1 // Copyright 2014 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
12 "golang.org/x/crypto/hkdf"
16 // Usage example that expands one master key into three other cryptographically
18 func Example_usage() {
19 // Underlying hash function to use
22 // Cryptographically secure master key.
23 master := []byte{0x00, 0x01, 0x02, 0x03} // i.e. NOT this.
25 // Non secret salt, optional (can be nil)
26 // Recommended: hash-length sized random
27 salt := make([]byte, hash().Size())
28 n, err := io.ReadFull(rand.Reader, salt)
29 if n != len(salt) || err != nil {
30 fmt.Println("error:", err)
34 // Non secret context specific info, optional (can be nil).
35 // Note, independent from the master key.
36 info := []byte{0x03, 0x14, 0x15, 0x92, 0x65}
38 // Create the key derivation function
39 hkdf := hkdf.New(hash, master, salt, info)
41 // Generate the required keys
42 keys := make([][]byte, 3)
43 for i := 0; i < len(keys); i++ {
44 keys[i] = make([]byte, 24)
45 n, err := io.ReadFull(hkdf, keys[i])
46 if n != len(keys[i]) || err != nil {
47 fmt.Println("error:", err)
52 // Keys should contain 192 bit random keys
53 for i := 1; i <= len(keys); i++ {
54 fmt.Printf("Key #%d: %v\n", i, !bytes.Equal(keys[i-1], make([]byte, 24)))