insider attack , cryptogrraphy, password policy

umairchill5

boyle_ccs3_pp_03.ppt

Home >Information Systems homework help >insider attack , cryptogrraphy, password policy

Cryptography

Chapter 3

Explain the concept of cryptography.
Describe symmetric key encryption and the importance of key length.
Explain negotiation stage.
Explain initial authentication, including MS-CHAP.
Describe keying, including public key encryption.
Explain how electronic signatures, including digital signatures, digital certificates, and key-hashed message authentication codes (HMACs) work.
Describe public key encryption for authentication.
Describe quantum security.
Explain cryptographic systems including VPNs, SSL, and IPsec.

Chapter 1 introduced the threat environment
Chapter 2 introduced the plan-protect-respond cycle and covered the planning phase
Chapters 3 through 9 will cover the protection phase
Chapter 3 introduces cryptography, which is important in itself and which is used in many other protections

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Cryptography is the use of mathematical operations to protect messages traveling between parties or stored on a computer
Confidentiality means that someone intercepting your communications cannot read them

???

Confidentiality is only one cryptographic protection
Authentication means proving one’s identity to another so they can trust you more
Integrity means that the message cannot be changed or, if it is changed, that this change will be detected
Known as the CIA of cryptography

No, not that CIA

Encryption for confidentiality needs a cipher (mathematical method) to encrypt and decrypt

The cipher cannot be kept secret

The two parties using the cipher also need to know a secret key or keys

A key is merely a long stream of bits (1s and 0s)

The key or keys must be kept secret

Cryptanalysts attempt to crack (find) the key

n o p q r

This is a very weak cipher.

Real ciphers use complex math.

Figure 3-2

Plaintext	Key	Ciphertext
n	4	r
o	8	w
w	15	l
i	16	…
s	23	…
t	16	…
h	3	…
e	9	…
t	12	…
i	20	…
m	6	…
e	25	…

Substitution Ciphers

Substitute one letter (or bit) for another in each place

The cipher we saw in Figure 3-2 is a substitution cipher

Transposition Ciphers

Transposition ciphers do not change individual letters or bits, but they change their order

Most real ciphers use both substitution and transposition

Key (Part 1)
Key (Part 2)	1	3	2
2	n	o	w
3	i	s	t
1	h	e	t
Key = 132 231

Ciphers can encrypt any message expressed in binary (1s and 0s)

This flexibility and the speed of computing makes this ciphers dominant for encryption today

Codes are more specialized

They substitute one thing for another

Usually a word for another word or a number for a word

Codes are good for humans and may be included in messages sent via encipherment

Transmitted:

174346371783971…

Message	Code
From	17434
Akagi	63717
To	83971
Truk	11131
STOP	34058
ETA	53764
6 PM	73104
STOP	26733
Require	29798
B	72135
N	54678
STOP	61552

Each extra bit

doubles the number of keys

Shaded keys are

Strong symmetric keys (>=100 bits)

Key Length in Bits	Number of Possible Keys
1	2
2	4
4	16
8	256
16	65,536
40	1,099,511,627,776
56	72,057,594,037,927,900
112	5,192,296,858,534,830,000,000,000,000,000,000
112	5.1923E+33
168	3.74144E+50
256	1.15792E+77
512	1.3408E+154

Note:

Public key/private key pairs (discussed later in the chapter) must be much longer than symmetric keys to be considered to be strong because of the disastrous consequences that could occur if a private key is cracked and because private keys cannot be changed frequently. Public keys and private keys must be at least 512 to 1,024 bits long

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

RC4	DES	3DES	AES
Key Length (bits)	40 bits or more	56	112 or 168	128, 192, or 256
Key Strength	Very weak at 40 bits	Weak	Strong	Strong
Processing Requirements	Low	Moderate	High	Low
RAM Requirements	Low	Moderate	Moderate	Low
Remarks	Can use keys of variable lengths	Created in the 1970s	Applies DES three times with two or three different DES keys	Today’s gold standard for symmetric key encryption

The DES cipher encrypts messages 64 bits at a time

The DES cipher (in codebook mode) needs two inputs

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Cryptographic Systems

Encryption for confidentiality is only one cryptographic protection

Individual users and corporations cannot be expected to master these many aspects of cryptography

Consequently, crypto protections are organized into complete cryptographic systems that provide a broad set of cryptographic protection

Cryptographic Systems

Two parties first agree upon a particular cryptographic system to use

Each cryptographic system dialogue begins with three brief handshaking stages

The two parties then engage in cryptographically protected communication

This ongoing communication stage usually constitutes nearly all of the dialogue

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Selecting methods and parameters

Authentication

Keying (the secure exchange of secrets)

