Crypto Tutorial (shrt)  6-16-99
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Crypto Tutorial (shrt) 6-16-99


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Crypto Concepts CrypTEC SystemsField-Maintainable Secure Operating SystemsCertificate VersionCryptographic Serial NumberSignature AlgorithmIssuer (authority)Concepts Validity DatesSubject (owner)Public Key InformationCertificate CAA Tutorial For BusyAuthoritySSignatureCA CABusiness Executives. Cert.Hash DigestSFundamental security objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Privacy with secret-key and public key encryption . . . . . . . . . . . . . . . . . .6Integrity and non-repudiation with digital signatures . . . . . . . . . . . . . . . .8Authentication with digital certificates . . . . . . . . . . . . . . . . . . . . . . . . . .10An example of a hybrid crypto system — privacy-enhanced mail . . . . . .12Dual key sets for messaging and signing . . . . . . . . . . . . . . . . . . . . . . . . .13Cryptography summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Simple examples of public key mathematics . . . . . . . . . . . . . . . . . . . . . .15Cryptographic Legend Please take a minute Hashing operation, resulting in a Digital certificate, signed by a CertificateHash P to learn these symbols. message digest Authority (CA)CAC.T.Message digestDigest Understanding them Symmetric key encrypting operation: lockingPublic key encrypting operation: creating ana secret message is essential to under-M electronic envelope or verifying a signatureM Private key decrypting operation: opening an ...



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Crypto Concepts CrypTEC Systems
Field-Maintainable Secure Operating Systems
Certificate VersionCryptographic Serial Number
Signature Algorithm
Issuer (authority)Concepts Validity Dates
Subject (owner)
Public Key Information
Certificate CAA Tutorial For Busy
CA CABusiness Executives. Cert.
Hash DigestSFundamental security objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Privacy with secret-key and public key encryption . . . . . . . . . . . . . . . . . .6
Integrity and non-repudiation with digital signatures . . . . . . . . . . . . . . . .8
Authentication with digital certificates . . . . . . . . . . . . . . . . . . . . . . . . . .10
An example of a hybrid crypto system — privacy-enhanced mail . . . . . .12
Dual key sets for messaging and signing . . . . . . . . . . . . . . . . . . . . . . . . .13
Cryptography summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Simple examples of public key mathematics . . . . . . . . . . . . . . . . . . . . . .15
Cryptographic Legend Please take a minute
Hashing operation, resulting in a Digital certificate, signed by a Certificate
Hash P to learn these symbols. message digest Authority (CA)
Message digestDigest Understanding them
Symmetric key encrypting operation: lockingPublic key encrypting operation: creating an
a secret message is essential to under-M electronic envelope or verifying a signature
M Private key decrypting operation: opening an Symmetric key decrypting operation: unlock-
standing Cryptography. electronic envelope or creating a signature ing a secret message
Locked electronic envelope (typically con-
M C.R. Locked (symmetrically encrypted) message They will be used taining an encrypted session key)
CA Digital signature (a message digest, en-
? throughout the paper.Comparison: do these two equal each other?crypted with a private key)This document is for the busy executive who does not have time to become a “crypto
expert” to understand what technical people are saying. Cryptography is a complex
subject. However, it also is like a modern automobile: you don't have to know how to
build or fix a car to be qualified to drive it. This tutorial will give you enough informa-
tion to “drive” a crypto decision.
We are living in the Information Revolution, the third great revolution of humanity.
The Information Revolution succeeds the Agricultural Revolution and the Industrial
Revolution and, like the two that have gone before, is accelerating at a pace that has
not been experienced before. A dramatic alteration is taking place in the way informa-
tion is transmitted and exchanged. The traditional face-to-face, paper-based system we
have been using for the last thousand years or so is giving way to a new, faceless elec-
tronic commerce system that is rapidly expanding on a worldwide basis. We are cur-
rently caught between paper-based systems and the electronic versions that are replac-
ing them. This middle ground is painful. The paper-based systems still dominate, but
they are falling prey to advances in counterfeiting technologies at an alarming rate. (As
an example, in Northern California, a counterfeit California driver's license can be
bought on the street for $90, and that includes entering the illicit data in the
Department of Motor Vehicles’ computer!)
