) (jigneshhk1992@gmail.com)

Ajay Dhameliya (200901203) (dhameliyaajay26@yahoo.in)

Topics

Why E-mail security?

CEM - Certified Electronic Mail

Properties of CEM

Existing Protocol - S/MIME – properties

Missing properties in S/MIME and their importance

Sample Certified Email Protocol

How to do- Design

Conclusion and our thoughts

References

Why E-mail Security?

Primitive E-Mail service – different intended purpose.

Exchange of messages between small universities in a closed network.

Not much concern about misuse.

Different Game Altogether Today.

Internet an open network - large number of messages sent.

Can contain sensitive, valuable information. Security is essential.

We shall examine Certified Electronic Mail as a theoretical measure of E-

mail Security.

Certified Electronic Mail (CEM)

Added value to traditional electronic mail.

Examination of various properties.

Use a sample certified email protocols to demonstrate properties.

Its use in improvement of existing protocol : S/MIME

Properties of CEM : Non-Repudiation

Postal services force the recipient to sign a receipt token before delivering

the envelope which contains the certified message.

Here the recipient only recognizes that it received an envelope which, in turn,

can be empty (intentionally or not).

Hence there is a difference with respect to the digital evidence of receipt

(linked to the message and not to the envelope).

Types of non-repudiation

Direct Communication Model

Non-Repudiation of Origin (NRO) is intended to protect against the originator’s falsedenial of having originated the message. Evidence of Origin (EOO) is generated by theoriginator, or a TTP on its behalf, and will be held by the recipient.

Non-Repudiation of Receipt (NRR) is intended to protect against the recipient’s falsedenial of having received the message. Evidence of Receipt (EOR) is generated by therecipient, or a TTP on its behalf, and will be held by the originator.

Indirect Communication Model

Non-Repudiation of Submission (NRS) is intended to provide evidence that the originatorsubmitted the message for delivery. Evidence of Submission (EOS) is generated by thedelivery agent, and will be held by the originator.

Non-Repudiation of Delivery (NRD) is intended to provide evidence that the messagehas been delivered to the recipient. Evidence of Delivery (EOD) is generated by thedelivery agent, and will be held by the originator

Properties of CEM : Non-Repudiation

(Contd…)

Different Possible Message Transfer Combinations:

• Exchange of message and NRO for NRR linked to the message.

• Exchange of message and NRO for acknowledgement of receipt.

• Exchange of message for NRR linked to the message.

• Exchange of message for acknowledgement of receipt.

• Exchange of envelope and, if possible, NRO for NRR, if possible,linked to the message.

• Exchange of envelope and, if possible, NRO for acknowledgementof receipt.

• Exchange of envelope for NRR, if possible, linked to the message.

• Exchange of envelope for acknowledgement of receipt.

Communication Model

The originator and the recipient potentially do not trust each other.

The originator is not sure that the recipient will acknowledge a message it

has received.

On the other hand, the recipient will only acknowledge messages it has

received.

In order to facilitate a fair exchange in which neither party will gain an

advantage during the transaction, a TTP will usually be involved.

The extent of the trusted third party’s involvement varies among different

protocols

Evidence

This is the data that can be used if a dispute arises.

It can be either generated and stored by the local user or by a third party.

Its format depends on the cryptographic mechanisms agreed in the

service.

Examples: digital signatures (public key cryptography) and secure

envelopes (secret key cryptography).

Common Elements of Evidence format

Non-repudiation service to which evidence is related

Non-repudiation policy identifier

Originator identity

Recipient identity

Third party identity if evidence generator differs from the originator

Message or a digital fingerprint

Common Elements of Evidence format

(Contd … )

Information needed for verifying evidence (i.e. digital certificate, symmetric

secret key info) if it is not publicly available

TTP’s identifier

Time information (time and date that evidence was generated, expiry

date, . . . ).

If this data is certified by a Time Stamp Authority (TSA), it could include a

time-stamp service identifier.

Properties of CEM : Fairness

A certified e-mail protocol is fair if and only if at the end of a protocol

execution either Alice got the non-repudiation of receipt evidence, and

Bob got the corresponding mail (as well as the non-repudiation of origin

evidence if required), or none of them got any valuable information.

Types of Fairness

Strong, Weak, Light, True, Probabilistic

Fairness is mandatory, so one of these properties must be compulsory.

Weak Fairness is enough, although strong fairness is desirable. Probabilistic

Fairness is not desirable

Properties of CEM : TTP

The probability to cheat the other entity in a protocol can be decreased by

increasing the number of messages necessary in the protocol. To avoid the

communication overhead, a different approach using a trusted third party

(TTP) can be introduced. Both entities can send their items to the TTP that

forwards them to the respective entities.

Types of TTP

In-line TTP, On-line TTP, Off-line TTP, Transparent TTP, Verifiable TTP

Off-line TTP is desired, but the involvement of the TTP depends on the

application.

Transparent and Verifiable TTP are desired, but only one of them can be

achieved because they are incompatible.

Properties of CEM : Timeliness

A certifed e-mail protocol provides timeliness if and only if all honest parties

always have the ability to reach, in a finite amount of time, a point in the

protocol where they can stop the protocol while preserving fairness.

Types of Timeliness

Synchronous Timeliness – Here deadlines are used and the TTP clock is assumed

as the reference time.

Asynchronous Timeliness – There are no deadlines here for participants.

Asynchronous Timeliness is desirable as it is difficult to achieve clock

synchronization.

Properties of CEM : State Storage

TTPs can be classified with respect to how long (temporal criteria) do they

need, if applicable, to store state information.

Types of State Storage

Strong Stateless TTP

Weak Stateless TTP

Strong Stateful TTP

Weak Stateful TTP

Strong Stateless TTP is the most desirable property from a resource and

storage point of view.

