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of a digital signature depends on the rigor of its registration process. In some cases, a
Certification Authority may register new private key holders by simply asking users to
type in their email addresses. In other cases, the Certification Authority asks registrants
for several pieces of private information, such as Social Security numbers, the last four
digits of their driver licenses or the amount of the last check they wrote. If even greater
security is called for, registrants could be required to appear in person at the certificate
authority™s premises with multiple forms of identification. When this last term is used,
the electronic signatures made with assistance of the digital signature is taken as
equivalent to handwriting signatures in most national legislation regarding electronic
business and electronic commerce.
Public Key Infrastructure strength is a new issue at the signer side “ users (signers) must
keep their private keys private. That private key is on a computer or on a smart card and
the user has got to protect it, otherwise someone could get a hold of it and sign with it.
Because Electronic Signatures within Public Key Infrastructure environment are created
and verified by asymmetric cryptography, they use public-key cryptography, where one
key is for creating a digital signature and another key is for verifying a digital signature.
These two keys (which forms a key pair) are collectively termed as asymmetric
cryptosystem. The processes of creating a electronic signature and verifying it through
the Public Key Infrastructure accomplish the essential effects desired of a signature for
many legal purposes:
• Signer authentication: If a public and private key pair is associated with an
identified signer, the electronic signature attributes the message to the signer. The
electronic signature cannot be forged, unless the signer loses control of the private
key, such as losing the media or device in which it is contained.
• Message authentication: The electronic signature also identifies the signed
message, typically with far greater certainty and precision than paper signatures.
Verification reveals any tampering, since the comparison of the hash results (one
made at signing and the other made at verifying) shows whether the message is the
same as when signed.
• Affirmative act: Creating an electronic signature requires the signer to use the
signer™s private key. This act can perform the ceremonial function of alerting the
signer to the fact that the signer is consummating a transaction with legal
consequences.
• Efficiency: The processes of creating and verifying an electronic signature provide
a high level of assurance that the electronic signature is genuinely the signer™s.
Compared to paper methods (such as checking specimen signature cards - methods
so tedious and labor-intensive that they are rarely actually used in practice) digital
signatures yield a high degree of assurance without adding greatly to the resources
required for processing.


Digital signatures are a reversal of public-key cryptography “ data encrypted using a
sender™s private key can only be decrypted using the sender™s public key. By obtaining
the sender™s public key to decrypt the digital signature, the recipient ensures that the
digital signature was generated by the sender™s private key. Anyone with access to the


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Electronic Signature 115


Figure 2. Digital signature verification




sender™s public key can verify the digital signature. By comparing the hash values
generated from the data by the sender and the recipient, the recipient ensures that the
data did not change during the transfer.
Can a digital signature be forged? Not likely. It is protected by several layers of highly
complex encryption. We like to think that a handwritten signature is unique to the signer
and to the pieces of paper which hold it. What if someone produces a good likeness of
your handwritten signature? Or, what if on a long contract, someone changes the text of
the pages previous to the signature page? In these instances, the signature is valid, but
the document has been altered. With digital signatures, forgery is next to impossible “
much more difficult than forging a handwritten signature. First, a digital signature is more
of a process than just affixing a signature. For example, when the document is “digitally
signed,” the digital software scans the document and creates a calculation which
represents the document. This calculation becomes part of the “digital signature.” When
the recipient authenticates the signature, a similar process is carried out. The sender™s
and the receiver™s calculations are then compared. If the results are the same, the
signature is valid. If they are different, the signature is not valid.


Figure 3. Signed document flow within PKI environment




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116 Ruzic


The process of creating a digital signature in E-Business communication is accomplished
by the sender. The verification of the digital signature is performed by the receiver of the
digital signature. The writing and sending a check example, illustrates how digital
signature technology works.


Digital Signature Creation
• Sign: To begin the process, a check must be created. In order to create a digital
signature with the check, a process known as hash function, must occur. A hash
function is a mathematical algorithm that creates a digital representation or
fingerprint in the form of message digest. The hash function generally consists of
a standard length that is usually much smaller than the message but nevertheless
substantially unique to it. Hash functions ensure that there has been no modifica-
tion to the check (message) since it was digitally signed. The next step is to encrypt
the check and signature. The sender™s digital signature software transforms the
hash result into a digital signature using the sender™s private key. The resulting
digital signature is thus unique to both the message and the private key used to
create it. Typically, a digital signature is appended to its message and stored or
transmitted with its message. However, it may also be sent or stored as a separate
data element, so long as it maintains a reliable association with its message. Since
a digital signature is unique to its message, it is useless if wholly disassociated from
its message.
• Seal: Since public-key algorithms can be slow to transmit, the next step is to encrypt
this information. The check is encrypted with a fast symmetric key (uniquely
generated for this occasion) and then the symmetric key is encrypted with the
receiver™s public key. Now only the private key of the receiver can recover the
symmetric key, and thus decrypt the check. A digital version of the envelope has
been created.
• Deliver: At this point, the digital envelope is electronically sent to the receiver and
the verification process begins.