As the Information Revolution progresses, more and more paper-based systems are
being replaced by electronic means. Examples include paying for groceries at the
supermarket with our ATM cards, keeping our check registers on-line with
Quicken, sending e-mail to our business associates, and browsing the World
Wide Web to obtain dealer costs before negotiating with auto dealers.
Unfortunately, the very thing that attracts us to electronic com-
merce––the ease of manipulating information––also works for an
attacker in gaining access to critical information and using it
to damage the legitimate participants. Examples of elec-
tronic break-ins abound in daily life.
Digital transaction security has become a highly visible topic as more and more organi-
zations attempt to move critical and sensitive applications to open networks such as the
Internet. Companies have had to face the hard reality that the penalty for using the
Internet can be inferior security, which in turn has deterred many companies from
putting applications on the Internet or on internal intranets.
Modern cryptography can change that by providing digital security that is not only
equivalent, but is vastly superior to the paper-based system we have had for centuries.Fundamental
Security Objectives
As the information revolution has
entered our lives, some of our paper-
based transaction elements have been
replaced by electronic means.
Examples are when credit-card trans- very benefits that attracts us to elec-
actions are authorized over the phone tronic transactions —also works
or debit-card cash withdrawals are against us in terms of security. It is
authorized at the supermarket. simply too easy for a talented attacker
to gain access to critical information,
Unfortunately, the ease of moving
and in many cases, to change that
and storing information —one of the
information in ways that are damag-
ing to the interests of the legitimate
If the promise of electronic com-
merce is to be fulfilled, electronic
security elements have to be at leastProper security should
as good as face-to-face, paper-based
allow the transaction to security. And given the increasing vul-
nerability of paper systems to coun-
happen, prevent either terfeiting, and the fact that electronic
commerce breaks through the naturalparticipant from falsify-
ing any aspects of the
transaction (including
their identity), keep all
elements of the transac-
tion private, and leave
an audit trail for third
parties and law enforce-
ment to follow in case
of disputes or fraud.
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4What is security? How
do you know when you
have it? If the face-to-
face system we have
barriers of geography, time and physi-
used for thousands ofcal instruments, the need for electron-
ic substitutes is ever increasing.
years is examined, it
The good news is that with modern
becomes obvious thatcryptography, all of the elements of
face-to-face, paper-based transactions transactional security
can be replaced with electronic trans-
actions, which include: consists of four critical
• Privacy components: privacy,
• Authentication is usually a matter of transport such authentication, integri-
that the transacting entities are close
• Integrity
enough to communicate and transact. ty, and non-repudiation.
• Non-repudiation However, when the transaction takes
place over electronic facilities —even
Added to these four is one more ele-
if that transaction has all of the prop-
ment needed to accomplish security
er, digital-transaction security
over electronic networks: availability.
features —it is still possible for an
Legitimate users should not be denied
attacker to harm the participants by
access to information and resources.
denying them service (e.g., cut the
In the face-to-face world, availability
line, kill the power, jam the channel).
Of course, even if all four elements of
transactional security are in place, you
still may be defrauded by an unscrupu-
lous person—say, someone takes your
money and fails to deliver their end of
the bargain. However, if your security
is proper, that unscrupulous person
will have left an audit trail for the
authorities to follow and will not be
able to stay in business for very long.
Traditional paper method Electronic crypto method
Privacy is enforced by physical limitations such as dis- Digital privacy is enforced by symmetric encryption that is virtuallyPrivacy
tance, closed doors, safes, cabinets, and envelopes. impossible to break when used properly. Others may be able to copy the
These are used so others cannot see our transactions. transactions, but they will not be able to decode and understand them.
