When hashing passwords, the two most important considerations are the computational expense, and the salt. The more computationally expensive the hashing algorithm, the longer it will take to brute force its output.

PHP 5.5 provides a native password hashing API that safely handles both hashing and verifying passwords in a secure manner. There is also » a pure PHP compatibility library available for PHP 5.3.7 and later.

Another option is the crypt() function, which supports several hashing algorithms in PHP 5.3 and later. When using this function, you are guaranteed that the algorithm you select is available, as PHP contains native implementations of each supported algorithm, in case one or more are not supported by your system.

The suggested algorithm to use when hashing passwords is Blowfish, which is also the default used by the password hashing API, as it is significantly more computationally expensive than MD5 or SHA1, while still being scalable.

Note that if you are using crypt() to verify a password, you will need to take care to prevent timing attacks by using a constant time string comparison. Neither PHP's == and === operators nor strcmp() perform constant time string comparisons. As password_verify() will do this for you, you are strongly encouraged to use the native password hashing API whenever possible.

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