Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
What is the $key_length in PBKDF2
It says that it will be derived from the input, but I see people using key_lengths of 256 and greater, but when I enter 256 as a key_length the output is 512 characters. Is this intentional? Can I safely use 64 as the key_length so the output is 128 characters long?
$key_length is the number of output bytes that you desire from PBKDF2. (Note that if key_length is more than the number of output bytes of the hash algorithm, the process is repeated twice, slowing down that hashing perhaps more than you desire. SHA256 gives 32 bytes of output, for example, so asking for 33 bytes will take roughly twice as long as asking for 32.)
The doubling of the length that you mention is because the code converts the output bytes to hexadecimal (i.e. 2 characters per 1 byte) unless you specify $raw_output = true. The test vectors included specify $raw_output = false, since hexadecimal is simply easier to work with and post online. Depending on how you are storing the data in your application, you can decide if you want to store the results as hex, base64, or just raw binary data.