Internet Security Lectures by Prabhaker MatetiPrabhaker Mateti
Abstract:Data integrity and privacy on the Internet primarily rests on usingcryptography well. Unfortunately, it is easily compromised by errorsin (operating) system configuration. This lecture is a quick overviewof cryptography as relevant in Internet security and passwords.
Data integrity and privacy on the Internet primarily rests on usingcryptography well. The design and implementation of cryptographyrequires deep understanding of discrete mathematics and number theory.Unfortunately, when cryptography is deployed carelessly, it is easilycompromised by errors in (operating) system configuration. Thislecture is a quick overview of cryptography as relevant in Internetsecurity and passwords.
A cryptographic encryption algorithm, also known as cipher,transforms a “plain text” (e.g., humanreadable) pt and outputs cipher textct as the output,
so that it is possible to re-generate the pt fromthe ct through a companion decryption algorithm. Notethat we said “for example, human readable” and not”that is, human readable” as an explanation for the phrase”plain text”. Often, the so-called “plain text”is human un-readable binary data that is ready-to-be-used by acomputer.
Ciphers use keys together with plain text as the input to produce cipher text. It is in the key that the security of a modern cipher lies, not in the details of the algorithm.
Roughly speaking, computationally infeasible means that a certaincomputation that we are talking about takes way too long (hundreds ofyears) to compute using the fastest of (super)computers.
Suppose our key is a 128-bit number. There are
128-bit numbers starting from zero (i.e., 128 bits of 0). Torecover a particular key by brute force, one must, on average, searchhalf the key space:
If we use 1,000,000,000 machines that could try 1,000,000,000keys/sec, it would take all these machines longer than the universe aswe know it has existed to find the key.
This is not the same thing as saying that computationalinfeasibility is the same idea as Turing-incomputable. Nor is it thesame thing as saying that you cannot make a lucky guess, orheuristically arrive at a possible answer, and then systematicallyverify that the guessed answer is indeed the correct answer, all donewithin a matter of seconds on a lowly PC. Here is an example:Microsoft Windows NT uses the DES encryption algorithm in storing thepasswords. Brute-forcing such a scrambled password to compute theplain text password can take, according to Microsoft, “about abillion years.” But the L0pht team( http://www.l0pht.com) claims thatL0phtCrack breaks Windows passwords in about one week, running in thebackground on an old Pentium PC.
In the context of cryptography, the factorization of an arbitrarilylarge number N, into its constituent primes, determining the powersn2, n3, n5, n7, etc. of the primes, is computationally infeasible –as far as we know.
N = 2n2 * 3 n3* 5 n5 * 7 n7* …
Based on this, the decryption is computationally infeasible. Note thatthis is assuming that we are using known methods, including brute force.
Is it possible that some one or some country has actuallydiscovered fast algorithms, but chose to keep them secret, for these tasksthat we believe to be computationally infeasible?
A hash function maps input sequences of bytes into a fixed-lengthsequence. The fixed length is considerably shorter than thetypical length (thousands of bytes) of the input, and hence thefunction is a hash function.
The nature of all hash functions is that there must exist multipleinput sequences that map to the same hash. The inverse is amathematical relation, not a mathematical function. But, good hashfunctions have the following properties: It is hard to find twostrings, from the expected set of typically used strings, that wouldproduce the same hash value. A slight change in an input stringcauses the hash value to change drastically.
A “one way” hash function is designed to be computationallyinfeasible to reverse the process, that is, to algorithmicallydiscover a string that hashes to a given value.
One-way hashfunctions are also known as message digests (MD), fingerprints, orcompression functions. The most popular one-way hash algorithms areMD4 and MD5 (both producing a 128-bit hash value), and SHA, also knownas SHA1 (producing a 160-bit hash value).
As of 2006, both MD5 and SHA1 are considered separately broken. Thatis, given plain text p, it is possible to modify p to a desired p’ sothat md5(p) == md5(p’); similarly, for SHA1. What is not known is ifwe can modify p to a p’ so that md5(p) == md5(p’) and sha1(p)== sha1(p’).
