使用aerogear生成totp

序

本文主要讲述一下如何使用aerogear-otp生成otp，以及相关源码分析

otp分类

全称是one time password，通常用来支持双因素认证。主要可以分两类

HMAC-Based One-time Password (HOTP)

在RFC 4226规范中

Time-based One-time Password (TOTP)

在RFC 6238规范中

客户端

其常见的手机客户端有Google Authenticator APP以及阿里云的身份宝。由于google的软件在国内被墙，因此可以使用阿里云的身份宝

服务端

服务端的话，google官方有c的代码，java的话很多第三方都有实现，这里选择jboss提供的aerogear-otp-java，其maven如下

        <dependency>
            <groupId>org.jboss.aerogear</groupId>
            <artifactId>aerogear-otp-java</artifactId>
            <version>1.0.0</version>
        </dependency>

步骤

主要的步骤如下：

绑定密钥

服务端为每个账户生成一个secret并保存下来
服务端提供该密钥的二维码扫描功能，方便客户端扫描绑定账号
用户手机安装Google Authenticator APP或阿里云的身份宝，扫描二维码绑定该账号的secret

使用otp验证

绑定secret之后，就可以使用one time password进行验证了。

实例

生成客户端密钥的二维码

String secret = Base32.random();
Totp totp = new Totp(secret);
String uri = totp.uri(account);

    /**
     * Prover - To be used only on the client side
     * Retrieves the encoded URI to generated the QRCode required by Google Authenticator
     *
     * @param name Account name
     * @return Encoded URI
     */
    public String uri(String name) {
        try {
            return String.format("otpauth://totp/%s?secret=%s", URLEncoder.encode(name, "UTF-8"), secret);
        } catch (UnsupportedEncodingException e) {
            throw new IllegalArgumentException(e.getMessage(), e);
        }
    }

校验

 boolean isValid = totp.verify(code);

其源码如下

    /**
     * Verifier - To be used only on the server side
     * <p/>
     * Taken from Google Authenticator with small modifications from
     * {@see <a href="http://code.google.com/p/google-authenticator/source/browse/src/com/google/android/apps/authenticator/PasscodeGenerator.java?repo=android#212">PasscodeGenerator.java</a>}
     * <p/>
     * Verify a timeout code. The timeout code will be valid for a time
     * determined by the interval period and the number of adjacent intervals
     * checked.
     *
     * @param otp Timeout code
     * @return True if the timeout code is valid
     *         <p/>
     *         Author: sweis@google.com (Steve Weis)
     */
    public boolean verify(String otp) {

        long code = Long.parseLong(otp);
        long currentInterval = clock.getCurrentInterval();

        int pastResponse = Math.max(DELAY_WINDOW, 0);

        for (int i = pastResponse; i >= 0; --i) {
            int candidate = generate(this.secret, currentInterval - i);
            if (candidate == code) {
                return true;
            }
        }
        return false;
    }

clock

aerogear-otp-java-1.0.0-sources.jar!/org/jboss/aerogear/security/otp/api/Clock.java

public class Clock {

    private final int interval;
    private Calendar calendar;

    public Clock() {
        interval = 30;
    }

    public Clock(int interval) {
        this.interval = interval;
    }

    public long getCurrentInterval() {
        calendar = GregorianCalendar.getInstance(TimeZone.getTimeZone("UTC"));
        long currentTimeSeconds = calendar.getTimeInMillis() / 1000;
        return currentTimeSeconds / interval;
    }
}

code生成源码

aerogear-otp-java-1.0.0-sources.jar!/org/jboss/aerogear/security/otp/Totp.java

    private int generate(String secret, long interval) {
        return hash(secret, interval);
    }

    private int hash(String secret, long interval) {
        byte[] hash = new byte[0];
        try {
            //Base32 encoding is just a requirement for google authenticator. We can remove it on the next releases.
            hash = new Hmac(Hash.SHA1, Base32.decode(secret), interval).digest();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            e.printStackTrace();
        } catch (Base32.DecodingException e) {
            e.printStackTrace();
        }
        return bytesToInt(hash);
    }

    private int bytesToInt(byte[] hash) {
        // put selected bytes into result int
        int offset = hash[hash.length - 1] & 0xf;

        int binary = ((hash[offset] & 0x7f) << 24) |
                ((hash[offset + 1] & 0xff) << 16) |
                ((hash[offset + 2] & 0xff) << 8) |
                (hash[offset + 3] & 0xff);

        return binary % Digits.SIX.getValue();
    }

    /**
     * Retrieves the current OTP
     *
     * @return OTP
     */
    public String now() {
        return leftPadding(hash(secret, clock.getCurrentInterval()));
    }

    private String leftPadding(int otp) {
        return String.format("%06d", otp);
    }

小结

interval

默认值为30，在Clock里头可以通过构造器修改interval。不过由于Google Authenticator APP或阿里云的身份宝均为30秒更换一次，因此这个参数可以按默认的来。

DELAY_WINDOW

aerogear-otp-java本身不提供DELAY_WINDOW的修改，不过你可以继承Totp，自己扩展一下。

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