Pass the ISC 2 Credentials SSCP Questions and answers with ExamsMirror

Cryptography is a detective control in the fact that it allows the detection of fraudulent insertion, deletion or modification. It also is a preventive control is the fact that it prevents disclosure, but it usually does not offers any means of detecting disclosure.

Source: DUPUIS, Clement, CISSP Open Study Guide on domain 5, cryptography, April 1999.

A Public Key is also known as an asymmetric algorithm and the use of a secret key would be a symmetric algorithm.

The following answers are incorrect:

Use of the recipient's public key for encryption and decryption based on the recipient's private key. Is incorrect this would be known as an asymmetric algorithm.

Use of software encryption assisted by a hardware encryption accelerator. This is incorrect, it is a distractor.

Use of Elliptic Curve Encryption. Is incorrect this would use an asymmetric algorithm.

An extremely simple example of conventional cryptography is a substitution cipher.

A substitution cipher substitutes one piece of information for another. This is most frequently done by offsetting letters of the alphabet. Two examples are Captain Midnight's Secret Decoder Ring, which you may have owned when you were a kid, and Julius Caesar's cipher. In both cases, the algorithm is to offset the alphabet and the key is the number of characters to offset it. So the offset could be one, two, or any number you wish. ROT-13 is an example where it is shifted 13 spaces. The Ceaser Cipher is another example where it is shifted 3 letters to the left.

ROT13 ("rotate by 13 places", sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the letter 13 letters after it in the alphabet. ROT13 is an example of the Caesar cipher, developed in ancient Rome.

In the basic Latin alphabet, ROT13 is its own inverse; that is, to undo ROT13, the same algorithm is applied, so the same action can be used for encoding and decoding. The algorithm provides virtually no cryptographic security, and is often cited as a canonical example of weak encryption.

ROT13 is used in online forums as a means of hiding spoilers, puzzle solutions, and offensive materials from the casual glance. ROT13 has been described as the "Usenet equivalent of a magazine printing the answer to a quiz upside down". ROT13 has inspired a variety of letter and word games on-line, and is frequently mentioned in newsgroup conversations. See diagram Below:

Rot 13 Cipher

The following are incorrect:

The Caesar cipher is a simple substitution cipher that involves shifting the alphabet three positions to the right. In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.

Caesar Cipher

Polyalphabetic cipher refers to using multiple alphabets at a time. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The Vigenère cipher is probably the best-known example of a polyalphabetic cipher, though it is a simplified special case.

Viginere Cipher

Transposition cipher is a different type of cipher. In cryptography, a transposition cipher is a method of encryption by which the positions held by units of plaintext (which are commonly characters or groups of characters) are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext. That is, the order of the units is changed. See the reference below for multiple examples of Transpositio Ciphers.

An exemple of Transposition cipher could be columnar transposition, the message is written out in rows of a fixed length, and then read out again column by column, and the columns are chosen in some scrambled order. Both the width of the rows and the permutation of the columns are usually defined by a keyword. For example, the word ZEBRAS is of length 6 (so the rows are of length 6), and the permutation is defined by the alphabetical order of the letters in the keyword. In this case, the order would be "6 3 2 4 1 5".

In a regular columnar transposition cipher, any spare spaces are filled with nulls; in an irregular columnar transposition cipher, the spaces are left blank. Finally, the message is read off in columns, in the order specified by the keyword. For example, suppose we use the keyword ZEBRAS and the message WE ARE DISCOVERED. FLEE AT ONCE. In a regular columnar transposition, we write this into the grid as Follows:

Transposition Cipher

Providing five nulls (QKJEU) at the end. The ciphertext is then read off as:

EVLNE ACDTK ESEAQ ROFOJ DEECU WIREE

Reference(s) used for this question:

http://en.wikipedia.org/wiki/ROT13

http://en.wikipedia.org/wiki/Caesar_cipher

http://en.wikipedia.org/wiki/Polyalphabetic_cipher

http://en.wikipedia.org/wiki/Transposition_cipher

In cryptography, a public key certificate (or identity certificate) is an electronic document which incorporates a digital signature to bind together a public key with an identity — information such as the name of a person or an organization, their address, and so forth. The certificate can be used to verify that a public key belongs to an individual.

