Codevault initial commit

internal/auth/password.go

@@ -0,0 +1,37 @@
+package auth
+
+import (
+	"crypto/sha256"
+	"encoding/base64"
+
+	"golang.org/x/crypto/bcrypt"
+)
+
+// saltedInput mixes the login into the password material before bcrypt hashing, using
+// the login as a per-user salt: a leaked hash can't be replayed against a different
+// login, and pre-hashing keeps the input short regardless of login/password length
+// (bcrypt only considers the first 72 bytes of its input).
+func saltedInput(login, password string) []byte {
+	sum := sha256.Sum256([]byte(login + "\x00" + password))
+	return []byte(base64.StdEncoding.EncodeToString(sum[:]))
+}
+
+// dummyHash is compared against on unknown logins so that a failed lookup takes
+// roughly the same time as a real password comparison, avoiding user enumeration.
+var dummyHash, _ = bcrypt.GenerateFromPassword(saltedInput("dummy-login", "dummy-password"), bcrypt.DefaultCost)
+
+func Hash(login, password string) (string, error) {
+	hash, err := bcrypt.GenerateFromPassword(saltedInput(login, password), bcrypt.DefaultCost)
+	if err != nil {
+		return "", err
+	}
+	return string(hash), nil
+}
+
+func Compare(login, hash, password string) bool {
+	return bcrypt.CompareHashAndPassword([]byte(hash), saltedInput(login, password)) == nil
+}
+
+func CompareDummy() {
+	_ = bcrypt.CompareHashAndPassword(dummyHash, saltedInput("dummy-login", "dummy-password"))
+}