Digital Signature Verification
• Accept: The encrypted digital envelope arrives at the destination.
• Open: The receiver of the check decrypts the one-time symmetric key by using the
receiver™s private key. Then the check is decrypted using the one-time symmetric
key. Once this has been completed, the verification process begins.
• Verify: Verification of a digital signature is accomplished by computing a new hash
result of the original message. Then, using the sender™s public key and the new
hash result, the verifier checks: 1) whether the digital signature was created using
the corresponding private key; and 2) whether the newly computed hash result
matches the original hash result. The software will confirm the digital signature as
verified “ the sender™s private key was used to digitally sign the message and the




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Electronic Signature 117


message was unaltered. If the verification cannot be made, the software will identify
that verification has failed.


An electronic signature is a convenient, timesaving, and secure way of signing electronic
documents. An electronic document is any document that is generated or stored on a
computer, such as a letter, a contract, or a will. In addition, an electronic document can
be an image, such as a blueprint, a survey plat, a drawing, or even a photograph. and an
electronic signature can be used to sign these documents. It means that the authenticity
of any electronic document can be verified by an e-signature, but only if the document
originally was “signed” using an e-signature program (software). Although this
sounds complicated., it is a simple process and may vary slightly in the software in use,
and e-signature software does all the work. The signer selects the signature option, then
selects the document, and finally enters a secret Authorization Code. Everything is
accomplished electronically. In the PKI environment, a digital certificate is added to the
signed document, thus making verification available at any time after the document is
signed.
Unfortunately, nobody can actually see the signers™ handwritten signature, and there is
no relationship to the signer™s handwritten signature. While there™s more to it behind the
scenes, the visible portion of the digital signature is the signer™s name, title and firm name,
along with the certificate serial number and the Certification Authority name.
Digital signatures still face some cultural hurdles, such as convincing users to accept a
line of hash code instead of a penned name. Several software solutions cover both
ideologies by combining a PKI-based digital signature and a pictorial representation of
the handwritten signature.
Visible Electronic Signature Protocol is a digital electronic signature protocol that allows
the recipient of a secure electronic document to visually confirm the signature of the
author and the authenticity of the document, just as with a paper document. A signature
image, such as a seal or a written signature, is presented to the end user for verification.
This intuitive approach to the digital signature process allows for extremely high
confidence in the security and privacy of the encryption-decryption process, and



Figure 4. Verifying graphically presented e-signature; if the document is changed or
used certificate is not valid, the cross-circled mark is presented to the reader

valid signature non valid signature




verifies your signature identifies when a
and document document is modified




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118 Ruzic


provides for a tamper-resistant way to transmit documents which must remain secure,
such as e-commerce orders, contracts, blueprints, surveys, drawings, or photographs.
the protocol works by encrypting the signature image.
As E-Business searches for more secure authentication methods for user access, e-
commerce, and other security applications, it should be noticed that the security field
uses three different types of authentication:
• something user knows - a password, PIN, or piece of personal information
• something user has - a card key, smart card, or token
• something user is - a biometrics


If an E-Business system is carefully constructed, almost any of these technologies could
provide industrial-strength e-signatures with a number of additional tools that are not
available yet:


Smart Cards
With a digital certificate or smart card protected by a password, there is a two-factor
authentication - something owner knows and something owner has”and that makes e-
signature protection stronger. Smart cards have finally entered the public domain and are
used in a variety of applications, sometimes without the user being aware that they are
actually using a smart card. The smart card itself is simply a plastic card with an integral
embedded chip. This provides a degree of tamper resistance and security for the
information held within the card. Smart cards may be categorized into two primary types,
memory cards or microprocessor cards. Memory cards simply store data and allow that
data to be subsequently read from the card. Microprocessor cards on the other hand,
allow for additions and deletions to the data, as well as various manipulations and
processing of the data. The smart cards may be further categorized into contact or
contactless cards. Contact cards required the card to be physically inserted into a smart
card reader. Contactless cards enable the card to be read without physical contact via
a radio frequency link with an antenna embedded into the card. There is in fact another