In a typical public key infrastructure (PKI) scheme, the signature will be of a certificate authority (CA). In a web of trust scheme, the signature is of either the user (a self-signed certificate) or other users ("endorsements"). In either case, the signatures on a certificate are attestations by the certificate signer that the identity information and the public key belong together.

In computer security, an authorization certificate (also known as an attribute certificate) is a digital document that describes a written permission from the issuer to use a service or a resource that the issuer controls or has access to use. The permission can be delegated.

Some people constantly confuse PKCs and ACs. An analogy may make the distinction clear. A PKC can be considered to be like a passport: it identifies the holder, tends to last for a long time, and should not be trivial to obtain. An AC is more like an entry visa: it is typically issued by a different authority and does not last for as long a time. As acquiring an entry visa typically requires presenting a passport, getting a visa can be a simpler process.

A real life example of this can be found in the mobile software deployments by large service providers and are typically applied to platforms such as Microsoft Smartphone (and related), Symbian OS, J2ME, and others.

In each of these systems a mobile communications service provider may customize the mobile terminal client distribution (ie. the mobile phone operating system or application environment) to include one or more root certificates each associated with a set of capabilities or permissions such as "update firmware", "access address book", "use radio interface", and the most basic one, "install and execute". When a developer wishes to enable distribution and execution in one of these controlled environments they must acquire a certificate from an appropriate CA, typically a large commercial CA, and in the process they usually have their identity verified using out-of-band mechanisms such as a combination of phone call, validation of their legal entity through government and commercial databases, etc., similar to the high assurance SSL certificate vetting process, though often there are additional specific requirements imposed on would-be developers/publishers.

Once the identity has been validated they are issued an identity certificate they can use to sign their software; generally the software signed by the developer or publisher's identity certificate is not distributed but rather it is submitted to processor to possibly test or profile the content before generating an authorization certificate which is unique to the particular software release. That certificate is then used with an ephemeral asymmetric key-pair to sign the software as the last step of preparation for distribution. There are many advantages to separating the identity and authorization certificates especially relating to risk mitigation of new content being accepted into the system and key management as well as recovery from errant software which can be used as attack vectors.

References:

HARRIS, Shon, All-In-One CISSP Certification Exam Guide, 2001, McGraw-Hill/Osborne, page 540.

http://en.wikipedia.org/wiki/Attribute_certificate

http://en.wikipedia.org/wiki/Public_key_certificate

Kerberos depends on secret keys (symmetric ciphers). Kerberos is a third party authentication protocol. It was designed and developed in the mid 1980's by MIT. It is considered open source but is copyrighted and owned by MIT. It relies on the user's secret keys. The password is used to encrypt and decrypt the keys.

The following answers are incorrect:

It utilizes public key cryptography. Is incorrect because Kerberos depends on secret keys (symmetric ciphers).

It encrypts data after a ticket is granted, but passwords are exchanged in plain text. Is incorrect because the passwords are not exchanged but used for encryption and decryption of the keys.

It is a second party authentication system. Is incorrect because Kerberos is a third party authentication system, you authenticate to the third party (Kerberos) and not the system you are accessing.

References:

MIT http://web.mit.edu/kerberos/

Wikipedi http://en.wikipedia.org/wiki/Kerberos_%28protocol%29

OIG CBK Access Control (pages 181 - 184)

AIOv3 Access Control (pages 151 - 155)

A Birthday attack is usually applied to the probability of two different messages using the same hash function producing a common message digest.

The term "birthday" comes from the fact that in a room with 23 people, the probability of two of more people having the same birthday is greater than 50%.

Linear cryptanalysis is a general form of cryptanalysis based on finding affine approximations to the action of a cipher. Attacks have been developed for block ciphers and stream ciphers. Linear cryptanalysis is one of the two most widely used attacks on block ciphers; the other being differential cryptanalysis.

Differential Cryptanalysis is a potent cryptanalytic technique introduced by Biham and Shamir. Differential cryptanalysis is designed for the study and attack of DES-like cryptosystems. A DES-like cryptosystem is an iterated cryptosystem which relies on conventional cryptographic techniques such as substitution and diffusion.

Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in an input can affect the resultant difference at the output. In the case of a block cipher, it refers to a set of techniques for tracing differences through the network of transformations, discovering where the cipher exhibits non-random behaviour, and exploiting such properties to recover the secret key.

