Chapter 3: Basic Cryptography

Diffie-Hellman Ephemeral (DHE)

A Diffie-Hellman key exchange that uses different keys that are temporary and discarded after use.

Elliptic Curve Diffie-Hellman (ECDH)

A Diffie-Hellman key exchange that uses elliptic curve cryptography instead of prime numbers in its computation.

Digital Signature Algorithm (DSA)

A U.S. federal government standard for digital signatures. DSA was proposed by NIST in 1991 for use in their Digital Signature Standard (DSS). Although patented, NIST has made this patent available world wide royalty-free. The standard continues to be revised and updated periodically by NIST.

Blowfish

A block cipher that operates on 64-bit blocks and can have a key length from 32 to 448 bits. Blowfish was designed to run efficiently on 32-bit computers. To date, no significant weaknesses have been identified.

block cipher

A cipher that manipulates an entire block of plaintext at one time. Usually 8 to 16 bits.

deprecated algorithm

A cryptographic algorithm that is still available but should not be used because of known vulnerabilities. Selecting weak algorithms, like DES or SHA-1, should be avoided since these could be broken by a threat actor.

Hardware Security Module (HSM)

A dedicated cryptographic processor that provides protection for cryptographic keys. An HSM includes an onboard key generator and key storage facility, as well as accelerated symmetric and asymmetric encryption, and can even back up sensitive material in encrypted form. Most HSMs are local area network (LAN)-based appliances that can provide services to multiple devices.

Twofish

A derivation of the Blowfish algorithm that is also considered to be a strong algorithm, although it has not been used as widely as Blowfish.

Hashing Property: Fixed Size

A digest of a short set of data should produce the same size as a digest of a long set of data.

security through obscurity

A false notion that virtually any system can be made secure so long as outsiders are unaware of it or how it functions. This is a flawed approach since it is essentially impossible to keep "secrets" from everyone.

BitLocker

A full disk encryption (FDE) software created by Microsoft encrypts the entire system volume, including the Windows Registry and any temporary files that might hold confidential information. BitLocker prevents attackers from accessing data by booting from another operating system or placing the hard drive in another computer.

RACE Integrity Primitives Evaluation Message Digest (RIPEMD)

A hash algorithm that uses two different and independent parallel chains of computation and then combines the result at the end of the process. Developed by the Research and Development in Advanced Communications Technologies (RACE), an organization that is affiliated with the European Union (EU). The primary design feature of RIPEMD is two different and independent parallel chains of computation, the results of which are then combined at the end of the process.

Hashed Message Authentication Code (HMAC)

A hash function used to authenticate the sender. It does this by using both a hash function and a secret cryptographic key. A message authentication code (MAC) combines the original message with a shared secret key that only the sender and receiver know. A hash function is then applied to both the key and the message, and for added security they are hashed in separate steps. When the receiver gets the HMAC it then creates its own HMAC to compare with what was sent: if they match then it knows that the MAC came from the sender (because only the sender has the secret key), thus authenticating the sender of the message.

Diffie-Hellman (DH)

A key exchange that requires all parties to agree upon a large prime number and related integer so that the same key can be separately created.

resource vs. security constraint

A limitation in providing strong cryptography due to the tug-of-war between the available resources (time and energy) and the security provided by cryptography. common with low-power devices. Ideally, for a cryptographic algorithm there should be low latency but this can be a struggle do to resources.

Diffusion

A means to thwart statistical analysis so that if a single character of plaintext is changed then it should result in multiple characters of the ciphertext changing. Eliminating a one to one correspondence between the plaintext and the ciphertext makes it more difficult for a threat actor to perform cryptoanalysis, since the plaintext is diffused across several characters of the ciphertext.

confusion

A means to thwart statistical analysis so that the key does not relate in a simple way to the ciphertext.

