Android加密算法之RSA(二)

The RSA algorithm can only encrypt data that has a maximum byte length of the RSA key length in bits divided with eight minus eleven padding bytes, i.e. number of maximum bytes = key length in bits / 8 - 11.

使用RSA时，数据过长会报错，如：

javax.crypto.IllegalBlockSizeException: input must be under 256 bytes

因此，基本上，您将密钥长度除以8 -11（如果有填充）。例如，如果您具有2048位密钥，则可以加密2048/8 = 256字节（如果有填充则为11字节）。因此，可以使用更大的密钥，也可以使用对称密钥加密数据，然后使用rsa加密该密钥（推荐的方法）
参考：https://stackoverflow.com/questions/10007147/getting-a-illegalblocksizeexception-data-must-not-be-longer-than-256-bytes-when

通过分段加密解决

1.生成公钥私钥

@Throws(Exception::class)
    fun genKeyPair(): Map<String?, String> {
        val keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM)
        keyPairGen.initialize(2048)
        val keyPair = keyPairGen.generateKeyPair()
        val publicKey = keyPair.public as RSAPublicKey
        val privateKey = keyPair.private as RSAPrivateKey
        val keyMap: MutableMap<String?, String> = HashMap(2)
        keyMap[PUBLIC_KEY] = Base64.encodeToString(publicKey.encoded, Base64.DEFAULT)
        keyMap[PRIVATE_KEY] = Base64.encodeToString(privateKey.encoded, Base64.DEFAULT)
        return keyMap
    }

2.公钥加密

    @Throws(Exception::class)
    fun encryptByPublicKey(data: ByteArray, publicKey: String?): ByteArray {
        val keyBytes: ByteArray = Base64.decode(publicKey, Base64.DEFAULT)
        val x509KeySpec = X509EncodedKeySpec(keyBytes)
        val keyFactory = KeyFactory.getInstance(KEY_ALGORITHM)
        val publicK: Key = keyFactory.generatePublic(x509KeySpec)
        // 对数据加密
        val cipher = Cipher.getInstance(keyFactory.algorithm)
        cipher.init(Cipher.ENCRYPT_MODE, publicK)
        val inputLen = data.size
        val out = ByteArrayOutputStream()
        var offSet = 0
        var cache: ByteArray
        var i = 0
        // 对数据分段加密
        while (inputLen - offSet > 0) {
            cache = if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK)
            } else {
                cipher.doFinal(data, offSet, inputLen - offSet)
            }
            out.write(cache, 0, cache.size)
            i++
            offSet = i * MAX_ENCRYPT_BLOCK
        }
        val encryptedData = out.toByteArray()
        out.close()
        return encryptedData
    }

3.私钥解密

    @Throws(Exception::class)
    fun decryptByPrivateKey(encryptedData: ByteArray, privateKey: String?): ByteArray {
        val keyBytes: ByteArray = Base64.decode(privateKey, Base64.DEFAULT)
        val pkcs8KeySpec = PKCS8EncodedKeySpec(keyBytes)
        val keyFactory = KeyFactory.getInstance(KEY_ALGORITHM)
        val privateK: Key = keyFactory.generatePrivate(pkcs8KeySpec)
        val cipher = Cipher.getInstance(keyFactory.algorithm)
        cipher.init(Cipher.DECRYPT_MODE, privateK)
        val inputLen = encryptedData.size
        val out = ByteArrayOutputStream()
        var offSet = 0
        var cache: ByteArray
        var i = 0
        // 对数据分段解密
        while (inputLen - offSet > 0) {
            cache = if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK)
            } else {
                cipher.doFinal(encryptedData, offSet, inputLen - offSet)
            }
            out.write(cache, 0, cache.size)
            i++
            offSet = i * MAX_DECRYPT_BLOCK
        }
        val decryptedData = out.toByteArray()
        out.close()
        return decryptedData
    }

4.调用方法：

        val keyMap: Map<String?, String?> = RSACrypt.genKeyPair()
        val publicKey = keyMap[RSACrypt.PUBLIC_KEY]
        val privateKey = keyMap[RSACrypt.PRIVATE_KEY]
        val source =
            "身高一米七左右，标准的九头身，五官立体宛如艺术大师鬼斧神工之作，肌肤赛雪，宛如白玉般似能反射光彩。" +
            "“我和茹雪两情相悦，但对我们而言，你是第三者，所以请你自己主动退出，我愿意给你一笔钱，你开个价码吧！”啪，一声清脆的响声，干净利落地狠狠扇在韩斌的脸上。" +
            "乔智愿意当陶家的女婿，除了偿还父亲欠下的人情债之外，还有一个重要原因，陶茹雪本身出众，是琼金一枝花，知名度高，追求者众多。"
        val data = source.encodeToByteArray()
        val encodedData: ByteArray = RSACrypt.encryptByPublicKey(data, publicKey)
        Log.w("rsa", "加密后文字：${Base64.encodeToString(encodedData, Base64.DEFAULT)}")
        val decodedData: ByteArray = RSACrypt.decryptByPrivateKey(encodedData, privateKey)
        Log.w("rsa", "解密后文字: \r\n${String(decodedData)}")

