code: func (c *RemoteClient) putMD5(sum []byte) error {
  	if c.ddbTable == "" {
  		return nil
  	}
  
  	if len(sum) != md5.Size {
  		return errors.New("invalid payload md5")
  	}
  
  	putParams := &dynamodb.PutItemInput{
  		Item: map[string]*dynamodb.AttributeValue{
  			"LockID": {S: aws.String(c.lockPath() + stateIDSuffix)},
  			"Digest": {S: aws.String(hex.EncodeToString(sum))},
  		},
  		TableName: aws.String(c.ddbTable),
  	}
  	_, err := c.dynClient.PutItem(putParams)
  	if err != nil {
  		log.Printf("[WARN] failed to record state serial in dynamodb: %s", err)
  	}
  
  	return nil
  }
docs: // store the hash of the state to that clients can check for stale state files.