When we want to ensure that the people we deal with Digital authentication is produced via certificates—electronic “driver’sAuthentication
are who they say they are, we inspect a driver’s license licenses” digitally “signed” (hashed and encrypted by a private key) by a
or passport—examples of authentication. trusted authority—and a digital signature on a challenge file.
A transaction can be verified by carefully inspecting Digital verification reverses the signing process: a signature is decryptedIntegrity
the document that is authorized, to insure it properly with the authorizer’s public key to obtain the message digest. The mes-
represents the correct characteristics of the transac- sage is hashed to create a second digest. If the digests are identical, the
tion and was properly authorized, typically through a message is authentic and the signer’s identity is proven. Digital security
signature. The integrity of paper transaction protocols requires properly secured secret and private keys, and tamper-resistant
are protected by civil and criminal justice systems. protocols for system integrity.
A hand-written signature is used to prevent repudiated Digital non-repudiation is provided via digital signatures, which are creat-Non-repudiation
transactions, and is used to sign checks, credit card ed by hashing a message (file) and encrypting the result with the private
transactions, and contracts. key of the authorizer. This binds the digital signature to the digital mes-
sage (file) being authorized, making it extremely difficult to counterfeit.
5The problem with sym-Privacy
metric-key encryption isWith Secret Key And
a single key must be
Public Key Encryption
shared between each
One of the first components of elec- tions of a complex shifting, exclusive sender and receiver pair.
tronic security is privacy. The tradition- ORing, substituting and expanding of
al method of privacy is physical limi- the key and each 64 bits of data. If this
This shared key meanstations, such as being behind closed sounds complicated, that’s because it
doors. Privacy equates to confidential- is. That’s what makes it so secure. that the parties need to
ity, letting only selected people view a
DES has a drawback—its key lengths
particular transaction. Electronically, have established a rela-
are fixed at 56 bits (64 bits with parity).
privacy is established through encryp-
Thus, as computers get faster, the secu- tionship prior to com-tion—encoding a message or file so
rity of DES has come into question,
that no one can read it. municating.since a superfast computer could con-
To encrypt a file means to scramble a ceivably guess at all of the combinations
stream of data so that its original con- of 2 to the 56th power (72,057,594, key length. If a computer was ever built
tents cannot be read. Restoring the 037,927,900 choices). If a computer that could break DES in one second, it
data to its original form is known as could try a million guesses per second, would take over two billion years to try
decryption. Both encryption and then it could try all possible guesses in all the combinations of two-key 3DES!
decryption require a key, a digital 2,283 years. At a billion guesses per sec-
A single key must be shared. In symmet-message, and an encryption algorithm. ond, it would only take 2.28 years. At a
ric-key encryption, a single key mustThe two types of encryption methods trillion guesses per second, it would
be shared between each sender andused today are symmetric (or secret only take 20 hours!
receiver combination. (See Figure 2.)key) and asymmetric (or public key).
Other symmetric encryption algorithms This usually is inconvenient in appli-
such as RC4, RC5, BEST, CAST, etc. cations where electronic mail is used.Symmetric key encryption
have variable key lengths that allow us- To communicate with a large number
Symmetric (or secret key) encryption ing longer keys to keep ahead of the of people, you either need a separate,
is based on a single key used for en- crypto attackers as they benefit from secret key for each sender-receiver
cryption and decryption. The Data ever-faster computers. To increase the combination, or you must give several
Encryption Standard (DES) is the security of DES, users have gone to people the same secret key, thus mak-
most common symmetric algorithm in running the algorithm three times with ing it anything but a secret.
