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doc: add note about key derivation 

adds a note to the crypto docs passing along
the advice that openssl gives about what
key derivation function they recommend.

PR-URL: https://github.com/joyent/node/pull/8580
Reviewed-by: Fedor Indutny <fedor@indutny.com>

Cherry-picked-from: 7dbc024c85
This commit is contained in:
Calvin Metcalf 2014-10-19 10:31:22 -04:00 committed by Bert Belder
parent 90f07a7b3e
commit 43226dd40e
1 changed files with 12 additions and 0 deletions
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doc/api/crypto.markdown
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@ -191,6 +191,16 @@ written data is used to compute the hash. Once the writable side of
the stream is ended, use the `read()` method to get the enciphered
contents. The legacy `update` and `final` methods are also supported.
Note: `createCipher` derives keys with the OpenSSL function [EVP_BytesToKey][]
with the digest algorithm set to MD5, one iteration, and no salt. The lack of
salt allows dictionary attacks as the same password always creates the same key.
The low iteration count and non-cryptographically secure hash algorithm allow
passwords to be tested very rapidly.
In line with OpenSSL's recommendation to use pbkdf2 instead of EVP_BytesToKey it
is recommended you derive a key and iv yourself with [crypto.pbkdf2][] and to
then use [createCipheriv()][] to create the cipher stream.
## crypto.createCipheriv(algorithm, key, iv)
Creates and returns a cipher object, with the given algorithm, key and
@ -756,3 +766,5 @@ temporary measure.
[diffieHellman.setPublicKey()]: #crypto_diffiehellman_setpublickey_public_key_encoding
[RFC 2412]: http://www.rfc-editor.org/rfc/rfc2412.txt
[RFC 3526]: http://www.rfc-editor.org/rfc/rfc3526.txt
[crypto.pbkdf2]: #crypto_crypto_pbkdf2_password_salt_iterations_keylen_callback
[EVP_BytesToKey]: https://www.openssl.org/docs/crypto/EVP_BytesToKey.html