Secure Hash Algorithm (SHA)

A secure hash algorithm that creates more secure hash values than Message Digest (MD) algorithms. The first version was SHA-0, which due to a flaw was withdrawn shortly after it was first released. Its successor, SHA-1, was developed in 1993 by the U.S. National Security Agency (NSA) and the National Institute of Standards and Technology (NIST). It creates a digest that is 160 bits instead of 128 bits in length (MD4). It pads messages of less than 512 bits with zeros and an integer that describes the original length of the message. The padded message is then processed through the SHA algorithm to produce the digest. Because SHA-3 is relatively compact, it may be suitable for some low-power devices. One of the design goals of SHA-3 was for it to be dissimilar to previous hash algorithms to prevent threat actors from building upon any previous work of compromising these algorithms.

low latency

A small amount of time that occurs between when a byte is input into a cryptographic algorithm and the time the output is obtained. One way to decrease latency is to make the cryptographic algorithm run faster. But this increases power consumption, which is either not available to low-power devices or would slow down the normal operations of the device.

birthday attack

A statistical phenomenon that makes finding collisions easier. It is based on the birthday paradox, which says that for there to be a 50 percent chance that someone in a given room shares your birthday, 253 people would need to be in the room. If, however, you are looking for a greater than 50 percent chance that any two people in the room have the same birthday, you only need 23 people. That's because the matches are based on pairs. If you choose yourself as one side of the pair, then you will need 253 people to have 253 pairs (in other words, it is you combined with 253 other people to make up all 253 sets). But if you are only concerned with matches and not concerned with matching someone with you specifically, then you only need 23 people in the room, because it only takes 23 people to form 253 pairs when cross-matched with each other. This applies to hashing collisions in that it is much harder to find something that collides with a specific hash than it is to find any two inputs that hash to the same value.

Advanced Encryption Standard (AES)

A symmetric cipher that was approved by the NIST in late 2000 as a replacement for DES. AES performs three steps on every block (128 bits) of plaintext. Within step 2, multiple rounds are performed depending upon the key size: a 128-bit key performs 9 rounds, a 192-bit key performs 11 rounds,and a 256-bit key, known as AES-256, uses 13 rounds. Within each round, bytes are substituted and rearranged, and then special multiplication is performed based on the new arrangement. To date, no attacks have been successful against AES and it is therefore the most secure symmetric cipher.

Triple Data Encryption Standard (3DES)

A symmetric cipher that was designed to replace DES. As its name implies, 3DES uses three rounds of encryption instead of just one. Although 3DES addresses several of the key weaknesses of DES, it is no longer considered the most secure symmetric cryptographic algorithm.

ephemeral key

A temporary key that is used only once before it is discarded.

data-in-transit

Actions that transmit the data across a network.

asymmetric cryptographic algorithm

Also known as public key cryptography. Asymmetric encryption uses two keys instead of only one. These keys are mathematically related and are called the public key and the private key.

RC4 (Rivest Cipher 4)

An RC stream cipher that will accept keys up to 128 bits in length. Part of a family of 6 ciphers each different in how they operate.

pseudorandom number generator (PRNG)

An algorithm for creating a sequence of numbers whose properties approximate those of a random number.

Hash

An algorithm that creates a unique digital fingerprint called a "digest" (sometimes called a message digest or hash). Hashing is used primarily for comparison purposes. Although hashing is a cryptographic algorithm, its purpose is not to create ciphertext that can later be decrypted. Instead, hashing is intended to be oneway in that its digest cannot be reversed to reveal the original set of data.

stream cipher

An algorithm that takes one character and replaces it with one character. Works on one character at a time.

private key

An asymmetric encryption key that does have to be protected. And is used to encrypt usually but can be used to decrypt.

public key

An asymmetric encryption key that does not have to be protected. Is used to encrypt usually, but can be used to decrypt.

downgrade attack

An attack in which the system is forced to abandon the current higher security mode of operation and fall back to implementing an older and less secure mode. Because of the frequent introduction of new hardware and software often they include backwards compatibility so that a newer version can still function with the older version.

collision attack

An attempt to find two input strings of a hash function that produce the same hash result.

Digital signature

An electronic verification of the sender. In addition it can prevent the sender from disowning the message. The signer cannot later attempt to disown it by claiming the signature was forged (non-repudiation) and can prove that the message has not been altered since it was signed.