Ongoing communication

Cipher Suite	Key Negotiation	Digital Signature Method	Symmetric Key Encryption Method	Hashing Method for HMAC	Strength
NULL_WITH_NULL_NULL	None	None	None	None	None
RSA_EXPORT_WITH_ RC4_40_MD5	RSA export strength (40 bits)	RSA export strength (40 bits)	RC4 (40-bit key)	MD5	Weak
RSA_WITH_DES_CBC_ SHA	RSA	RSA	DES_CBC	SHA-1	Stronger but not very strong
DH_DSS_WITH_3DES_ EDE_CBC_SHA	Diffie–Hellman	Digital Signature Standard	3DES_ EDE_CBC	SHA-1	Strong
RSA_WITH_AES_256_CBC_SHA256	RSA	RSA	AES 256 bits	SHA-256	Very strong

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Selecting methods and parameters

Authentication

Keying (the secure exchange of secrets)

Ongoing communication

Hashing

A hashing algorithm is applied to a bit string of any length

The result of the calculation is called the hash

For a given hashing algorithm, all hashes are the same short length

Bit string of any length

Hash: bit string of small fixed length

Hashing

Algorithm

Hashing versus Encryption

Characteristic	Encryption	Hashing
Result length	About the same length as the plaintext	Short fixed length regardless of message length
Reversible?	Yes. Decryption	No. There is no way to get from the short hash back to the long original message

Hashing Algorithms

MD5 (128-bit hashes)

SHA-1 (160-bit hashes)

SHA-224, SHA-256, SHA-384, and SHA-512 (name gives hash length in bits)

Note: MD5 and SHA-1 should not be used because have been shown to be unsecure

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Selecting methods and parameters

Authentication

Keying (the secure exchange of secrets)

Ongoing communication

There are two types of ciphers used for confidentiality

In symmetric key encryption for confidentiality, the two sides use the same key

For each dialogue (session), a new symmetric key is generated: the symmetric session key

In public key encryption, each party has a public key and a private key that are never changed

A person’s public key is available to anyone

A person keeps his or her private key secret

The two parties exchange parameters p and g
Each uses a number that is never shared explicitly to compute a second number

Each sends the other their second number

Each does another computation on the second computed number
Both get the third number, which is the key
All of this communication is sent in the clear

The gory details

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Selecting methods and parameters

Authentication

Keying (the secure exchange of secrets)

Ongoing communication

Consumes nearly all of the dialogues
Message-by-Message Encryption

Nearly always uses symmetric key encryption

Already covered

Public key encryption is too inefficient

Message-by-Message Authentication

Digital signatures

Message authentication codes (MACs)

Also provide message-by-message integrity

Encryption is done to protect the plaintext

It is not needed for message-by-message authentication

Point of frequent confusion

Encryption Goal	Sender Encrypts with	Receiver Decrypts with
Public Key Encryption for Confidentiality	The receiver’s public key	The receiver’s private key
Public Key Encryption for Authentication	The sender’s private key	The True Party’s public key (not the sender’s public key)

Cannot use the sender’s public key

It would always “validate” the sender’s digital signature

Normally requires a digital certificate

File provided by a certificate authority (CA)

The certificate authority must be trustworthy

Digital certificate provides the subject’s (True Party’s) name and public key

Don’t confuse digital signatures and the digital certificates used to test digital signatures!

Certificate provides the True Party’s public key

Serial number allows the receiver to check if the digital certificate has been revoked by the CA

Field	Description
Version Number	Version number of the X.509 standard. Most certificates follow Version 3. Different versions have different fields. This figure reflects the Version 3 standard.
Issuer	Name of the Certificate Authority (CA).
Serial Number	Unique serial number for the certificate, set by the CA.
Subject (True Party)	The name of the person, organization, computer, or program to which the certificate has been issued. This is the true party.
Public Key	The public key of the subject (the true party).
Public Key Algorithm	The algorithm the subject uses to sign messages with digital signatures.

The CA signs the cert with its own private key so that the cert’s validity can be checked for alterations.

