在 Android 5 上使用 Sha256 的 PBKDF2

Question

我正在制作一个使用 PBKDF2 和 Hmac Sha256 的 android 应用程序。我实现了这个功能，但是当我在 android 5.0 设备上测试它时，它给出了 NoSuchAlgorithmException。如何为 android 5.0 手动实现 PBKDF2？

我将它用于 PBKDF2 和 AES 256 加密：

@RequiresApi(api = Build.VERSION_CODES.O)
public static String encrypt(String strToEncrypt, String SECRET_KEY, String SALT) {
    try {
        byte[] iv = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
        IvParameterSpec ivspec = new IvParameterSpec(iv);

        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        KeySpec spec = new PBEKeySpec(SECRET_KEY.toCharArray(), SALT.getBytes(), 100000, 256);
        SecretKey tmp = factory.generateSecret(spec);
        SecretKeySpec secretKey = new SecretKeySpec(tmp.getEncoded(), "AES");

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey, ivspec);
        return Base64.getEncoder().encodeToString(cipher.doFinal(strToEncrypt.getBytes(StandardCharsets.UTF_8)));
    } catch (Exception e) {
        System.out.println("Error while encrypting: " + e.toString());
    }
    return null;
}

谢谢！

Answer 1

对于 Android SDK https://github.com/wg/scrypt/blob/master/src/main/java/com/lambdaworks/crypto/PBKDF.java。

要为 AES-256 派生密钥，您可以这样调用类：

byte[] secretKey = PBKDF.pbkdf2("HmacSHA256", passphraseByte, salt, PBKDF2_ITERATIONS, 32);

这里是完整的类代码，以防它在未来消失：

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.security.GeneralSecurityException;
import static java.lang.System.arraycopy;

/**
 * An implementation of the Password-Based Key Derivation Function as specified
 * in RFC 2898.
 *
 * @author  Will Glozer
 */

// source: https://github.com/wg/scrypt/blob/master/src/main/java/com/lambdaworks/crypto/PBKDF.java
// license: Apache License 2.0

public class PBKDF {
    /**
     * Implementation of PBKDF2 (RFC2898).
     *
     * @param   alg     HMAC algorithm to use.
     * @param   P       Password.
     * @param   S       Salt.
     * @param   c       Iteration count.
     * @param   dkLen   Intended length, in octets, of the derived key.
     *
     * @return  The derived key.
     *
     * @throws  GeneralSecurityException
     */
    public static byte[] pbkdf2(String alg, byte[] P, byte[] S, int c, int dkLen) throws GeneralSecurityException {
        Mac mac = Mac.getInstance(alg);
        mac.init(new SecretKeySpec(P, alg));
        byte[] DK = new byte[dkLen];
        pbkdf2(mac, S, c, DK, dkLen);
        return DK;
    }

    /**
     * Implementation of PBKDF2 (RFC2898).
     *
     * @param   mac     Pre-initialized {@link Mac} instance to use.
     * @param   S       Salt.
     * @param   c       Iteration count.
     * @param   DK      Byte array that derived key will be placed in.
     * @param   dkLen   Intended length, in octets, of the derived key.
     *
     * @throws  GeneralSecurityException
     */
    public static void pbkdf2(Mac mac, byte[] S, int c, byte[] DK, int dkLen) throws GeneralSecurityException {
        int hLen = mac.getMacLength();

        if (dkLen > (Math.pow(2, 32) - 1) * hLen) {
            throw new GeneralSecurityException("Requested key length too long");
        }

        byte[] U      = new byte[hLen];
        byte[] T      = new byte[hLen];
        byte[] block1 = new byte[S.length + 4];

        int l = (int) Math.ceil((double) dkLen / hLen);
        int r = dkLen - (l - 1) * hLen;

        arraycopy(S, 0, block1, 0, S.length);

        for (int i = 1; i <= l; i++) {
            block1[S.length + 0] = (byte) (i >> 24 & 0xff);
            block1[S.length + 1] = (byte) (i >> 16 & 0xff);
            block1[S.length + 2] = (byte) (i >> 8  & 0xff);
            block1[S.length + 3] = (byte) (i >> 0  & 0xff);

            mac.update(block1);
            mac.doFinal(U, 0);
            arraycopy(U, 0, T, 0, hLen);

            for (int j = 1; j < c; j++) {
                mac.update(U);
                mac.doFinal(U, 0);

                for (int k = 0; k < hLen; k++) {
                    T[k] ^= U[k];
                }
            }

            arraycopy(T, 0, DK, (i - 1) * hLen, (i == l ? r : hLen));
        }
    }
}