Symmetric-key cryptography is an encryption system in which thesender and receiver of a message share a single, common key to encryptand decrypt the message. Symmetric-key systems are simpler andfaster, but their main drawback is that the two parties must somehowexchange the key in a secure way. Symmetric-key cryptography issometimes also called secret-key cryptography.
If ct = encryption (pt, key), then pt = decryption (ct, key).
The most popular symmetric-key system is the DES, short for DataEncryption Standard. DES was developed in 1975 andstandardized by ANSI in 1981 as ANSI X.3.92. DES encrypts data in64-bit blocks using a 56-bit key. The algorithm transforms theinput in a series of steps into a 64-bit output.
IDEA (International Data Encryption Algorithm) is a block cipherwhich uses a 128-bit length key to encrypt successive 64-bit blocks ofplain text. The procedure is quite complicated using subkeys generatedfrom the key to carry out a series of modular arithmetic and XORoperations on segments of the 64-bit plaintext block. The encryptionscheme uses a total of fifty-two 16-bit subkeys.
Blowfish is a symmetric block cipher that can be used as a drop-inreplacement for DES or IDEA. It takes a variable-length key, from 32bits to 448 bits, making it ideal for both domestic and exportableuse. Blowfish is unpatented and license-free, and is availablefree for all uses.
Public key cryptography uses two keys — a public key knownto everyone, and a private or secret key that is safeguarded. Public key cryptography was invented in 1976 by WhitfieldDiffie and Martin Hellman. For this reason, it is sometimes alsocalled Diffie-Hellman encryption. It is also calledasymmetric encryption because it uses two keys instead of one key. The two keys are mathematically related, yet it is computationally infeasible to deduce one from the other.
Unfortunately, public-key cryptography is about 1000 times slowerthan symmetric key cryptography.
The most well-known of the public-key encryption algorithms is RSA, named after its designers Rivest, Shamir, and Adelman. The un-breakability of the algorithm is based on the fact that there is no efficient way to factor very large numbers into their primes.
An example of the above numbers: rsa.txt. Look up the man page: openssl(1).
The e and d are symmetric in that using either ((n,e) or (n,d)) as the encryption key, the other can be used as the decryption key.
The only way known to find d is to know p and q. If the number n is small, p and q are easy todiscover by prime factorization. Thus, p and q are chosen to be as large as possible,say, a few hundred digits long. Obviously, p and qshould never be revealed, preferably destroyed.
Encryption isdone as follows. Consider the entire message to be encrypted asa sequence of bits. Suppose the length of n in bits is b. Split the message into blocks of length b or b-1. A block viewedas a b-bit number should be less than n; if it is not, choose it to beb-1 bits long. Each block is separately encrypted, and theencryption of the entire message is the catenation of the encryptionof the blocks. Let m stand for a block viewed as a number. Multiply m with itself e times, and take the modulo n result as c,which is the encryption of m. That is, c = m^emod n.
Decryption is the “inverse” operation: m = c^dmod n.
The Digital Signature Algorithm (DSA) is a United States Federal Government standard for digital signatures.
An example of the above numbers: dsa.txt.Look up the man page: openssl(1).
Public-key systems, such as Pretty Good Privacy (PGP), are popular for transmitting information via the Internet. They are extremely secure and relatively simple to use. You need to retrieve the recipient’s public key from one of several world-wide registries of public keys that now exist to encrypt a message.
When John wants to send a secure message to Jane, he uses Jane’s public key to encrypt the message. Jane then uses her private key to decrypt it.
In real-world implementations, public keys are rarely used to encrypt actual messages because public-key cryptography is slow. Instead, public-key cryptography is used to distribute symmetric keys, which are then used to encrypt and decrypt actual messages, as follows:
A digital signature is a way to authenticate to a recipient that a received object is indeed that of the sender.
The public key-based communication between Alice and Bob described above is vulnerable to a man-in-the-middle attack.
