Charles A. Shoniregun and Songhe Zhao
School of Computing & Technology, University of East London
4-6 University Way Docklands, London
United Kingdom, E6 5NJ
Keywords: Secure Electronic Transaction (SET), Dual Signature, Elliptic Curve Cryptography (ECC).
Abstract: The Secure Electronic Transaction (SET) was developed by Visa and MasterCard in 1997. The SET is a
protocol that is theoretically perfect with very high expectation to provide secured electronic financial
transactions. It also provides a ‘dual signature’ as it hides credit card numbers from the merchants, and
purchase details from the bank. This paper exploits the weaknesses that led to SET’s failure and proposed
SET’s encryption process with elliptic curve cryptography (ECC).
The SET is a standard protocol for ensuring the
security of electronic financial transactions on the
Internet, which has been endorsed by virtually all the
major players in the electronic commerce arena,
including IBM, MasterCard International, Visa
International, Microsoft, Netscape, GTE, ViriSign,
SAIC and Terisa. The SET defines a detailed secure
transaction process among all participants. It mainly
replies on the sciences of cryptography to implement
its functions for securing electronic transactions on
the Internet. The cryptography provides two different
encryption mechanisms and an authentication
mechanism. SET employs DES symmetric
encryption and RSA asymmetric encryption to
provide functions of data encryption, digital signature
and digital envelope, which can provide guarantee for
the security of information transmitted over the
Internet. To enable merchants to verify transactions,
SET put the public key into an electronic document
(i.e. digital certificate). The certificate is then signed
by a trusted third-party, such as certificate authority
(CA), which can then be verified from their
certificate and so on in a hierarchy of trust. And it will
also protect buyers by providing a mechanism for
their credit card number to be transferred directly to
the credit card issuer for verification and billing
without the merchant being able to see the number.
With SET, a user is given an electronic wallet (digital
certificate) and a transaction is conducted and
verified using a combination of digital certificates
and digital signatures among the purchaser, a
merchant and the purchaser's bank in a way that
ensures authenticity and privacy.
The SET handles processes for once-off merchant
and card holder registration, for making a purchase
and getting the payment authorized through a bank’s
network gateway and for subsequent payment to the
merchants. SET pilots have been conducted around
the world, but very few have yet been implemented.
The SET protocol provides four main advantages for
securing data/information transfer:
Confidentiality: using two forms of
cryptography---DES and RSA to protect transmitted
messages from intercepting.
Integrity: using one-way cryptographic hashing
algorithms and digital signatures to make sure that
the messages transmitted have not been modified in
Authentication: using X.509v3 digital certificates
which assure that
the parties involved in the
transaction are who they claim to be, and prevent
them from denying that they sent a message (i.e.
¾ Privacy: using cryptography to make sure the
information is only available to parties in a
transaction when and where necessary.
A. Shoniregun C. and Zhao S. (2007).
In Proceedings of the Third International Conference on Web Information Systems and Technologies - Internet Technology, pages 313-319
DOI: 10.5220/0001291903130319
There have been remarkable efforts aimed at the
SET’s weaknesses. These efforts are effective in
overcoming the weaknesses and reducing
redundancies. Abbott (1999) presented that although
SET offers a complete card payment system that
manages financial risk and defines interoperability, it
requires that software be installed in the banking
network, at merchants’ locations, and on consumers’
PCs. This deployment obstacle has slowed and
complicated the adoption. Weishaupl et al. (2006)
developed gSET as a solution for the unsolved
problems in the field of dynamic trust management
and secure accounting in commercial virtual
organizations. The gSET establishes trust and
privacy between entities in a Grid environment by
adapting the concept of SET used for electronic
credit card transfers in e-Commerce. However, this
solution is known as an enabling step to make Grids
a platform for commercial workflows but it is not a
solution to address problems of SET’s adoption and
deployment. Bella et al. (2005) produced an accurate
formal model to identify the SET protocol goals and
then to prove them. In their study, they were
troubled by the complexity of SET protocol so that
they are not clear whether model checking could
cope with this SET’s complexity. it is very clear that
the complexity of SET is the crucial problem for its
adoption. This rather serious time lag issue could
come to be resolved by another more efficient
method called elliptic curve security. Although RSA
employed by SET is the most popular public-key
cryptosystem today, the long-term trends such as the
proliferation of smaller, simpler devices and
increasing security needs will make continued
reliance on RSA more challenging over time.
