Key stretching

In cryptography, key stretching techniques are used to make a possibly weak key, typically a password or passphrase, more secure against a brute-force attack by increasing the resources (time and possibly space) it takes to test each possible key. Passwords or passphrases created by humans are often short or predictable enough to allow password cracking, and key stretching is intended to make such attacks more difficult by complicating a basic step of trying a single password candidate. Key stretching also improves security in some real-world applications where the key length has been constrained, by mimicking a longer key length from the perspective of a brute-force attacker. There are several ways to perform key stretching. One way is to apply a cryptographic hash function or a block cipher repeatedly in a loop. For example, in applications where the key is used for a cipher, the key schedule in the cipher may be modified so that it takes a specific length of time to perform. Another way is to use cryptographic hash functions that have large memory requirements – these can be effective in frustrating attacks by memory-bound adversaries. Key stretching algorithms depend on an algorithm which receives an input key and then expends considerable effort to generate a stretched cipher (called an enhanced key) mimicking randomness and longer key length. The algorithm must have no known shortcut, so the most efficient way to relate the input and cipher is to repeat the key stretching algorithm itself. This compels brute-force attackers to expend the same effort for each attempt. If this added effort compares to a brute-force key search of all keys with a certain key length, then the input key may be described as stretched by that same length. Key stretching leaves an attacker with two options: Attempt possible combinations of the enhanced key, but this is infeasible if the enhanced key is sufficiently long and unpredictable ( ⁠i.e.

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related concepts (22)

Related courses (4)

Related lectures (51)

Commitment Scheme: Key Derivation and Hash Function COM-401: Cryptography and security

Explains the commitment scheme, key derivation, and hash function for data security.

Symmetric Encryption Schemes COM-401: Cryptography and security

Explores symmetric encryption schemes, including block and stream ciphers, their vulnerabilities, and the importance of key lengths.

Business Model: Design and Optimization

Covers different business models and the holistic approach to designing them.

Passphrase

A passphrase is a sequence of words or other text used to control access to a computer system, program or data. It is similar to a password in usage, but a passphrase is generally longer for added security. Passphrases are often used to control both access to, and the operation of, cryptographic programs and systems, especially those that derive an encryption key from a passphrase. The origin of the term is by analogy with password. The modern concept of passphrases is believed to have been invented by Sigmund N.

Salt (cryptography)

In cryptography, a salt is random data fed as an additional input to a one-way function that hashes data, a password or passphrase. Salting helps defend against attacks that use precomputed tables (e.g. rainbow tables), by vastly growing the size of table needed for a successful attack. It also helps protect passwords that occur multiple times in a database, as a new salt is used for each password instance. Additionally, salting does not place any burden on users.

Key derivation function

In cryptography, a key derivation function (KDF) is a cryptographic algorithm that derives one or more secret keys from a secret value such as a master key, a password, or a passphrase using a pseudorandom function (which typically uses a cryptographic hash function or block cipher). KDFs can be used to stretch keys into longer keys or to obtain keys of a required format, such as converting a group element that is the result of a Diffie–Hellman key exchange into a symmetric key for use with AES.

ChE-430: Nanomaterials for chemical engineering application

This course aims at understanding classical and non-classical nucleation theory, at reviewing different techniques for the synthesis of nanomaterials (mainly nanoparticles and thin films) and at learn

COM-401: Cryptography and security

This course introduces the basics of cryptography. We review several types of cryptographic primitives, when it is safe to use them and how to select the appropriate security parameters. We detail how

MICRO-617: Energy Autonomous Wireless Smart Systems

The course provides in depth knowledge on how to design an energy autonomous microsystem embedding sensors with wireless transmission of information. It covers the energy generation, power management,