Let us assume that Mallory, a cracker, not only can listen to thetraffic between Alice and Bob, but also can modify, delete, andsubstitute Alice’s and Bob’s messages, as well as introduce newones. Mallory can impersonate Alice when talking to Bob andimpersonate Bob when talking to Alice. Here is how the attackworks.
A man-in-the-middle attack works because Alice and Bob have no wayto verify they are talking to each other. An independent third partythat everyone trusts is needed to foil the attack. This third partycould bundle the name “Bob” with Bob’s public key and signthe package with its own private key. When Alice receives the signedpublic key from Bob, she can verify the third party’s signature. Thisway she knows that the public key really belongs to Bob, and notMallory.
A package containing a person’s name (and possibly some otherinformation such as an E-mail address and company name) and his publickey and signed by a trusted third party is called a digital certificate (ordigital ID). An independent third party that everyone trusts, whoseresponsibility is to issue certificates, is called a CertificationAuthority (CA). A digital certificate serves two purposes. First, itprovides a cryptographic key that allows another party to encryptinformation for the certificate’s owner. Second, it provides a measureof proof that the holder of the certificate is who they claim to be -because otherwise, they will not be able to decrypt any informationthat was encrypted using the key in the certificate.
The recipient of an encrypted message uses the CA’s public key todecode the digital certificate attached to the message, verifies it asissued by the CA and then obtains the sender’s public key andidentification information held within the certificate. With thisinformation, the recipient can send an encrypted reply.
The most widely used standard for digital certificates is X.509,which defines the following structure for public-key certificates:
You can obtain a personal certificate from companies likeverisign.com or comodo.com.
- Trend Micro - Simply Security News, Views and Opinions from ... - May 30th, 2019
- Kaspersky Internet Security - Wikipedia - May 13th, 2019
- Anti-Virus Web Protection & Spyware Removal | StopSign ... - May 13th, 2019
- Internet security Great-West Life - ssl.grsaccess.com - March 22nd, 2019
- Download COMODO Internet Security 18.104.22.16844 - softpedia.com - January 31st, 2019
- Avast Internet Security Review 2018 - We Hate Malware - November 8th, 2018
- Security Packages | High-Speed Internet | Windstream - November 8th, 2018
- Antivirus vs Internet Security [Security Software Comparison] - November 8th, 2018
- Vipre Internet Security 2016 Free Download - Softlay - November 8th, 2018
- Internet security software Reviews 2018 - Compared & Reviewed - November 2nd, 2018
- Exhibit A - Internet Security Requirements - November 2nd, 2018
- CIS Benchmarks - Center for Internet Security - November 2nd, 2018
- Kaspersky Internet Security 2018 Crack + License Key [Latest] - October 12th, 2018
- Zillya! Internet Security | Best Security Solution for Active ... - October 12th, 2018
- Download Norton Internet Security 22.214.171.124 - softpedia.com - October 9th, 2018
- Avast Internet Security 2018 Activation Code, Serial Key Till ... - October 9th, 2018
- Download Avast Internet Security 18.6.2349 Build 18.6.3983 ... - October 9th, 2018
- Download McAfee Internet Security 19.0 Build 19.0.4016 - October 3rd, 2018
- AVG Internet Security 2018 Free Download - FileHippo - October 3rd, 2018
- Internet Security - Quick Heal - October 3rd, 2018
- Kaspersky Internet Security 2019 v126.96.36.1998 | Software ... - October 3rd, 2018
- VIPRE Internet Security Review & Comparison - September 22nd, 2018
- Internet Security Suite | Verizon Internet - September 20th, 2018
- Antivirus Security Software & Internet Security - Newegg.com - September 19th, 2018
- Amazon Best Sellers: Best Internet Security Suites - September 7th, 2018
- Download Bitdefender Internet Security 2019 188.8.131.52 - August 24th, 2018