XOR cipher

An encryption algorithm based on the binary operation eXclusive OR that compares two bits. If the bits are different a 1 is returned, but if they are identical then a 0 is returned.

substitution cipher

An encryption algorithm that substitutes one character for another.

OpenPGP

Another open-source alternative cryptography software that is based on PGP.

misconfiguration implementation

Breaches of cryptography that are the result of incorrect configuration or uses of the cryptography. Many cryptographic algorithms have several configuration options, and unless careful consideration is given to these options the cryptography may be improperly implemented. Also, careless users who, for example, choose SHA-224 when a much stronger SHA-512/256 can instead be used by a simple menu choice or those who expose their asymmetric private key can also seriously weaken cryptography.

data-in-use

Data actions being performed by "endpoint devices," such as printing a report from a desktop computer.

data-at-rest

Data that is stored on electronic media.

self-encrypting drives (SEDs)

Drives that can automatically encrypt any data stored on it. When the computer or other device with an SED is initially powered up, the drive and the host device perform an authentication process. If the authentication process fails, the drive can be configured to simply deny any access to the drive or even perform a cryptographic erase on specified blocks of data (a cryptographic erase deletes the decryption keys so that no data can be recovered). This also makes it impossible to install the drive on another computer to read its contents.

full disk encryption (FDE)

Encryption that protects all data on a hard drive.

symmetric cryptographic algorithm

Encryption that uses a single key to encrypt and decrypt a message. Unlike hashing, in which the hash is not intended to be decrypted, symmetric algorithms are designed to encrypt and decrypt the ciphertext. Symmetric encryption is also called private key cryptography.

key exchange

Even though asymmetric cryptography allows two users to send encrypted messages using separate public and private keys, it does not completely solve the problem of sending and receiving keys. One solution is to make the exchange outside of the normal communication channels. There are many ways to do this: Diffie-Hellman (DH), Diffie-Hellman Ephemeral (DHE), Elliptic Curve Diffie-Hellman (ECDH), Perfect forward secrecy.

elliptic curve cryptography (ECC)

First proposed in the mid-1980s. Instead of using large prime numbers as with RSA, elliptic curve cryptography uses sloping curves. An elliptic curve is a function drawn on an X-Y axis as a gently curved line. By adding the values of two points on the curve, a third point on the curve can be derived, of which the inverse. ECC is considered as an alternative for prime-number-based asymmetric cryptography for mobile and wireless devices. Because mobile devices are limited in terms of computing power due to their smaller size, ECC offers security that is comparable to other asymmetric cryptography but with smaller key sizes.

Message Digest 5 (MD5)

Five different versions of MD hashes were introduced over almost 20 years, this one is a revision of MD4 that was designed to address MD4's weaknesses. MD was one of the earliest Hashing Algorithms.

Trusted Platform Module (TPM)

For example, TPM includes a true random number generator instead of a PRNG as well as full support for asymmetric encryption (TPM can also generate public and private keys). Because all of this is done in hardware and not through the software of the operating system, malicious software cannot attack it. Also, TPM can measure and test key components as the computer is starting up. It will prevent the computer from booting if system files or data have been altered. With TPM, if the hard drive is moved to a different computer, the user must enter a recovery password before gaining access to the system volume.

GNU Privacy Guard (GNuPG)

Free and opensource software that is commonly used to encrypt and decrypt data.

steganography

Hiding the existence of data within another type of file, such as an image file. Data can be hidden in the file header fields that describe the file, between sections of the metadata (data that is used to describe the content or structure of the actual data), or in the areas of a file that contain the content itself.

Hashing Property: Original

It should not be possible to produce a data set that has a desired or predefined hash.

obfuscation

Making something obscure or unclear. One example may be disguising the operational details of software so that a threat actor cannot "reverse engineer" the program to determine how it is functioning to bypass its security protections. Cryptography can help ensure obfuscation by hiding the details so that the original code

random numbers

Numbers for which there is no identifiable pattern or sequence.

