Browse Definitions:
Definition

password entropy

Contributor(s): Matthew Haughn

Password entropy is a measurement of how unpredictable a password is.

Password entropy is based on the character set used (which is expansible by using lowercase, uppercase, numbers as well as symbols) as well as password length. Password entropy predicts how difficult a given password would be to crack through guessing, brute force cracking, dictionary attacks or other common methods.

Password entropy is usually expressed in terms of bits: A password that is already known has zero bits of entropy; one that would be guessed on the first attempt half the time would have 1 bit of entropy. A password's entropy can be calculated by finding the entropy per character, which is a log base 2 of the number of characters in the character set used, multiplied by the number of characters
in the password itself.

NIST provides the following guidelines for user-selected passwords with 30 bits of entropy:

  • Use a minimum of 8 characters selected from  a 94-character set.
  • Include at least one upper case letter, one lower case letter, one number and one special character.
  • Use a dictionary of common words that users should avoid, like a password blacklist.
  • Don’t use any permutations of your username as your password.

Of course password entropy can't be the only thing considered or passwords would be too long, complex and unmemorable. Best practices involve employing something memorable to the user but not easily guessed by anyone else. Because password length is one of the most important factors affecting password entropy and overall strength, a longer password can be simpler than a shorter one and still be effective.

See also: password strength meter

This was last updated in January 2014

Continue Reading About password entropy

Start the conversation

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

  • PCAOB (Public Company Accounting Oversight Board)

    The Public Company Accounting Oversight Board (PCAOB) is a Congressionally-established nonprofit that assesses audits of public ...

  • cyborg anthropologist

    A cyborg anthropologist is an individual who studies the interaction between humans and technology, observing how technology can ...

  • RegTech

    RegTech, or regulatory technology, is a term used to describe technology that is used to help streamline the process of ...

SearchSecurity

  • email spam

    Email spam, or junk email, is unsolicited bulk messages sent through email with commercial, fraudulent or malicious intent.

  • distributed denial of service (DDoS) attack

    A distributed denial-of-service attack occurs when an attack originates from multiple computers or devices, usually from multiple...

  • application whitelisting

    Application whitelisting is the practice of identifying applications that have been deemed safe for execution and restricting all...

SearchHealthIT

  • athenahealth Inc.

    Based in Watertown, Mass., athenahealth Inc. is a leading vendor of cloud-based EHRs for small to medium-sized physician ...

  • Affordable Care Act (ACA or Obamacare)

    The Affordable Care Act (ACA) is legislation passed in 2010 that changed how uninsured Americans enroll in and receive healthcare...

  • HIPAA Privacy Rule

    The Standards for Privacy of Individually Identifiable Health Information, commonly known as the HIPAA Privacy Rule, establishes ...

SearchDisasterRecovery

  • disaster recovery as a service (DRaaS)

    One approach to a strong disaster recovery plan is DRaaS, where companies offload data replication and restoration ...

  • data recovery

    Data recovery restores data that has been lost, accidentally deleted, corrupted or made inaccessible. Learn how data recovery ...

  • disaster recovery plan (DRP)

    A company's disaster recovery policy is enhanced with a documented DR plan that formulates strategies, and outlines preparation ...

SearchStorage

  • yottabyte (YB)

    A yottabyte is a measure of theoretical storage capacity and is 2 to the 80th power bytes, or, in decimal, approximately 1,000 ...

  • Kilo, mega, giga, tera, peta, exa, zetta and all that

    Kilo, mega, giga, tera, peta, exa, zetta are among the list of prefixes used to denote the quantity of something, such as a byte ...

  • brontobyte

    A brontobyte is a measure of memory or data storage that is equal to 10 to the 27th power of bytes.

SearchSolidStateStorage

  • PCIe SSD (PCIe solid-state drive)

    A PCIe SSD (PCIe solid-state drive) is a high-speed expansion card that attaches a computer to its peripherals.

  • SSD caching

    SSD caching, also known as flash caching, is the temporary storage of data on NAND flash memory chips in a solid-state drive so ...

  • NVDIMM (Non-Volatile Dual In-line Memory Module)

    An NVDIMM (non-volatile dual in-line memory module) is hybrid computer memory that retains data during a service outage.

SearchCloudStorage

  • RESTful API

    A RESTful application program interface breaks down a transaction to create a series of small modules, each of which addresses an...

  • cloud storage infrastructure

    Cloud storage infrastructure is the hardware and software framework that supports the computing requirements of a private or ...

  • Zadara VPSA and ZIOS

    Zadara Storage provides block, file or object storage with varying levels of compute and capacity through its ZIOS and VPSA ...

Close