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package s2k
// Cache stores keys derived with s2k functions from one passphrase
// to avoid recomputation if multiple items are encrypted with
// the same parameters.
type Cache map[Params][]byte
// GetOrComputeDerivedKey tries to retrieve the key
// for the given s2k parameters from the cache.
// If there is no hit, it derives the key with the s2k function from the passphrase,
// updates the cache, and returns the key.
func (c *Cache) GetOrComputeDerivedKey(passphrase []byte, params *Params, expectedKeySize int) ([]byte, error) {
key, found := (*c)[*params]
if !found || len(key) != expectedKeySize {
var err error
derivedKey := make([]byte, expectedKeySize)
s2k, err := params.Function()
if err != nil {
return nil, err
}
s2k(derivedKey, passphrase)
(*c)[*params] = key
return derivedKey, nil
}
return key, nil
}
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