the U.S. (See Figure 1) and is used by three different DES keys (encrypt with
The Internet is too big for secret keys. federal agencies and the banking com- one key, decrypt with a second, and en-
In secret-key cryptography, the num-munity to protect non-classified data. crypt with a third.) This is called triple
ber of keys needed to do business isDES (3DES) and has the same effect asDES encryption also is known as
n(n-1)/2. So the Internet and its 100a 168-bit key. A variant of triple DES isblock encryption since data is encrypt-
million users would require 5,000 tril-two-key 3DES (encrypt with one key,ed in blocks of 64 bits, using a 56-bit
lion keys, approximately 100 milliondecrypt with the second, and then en-DES key (there are 8 parity bits as
of which would have to be put in acrypt with the first again). Two-keywell), and utilizing 16 different itera-
secret database for each user. 3DES is the equivalent of 112 bits of
Secret key: DES algorithm
Return for the next round (16 total)
Figure 1. Symmetric (or secret key)
encryption is based on a single key
My credit Message
card number (In 8-character used for encryption and decryption.DES is 3456 6348
blocks)Key 2643 1276...
The Data Encryption Standard (DES)
is the most common symmetric
Message BlockThe DES Key Bonding Bonding algorithm in the U.S., and is used(56 bits + 8 parity bits) (8 Characters [bytes]) (Exclusive OR) (Exclusive OR)
by federal agencies and the bank-
NewNewPermutation & Permutation Blocking Left Right
Blocking SideSide ing community to protect non-clas-
Blocking Blocking Substitution &Permutation & sified information.
(Left) (Right) CompactionBlocking
k1 w
s n b=1 e
Permutation & r v v i u /PermutationExpansion 8v ?$ [Compaction
Encrypted Message6 (At the end of 16 rounds)¥

Parties need to have a prior relationship.
Public-key encryption is based on two mathematicallyAnother problem with symmetric-key
distribution is the parties need to have related keys where each key in the pair performs a one-
had a prior relationship to transmit
way transformation on the data. There are two problemsnew keys. For example, for decades
the U.S. government sent secret sym-
with public-key encryption: performance issues and themetric keys to military bases and
embassies via human couriers with man-in-the-middle attack.
locked briefcases chained to their
wrists. This works with a relatively
encryption, one of the keys in the pair large numbers, and these operationssmall number of locations, but it does
is made publicly available, and the take a hundred to a thousand timesnot work with large numbers.
other is kept private, either on a hard- longer to compute than DES; and (b)
Symmetric encryption is fast. Although ware token or in computer software. public-key encryption lends itself to a
symmetric encryption is relatively fast cryptographic “man-in-the-middle”To send a protected message usingin computation, the problem of how attack. (where two people —Bill andpublic key encryption, the senderto transmit keys around a message Sue —want to communicate in secret,composes a message, then encrypts itgroup makes it extremely difficult to but an attacker —Te d —pops upwith the recipient’s public key. Onceadminister in a commercial setting. between them and convinces Bill thatencrypted, it can only be decrypted
he is Sue and Sue that he is Bill.)Public key encryption s private key. As
long as only the recipient has access Combining public key and Public key is the solution for a huge number
to the private key, the sender can be symmetric-key encryption of participants. Public key encryption is
assured that only the recipient can
the only rational solution for the huge To solve the problem of performance,decrypt the message. Also if a message
number of participants involved in modern encryption systems use a hy-can be decrypted with the sender’s
electronic commerce applications. brid combination of encryption: first,public key, the recipient can be as-
Public key encryption solves the prob- symmetric encryption —typicallysured that only the sender could have
lem of key distribution in large DES—is used to encrypt the actualencrypted it, because only the sender
groups by introducing the concepts of message, and then public key encryp-possesses the private key. (The prob-
digital signatures and certificates. tion is used for authentication, keylem here is that signing a message by
distribution (sending symmetric keysPublic-key: Asymmetric encryption. Public encrypting it with a private key means
to recipients), and digital signatures. key encryption is based on two math- the message will no longer be secret,
ematically related keys that are gener- since the “verifying” key is public. We Symmetric encryption is fast, but can-
ated together. Each key in the pair will solve this problem later on.) not provide a scalable key exchange
performs the inverse function of the capability or a digital signature,Public-key calculations involve the expo-
other so what one key encrypts, the whereas public key encryption cannentiation of very large numbers. Public-
other key decrypts, and vice versa. provide these features, but is muchkey encryption solves the key-distribu-
Since each key only encrypts or slower. A hybrid crypto systemtion problem, but has two major
decrypts in a single direction, public- extracts the best of both while simul-drawbacks: (a) public-key calculations
key encryption is also known as asym- taneously avoiding the worst. take much longer than symmetric key
metric encryption. (See Figure 3.)
