Spring security BCryptPasswordEncoder密码验证原理详解

public interface PasswordEncoder {
  String encode(CharSequence rawPassword);
  boolean matches(CharSequence rawPassword, String encodedPassword);
}

public String encode(CharSequence rawPassword) {
  String salt;
  if (strength > 0) {
    if (random != null) {
      salt = BCrypt.gensalt(strength, random);
    }
    else {
      salt = BCrypt.gensalt(strength);
    }
  }
  else {
    salt = BCrypt.gensalt();
  }
  return BCrypt.hashpw(rawPassword.toString(), salt);
}

public static String hashpw(String password, String salt) throws IllegalArgumentException {
    BCrypt B;
    String real_salt;
    byte passwordb[], saltb[], hashed[];
    char minor = (char) 0;
    int rounds, off = 0;
    StringBuilder rs = new StringBuilder();

    if (salt == null) {
      throw new IllegalArgumentException("salt cannot be null");
    }

    int saltLength = salt.length();

    if (saltLength < 28) {
      throw new IllegalArgumentException("Invalid salt");
    }

    if (salt.charAt(0) != '$' || salt.charAt(1) != '2') {
      throw new IllegalArgumentException("Invalid salt version");
    }
    if (salt.charAt(2) == '$') {
      off = 3;
    }
    else {
      minor = salt.charAt(2);
      if (minor != 'a' || salt.charAt(3) != '$') {
        throw new IllegalArgumentException("Invalid salt revision");
      }
      off = 4;
    }

    if (saltLength - off < 25) {
      throw new IllegalArgumentException("Invalid salt");
    }

    // Extract number of rounds
    if (salt.charAt(off + 2) > '$') {
      throw new IllegalArgumentException("Missing salt rounds");
    }
    rounds = Integer.parseInt(salt.substring(off, off + 2));

    real_salt = salt.substring(off + 3, off + 25);
    try {
      passwordb = (password + (minor >= 'a' ? "\000" : "")).getBytes("UTF-8");
    }
    catch (UnsupportedEncodingException uee) {
      throw new AssertionError("UTF-8 is not supported");
    }

    saltb = decode_base64(real_salt, BCRYPT_SALT_LEN);

    B = new BCrypt();
    hashed = B.crypt_raw(passwordb, saltb, rounds);

    rs.append("$2");
    if (minor >= 'a') {
      rs.append(minor);
    }
    rs.append("$");
    if (rounds < 10) {
      rs.append("0");
    }
    rs.append(rounds);
    rs.append("$");
    encode_base64(saltb, saltb.length, rs);
    encode_base64(hashed, bf_crypt_ciphertext.length * 4 - 1, rs);
    return rs.toString();
  }

public boolean matches(CharSequence rawPassword, String encodedPassword) {
  if (encodedPassword == null || encodedPassword.length() == 0) {
    logger.warn("Empty encoded password");
    return false;
  }

  if (!BCRYPT_PATTERN.matcher(encodedPassword).matches()) {
    logger.warn("Encoded password does not look like BCrypt");
    return false;
  }
  return BCrypt.checkpw(rawPassword.toString(), encodedPassword);
}

public static boolean checkpw(String plaintext, String hashed) {
  return equalsNoEarlyReturn(hashed, hashpw(plaintext, hashed));
}

static boolean equalsNoEarlyReturn(String a, String b) {
  char[] caa = a.toCharArray();
  char[] cab = b.toCharArray();

  if (caa.length != cab.length) {
    return false;
  }

  byte ret = 0;
  for (int i = 0; i < caa.length; i++) {
    ret |= caa[i] ^ cab[i];
  }
  return ret == 0;
}