Source:

KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 4: Cryptography (page 163).

and

http://en.wikipedia.org/wiki/Differential_cryptanalysis

Source: TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.

Split knowledge involves encryption keys being separated into two components, each of which does not reveal the other. Split knowledge is the other complementary access control principle to dual control.

In cryptographic terms, one could say dual control and split knowledge are properly implemented if no one person has access to or knowledge of the content of the complete cryptographic key being protected by the two rocesses.

The sound implementation of dual control and split knowledge in a cryptographic environment necessarily means that the quickest way to break the key would be through the best attack known for the algorithm of that key. The principles of dual control and split knowledge primarily apply to access to plaintext keys.

Access to cryptographic keys used for encrypting and decrypting data or access to keys that are encrypted under a master key (which may or may not be maintained under dual control and split knowledge) do not require dual control and split knowledge. Dual control and split knowledge can be summed up as the determination of any part of a key being protected must require the collusion between two or more persons with each supplying unique cryptographic materials that must be joined together to access the protected key.

Any feasible method to violate the axiom means that the principles of dual control and split knowledge are not being upheld.

Split knowledge is the unique “what each must bring” and joined together when implementing dual control. To illustrate, a box containing petty cash is secured by one combination lock and one keyed lock. One employee is given the combination to the combo lock and another employee has possession of the correct key to the keyed lock.

In order to get the cash out of the box both employees must be present at the cash box at the same time. One cannot open the box without the other. This is the aspect of dual control.

On the other hand, split knowledge is exemplified here by the different objects (the combination to the combo lock and the correct physical key), both of which are unique and necessary, that each brings to the meeting. Split knowledge focuses on the uniqueness of separate objects that must be joined together.

Dual control has to do with forcing the collusion of at least two or more persons to combine their split knowledge to gain access to an asset. Both split knowledge and dual control complement each other and are necessary functions that implement the segregation of duties in high integrity cryptographic environments.

The following are incorrect answers:

Dual control is a procedure that uses two or more entities (usually persons) operating in concert to protect a system resource, such that no single entity acting alone can access that resource. Dual control is implemented as a security procedure that requires two or more persons to come together and collude to complete a process. In a cryptographic system the two (or more) persons would each supply a unique key, that when taken together, performs a cryptographic process. Split knowledge is the other complementary access control principle to dual control.

Separation of duties - The practice of dividing the steps in a system function among different individuals, so as to keep a single individual from subverting the process.

The need-to-know principle requires a user having necessity for access to, knowledge of, or possession of specific information required to perform official tasks or services.

Reference(s) used for this question:

Schneiter, Andrew (2013-04-15). Official (ISC)2 Guide to the CISSP CBK, Third Edition : Cryptography (Kindle Locations 1621-1635). . Kindle Edition.

and

Schneiter, Andrew (2013-04-15). Official (ISC)2 Guide to the CISSP CBK, Third Edition : Cryptography (Kindle Locations 1643-1650). . Kindle Edition.

and

Shon Harris, CISSP All In One (AIO), 6th Edition , page 126

There is no DES mode call DES-EEE1. It does not exist.

The following are the correct modes for triple-DES (3DES):

DES-EEE3 uses three keys for encryption and the data is encrypted, encrypted, encrypted;

DES-EDE3 uses three keys and encrypts, decrypts and encrypts data.

DES-EEE2 and DES-EDE2 are the same as the previous modes, but the first and third operations use the same key.

Reference(s) used for this question:

Shon Harris, CISSP All In One (AIO) book, 6th edition , page 808

and

Official ISC2 Guide to the CISSP CBK, 2nd Edition (2010) , page 344-345

RFC 2828 (Internet Security Glossary) defines a digital signature as a value computed with a cryptographic algorithm and appended to a data object in such a way that any recipient of the data can use the signature to verify the data's origin and integrity.

The steps to create a Digital Signature are very simple:

1. You create a Message Digest of the message you wish to send

2. You encrypt the message digest using your Private Key which is the action of Signing

3. You send the Message along with the Digital Signature to the recipient

To validate the Digital Signature the recipient will make use of the sender Public Key. Here are the steps:

1. The receiver will decrypt the Digital Signature using the sender Publick Key producing a clear text message digest.

2. The receiver will produce his own message digest of the message received.

3. At this point the receiver will compare the two message digest (the one sent and the one produce by the receiver), if the two matches, it proves the authenticity of the message and it confirms that the message was not modified in transit validating the integrity as well. Digital Signatures provides for Authenticity and Integrity only. There is no confidentiality in place, if you wish to get confidentiality it would be needed for the sender to encrypt everything with the receiver public key as a last step before sending the message.

