refactoring, added documentation

keys.go

@@ -2,10 +2,11 @@ package roots
 
 import (
 	"encoding/hex"
-	"fmt"
 	"github.com/decred/dcrd/dcrec/secp256k1/v4"
 )
 
+// GeneratePrivateKey generates a new, random secp256k1 private key and returns
+// it as a 64-character, lowercase hexadecimal string.
 func GeneratePrivateKey() (string, error) {
 	sk, err := secp256k1.GeneratePrivateKey()
 	if err != nil {
@@ -15,13 +16,15 @@ func GeneratePrivateKey() (string, error) {
 	return hex.EncodeToString(skBytes), nil
 }
 
+// GetPublicKey derives the public key from a private key hex string
+// and returns the x-coordinate as 64 lowercase hex characters.
 func GetPublicKey(privateKeyHex string) (string, error) {
 	if len(privateKeyHex) != 64 {
-		return "", fmt.Errorf("private key must be 64 hex characters")
+		return "", ErrMalformedPrivKey
 	}
 	skBytes, err := hex.DecodeString(privateKeyHex)
 	if err != nil {
-		return "", fmt.Errorf("invalid private key hex: %w", err)
+		return "", ErrMalformedPrivKey
 	}
 
 	pk := secp256k1.PrivKeyFromBytes(skBytes).PubKey()