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doc: Adding best practises for crypto.pbkdf2
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Added some information around usages of how to use iterations, how to
choose decent salts and updating the example to have a significant
work factor and to use sha512.

PR-URL: #3290
Reviewed-By: Fedor Indutny <[email protected]>
Reviewed-By: Shigeki Ohtsu <[email protected]>
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tomgco authored and Shigeki Ohtsu committed Nov 23, 2015
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10 changes: 9 additions & 1 deletion doc/api/crypto.markdown
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Expand Up @@ -620,9 +620,16 @@ Asynchronous PBKDF2 function. Applies the selected HMAC digest function
salt and number of iterations. The callback gets two arguments:
`(err, derivedKey)`.

The number of iterations passed to pbkdf2 should be as high as possible, the
higher the number, the more secure it will be, but will take a longer amount of
time to complete.

Chosen salts should also be unique. It is recommended that the salts are random
and their length is greater than 16 bytes. See [NIST SP 800-132] for details.

Example:

crypto.pbkdf2('secret', 'salt', 4096, 64, 'sha256', function(err, key) {
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', function(err, key) {
if (err)
throw err;
console.log(key.toString('hex')); // 'c5e478d...1469e50'
Expand Down Expand Up @@ -789,6 +796,7 @@ See the reference for other recommendations and details.
[RFC 3526]: http://www.rfc-editor.org/rfc/rfc3526.txt
[crypto.pbkdf2]: #crypto_crypto_pbkdf2_password_salt_iterations_keylen_digest_callback
[EVP_BytesToKey]: https://www.openssl.org/docs/crypto/EVP_BytesToKey.html
[NIST SP 800-132]: http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf
[NIST SP 800-131A]: http://csrc.nist.gov/publications/nistpubs/800-131A/sp800-131A.pdf
[initialization vector]: http://en.wikipedia.org/wiki/Initialization_vector
[Caveats]: #crypto_caveats
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