The SET uses digital signatures and certificates
stored in an electronic “wallet” on the users’
personal computers and on the merchants’ websites.
The dual signature which is employed as the SET’s
digital signature is issued by a trusted third party
certificate authority and the user's certificate
contains card details. It is encrypted in such a way
that it can only be read by the card issuer, not the
The dual signature is generated by creating the
message digest of both messages sent by a sender,
concatenating the two digests together, computing
the message digest of the result and encrypting this
digest with the senders private signature key. A
recipient of either message can check its authenticity
by generating the message digest on its copy of the
message, concatenating it with the message digest of
the other message (as provided by the sender) and
computing the message digest of the result. If the
newly generated digest matches the decrypted dual
signature, the recipient can trust the authenticity of
the message (Secure Electronic Transaction LLC,
1997). Privacy and Authentication are achieved
through the use of digital signatures. Digital
signatures are aimed at achieving the same level of
trust as a written signature has in real life. This helps
achieve non-repudiation, as the consumer cannot
later establish that the message wasn't sent using his
private key (IBM Corporation, 1998).
3.1 Construction of Dual Signature
In SET, when a customer has place an order from a
merchant’s website and is going to make a payment
for the order, he/she needs to send the order
information (OI) to the merchant and payment
information (PI) to the merchants acquirer through
the merchant. In the progress of sending OI and PI to
destinations, the customer needs to use hash
algorithm (SHA-1) to produce message digest (MD)
respectively for OI and PI. These two MDs are then
concatenated and then computed to payment and
order message digest (POMD) by using the hash
algorithm again. Finally, the customer encrypts the
POMD with the customer’s private signature key
(KRc) in order to create the dual signature (DS). The
operation formula is:
When the merchant is in the possession of OI,
PIMD and DS, and PI, the merchant can use the
customer’s public key (KUc), which is taken from
the customer's certificate to compute two quantities.
The operation formula is:
If these two quantities are equal, the merchant
has verified the signature. Similarly, when the
acquirer is in the possession of PI, OIMD and DS,
the acquirer can use KUc to compute other two
quantities. The operation formula is:
WEBIST 2007 - International Conference on Web Information Systems and Technologies
Again, if these two quantities are equal, the
acquirer has verified the signature. In summary:
¾ The merchant has received OI and verified
the signature.
¾ The acquirer has received PI and verified
the signature.
¾ The customer has linked the OI and PI and
can prove the linkage.
Within SET, dual signatures are used to link an
order message sent to the merchant with the
payment instructions containing account information
sent to the Acquirer. When the merchant sends an
authorization request to the Acquirer, it includes the
payment instructions sent to it by the cardholder and
the message digest of the order information. The
Acquirer uses the message digest from the merchant
and computes the message digest of the payment
instructions to check the dual signature.
Although the advantages of SET had ever attracted
our sight, this focus quickly moved to its weaknesses
and the relevant researches were carried out soon
after the failure of SET happened.
4.1 Weaknesses of SET
The SET protocol has the potential of securing the
electronic financial transactions over the Internet so
as to enable e-Commerce to be safe and attractive to
consumers, but unresolved problems and issues
which caused the failure of employing SET as a
dominate protocol in e-Commerce as follows:
i Complex and slow processing:
The SET models all of the players involved in
electronic financial transactions. It is a complex
protocol because it so totally simulates these
existing real world processes. The ultimate
high level of security that SET provides is
implemented by a very complex system which
causes the processing transactions to be quite
slow. Generally, the access operations to the
merchant’s server can approach 6 times (Zhao,
2005); moreover, SET also implements a deal
of computing for public key encryption. The
workload of the merchants server hereby is
quite heavy so that overload is most likely to
happen. Lag times of up to 50 seconds have
been reported for the processing of a typical
cardholder initiated purchase request to the
approval response from the acquirer and the
finalization of the transaction by the merchant’s
server (Keenan, Disenso and Green, 1998).
This matter is critical for average SET’s
consumers because the key advantage of
e-Commerce is to provide ease-of-use
applications for its participants. Nobody would
like to wait for a response around 50 seconds
after sending a purchase request. A common
download time for a Webpage should be around
15 seconds and if it above 30 seconds then the
customer will stop waiting and move over to
another Website (Shoniregun, 2005), not even
for a very attractive Webpage. As a result, it’s
not recommended that that any response over
15 seconds is proper, especially since there is
little or no feedback to reassure and update the
cardholder about the progress of the transaction
processing (Wolrath, 1998).
ii Inconvenient and expensive deployment and
To implement SET, merchants are required to
invest in new software and build their
businesses around a complex transaction
infrastructure, but it doesn’t make them jump
with joy (Friedman, 1998). Merchants who
want to benefit from SET have to install
SET-enabled applications in their systems. It
doesn’t look inconvenient and expensive to the
installation in a single merchant’s system.
