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Password hashing

dygo g security and dygo g auth write a password.go file into the generated package. It uses only the standard library: PBKDF2-HMAC-SHA256 with 600,000 iterations, as OWASP advises, and a random 16 byte salt.

// passwordIterations follows the OWASP advice for PBKDF2-HMAC-SHA256.
const passwordIterations = 600_000


// HashPassword returns "pbkdf2-sha256$<iterations>$<salt>$<hash>".
func HashPassword(password string) (string, error) {
  salt := make([]byte, 16)
  if _, err := rand.Read(salt); err != nil {
    return "", err
  }
  key, err := pbkdf2.Key(sha256.New, password, salt, passwordIterations, 32)
  if err != nil {
    return "", err
  }
  enc := base64.RawStdEncoding
  return fmt.Sprintf("pbkdf2-sha256$%d$%s$%s", passwordIterations, enc.EncodeToString(salt), enc.EncodeToString(key)), nil
}
  • CheckPassword(hash, password) compares in constant time.
  • NeedsRehash(hash) reports a hash made with fewer iterations. The generated login then saves a new hash, so raising passwordIterations upgrades users as they sign in.
  • Login takes the same time for an unknown email and for a wrong password.

The authentication page covers the rest of the generated package.

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