supporting TeslaMate encryption of API tokens (#141)

* updating sql of getting data from psql
* adding decrypt of token

Co-authored-by: Leland Sindt <leland@sway.org>

src/EncryptionSupport.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/sha256"
+	"log"
+
+	"github.com/gin-gonic/gin"
+)
+
+// decryptAccessToken funct to decrypt tokens from database
+func decryptAccessToken(data string, encryptionKey string) string {
+
+	/*
+	   From Adrian....
+	   I had a look at how to decode the binary input without additional libraries. Below is sample code for Elixir. An important detail is that  "Additional Authenticated Data (AAD) " is required to decrypt the tokens. The AAD is a fixed string, in this case "AES256GCM”.
+	   << _type::bytes-1, length::integer, _tag::bytes-size(length), iv::bytes-12, ciphertag::bytes-16, ciphertext::bytes >> = input
+	   key = :crypto.hash(:sha256, key)
+	   aad = "AES256GCM"
+	   plaintext = :crypto.crypto_one_time_aead(:aes_256_gcm, key, iv, ciphertext, aad, ciphertag, false)
+
+	   How the encrypted content looks like....
+	   +----------------------------------------------------------+----------------------+
+	   |                          HEADER                          |         BODY         |
+	   +-------------------+---------------+----------------------+----------------------+
+	   | Key Tag (n bytes) | IV (n bytes)  | Ciphertag (16 bytes) | Ciphertext (n bytes) |
+	   +-------------------+---------------+----------------------+----------------------+
+	   |                   |_________________________________
+	   |                                                     |
+	   +---------------+-----------------+-------------------+
+	   | Type (1 byte) | Length (1 byte) | Key Tag (n bytes) |
+	   +---------------+-----------------+-------------------+
+	*/
+
+	h := sha256.New()
+	h.Write([]byte(encryptionKey))
+	if gin.IsDebugging() {
+		log.Printf("[debug] decryptAccessToken - Key: %x \n", h.Sum(nil))
+	}
+
+	key := h.Sum(nil)
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		panic(err.Error())
+	}
+
+	// first byte
+	keyType := int([]rune(data)[0])
+	// second byte
+	keyLen := int([]rune(data)[1])
+	keyTag := data[2 : 2+keyLen]
+	if gin.IsDebugging() {
+		log.Printf("[debug] decryptAccessToken - Type: %d \n", keyType)
+		log.Printf("[debug] decryptAccessToken - Length: %d \n", keyLen)
+		log.Printf("[debug] decryptAccessToken - Key Tag: %s \n", keyTag)
+	}
+
+	/*
+	   With AES.GCM, 12-byte IV length is necessary for interoperability reasons.
+	   See https://github.com/danielberkompas/cloak/issues/93
+	   IV and nonce are often used interchangeably. Essentially though, an IV is a nonce with an additional requirement: it must be selected in a non-predictable way
+	   https://medium.com/@fridakahsas/salt-nonces-and-ivs-whats-the-difference-d7a44724a447#:~:text=IV%20and%20nonce%20are%20often,an%20IV%20must%20be%20random.
+	*/
+
+	nonce := data[2+keyLen : 2+keyLen+12]
+	if gin.IsDebugging() {
+		log.Printf("[debug] decryptAccessToken - IV (hex): %x \n", nonce)
+
+		ciphertag := data[2+keyLen+12 : 2+keyLen+12+16]
+		log.Printf("[debug] decryptAccessToken - Ciphertag (hex): %x \n", ciphertag)
+	}
+
+	aesgcm, err := cipher.NewGCMWithTagSize(block, 16)
+	if err != nil {
+		panic(err.Error())
+	}
+
+	// https://stackoverflow.com/a/68353192
+	// golang aes expects cipertag to append ciphertext....
+	ciphertextTag := data[2+keyLen+12+16:] + data[2+keyLen+12:2+keyLen+12+16]
+
+	// AES256GCM -- Additional Authenticated Data (AAD)
+	plaintext, err := aesgcm.Open(nil, []byte(nonce), []byte(ciphertextTag), []byte("AES256GCM"))
+	if err != nil {
+		panic(err.Error())
+	}
+
+	if gin.IsDebugging() {
+		// fmt.Printf("[debug] decryptAccessToken - Decrypted: %s\n", plaintext)
+	}
+
+	return string(plaintext)
+}

src/v1_TeslaMateAPICarsCommand.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"database/sql"
 	"encoding/json"
 	"io/ioutil"
 	"log"
@@ -16,6 +17,7 @@ func TeslaMateAPICarsCommandV1(c *gin.Context) {
 
 	// creating required vars
 	var (
+		CarsCommandsError1               = "Unable to load cars."
 		TeslaAccessToken, TeslaVehicleID string
 		jsonData                         map[string]interface{}
 		err                              error
@@ -78,33 +80,36 @@ func TeslaMateAPICarsCommandV1(c *gin.Context) {
 		FROM cars
 		WHERE id = $1
 		LIMIT 1;`
-	rows, err := db.Query(query, CarID)
+	row := db.QueryRow(query, CarID)
 
-	// checking for errors in query
-	if err != nil {
-		TeslaMateAPIHandleErrorResponse(c, "TeslaMateAPICarsCommandV1", "Unable to load cars.", err.Error())
+	err = row.Scan(
+		&TeslaVehicleID,
+		&TeslaAccessToken,
+	)
+
+	switch err {
+	case sql.ErrNoRows:
+		TeslaMateAPIHandleErrorResponse(c, "TeslaMateAPICarsCommandV1", "No rows were returned!", err.Error())
+		return
+	case nil:
+		// nothing wrong.. continuing
+		break
+	default:
+		TeslaMateAPIHandleErrorResponse(c, "TeslaMateAPICarsCommandV1", CarsCommandsError1, err.Error())
 		return
 	}
 
-	// defer closing rows
-	defer rows.Close()
-
-	// looping through all results (even if it's only one..)
-	for rows.Next() {
-		// scanning row and putting values into the drive
-		err = rows.Scan(
-			&TeslaVehicleID,
-			&TeslaAccessToken,
-		)
-	}
-
-	// checking for errors in query when doing scan action
-	if err != nil {
-		log.Println("[error] TeslaMateAPICarsCommandV1 error in sql query:", err)
-		TeslaMateAPIHandleOtherResponse(c, http.StatusInternalServerError, "TeslaMateAPICarsCommandV1", gin.H{"error": "internal sql query error"})
+	// load ENCRYPTION_KEY environment variable
+	teslaMateEncryptionKey := getEnv("ENCRYPTION_KEY", "")
+	if teslaMateEncryptionKey == "" {
+		log.Println("[error] TeslaMateAPICarsCommandV1 can't get ENCRYPTION_KEY.. will fail to perform command.")
+		TeslaMateAPIHandleOtherResponse(c, http.StatusInternalServerError, "TeslaMateAPICarsCommandV1", gin.H{"error": "missing ENCRYPTION_KEY env variable"})
 		return
 	}
 
+	// decrypt access token
+	TeslaAccessToken = decryptAccessToken(TeslaAccessToken, teslaMateEncryptionKey)
+
 	client := &http.Client{}
 	req, _ := http.NewRequest(http.MethodPost, "https://owner-api.teslamotors.com/api/1/vehicles/"+TeslaVehicleID+command, strings.NewReader(string(reqBody)))
 	req.Header.Set("Authorization", "Bearer "+TeslaAccessToken)