calculations. Public key calculations
A public key has two parts. In public-key involve the exponentiation of very
The symmetric key concept The public key concept
Sell 100Sell 100 Sell 100 Sell 100ert Ú›u ert Ú›uk1 w k1 w shares ofshares of shares of shares ofet… isd568 et… isd568 s n b=1 e s n b=1 e ABCDABCD ABCD ABCDøªbnbˆ6B 78 øªbnbˆ6B 78r v v i u / r v v i u / Industries—Industries— Industries— Industries—B¨´ÎbBT ¥˙ B¨´ÎbBT ¥˙ 8v ?$ [ 8v ?$ [ John SmithJohn Smith John Smith John Smithpo po
Encrypt Decrypt
Encrypt Decrypt Plaintext Cyphertext Cyphertext PlaintextPlaintext Cyphertext Cyphertext Plaintext
Anything encrypted with the public key can only be decrypted with the correspondingAnything encrypted with the symmetric (“secret,” “session,” “message,” “file,” etc.) key
private key, and anything encrypted with the private key can only be decrypted with thecan be decrypted with the same symmetric key, and vice versa.
corresponding public key.
Figure 2. With symmetric key encryption, ship to transmit new keys. Although this Figure 3. Public key encryption is based available and the other is kept private,
a single key must be shared between each method works well with a small number of on two mathematically related keys. Each either on a hardware token or in software.
sender and receiver combination. Both parties, it is doesn’t work efficiently with a key in the pair performs the inverse of the Public key encryption also solves the prob-
parties also need to have a prior relation- large number of participants. other so what one key encrypts, the other lem of key distribution in large groups with
decrypts. One of the keys is made publicly the concept of certificates.
7Integrity And
Non-Repudiation With
Digital Signatures
duces the same value for both parties,
it proves the document has not been
altered along the way.
is similar —if the transmitted “remain-The use of public key encryption calls
Hashing is a difficult concept for der” (digest) is the same as the newlyfor digital signatures and certificates.
many people to understand. A similar calculated “remainder” (digest), theThese tools create integrity, another
process, used in computer communi- message has not been altered.major fundamental component of
cations for decades, was cyclic redun-electronic security. Traditional meth- Digital integrity is a digital signature.dancy checking (CRC)—a way to veri-ods of establishing integrity would be
fy that what the sender transmitted Remember the privacy problem ofto visually examine a document to
was what the recipient received. With “signing” a message by encrypting itverify that it legitimately represented
CRC, a digital message is considered with the sender's private key? Hashinga particular transaction. For example,
to be a very large number. A sender solves this problem. Instead of en-you would read a contract to ensure
would divide that large number by a crypting the message with the sender'sthe document included all information
smaller number (divisor) and keep private key as a signature, modernregarding a specific legal transaction.
dividing until all that was left was a cryptography has the sender encryptFor digital signatures to also maintain
remainder. The remainder and divisor the message digest with his or her pri-privacy, hashing is used. Digital signa-
would be transmitted to the recipient vate key. Since the recipient also ob-tures also enable a mechanism called a
who would execute the same division tains the message in an encrypteddigital certificate.