Properties of CEM : Confidentiality

A certified e-mail protocol is said to provide data confidentiality, if and only

if Alice and Bob are the only entities that can extract the content of the

sent mail out of the protocol messages.

Confidentiality is not always required as adding confidentiality may harm

the efficiency of the protocol.

Types of Confidentiality

Data confidentiality

Identity confidentiality

We could also consider privacy of the originator (anonymity). However

anonymity and NRO cannot be provided at the same time.

Properties of CEM : Evidence

Transferability

It mainly consists of the sending and reception of evidence among participants.

It is greatly influenced by communication channel properties. The different options

are as follows:

1. The communication channel is unreliable. In this case, data can be lost.

2. The communication channel is resilient (also called asynchronous network). In

this case, data is delivered after a finite but unknown amount of time.

3. The communication channel is operational (also called synchronous network).In this

case, data is delivered after a known, constant amount of time.

An unreliable channel will in most cases be transformed into a resilient channel by the use of an appropriate transport protocol (e.g. retransmissions).

Dispute Resolution in CEM

Dispute resolution is the last phase in a non-repudiation service. This phase

will not be activated unless disputes related to a transaction arise.

When a dispute arises, an adjudicator will be invoked to settle the dispute

according to the non-repudiation evidence provided by the disputing

parties and the non-repudiation policy in effect. This policy should be

agreed in advance by the parties involved in the service.

Protocol : Key chain Based CEM

Protocol with Transparent TTP

In 2010, Zhiyuan Liu, Jun Pang and Chenyi Zhang proposed an optimistic

certified email protocol, which employs key chains to reduce the storage

requirement of the trusted third party (TTP).

Satisfies the following CEM properties:

NOR,NRR

Strong Fairness

Timeliness

TTP Transparency

Protocol : Key chain Based CEM

Protocol with Transparent TTP

Key Terms in Protocol:

EOO : Evidence of Origin

EOR: Evidence of Receipt

M : Message

T : TTP

sid : sender ID

A,B : Sender , Receiver

h(i) : hash of the I

label : It is used to identify the protocol run.

fT : flag indicating the purpose of the message where T identifies the corresponding message in that protocol

Protocol : Key chain Based CEM

Protocol with Transparent TTP

Protocol

Protocol : Key chain Based CEM

Protocol with Transparent TTP

Recovery Protocol for the Sender

Protocol : Key chain Based CEM

Protocol with Transparent TTP

Recovery Protocol for the Receiver

where label is h(A,B,TTP, h(m), h(k), t)

Working of S/MIME (in brief)

Message sending mechanism:

Working of S/MIME (in brief)

Message receiving mechanism:

Security Properties met by S/MIME

Message confidentiality via encryption

Message integrity via digital signature

Message origin authentication via digital signature

Non-repudiation of origin via digital signature

Security property not met by S/MIME

Non-repudiation of receipt

S/MIME does not protect the sender of information against the denial of the

receiver, who may say the sender never sent the information, or that he/she did

not send it on time.

Lack of this property prevents professional use of email.

Addition of NRR with Fairness in S/Mime

Sender sends encrypted message and encryption key for message derived

from message.

some function of hash of message for e.g.)

encrypted by public key of receiver.

TTP calculates hash of this and sends it to receiver.

Receiver signs this hash and sends back to TTP.

Now TTP sends signed hash back to sender encrypted by sender’s public

key (which he can verify) and also sends message to receiver.

Conclusion and our Thought

Certified e-mail, also known as authenticated e-mail or stamped e-mail, is a

system in which senders of commercial e-mail messages pay a small fee to

ensure that their messages will bypass spam filter s to reach intended

recipients.

Both America Online ( AOL ) and Yahoo have announced certified e-mail

plans based on a technology developed by Goodmail Systems.

For a fee of approximately 1/4 of a cent (USD $0.0025) per e-mail, or USD

$2.00 to $3.00 for every 1000 messages sent, advertisers can post e-mail

messages that defeat most spam filters commonly used at the server level

by Internet service providers ( ISP s).

References

Josep Lluis Ferrer-Gomilla a , Jose A. Onieva b , Magdalena Payeras a ,

Javier Lopez b, * : Certified electronic mail: Properties revisited Computers &

Security Volume 29, Issue 2, March 2010, Pages 167–179

Secure Multi-Party Non-Repudiation Protocols and Applications, José A.

Onieva, University of Malaga Spain, Javier Lopez ,University of Malaga

,Spain, Jianying Zhou, Institute for Infocomm Research, Singapore Ch – 2

Fundamentals of Non-Repudiation Pages 17-34

Selective Receipt in Certified E-Mail, Steve Kremer and Olivier Markowitch

fskremer,omarkowg@ulb.ac.be, 2001 (http://www.ulb.ac.be/di/scsi/markowitch/publications/ic01.pdf)

Oppliger R. Certified mail: the next challenge for secure messaging. ACM

Press. Communications of the ACM 2004;47: 75–9

References

Extending a Key-Chain Based Certified Email Protocol with Transparent TTP

Zhiyuan Liu, Jun Pang, Chenyi Zhang, Conference: Embedded and

Ubiquitous Computing - EUC , pp. 630-636, 2010, DOI: 10.1109/EUC.2010.101

Understanding S/MIME (http://technet.microsoft.com/en-us/library/aa995740(v=exchg.65).aspx)

Prof. Manik Lal Das Slides (L11 - E-Mail Security.pdf)

Certified e-mail (authenticated e-mail or stamped e-mail)

(http://whatis.techtarget.com/definition/certified-e-mail-authenticated-e-mail-or-stamped-e-mail)