However, e-Commerce is a global electronic
transaction over the Internet. It may create
considerable profit only if a great number of
people step into this virtual business world to
play this game. Therefore, it’s necessary for
absolute majority of merchants to install
SET-enabled applications in their systems. This
needs a huge investment and long time to
deploy far and wide, but most people don’t
want to be at risk before making an investment
and seeing other’s implementation. The latter
slows down the deployment of SET’s, not only
to merchants, but also to the installation of
SET-enabled applications in client end is also
obstacle for SET’s implementation. Ease-of-use
is the key to e-Commerce as well as SET. But
the serious question remains about just how
intuitive it will be for users to install the
necessary applications to do SET-based
transactions. Neither Microsoft nor Netscape
are in any rush to build SET into their browsers
until there is a demand for it. But merchants
won’t support it until their customers ask for it,
and their customers won’t ask for it until it’s
built into their browsers. Although Vendors like
VeriFone and IBM have developed SET wallet
plug-ins for the popular Web browsers, Internet
users are not keen on using external plug-ins.
Because they have to install SET from the
external plug-ins that adds payment
functionality to a browser, and also register
with a financial institution or trusted third party,
which then issues digital certificates that
identify the cardholder to the merchant and
vice versa. Although in the long run SET
backers expect certificates to be included in
wallets -- which in turn will be built into
Generally speaking, different versions of
SET software are currently available in the
market but it is critical that these packages
interoperate. Without interoperability, any
protocol is dead. SET defines interoperability
between all parts of the card-payment process.
A system can be built with parts from multiple
vendors. To offer these benefits, SET requires
that software be installed in the banking
network, in merchants systems, and on
consumers’ PCs. This “deployment obstacle”
has slowed the adoption of SET, which also
requires that certificates be issued to all parties.
These requirements make SET quite
inconvenient and expensive to deploy all over
the world.
iii Lack key and certificate management:
Today’s popular operating systems are
unreliable and insecure, so they are highly
vulnerable to attack, particularly when
connected to the Internet. For this reason,
non-repudiation really exists only when private
signing keys are kept out of untrusty PCs
(Abbott, 1999). But SET refers nothing about
how to securely keep keys and certificates out
of attacks after finishing an electronic
transaction. It appears that these will need to be
stored on participants' workstations and servers,
or additional peripherals installed on
workstations and servers to handle a secure
token (Clark, 1996). A secure token, such as a
smart card, is a good tool to store and exercise
private signing keys and certificates for its
holder. It can also provide an easy way for
signing keys and certificates to be issued and
carried around. The SET was designed
specifically for smart cards, and all SET wallets
support tokens. This beneficially ties token
directly to e-Commerce, because the certificate
authenticates the customer as a cardholder and
directly signifies that transaction is taking place.
However, smart cards are distributed very
slowly, because no one has solved the problem
of how to get card readers attached to
everyone’s PC. But other form-factor tokens
are appearing, including small
universal-serialbus tokens (key fobs, for
example) that can do the same job. Some SET
pilots also are being conducted without tokens,
with the expense of the added complexity of
distributing and managing certificates as
software files. In fact, the smart card’s set-up is
beyond the average cardholder. Actually it's a
very troublesome procedure.
4.2 ECC-based Improvement of SET
Our proposition is based on substituting RSA
algorithm by using ECC to provide SETs
cryptography (See Figure 1). Our laboratory
experiments have proved that ECC provides greater
security and more efficient performance than the
first generation public key techniques.
i ECC from the consumer:
The consumer use the ECC hash algorithm
(SHA-1) to produce message digest for the
original message and encrypt the message
digest with ECC private key to produce the
digital signature. This generates a random
symmetric key that encrypt the original
message, digital signature and a copy of the
consumers certificate, which contains public
signature key. The symmetric key is encrypted
by using the merchant’s ECC public
key-exchange key and the encrypted key
(digital envelope) will be sent to the merchant
along with the encrypted message. Sending a
set of message to the merchant consists of the
symmetric encrypted original message, as well
as the asymmetrically encrypted symmetric key
(the digital envelope).
