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  }