kubernetes/vendor/golang.org/x/crypto/hkdf/hkdf.go

// Extract generates a pseudorandom key for use with Expand from an input secret
// and an optional independent salt.
//
// Only use this function if you need to reuse the extracted key with multiple
// Expand invocations and different context values. Most common scenarios,
// including the generation of multiple keys, should use New instead.
func Extract(hash func() hash.Hash, secret, salt []byte) []byte { … }

type hkdf …

func (f *hkdf) Read(p []byte) (int, error) { … }

// Expand returns a Reader, from which keys can be read, using the given
// pseudorandom key and optional context info, skipping the extraction step.
//
// The pseudorandomKey should have been generated by Extract, or be a uniformly
// random or pseudorandom cryptographically strong key. See RFC 5869, Section
// 3.3. Most common scenarios will want to use New instead.
func Expand(hash func() hash.Hash, pseudorandomKey, info []byte) io.Reader { … }

// New returns a Reader, from which keys can be read, using the given hash,
// secret, salt and context info. Salt and info can be nil.
func New(hash func() hash.Hash, secret, salt, info []byte) io.Reader { … }