// Key derives a key from the password, salt and iteration count, returning a // []byte of length keylen that can be used as cryptographic key. The key is // derived based on the method described as PBKDF2 with the HMAC variant using // the supplied hash function. // // For example, to use a HMAC-SHA-1 based PBKDF2 key derivation function, you // can get a derived key for e.g. AES-256 (which needs a 32-byte key) by // doing: // // dk := pbkdf2.Key([]byte("some password"), salt, 4096, 32, sha1.New) // // Remember to get a good random salt. At least 8 bytes is recommended by the // RFC. // // Using a higher iteration count will increase the cost of an exhaustive // search but will also make derivation proportionally slower. func Key(password []byte, salt []byte, iter int, keyLen int, h func() hash.Hash) []byte