process to see if the same remainder fashion (say, DES-encrypted), then
was left. If the transmitted remainderHashing and message digests only the recipient will have the right
and the calculated remainder were the message to hash and compare with theA hash is a complex, one-way, math-
same, the recipient was assured that sender's message digest, which isematical function that reduces a mes-
the message had not been altered dur- derived by decrypting the sender'ssage of any length to a unique, 160-
ing the transmission. digital signature and obtaining thebit (secure hash algorithm) or 128-bit
sender's message digest.Conceptually, hashing is the same(RSA MD 2 & MD 5 hashing algo-
idea. Figure 4 illustrates the Securerithms) message digest. The same Therefore, a digital signature is de-
Hash Algorithm (SHA). Notice that atmessage will always hash to the same fined to be a message digest encrypted
message-digest value. So, if even one the end of the hashing process, what is with the signer's (sender's) private key.
bit in the message is changed, the left —no matter how long the message
Digital integrity is established throughmessage digest will change dramati- —is a 160-bit “remainder value” called
a digital signature, which uniquelya message digest. Although hashing iscally. The sender and the recipient
creates extra data for a message thata much more sophisticated mathemati-each perform the same hash computa-
identifies and authenticates the signercal process than long division, the resulttion on the message. If the hash pro-
and the message data.
An example of hashing
Figure 4. A hash is a complex, one- (1-512 bits) length (K)
Lx512 bits=Nx32 bits
way, mathematical function that 64
K bits (< 2 bits)
reduces a message of any length to a
Message 1000…0
unique 160-bit or 128-bit message. The
same message will always hash to the
512 bits 512 bits 512 bits 512 bits
same message digest value. So, if even
Y Y Y Y0 1 x L-1one bit in the message is changed, the
512 512 512 512message digest will change dramatical-
ly. If the hash produces the same value
Hash Hash Hash Hash
160 160 160for both parties, and it was signed by
the sender, it proves the document has 160
not been altered.
ABCDE 160-bit8
(Initial value) Message
Digestwe all know, a written signature by itself
A digital signature is a does not prove that the message is valid.
When a recipient of a secure messagemessage digest that has
wants to verify a digital signature (and
that the message has not been alteredbeen encrypted by the drawings––anything that can be digi-since the sender signed it), the recipi-
tized (See Figure 5.) Digital signa-ent uses their crypto system to:private key of the signer. tures can be used to prove that a con-
• Recalculate the document's message tract previously signed has not been
digest (by hashing). altered, and to certify items such asSince a digital signature is created by
certificates, credit accounts, reportshashing the message and then • Retrieve the original message digest
and other kinds of digital informa-encrypting the resulting message by decrypting the signature with the
tion.digest with the private key of the sign- signer's public key.
er, a digital signature binds the con- Digital signatures also are very useful• Compare the recalculated message
tents of the message to the signing of for enforcing required rules for com-digest to the transmitted message
the message, such that a signature patibility with a hardware or softwaredigest that was just decrypted from
cannot be moved from one message to system. For example, if a video-gamethe signature.
another. If even one single bit of data manufacturer wants to make sure that
has changed, the message digests will If the two message digests match, the no competing manufacturer’s games
differ and the signature will not verify. recipient knows that: will work on the first manufacturer's
Since only the sender has access to the game player, it digitally signs all• The document has not been altered.
private key, no one else can create this approved games and has the player
signature. • Only the signer, with their corre- check for the proper signature.
sponding private key, could have Without the manufacturer's private
Digital signatures are better than created the digital signature. key, the pirate company cannot make
written signatures.
any games that will run on that play-
Digital signatures are a powerful
er.The purpose of a hand-written signa- encryption tool.
ture on a paper document is to uni-
quely identify the sender and provide Digital signatures are used not only to
authentication/authorization for a authenticate messages, but also to
message or a transaction. However, as authenticate program code or data
files that have been downloaded from
a remote source, pictures, movies,
A signature can be applied to anything digital
Figure 5. Anything that can be digi-
tized can be digitally signed, includ-
Sell 100 Sell 100
shares of shares of ing messages, program code, pic-ABCD ABCD SCodeSIndustries— Msg HashIndustries—Hash DigestJohn Smith Digest John Smith tures, and fingerprint templates.