A Digital Envelope is a combination of encrypted data and its encryption key in an encrypted form that has been prepared for use of the recipient. In simple term it is a type of security that uses two layers of encryption to protect a message. First, the message itself is encoded using symmetric encryption, and then the key to decode the message is encrypted using public-key encryption. This technique overcomes one of the problems of public-key encryption, which is that it is slower than symmetric encryption. Because only the key is protected with public-key encryption, there is very little overhead.

A cryptographic hash is the result of a cryptographic hash function such as MD5, SHA-1, or SHA-2. A hash value also called a Message Digest is like a fingerprint of a message. It is used to proves integrity and ensure the message was not changed either in transit or in storage.

A Message Authentication Code (MAC) refers to an ANSI standard for a checksum that is computed with a keyed hash that is based on DES or it can also be produced without using DES by concataning the Secret Key at the end of the message (simply adding it at the end of the message) being sent and then producing a Message digest of the Message+Secret Key together. The MAC is then attached and sent along with the message but the Secret Key is NEVER sent in clear text over the network.

In cryptography, HMAC (Hash-based Message Authentication Code), is a specific construction for calculating a message authentication code (MAC) involving a cryptographic hash function in combination with a secret key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authenticity of a message. Any cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly. The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output length in bits and on the size and quality of the cryptographic key.

There is more than one type of MAC: Meet CBC-MAC

In cryptography, a Cipher Block Chaining Message Authentication Code, abbreviated CBC-MAC, is a technique for constructing a message authentication code from a block cipher. The message is encrypted with some block cipher algorithm in CBC mode to create a chain of blocks such that each block depends on the proper encryption of the previous block. This interdependence ensures that a change to any of the plaintext bits will cause the final encrypted block to change in a way that cannot be predicted or counteracted without knowing the key to the block cipher.

References:

SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000.

and

http://www.webopedia.com/TERM/D/digital_envelope.html

and

http://en.wikipedia.org/wiki/CBC-MAC

DES is also known as a Symmetric Key or Secret Key algorithm.

DES is a Symmetric Key algorithm, meaning the same key is used for encryption and decryption.

For the exam remember that:

DES key Sequence is 8 Bytes or 64 bits (8 x 8 = 64 bits)

DES has an Effective key length of only 56 Bits. 8 of the Bits are used for parity purpose only.

DES has a total key length of 64 Bits.

The following answers are incorrect:

Two-key This is incorrect because DES uses the same key for encryption and decryption.

Asymmetric Key This is incorrect because DES is a Symmetric Key algorithm using the same key for encryption and decryption and an Asymmetric Key algorithm uses both a Public Key and a Private Key.

Public Key. This is incorrect because Public Key or algorithm Asymmetric Key does not use the same key is used for encryption and decryption.

References used for this question:

http://en.wikipedia.org/wiki/Data_Encryption_Standard

S/MIME (for Secure MIME, or Secure Multipurpose Mail Extension) is a security process used for e-mail exchanges that makes it possible to guarantee the confidentiality and non-repudiation of electronic messages.

S/MIME is based on the MIME standard, the goal of which is to let users attach files other than ASCII text files to electronic messages. The MIME standard therefore makes it possible to attach all types of files to e-mails.

S/MIME was originally developed by the company RSA Data Security. Ratified in July 1999 by the IETF, S/MIME has become a standard, whose specifications are contained in RFCs 2630 to 2633.

How S/MIME works

The S/MIME standard is based on the principle of public-key encryption. S/MIME therefore makes it possible to encrypt the content of messages but does not encrypt the communication.

The various sections of an electronic message, encoded according to the MIME standard, are each encrypted using a session key.

The session key is inserted in each section's header, and is encrypted using the recipient's public key. Only the recipient can open the message's body, using his private key, which guarantees the confidentiality and integrity of the received message.

In addition, the message's signature is encrypted with the sender's private key. Anyone intercepting the communication can read the content of the message's signature, but this ensures the recipient of the sender's identity, since only the sender is capable of encrypting a message (with his private key) that can be decrypted with his public key.

