zxcvbn-c
This is a C/C++ implementation of the zxcvbn password strength estimation.
The code is intended to be included as part of the source of a C/C++ program. Like the original this code is for character sets which use single byte characters primarily in the code range 0x20 to 0x7E.
The original CoffeeScript version is available at https://github.com/lowe/zxcvbn
An article on the reasons for zxcvbn is at https://blogs.dropbox.com/tech/2012/04/zxcvbn-realistic-password-strength-estimation/
Using
Call ZxcvbnMatch() with the password and optional user dictionary to get the entropy
estimation and optional information on the password parts (which will need freeing with
ZxcvbnFreeInfo() after use). Do this for each password to be tested, or as each character
of it is entered into your program. The optional user dictionary can change between each
call.
Review the test program in examples/test.c for an example.
Differences from the original version
The entropy calculated will sometimes differ from the original because of
- The UK keyboard layout is also included, so there are additional spacial sequences, e.g. ;'# is a spacial sequence.
- The different character classes in a password are taken into account when calculating the strength of brute-force matches.
- Dijkstra's path searching algorithm is used to combine parts of the entered password. This can result in the found parts of the password being combined differently than the original CoffeeScript. E.g. the password passwordassword is combined by the original CoffeeScript as p (3.5 bits) + asswordassword (12.6 bits) + multiple part allowance (1.0bit) to give total entropy of 17.1 bits. This implementation combines it as password (1.0 bit) + assword (11.6 bits) + multiple part allowance (1.0bit) to give 13.6 bits.
- For multi-part passwords the original CoffeeScript version multiplies the number of guesses needed by the factorial of the number of parts. This is not possible in this version as Dijkstra's algorithm is used. Instead one bit entropy is added for the part at the end of the password, 1.7 bits for each part in the middle of a password and nothing for the part at the beginning. This gives similar results compared to the CoffeeScript version when there are 4 or less parts, but will differ significantly when there are many parts (which is likely to be a rare occurrence).
- Only the first 100 characters of a password are used in the full entropy estimation calculation. This length is given by the ZXCVBN_DETAIL_LEN preprocessor macro and can be altered on the compiler command line. The remaining characters are given a low entropy value, roughly equivalent to incrementing sequence of the same length.
References
The original CoffeeScript version is available at https://github.com/lowe/zxcvbn
The dictionary words are taken from the original CoffeeScript version.
Dictionary trie encoding (used for by the word lookup code) based on idea from the Caroline Word Graph from http://www.pathcom.com/~vadco/cwg.html
License
MIT License
- http://www.opensource.org/licenses/mit-license.php