1// Copyright 2020 Google LLC 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14// 15//////////////////////////////////////////////////////////////////////////////// 16 17package subtle 18 19import ( 20 "crypto/hmac" 21 "fmt" 22 "hash" 23 24 "github.com/google/tink/go/subtle" 25) 26 27const ( 28 minHMACKeySizeInBytes = uint32(16) 29) 30 31// HMACPRF is a type that can be used to compute several HMACs with the same key material. 32type HMACPRF struct { 33 h func() hash.Hash 34 key []byte 35} 36 37// NewHMACPRF creates a new HMACPRF object and initializes it with the correct key material. 38func NewHMACPRF(hashAlg string, key []byte) (*HMACPRF, error) { 39 h := &HMACPRF{} 40 hashFunc := subtle.GetHashFunc(hashAlg) 41 if hashFunc == nil { 42 return nil, fmt.Errorf("hmac: invalid hash algorithm") 43 } 44 h.h = hashFunc 45 h.key = key 46 return h, nil 47} 48 49// ValidateHMACPRFParams validates parameters of HMAC constructor. 50func ValidateHMACPRFParams(hash string, keySize uint32) error { 51 // validate key size 52 if keySize < minHMACKeySizeInBytes { 53 return fmt.Errorf("key too short") 54 } 55 if subtle.GetHashFunc(hash) == nil { 56 return fmt.Errorf("invalid hash function") 57 } 58 return nil 59} 60 61// ComputePRF computes the HMAC for the given key and data, returning outputLength bytes. 62func (h HMACPRF) ComputePRF(data []byte, outputLength uint32) ([]byte, error) { 63 mac := hmac.New(h.h, h.key) 64 if outputLength > uint32(mac.Size()) { 65 return nil, fmt.Errorf("outputLength must be between 0 and %d", mac.Size()) 66 } 67 mac.Write(data) 68 return mac.Sum(nil)[:outputLength], nil 69} 70