Reference(s) used for this question:

http://en.kioskea.net/contents/139-cryptography-s-mime

RFC 2630: Cryptographic Message Syntax;

OPPLIGER, Rolf, Secure Messaging with PGP and S/MIME, 2000, Artech House;

HARRIS, Shon, All-In-One CISSP Certification Exam Guide, 2001, McGraw-Hill/Osborne, page 570;

SMITH, Richard E., Internet Cryptography, 1997, Addison-Wesley Pub Co.

Data Encryption Standard (DES) is a symmetric key algorithm. Originally developed by IBM, under project name Lucifer, this 128-bit algorithm was accepted by the NIST in 1974, but the total key size was reduced to 64 bits, 56 of which make up the effective key, plus and extra 8 bits for parity. It somehow became a national cryptographic standard in 1977, and an American National Standard Institute (ANSI) standard in 1978. DES was later replaced by the Advanced Encryption Standard (AES) by the NIST.

Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter 8: Cryptography (page 525).

The above statement is NOT true and thus the correct answer. The maximum key size on Rijndael is 256 bits.

There are some differences between Rijndael and the official FIPS-197 specification for AES.

Rijndael specification per se is specified with block and key sizes that must be a multiple of 32 bits, both with a minimum of 128 and a maximum of 256 bits. Namely, Rijndael allows for both key and block sizes to be chosen independently from the set of { 128, 160, 192, 224, 256 } bits. (And the key size does not in fact have to match the block size).

However, FIPS-197 specifies that the block size must always be 128 bits in AES, and that the key size may be either 128, 192, or 256 bits. Therefore AES-128, AES-192, and AES-256 are actually:

Key Size (bits) Block Size (bits)

AES-128 128 128

AES-192 192 128

AES-256 256 128

So in short:

Rijndael and AES differ only in the range of supported values for the block length and cipher key length.

For Rijndael, the block length and the key length can be independently specified to any multiple of 32 bits, with a minimum of 128 bits, and a maximum of 256 bits.

AES fixes the block length to 128 bits, and supports key lengths of 128, 192 or 256 bits only.

References used for this question:

http://blogs.msdn.com/b/shawnfa/archive/2006/10/09/the-differences-between-rijndael-and-aes.aspx

and

http://csrc.nist.gov/CryptoToolkit/aes/rijndael/Rijndael.pdf

RFC 2828 (Internet Security Glossary) defines the Internet Security Association and Key Management Protocol (ISAKMP) as an Internet IPsec protocol to negotiate, establish, modify, and delete security associations, and to exchange key generation and authentication data, independent of the details of any specific key generation technique, key establishment protocol, encryption algorithm, or authentication mechanism.

Let's clear up some confusion here first. Internet Key Exchange (IKE) is a hybrid protocol, it consists of 3 "protocols"

ISAKMP: It's not a key exchange protocol per se, it's a framework on which key exchange protocols operate. ISAKMP is part of IKE. IKE establishs the shared security policy and authenticated keys. ISAKMP is the protocol that specifies the mechanics of the key exchange.

Oakley: Describes the "modes" of key exchange (e.g. perfect forward secrecy for keys, identity protection, and authentication). Oakley describes a series of key exchanges and services.

SKEME: Provides support for public-key-based key exchange, key distribution centres, and manual installation, it also outlines methods of secure and fast key refreshment.

So yes, IPSec does use IKE, but ISAKMP is part of IKE.

The questions did not ask for the actual key negotiation being done but only for the "exchange of key generation and authentication data" being done. Under Oakly it would be Diffie Hellman (DH) that would be used for the actual key nogotiation.

The following are incorrect answers:

Simple Key-management for Internet Protocols (SKIP) is a key distribution protocol that uses hybrid encryption to convey session keys that are used to encrypt data in IP packets.

OAKLEY is a key establishment protocol (proposed for IPsec but superseded by IKE) based on the Diffie-Hellman algorithm and designed to be a compatible component of ISAKMP.

IPsec Key Exchange (IKE) is an Internet, IPsec, key-establishment protocol [R2409] (partly based on OAKLEY) that is intended for putting in place authenticated keying material for use with ISAKMP and for other security associations, such as in AH and ESP.

Reference used for this question:

SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000.