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Figure 1: SET’s encryption process with ECC.
ii ECC from the merchant:
Receiving the set of message from the
consumer and decrypting the digital envelope
with the ECC private key-exchange key to
retrieve the symmetric key. The consumers
digital signature and certificate would be
required in other to decrypt the original
message. Decrypting the consumers digital
signature with the ECC public key would
enabled the original message digest to produce
a new message digest of the decrypted original
message and compare the message digest
with the one obtained from the consumers
digital signature.
The ECC enhance the process in the SET’s
digital signature and inverse the process to provide
the message digest by decrypting the digital
signature. Moreover, the process related to the digital
envelope is also served by this solution. As a result
of this ECC-based solution, the duration of SET’s
encryption process can be reduced much more than
RSA-enabled process. The discussion section
focuses on how the security level of the encryption
will advance according to the features of ECC.
In comparison with RSA, ECC offers the same level
of security using much smaller keys but faster
computations and less resourceful on memory.
Table 1: Comparison of key sizes.
Key Size
RSA and
Key Size (bits)
Curve Key
Size (bits)
80 1024 160
112 2048 224
128 3072 256
192 7680 384
256 15360 521
The Table1 shows the key sizes that protected the
keys used in conventional encryption algorithms like
the (DES) and (AES) together with the key sizes for
RSA, Diffie-Hellman and elliptic curves that are
needed to provide equivalent security.
Notably, the use of 1024-bit RSA does not match
the 128-bit or even 112-bit security level now used
for symmetric ciphers in SET. This indicates the
need to migrate to larger RSA key sizes in order to
deliver the full security of symmetric algorithms
with more than 80-bit keys. However, RSA
Laboratories stated that 1024-bit RSA to be unsafe
for data that must be protected beyond 2010 and
recommends larger keys for longer term protection
(Kaliski, 2003). In the case of providing higher key
sizes, RSA will increase much more the time cost of
the encryption process in SET. For example,
employing RSA or Diffie-Hellman to protect 128-bit
AES keys should use 3072-bit parameters, which is
three times longer than the size of 1024-bit in use
throughout the Internet today. However, the
equivalent key size for elliptic curves is only 256
bits. It’s obvious that as symmetric key sizes
increase the required key sizes for RSA and
Diffie-Hellman increase at a much faster rate than
the required key sizes for ECC. Hence, ECC offer
more security per bit increase in key size than either
RSA or Diffie-Hellman public key systems.
Table 2: Relative computation costs of Diffie-Hellman and
elliptic curves.
Security Level (bits)
Ratio of DH Cost:
EC Cost
80 3:1
112 6:1
128 10:1
192 32:1
256 64:1
Besides providing better security, ECC also are
more computationally efficient than the first
generation public key systems, RSA and
Diffie-Hellman. Although elliptic curve arithmetic is
slightly more complex per bit than either RSA or DH
arithmetic, the added strength per bit more than
makes up for any extra compute time (See Table 2).
The following table shows the ratio of DH
computation versus EC computation for each of the
key sizes listed in Table 1.
Closely related to the key size of different public
key systems is the channel overhead required to
perform key exchanges and digital signatures on a
communications link. The key sizes for public key in
Table 1 (above) is also roughly the number of bits
that need to be transmitted each way over a
communications channel for a key exchange. In
channel-constrained environments, elliptic curves
offer a much better solution than first generation
public key systems like Diffie-Hellman.
In choosing an elliptic curve as the foundation of
a public key system there are a variety of different
choices. The National Institute of Standards and
Technology (NIST) has standardized on a list of 15
elliptic curves of varying sizes. Ten of these curves
are for what are known as binary fields and 5 are for
prime fields. Those curves listed provide
cryptography equivalent to symmetric encryption
algorithms with keys of length 80, 112, 128, 192,
and 256 bits and beyond. In our solution, it
recommends that SET employs the ECC with 256,
384, and 521 bits. It is expected to show enhanced
speed on the SET payment gateway and potential
cost savings. It also promises to lower the capability
threshold for small devices to perform strong
cryptography, and increase a servers capacity to
handle secure connections (Lenstra and Verheul,
The SET security guarantee is achieved by using the
cryptography but is a very costly technology. The
three main weaknesses of SET have been discussed
and we have also proposed the ECC model to
enhance not only the higher level security but also to
perform more efficient than RSA. Our future work
will focus on the SET key and certificate
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