完整代码

object RSACrypt {
    /**
     * 加密算法RSA
     */
    const val KEY_ALGORITHM = "RSA"

    /**
     * 签名算法
     */
    const val SIGNATURE_ALGORITHM = "MD5withRSA"

    /**
     * 获取公钥的key
     */
    const val PUBLIC_KEY = "RSAPublicKey"

    /**
     * 获取私钥的key
     */
    const val PRIVATE_KEY = "RSAPrivateKey"

    /**
     * RSA最大加密明文大小
     */
    private const val MAX_ENCRYPT_BLOCK = 245

    /**
     * RSA最大解密密文大小
     */
    private const val MAX_DECRYPT_BLOCK = 256

    /**
     * 生成密钥对(公钥和私钥)
     * @return
     * @throws Exception
     */
    @Throws(Exception::class)
    fun genKeyPair(): Map<String?, String> {
        val keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM)
        keyPairGen.initialize(2048)
        val keyPair = keyPairGen.generateKeyPair()
        val publicKey = keyPair.public as RSAPublicKey
        val privateKey = keyPair.private as RSAPrivateKey
        val keyMap: MutableMap<String?, String> = HashMap(2)
        keyMap[PUBLIC_KEY] = Base64.encodeToString(publicKey.encoded, Base64.DEFAULT)
        keyMap[PRIVATE_KEY] = Base64.encodeToString(privateKey.encoded, Base64.DEFAULT)
        return keyMap
    }

    /**
     * 私钥解密
     *
     * @param encryptedData 已加密数据
     * @param privateKey 私钥(BASE64编码)
     * @return
     * @throws Exception
     */
    @Throws(Exception::class)
    fun decryptByPrivateKey(encryptedData: ByteArray, privateKey: String?): ByteArray {
        val keyBytes: ByteArray = Base64.decode(privateKey, Base64.DEFAULT)
        val pkcs8KeySpec = PKCS8EncodedKeySpec(keyBytes)
        val keyFactory = KeyFactory.getInstance(KEY_ALGORITHM)
        val privateK: Key = keyFactory.generatePrivate(pkcs8KeySpec)
        val cipher = Cipher.getInstance(keyFactory.algorithm)
        cipher.init(Cipher.DECRYPT_MODE, privateK)
        val inputLen = encryptedData.size
        val out = ByteArrayOutputStream()
        var offSet = 0
        var cache: ByteArray
        var i = 0
        // 对数据分段解密
        while (inputLen - offSet > 0) {
            cache = if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK)
            } else {
                cipher.doFinal(encryptedData, offSet, inputLen - offSet)
            }
            out.write(cache, 0, cache.size)
            i++
            offSet = i * MAX_DECRYPT_BLOCK
        }
        val decryptedData = out.toByteArray()
        out.close()
        return decryptedData
    }

    /**
     *
     * 公钥加密
     *
     * @param data 源数据
     * @param publicKey 公钥(BASE64编码)
     * @return
     * @throws Exception
     */
    @Throws(Exception::class)
    fun encryptByPublicKey(data: ByteArray, publicKey: String?): ByteArray {
        val keyBytes: ByteArray = Base64.decode(publicKey, Base64.DEFAULT)
        val x509KeySpec = X509EncodedKeySpec(keyBytes)
        val keyFactory = KeyFactory.getInstance(KEY_ALGORITHM)
        val publicK: Key = keyFactory.generatePublic(x509KeySpec)
        // 对数据加密
        val cipher = Cipher.getInstance(keyFactory.algorithm)
        cipher.init(Cipher.ENCRYPT_MODE, publicK)
        val inputLen = data.size
        val out = ByteArrayOutputStream()
        var offSet = 0
        var cache: ByteArray
        var i = 0
        // 对数据分段加密
        while (inputLen - offSet > 0) {
            cache = if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK)
            } else {
                cipher.doFinal(data, offSet, inputLen - offSet)
            }
            out.write(cache, 0, cache.size)
            i++
            offSet = i * MAX_ENCRYPT_BLOCK
        }
        val encryptedData = out.toByteArray()
        out.close()
        return encryptedData
    }
}