Replace getFileMD5 with getFileSHA256

The function was using an MD5 for checking, whereas a more secure option like SHA-256 would be preferred.
See https://www.iacr.org/cryptodb/data/paper.php?pubkey=23903 (for example) for the (in-)security.

SHA256 was chosen over Blake2 because there's a widely deployed CLI sha256sum on unix systems, and performance is not an issue here.

Activates gosec G401 to fix such an issue, activates G501, G502, G503, G505 to tie up loose ends on less-secure hash functions..

.golangci.yml

@@ -13,7 +13,12 @@ linters-settings:
     # To select a subset of rules to run.
     # Available rules: https://github.com/securego/gosec#available-rules
     includes:
+      - G401
       - G402
+      - G501
+      - G502
+      - G503
+      - G505
 
 linters:
   enable:

cmd/bootstrap/transit/cmd/crypto_test.go

@@ -59,7 +59,7 @@ func TestEndToEnd(t *testing.T) {
 	}
 }
 
-func TestMd5(t *testing.T) {
+func TestSha256(t *testing.T) {
 	tmpFile, err := ioutil.TempFile(os.TempDir(), "prefix-")
 	assert.NoError(t, err)
 	defer os.Remove(tmpFile.Name())
@@ -70,7 +70,7 @@ func TestMd5(t *testing.T) {
 
 	assert.NoError(t, tmpFile.Close())
 
-	md5, err := getFileMD5(tmpFile.Name())
+	hash, err := getFileSHA256(tmpFile.Name())
 	assert.NoError(t, err)
-	assert.Equal(t, "1b8e86521e7e04d647faa9e6192a65f5", md5)
+	assert.Equal(t, "876a3eab5fe740cb864a3d62869b0eefd6fbc34ec331c3064a6ffac0f9485a88", hash)
 }

cmd/bootstrap/transit/cmd/pull.go

@@ -114,11 +114,11 @@ func pull(cmd *cobra.Command, args []string) {
 		}
 	}
 
-	// calculate MD5 of rootsnapshot
+	// calculate SHA256 of rootsnapshot
 	rootFile := filepath.Join(flagBootDir, model.PathRootProtocolStateSnapshot)
-	rootMD5, err := getFileMD5(rootFile)
+	rootSHA256, err := getFileSHA256(rootFile)
 	if err != nil {
-		log.Fatal().Err(err).Str("file", rootFile).Msg("failed to calculate md5")
+		log.Fatal().Err(err).Str("file", rootFile).Msg("failed to calculate SHA256 of root file")
 	}
-	log.Info().Str("md5", rootMD5).Msg("calculated MD5 of protocol snapshot")
+	log.Info().Str("sha256", rootSHA256).Msg("calculated SHA256 of protocol snapshot")
 }

cmd/bootstrap/transit/cmd/utils.go

@@ -1,8 +1,8 @@
 package cmd
 
 import (
-	"crypto/md5"
 	"crypto/rand"
+	"crypto/sha256"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -73,18 +73,17 @@ func getFilesToUpload(role flow.Role) []string {
 	}
 }
 
-func getFileMD5(file string) (string, error) {
+func getFileSHA256(file string) (string, error) {
 	f, err := os.Open(file)
 	if err != nil {
 		return "", err
 	}
 	defer f.Close()
 
-	h := md5.New()
+	h := sha256.New()
 	if _, err := io.Copy(h, f); err != nil {
 		return "", err
 	}
-
 	return fmt.Sprintf("%x", h.Sum(nil)), nil
 }