Digital S Since the signing entity is the onlyMessage
organization holding the private
COLOR="#ADA990" key, all counterfeiters are out ofCOLOR="#ADA990"
SIZE="2" SIZE="2"
FACE="Arial"> S FACE="Arial"> SCode Print <B> Hash <B> Hash business unless they can obtain a
Project Start: Digest Digest Project Start:
<BR> <BR> S
Project Finish: Project Finish: bootleg copy of that private key—a </B> Scanned </B> FingerprintS
Fingerprint TemplateProgram very difficult task if the signer isCode
exercizing good security procedures.
NAuthentication With Digital
Think of the digital cer- son who claims to own the certificate.
You may obtain certificates over the
tificate as an electronic
Internet from VeriSign at:A major component of electronic secu- is authentication. In the tradition- identity card or a digital
al method of security, examples of Hierarchical certificate chains
authentication are a driver’s license or driver’s license.
Digital certificates, like an identitya passport. These instruments are
card, expire and can be revoked if theissued by an authority and are gener-
corresponding private key has beenally accepted as factual and truthful. a certificate is only valid after it has
compromised. Maintenance of certifi-been “notarized” (digitally signed) by
Electronic authentication is established cates is the responsibility of the ad-a recognized authority. (See Figure 6.)
with digital certificates. ministrator. But how do you know
The CA’s chief function is to verify identity. that the authority that issued the userA digital certificate (also called pub- A certificate authority (CA) is an enti-
a certificate was authorized to do so? lic-key certificates or digital IDs) is a ty that attests to the identity of a per-
file that attests to someone’s or some The answer is that a certificate is typi-son or organization. A certificate
organization’s ownership of specific cally not a single file, but a chain ofauthority might be an external compa-
digital data (such as a public key). certificate files that leads back to anny, such as VeriSign, that offers cer-
Cryptographic operations are per- ultimate authority —typically thetificate services, or a CA might be an
formed on certificates to provide a company that licenses the technologyinternal organization such as a corpo-
higher level of assurance of someone’s or the association (e.g., VISA orrate MIS department. The CA’s chief
ownership than a simple, name/pass- MasterCard). function is to verify the identity of
word pair. entities and to issue digital certificates The certificate chain for the SET
attesting to that identity.Digital certificates are issued by recognized (Secure Electronic Transaction) speci-
authorities. A digital certificate is issued fication is shown in Figure 7. (SET isYou must obtain a valid public-key
by a trusted third-party and is used to a collection of transaction protocolscertificate from a recognized authori-
prevent someone from assuming a to securely conduct electronic com-ty to send and receive secured mes-
false cryptographic identity (e.g., a merce on the Internet.) At the end ofsages or data. An administrator typi-
man-in-the-middle attack). When you a certificate hierarchy is a top-levelcally issues digital certificates on
use the information in a digital cer- certifying authority, which is trustedbehalf of that authority, and will not
tificate to validate a signature or to without a certificate from any otherdigitally sign a certificate until they
find the public key of your intended. The public key ofcan vouch for the identity of the per-
recipient, you can be sure of the iden-
tity of the certificate’s owner because
How signature verification process happens
Certificate Version Figure 6. Digital certificates are
Serial Number
Certificate issued by a trusted third party andSignature Algorithm information
(in plaintext)
Issuer (authority) are used to validate a signature or to
Validity Dates
find the public key of a recipient. You
Subject (owner)
Public Key Information can be assured of the identity of the
CA Certifying Signature by certificate’s owner because a
the Certificate Authority
certificate is only valid after it has
Certificate Version been “notarized” or digitally signed
Serial Number
Signature Algorithm
Issuer (authority) by a recognized authority.Hash Digest
Validity Dates
Subject (owner)
Public Key Information ?