crypto: update {Load,Save}ECDSA comments to mention hex encoding

crypto/crypto.go

@@ -120,6 +120,7 @@ func HexToECDSA(hexkey string) (*ecdsa.PrivateKey, error) {
 }
 
 // LoadECDSA loads a secp256k1 private key from the given file.
+// The key data is expected to be hex-encoded.
 func LoadECDSA(file string) (*ecdsa.PrivateKey, error) {
 	buf := make([]byte, 64)
 	fd, err := os.Open(file)
@@ -139,8 +140,8 @@ func LoadECDSA(file string) (*ecdsa.PrivateKey, error) {
 	return ToECDSA(key), nil
 }
 
-// SaveECDSA saves a secp256k1 private key to the given file with restrictive
-// permissions
+// SaveECDSA saves a secp256k1 private key to the given file with
+// restrictive permissions. The key data is saved hex-encoded.
 func SaveECDSA(file string, key *ecdsa.PrivateKey) error {
 	k := hex.EncodeToString(FromECDSA(key))
 	return ioutil.WriteFile(file, []byte(k), 0600)