Field	Description
Digital Signature	The digital signature of the certificate, signed by the CA with the CA’s own private key. For testing certificate authentication and integrity. User must know the CA’s public key independently.
Signature Algorithm Identifier	The digital signature algorithm the CA uses to sign its certificates.
Other Fields	…

Testing the Digital Signature

The digital certificate has a digital signature of its own

Signed with the Certificate Authority’s (CA’s) private key

Must be tested with the CA’s well-known public key

If the test works, the certificate is authentic and unmodified

Checking the Valid Period

Certificate is valid only during the valid period in the digital certificate (not shown in the figure)

If the current time is not within the valid period, reject the digital certificate

Checking for Revocation

Certificates may be revoked for improper behavior or other reasons

Revocation must be tested

Cannot be done by looking at fields within the certificate

Receiver must check with the CA

Checking for Revocation

Verifier may download the entire certificate revocation list from the CA

See if the serial number is on the certificate revocation list

If so, do not accept the certificate

Or, the verifier may send a query to the CA

Requires the CA to support the Online Certificate Status Protocol

Also Brings Message Integrity

If the message has been altered, the authentication method will fail automatically

Digital Signature Authentication

Uses public key encryption for authentication

Very strong but expensive

Key-Hashed Message Authentication Codes

An alternate authentication method using hashing

Much less expensive than digital signature authentication

Much more widely used

As in the case of digital signatures, confidentiality is done to protect the plaintext.

It is not needed for authentication and has nothing to do with authentication.

Nonrepudiation means that the sender cannot deny that he or she sent a message
With digital signatures, the sender must use his or her private key

It is difficult to repudiate that you sent something if you use your private key

With HMACs, both parties know the key used to create the HMAC

The sender can repudiate the message, claiming that the receiver created it

However, packet-level nonrepudiation is unimportant in most cases
The application message—an e-mail message, a contract, etc., is the important thing
If the application layer message has its own digital signature, you have nonrepudiation for the application message, even if you use HMACs at the Internet layer for packet authentication

Replay Attacks

Capture and then retransmit an encrypted message later

May have a desired effect

Even if the attacker cannot read the message

Thwarting Replay Attacks

Time stamps to ensure freshness of each message

Sequence numbers so that repeated messages can be detected

Nonces

Unique randomly generated number placed in each request message

Reflected in the response message

If a request arrives with a previously used nonce, it is rejected

Confidentiality	Authentication
Symmetric Key Encryption	Applicable. Sender encrypts with key shared with the receiver.	Not applicable.
Public Key Encryption	Applicable. Sender encrypts with receiver’s public key. Receiver decrypts with the receiver’s own private key.	Applicable. Sender (supplicant) encrypts with own private key. Receiver (verifier) decrypts with the public key of the true party, usually obtained from the true party’s digital certificate.
Hashing	Not applicable.	Applicable. Used in MS-CHAP for initial authentication and in HMACs for message-by-message authentication.

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

Quantum Mechanics

Describes the behavior of fundamental particles

Complex and even weird results

Quantum Key Distribution

Transmits a very long key—as long as the message

This is a one-time key that will not be used again

A one-time key as long as a message cannot be cracked by cryptanalysis

If an interceptor reads part of the key in transit, this will be immediately apparent to the sender and receiver

Quantum Key Cracking

Tests many keys simultaneously

If quantum key cracking becomes capable of working on long keys, today’s strong key lengths will offer no protection

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

3.1 What Is Cryptography

3.2 Symmetric Key Encryption Ciphers

3.3 Cryptographic System Standards

3.4 The Negotiation Stage

3.5 Initial Authentication Stage

3.6 The Keying Stage

3.7 Message-by-Message Authentication

3.8 Quantum Security

3.9 Cryptographic Systems

3.10 SSL/TLS and IPsec

SSL/TLS	IPsec
Cryptographic security standard	Yes	Yes
Cryptographic security protections	Good	Gold Standard
Supports central management	No	Yes
Complexity and expense	Lower	Higher
Layer of operation	Transport	Internet
Transparently protects all higher-layer traffic	No	Yes
Works with IPv4 and IPv6	NA	Yes
Modes of operation	NA	Transport, Tunnel

End-to-End

Security

(Good)

Security in
Site Network

(Good)

Setup Cost

On Each Host

(Costly)

No Security in
Site Network

(Bad)

No Setup Cost

On Each Host

(Good)

Characteristic	Transport Mode	Tunnel Mode
Uses an IPsec VPN Gateway?	No	Yes
Cryptographic Protection	All the way from the source host to the destination host, including the Internet and the two site networks.	Only over the Internet between the IPsec gateways. Not within the two site networks.
Setup Costs	High. Setup requires the creation of a digital certificate for each client and significant configuration work.	Low. Only the IPsec gateways must implement IPsec, so only they need digital certificates and need to be configured.

Characteristic	Transport Mode	Tunnel Mode
Firewall Friendliness	Bad. A firewall at the border to a site cannot filter packets because the content is encrypted.	Good. Each packet is decrypted by the IPsec gateway. A border firewall after the IPsec gateway can filter the decrypted packet.
The “Bottom Line”	End-to-end security at high cost.	Low cost and protects the packet over the most dangerous part of its journey.

Publishing as Prentice Hall