Figure 5.: Smart card occurrences “ contact and contactless




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Electronic Signature 119


type of card called a combination card that combines both contact and contactless
technology. This allows for the card to be read by either type of card reader, alternatively,
to be read by both techniques at the same time, enabling a higher degree of security.
Smart cards support our contemporary networked society via a variety of applications,
including network access control, secure payment systems, health care applications,
ticketing applications, loyalty and other areas. They may also be used to store digital
certificates and passwords and can encrypt sensitive data. Perhaps one of the most
visible applications is that of SIM cards used for mobile phones. SIM stands for
Subscriber Identification Module and the SIM cards store subscriber information which
allows phones to be instantly personalized as well as providing roaming across different
networks and devices. The mobile phone SIM card also provides for a variety of value-
added services to be provided by the telecommunication companies as appropriate. An
often referred to aspect of smart card technology is the potential for the multi-application
card. The idea of multiple applications via the use of a single card is an attractive one.
However, for this to be possible there needs to be a degree of interoperability between
cards and applications. This interoperability has so far been rather weak, although there
are now various initiatives with the aim of improving this vital aspect of smart card
technology. There is of course an ISO standard for smart cards (7816 parts 1-10), although
other different industry sectors have tended to create their own proprietary versions
based around the ISO generic standard. There have also been related initiatives such as
the Microsoft PC/SC standard, which was originally for Windows-based systems only,
although this has now been opened up to be an across-platform initiative. Indeed, the
PC/SC initiative boasts an impressive membership of several distinguished companies
from the computer and telecommunications market place.
Another initiative called OpenCard has similar ambitions to provide interoperability
across applications. Perhaps most interesting development of all in this context is Java
Card (Wenderoth, 2001). Java card provides the potential for Java applets to run right
on the card itself, a very interesting capability for those seeking to develop smart card
applications. Smart cards are a valuable addition to this world because they interface
seamlessly with smart devices and intelligent systems, giving people convenient and
direct access to relevant information stored on powerful networks. The portable creden-
tials on the smart card can securely identify and authenticate its owner, across the range
of smart devices, providing a consistent means of authorization and digital signature for
E-Business transactions. With embedded applications, these reloadable personal data
carriers also allow users to tailor applications to fit personal needs. Smart cards are
becoming crucial components of the E-Business economy and contribute to the realiza-
tion of E-Business anytime, anywhere.
Public key cryptography is critical element in contactless systems. Traditionally,
contactless systems have employed little-to-no security, due in large part to the very
constrained nature (i.e., size or space limitations) of the token or card. To date, the
majority of the security leveraged has been password-based technology, symmetric
cryptography for authentication and/or confidentiality services or, in some very limited
situations, legacy public key algorithms like RSA. It is clear that no security at all is
unacceptable and that password-based systems have very well known management
issues and security vulnerabilities.



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120 Ruzic


Currently, the choice for strong security is between symmetric and public key cryptog-
raphy. Symmetric key cryptography is characterized by the use of a single key to perform
both the encryption and decryption of data. The primary weakness of symmetric key
cryptography is referred to as the key management problem. Since the same key is used
for encryption and decryption, it must be kept secure. Symmetric key cryptography
transforms the problem of transmitting messages securely into that of transmitting keys
securely. Ensuring that the sender and receiver are using the same key and that potential
adversaries do not know this key remains a major stumbling block for symmetric key
cryptography. In addition, when a new application is added to a symmetric key-based
system, it must be permitted the same level of trust as the existing applications. If this
new application (or any other trusted element of a symmetric key system) is compromised,
so too is the entire system. In a contactless system that has tens of thousands of tokens
or tags, the ramifications of this compromise can be catastrophic.
Public key cryptography overcomes the key management problem by using different
encryption and decryption key pairs. This presents a significant advantage because two
users can communicate securely without exchanging secret keys (Kozlov & Reyzin,
2003). The portable credentials on the smart card can securely identify and authenticate
its owner, across the range of smart devices, providing a consistent means of authori-
zation and digital signature for E-Business transactions. With embedded applications,
these reloadable personal data carriers also allow users to tailor applications to fit
personal needs. Smart cards are becoming crucial components of the E-Business
economy and contribute to the realization of E-Business anytime, anywhere.