Data Encryption Standard (DES)

One of the first widely popular symmetric cryptography algorithms. No longer considered secure. The predecessor of DES was a product originally designed in the early 1970s by IBM called Lucifer that had a key length of 128 bits. The key was later shortened to 56 bits and renamed DES. The U.S. government officially adopted DES as the standard for encrypting non-classified information.

ROT13

One type of substitution cipher in which the entire alphabet is rotated 13 steps: A 5N, B 5O, etc., so that the word security becomes frphevgl.

Pretty Good Privacy (PGP)

One widely used asymmetric cryptography software for encrypting files and email messages is a commercial product It uses both asymmetric and symmetric cryptography. PGP generates a random symmetric key and uses it to encrypt the message. The symmetric key is then encrypted using the receiver's public key and sent along with the message. When the recipient receives a message, PGP first decrypts the symmetric key with the recipient's private key. The decrypted symmetric key is then used to decrypt the rest of the message.

algorithm

Procedures based on a mathematical formula used to encrypt and decrypt the data. Also called a cipher.

perfect forward secrecy

Public key systems that generate random public keys that are different for each session. The value of perfect forward secrecy is that if the secret key is compromised, it cannot reveal the contents of more than one message.

cipher

See algorithm.

low-power devices

Small electronic devices that consume very small amounts of power. In recent years, the number of such devices has grown rapidly in recent years. Increasingly, these devices need to be protected from threat actors who could use data accumulated from these devices in nefarious ways. Cryptography is viewed as a necessary feature to be added to these devices to enable them to provide a higher level of security. In addition, many applications require extremely fast response times. This results in a resource vs. security constraint.

sponge function

Takes as input a string of any length, and returns a string of any requested variable length. This function repeatedly applies a process on the input that has been padded with additional characters until all characters are used (absorbed in the sponge).

high resiliency

The ability to quickly recover from resource vs. security constraints.

RSA

The most common asymmetric cryptography algorithm. The algorithm was published in 1977. The RSA algorithm multiplies two large prime numbers (a prime number is a number divisible only by itself and 1), p and q, to compute their product (n= pq). Next, a number e is chosen that is less than n and a prime factor to (p-1)(q-1). Another number d is determined, so that (ed-1) is divisible by (p-1)(q-1). The values of e and d are the public and private exponents. The public key is the pair (n,e) while the private key is (n,d). The numbers p and q can be discarded

cryptography

The practice of transforming information so that it is secure and cannot be accessed by unauthorized persons. (from Greek words meaning hidden writing)

encryption

The process of changing plaintext into ciphertext (the reverse process is decryption, or changing the message back to its original form).

non-repudiation

The process of proving that a user performed an action and prevents an individual from fraudulently reneging on an action. It is the inability to deny.

Hashing Property: Secure

The resulting hash cannot be reversed to determine the original plaintext.

lightweight cryptography

This has the goal of providing cryptographic solutions that are uniquely tailored for low-power devices that need to manage resource vs. security constraints. Lightweight cryptography is not a weakened cryptography but may have fewer features and be less robust than "normal" cryptography.

Cryptoanalysis

Threat actors often use sophisticated statistical analysis on the ciphertext to try to discover the underlying key to the cryptographic algorithm. One factor is diffusion, another factor is confusion.

Hashing Property: Unique

Two different sets of data cannot produce the same digest. Also called Collision Resistant

known ciphertext attack

Using statistical tools to attempt to discover a pattern in ciphertexts; also called ciphertext only attack. Sometimes called a ciphertext-only attack. Underlying language of plaintext, distribution of characters such as the frequency of their use in language, Null ciphertexts meaning distinguishing between actual ciphertexts and injected fake messages, and management frames meaning Analyze content of network management information are known ways to attack ciphertext.

collision

When two different files have the same hash.

International Data Encryption Algorithm (IDEA)

dates back to the early 1990s and is used in European nations. It is a block cipher that processes 64 bits with a 128-bit key with 8 rounds. It is generally considered to be secure.