1package s2k
 2
 3// Cache stores keys derived with s2k functions from one passphrase
 4// to avoid recomputation if multiple items are encrypted with
 5// the same parameters.
 6type Cache map[Params][]byte
 7
 8// GetOrComputeDerivedKey tries to retrieve the key
 9// for the given s2k parameters from the cache.
10// If there is no hit, it derives the key with the s2k function from the passphrase,
11// updates the cache, and returns the key.
12func (c *Cache) GetOrComputeDerivedKey(passphrase []byte, params *Params, expectedKeySize int) ([]byte, error) {
13	key, found := (*c)[*params]
14	if !found || len(key) != expectedKeySize {
15		var err error
16		derivedKey := make([]byte, expectedKeySize)
17		s2k, err := params.Function()
18		if err != nil {
19			return nil, err
20		}
21		s2k(derivedKey, passphrase)
22		(*c)[*params] = key
23		return derivedKey, nil
24	}
25	return key, nil
26}