Signature Pads
This is a strong way of signaling signer intent because the person is signing in a
traditional way. It™s hard for persons (signers) to argue that they didn™t know what they
were doing “ a signature pad also offers a biometric signature, so it is used to authenticate



Figure 6. Example of electronic pad system accepting written signature for digitalization
process in electronic signature-based applications




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Electronic Signature 121


the signature as well. It is helpful for E-Business to let customers sign applications in their
homes electronically. E-signature pads are used too, as the biometrics mechanism for
verifying a hand-written signature with the holder of a pen.
Biometrics refers to the automatic identification of a person based on his/her physiologi-
cal or behavioral characteristics. This technology of identification is preferred over
traditional methods involving passwords and PINs (Personal Identification Numbers) for
various reasons: the person to be identified is required to be physically present at the
point of identification, and there is no need to remember a password/PIN or carry a token.
At the same time, biometrics technology can potentially prevent unauthorized access to
or fraudulent use of computer networks and information appliances connected to the E-
Business environment. PINs and passwords may be forgotten, and tokens may be forged,
stolen or lost. Thus biometrics technology is used in two basic ways “ as an authenti-
cation systems or as an identification system. It is worthy to note that although
biometrics technology provides stronger identification, a biometric identification sys-
tem based solely on a single identification identifier (fingerprints, faces, voice or another
object) is not able to meet high performance requirements “ thus, identification based
on multiple biometrics represents an emerging trend.
Security systems use biometrics for two basic purposes: to verify or to identify users
(Nanavati, Thieme & Nanavati, 2002). Biometrics measures individuals™ unique physical
or behavioral characteristics to recognize or authenticate their identity. Common physi-
cal biometrics includes fingerprints; hand or palm geometry; and retina, iris, or facial
characteristics. E-commerce developers are exploring the use of biometrics and smart
cards to more accurately verify a trading party™s identity. For example, many banks are
interested in this combination to better authenticate customers and ensure non-repudia-
tion of online banking, trading, and purchasing transactions. Point-of-sales (POS)
system vendors are working on the cardholder verification method, which would enlist
smart cards and biometrics to replace signature verification (Schaechter, 2002). MasterCard
estimates that adding smart-card-based biometrics authentication to a POS credit card
payment will decrease fraud by 80 percent.
In the smart card “ biometrics convergence process, the biometric information could be
represented by a fingerprint (Struif, 2001). During the enrollment phase, a fingerprint
template of the user is stored in a secure environment (smart card). For integrity and
authenticity purposes, the (hashed) fingerprint is then inserted in an “attribute certifi-
cate” and the same smart card also stores an X.509 certificate of the user, which will be
used to digitally sign electronic documents. In order to validate the fingerprint-identity
pair, two important pieces of information are added to the attribute certificate:
a) the serial number of the smart card - in this way the fingerprint can only be used
with that smart card
b) the serial number of the X.509 user digital certificate - in this way, the fingerprint
can only be used together with its owner


Since fingerprints cannot be lost, duplicated, stolen or forgotten, a smart-card-finger-
print reader is providing a more reliable and convenient solution than traditional security
devices. Security is improved further by storing the fingerprint templates inside a SIM
card instead of the computer. This not only provides a more secure environment but it


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122 Ruzic


Figure 7: Visual presentation of the smart card “ biometrics integration smart card/
fingerprint reader (identification and verification unit for e-signature utilization)




also enhances portability and eliminates privacy concerns. What is more, it gives users
the flexibility of being able to carry their fingerprint template with them, safe in the
knowledge that no one else can use their smart card should it become lost or stolen. Such
devices enhance smart card and PKI security by requiring a fingerprint instead of a PIN
or password, and the credentials (digital certificate, etc.) are kept securely on portable
smart card.
Typical applications for such devices are remote electronic voting, secure home-
banking, secure e-commerce, secure e-finance.


Summary of Purposes of Electronic Signatures

The processes of creating an electronic signature and verifying it using Public Key
Infrastructure accomplishes the essential effects that a handwritten signature does
today for many legal purposes:
• Signer authentication: If a public and private key is associated with an identified
signer, the digital signature attributes the message to the signer. The digital
signature cannot be forged, unless the signer loses control of the private key;
• Message authentication: The digital signature also identifies the signed message,
typically with far greater certainty and precision than paper signatures. Verification
reveals any tampering, since the comparison of the hash results shows whether the

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