github.com/google/trillian-examples@v0.0.0-20240520080811-0d40d35cef0e/binary_transparency/firmware/devices/usbarmory/measurement.go (about) 1 // Copyright 2020 Google LLC. All Rights Reserved. 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 package usbarmory 16 17 import ( 18 "crypto/sha256" 19 "fmt" 20 ) 21 22 const measurementDomainPrefix = "armory_mkii" 23 24 // ExpectedMeasurement returns the expected on-device measurement hash for the 25 // given firmware image. 26 // 27 // For the USB Armory, this is SHA256("armory_mkii"||img) 28 func ExpectedMeasurement(img []byte) ([]byte, error) { 29 hasher := sha256.New() 30 if _, err := hasher.Write([]byte(measurementDomainPrefix)); err != nil { 31 return nil, fmt.Errorf("failed to write measurement domain prefix to hasher: %w", err) 32 } 33 if _, err := hasher.Write(img); err != nil { 34 return nil, fmt.Errorf("failed to write firmware image to hasher: %w", err) 35 } 36 fwHash := hasher.Sum(nil) 37 return fwHash[:], nil 38 }