1 // Copyright (c) 2016, Google Inc. 2 // 3 // Permission to use, copy, modify, and/or distribute this software for any 4 // purpose with or without fee is hereby granted, provided that the above 5 // copyright notice and this permission notice appear in all copies. 6 // 7 // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 8 // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 9 // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 10 // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 11 // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 12 // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 13 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 14 15 package runner 16 17 import ( 18 "crypto/hmac" 19 "hash" 20 ) 21 22 // hkdfExtract implements HKDF-Extract from RFC 5869. 23 func hkdfExtract(hash func() hash.Hash, salt, ikm []byte) []byte { 24 if salt == nil { 25 salt = make([]byte, hash().Size()) 26 } 27 hmac := hmac.New(hash, salt) 28 hmac.Write(ikm) 29 return hmac.Sum(nil) 30 } 31 32 // hkdfExpand implements HKDF-Expand from RFC 5869. 33 func hkdfExpand(hash func() hash.Hash, prk, info []byte, length int) []byte { 34 hashSize := hash().Size() 35 if length > 255*hashSize { 36 panic("hkdfExpand: length too long") 37 } 38 if len(prk) < hashSize { 39 panic("hkdfExpand: prk too short") 40 } 41 var lastBlock []byte 42 counter := byte(0) 43 okm := make([]byte, length) 44 hmac := hmac.New(hash, prk) 45 for length > 0 { 46 hmac.Reset() 47 counter++ 48 hmac.Write(lastBlock) 49 hmac.Write(info) 50 hmac.Write([]byte{counter}) 51 block := hmac.Sum(nil) 52 lastBlock = block 53 copy(okm[(int(counter)-1)*hashSize:], block) 54 length -= hashSize 55 } 56 return okm 57 } 58
