rfc:bcrypt_cost_2023

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rfc:bcrypt_cost_2023 [2023/09/07 16:12] – timwollarfc:bcrypt_cost_2023 [2023/10/06 14:34] (current) – Implemented timwolla
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   * Date: 2023-09-07   * Date: 2023-09-07
   * Author: Tim Düsterhus, timwolla@php.net   * Author: Tim Düsterhus, timwolla@php.net
-  * Status: Draft+  * Status: Implemented 
 +  * Target Version: PHP 8.4 
 +  * Implementation: https://github.com/php/php-src/commit/42a85fc5d95c0c5e867cafcca8ebfca9d90e6c88
   * First Published at: https://wiki.php.net/rfc/bcrypt_cost_2023   * First Published at: https://wiki.php.net/rfc/bcrypt_cost_2023
  
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 Any increase of the cost by ''1'' will double the time it takes to calculate a single BCrypt hash. Any increase of the cost by ''1'' will double the time it takes to calculate a single BCrypt hash.
 +
 +==== Choice of the cost factor ====
 +
 +The cost should be selected to be as large as possible without degrading the user experience and without introducing disproportional hardware requirements. [[https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html#work-factors|OWASP]] recommends “less than a second” as a rule of thumb.
  
 ==== Processing time for several different CPUs ==== ==== Processing time for several different CPUs ====
  
-These times were measured using PHP 8.2 with this script and were selected to represent a reasonable range of CPUs that might still be in use today. All tests were carried out using wall-power.+These times were measured using PHP 8.2 with this script and were selected to represent a reasonable range of CPUs that might still be in use today. All tests were carried out using wall-power (i.e. the Laptops were plugged in and not running from battery).
  
 <PHP> <PHP>
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 ===== Proposal ===== ===== Proposal =====
  
-The default BCrypt cost shall be increased from ''10'' to either ''11'' or ''12'' (depending on the secondary vote). +The default BCrypt cost shall be increased from ''10'' to either ''11'' (doubling the time) or ''12'' (quadrupling the time), depending on the secondary vote. 
 + 
 +A cost of ''12'' is well below 0.5 seconds on all tested CPUs (with the slowest CPU being at 330ms) and should feel sufficiently snappy for an interactive login in a website even when needing to rehash a cost ''10'' hash during login. 
 + 
 +The more conservative increase to ''11'' stays below 200ms for all tested CPUs and still provides reasonable response times when a handful of hashes need to be calculated within a single request (e.g. when generating and hashing multiple recovery codes for multi-factor authentication).
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
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 2/3 majority to increase the default costs: 2/3 majority to increase the default costs:
  
-<doodle title="Increase the default BCrypt cost?" auth="timwolla" voteType="single" closed="false" closeon="2022-01-01T00:00:00Z">+<doodle title="Increase the default BCrypt cost?" auth="timwolla" voteType="single" closed="true" closeon="2023-10-05T17:45:00Z">
    * Yes    * Yes
    * No    * No
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 Simple majority to decide the new costs: Simple majority to decide the new costs:
  
-<doodle title="Increase the default BCrypt cost to?" auth="timwolla" voteType="single" closed="false" closeon="2022-01-01T00:00:00Z"> +<doodle title="Increase the default BCrypt cost to?" auth="timwolla" voteType="single" closed="true" closeon="2023-10-05T17:45:00Z"> 
-   * 11 +   * 11 (less than 160ms per hash) 
-   * 12+   * 12 (less than 330ms per hash)
 </doodle> </doodle>
  
 ===== Patches and Tests ===== ===== Patches and Tests =====
  
-tbd+https://github.com/php/php-src/pull/12367
  
 ===== Implementation ===== ===== Implementation =====
  
-tbd+https://github.com/php/php-src/commit/42a85fc5d95c0c5e867cafcca8ebfca9d90e6c88
  
 ===== References ===== ===== References =====
  
   * https://externals.io/message/120993   * https://externals.io/message/120993
 +  * https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html
 +  * https://phpc.social/@tychotithonus@infosec.exchange/111025157601179075
  
 ===== Rejected Features ===== ===== Rejected Features =====
  
 None. None.
rfc/bcrypt_cost_2023.1694103137.txt.gz · Last modified: 2023/09/07 16:12 by timwolla

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