- Best (and Worst) Internet Security Software of 2018 for Windows - August 18th, 2018
- Amazon.com: Kaspersky Internet Security 2018 | 3 Device | 1 ... - August 8th, 2018
- AVG Internet Security - Free download and software reviews ... - August 3rd, 2018
- Top 3 Internet Security Software Suites Reviews ... - July 26th, 2018
- GRC | LeakTest -- Firewall Leakage Tester - July 26th, 2018
- Internet Security is an important part of Identity Theft ... - June 22nd, 2018
- V3 Internet Security | AhnLab - June 22nd, 2018
- Internet Security with Xfinity - Norton Security Online - June 17th, 2018
- Best Internet Security Software Compared - May 25th, 2018
- Computer and internet security software Chili Security - May 21st, 2018
- Internet Security Market Size, Share and Technology, 2021 - May 21st, 2018
- Center for Internet Security - Wikipedia - May 10th, 2018
- Download Webroot SecureAnywhere Antivirus & Internet ... - May 1st, 2018
- AVG Internet Security 2018 review | Ultimate antivirus ... - April 29th, 2018
- The Internet Security Academy - SAHCOM Technologies LLP - April 27th, 2018
- These files can't be opened. Your Internet security ... - April 20th, 2018
- How to Uninstall Norton Internet Security: 12 Steps - April 20th, 2018
- Internet Security Software at Office Depot OfficeMax - April 19th, 2018
- Why is Internet security important? | Reference.com - March 26th, 2018
- AVG Internet Security Unlimited 2018 18.2.3827 20% OFF ... - March 25th, 2018
- Trend Micro Titanium Internet Security - Download - March 21st, 2018
- Kaspersky Mobile Antivirus: AppLock & Web Security ... - March 21st, 2018
- Why do I Need Internet Security - The High Tech Society - March 21st, 2018
- Cincinnati Bell - Other Services Support - March 21st, 2018
- Internet Security Essentials for Business 2.0 | U.S ... - March 21st, 2018
- ESET Internet Security 10.0.386.0 Crack + License Keys ... - March 21st, 2018
- Privacy and Security in the Internet Age | WIRED - March 19th, 2018
- News & Events | K9 Web Protection - Free Internet Filter ... - March 19th, 2018
- 10 Internet Security Programs (for Windows), Ranked Best ... - March 7th, 2018
- AVG Internet Security 2015 Free Download - getintopc.com - March 3rd, 2018
- McAfee Internet Security Download - softpedia.com - February 28th, 2018
- COMODO Internet Security Download - softpedia.com - January 30th, 2018
- Best Internet Security Software 2018 - The best rated ... - January 28th, 2018
- Comodo Antivirus - Best Virus Removal Software 2018 - January 13th, 2018
- ZoneAlarm Antivirus Software | Virus Protection & Firewall - January 13th, 2018
- What Is the Meaning of Internet Security? | Techwalla.com - January 12th, 2018
- Download Avast Internet Security 17.7.2314 - FileHippo.com - January 12th, 2018
- Vipre Antivirus VIPRE Internet Security - January 12th, 2018
- AVG Internet Security 2018 License Key With Crack Full Version - January 8th, 2018
- CA Internet Security Suite Plus - Download - December 27th, 2017
- Collaborative Security: An approach to tackling Internet ... - December 27th, 2017
- Norton Internet Security - Download - December 20th, 2017
- Best Internet Security 2017 - Total Security Software for ... - December 20th, 2017
- Get the Best Internet Security Software of 2016! - December 20th, 2017
- Internet Security Administrator: Job Description and Requirements - December 19th, 2017
- Top 10 Cheap Antivirus and Internet Security Protection for ... - December 19th, 2017
- Download AVG Internet Security Unlimited - FileHippo.com - December 19th, 2017
- Norton Internet Security - softpedia.com - December 19th, 2017
- Internet Security - Cisco - December 19th, 2017
- Best Antivirus Software, Internet Security & Malware Removal - December 19th, 2017
- internet security | eBay - October 26th, 2017
- Avast Internet Security Download - softpedia.com - October 20th, 2017
- Internet Security Software | Trend Micro - October 3rd, 2017
- Lenovo Faces No Significant Penalty for Security-Destroying Superfish Debacle - ExtremeTech - September 7th, 2017