RSA 加密验证签名

package com.example.rsa;

import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SignatureException;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

import android.util.Log;

public class SignUtils {
    private static final String TAG = "SignUtils";

    private static final String ALGORITHM = "RSA";

    private static final String SIGN_ALGORITHMS = "SHA1WithRSA";

    private static final String DEFAULT_CHARSET = "UTF-8";

    public static String sign(String content, String privateKey) {
        try {
            PKCS8EncodedKeySpec priPKCS8 = new PKCS8EncodedKeySpec(
                    Base64.decode(privateKey));
            KeyFactory keyf = KeyFactory.getInstance(ALGORITHM);
            PrivateKey priKey = keyf.generatePrivate(priPKCS8);

            java.security.Signature signature = java.security.Signature
                    .getInstance(SIGN_ALGORITHMS);

            signature.initSign(priKey);
            signature.update(content.getBytes(DEFAULT_CHARSET));

            byte[] signed = signature.sign();

            return Base64.encode(signed);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    public static boolean verify(PublicKey publicKey, String signedData, String signature) {
        java.security.Signature sig;
        try {
            sig = java.security.Signature.getInstance(SIGN_ALGORITHMS);
            sig.initVerify(publicKey);
            sig.update(signedData.getBytes());
            if (!sig.verify(Base64.decode(signature))) {
                Log.e(TAG, "Signature verification failed.");
                return false;
            }
            return true;
        } catch (NoSuchAlgorithmException e) {
            Log.e(TAG, "NoSuchAlgorithmException.");
        } catch (InvalidKeyException e) {
            Log.e(TAG, "Invalid key specification.");
        } catch (SignatureException e) {
            Log.e(TAG, "Signature exception.");
        } catch (IllegalArgumentException e) {
            Log.e(TAG, "Base64 decoding failed.");
        }
        return false;
    }

    public static PublicKey generatePublicKey(String encodedPublicKey) {
        try {
            byte[] decodedKey = Base64.decode(encodedPublicKey);
            KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
            return keyFactory.generatePublic(new X509EncodedKeySpec(decodedKey));
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        } catch (InvalidKeySpecException e) {
            Log.e(TAG, "Invalid key specification.");
            throw new IllegalArgumentException(e);
        } catch (IllegalArgumentException e) {
            Log.e(TAG, "Base64 decoding failed.");
            throw e;
        }
    }

}