Android加密算法之AES

什么是高级加密标准或AES？

AES加密标准又称为高级加密标准Rijndael加密法，是美国国家标准技术研究所NIST旨在取代DES的21世纪的加密标准。

AES加密如何工作？

AES是一种对称的加密算法，可基于相同的密钥进行加密和解密。AES包含三个分组密码：AES-128，AES-192和AES-256。每个密码分别使用128 位，192位和256位的加密密钥对128 位块中的数据进行加密和解密。代码：

object AESCrypt {
    private const val AES_MODE = "AES/CBC/PKCS7Padding" //"算法/模式/补码方式"
    private const val CHARSET = "UTF-8"
    private const val CIPHER = "AES"
    private const val HASH_ALGORITHM = "SHA-256"
    private val IV_BYTES = byteArrayOf(0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00)

    /**
     * Generates SHA256 hash of the password which is used as key
     *
     * @param password used to generated key
     * @return SHA256 of the password
     */
    @Throws(NoSuchAlgorithmException::class, UnsupportedEncodingException::class)
    private fun generateKey(password: String): SecretKeySpec {
        val digest = MessageDigest.getInstance(HASH_ALGORITHM)
        val bytes = password.toByteArray(charset(CHARSET))
        digest.update(bytes, 0, bytes.size)
        val key = digest.digest()

        return SecretKeySpec(key, CIPHER)
    }


    /**
     * Encrypt and encode message using 256-bit AES with key generated from password.
     *
     * @param password used to generated key
     * @param message  the thing you want to encrypt assumed String UTF-8
     * @return Base64 encoded CipherText
     * @throws GeneralSecurityException if problems occur during encryption
     */
    @Throws(GeneralSecurityException::class)
    fun encrypt(password: String, message: String): String {
        try {
            val key = generateKey(password)
            val cipherText = encrypt(key, IV_BYTES, message.toByteArray(charset(CHARSET)))
            //NO_WRAP is important as was getting \n at the end
            return Base64.encodeToString(cipherText, Base64.NO_WRAP)
        } catch (e: UnsupportedEncodingException) {
            throw GeneralSecurityException(e)
        }

    }


    /**
     * More flexible AES encrypt that doesn't encode
     *
     * @param key     AES key typically 128, 192 or 256 bit
     * @param iv      Initiation Vector
     * @param message in bytes (assumed it's already been decoded)
     * @return Encrypted cipher text (not encoded)
     * @throws GeneralSecurityException if something goes wrong during encryption
     */
    @Throws(GeneralSecurityException::class)
    fun encrypt(key: SecretKeySpec, iv: ByteArray, message: ByteArray): ByteArray {
        val cipher = Cipher.getInstance(AES_MODE)
        val ivSpec = IvParameterSpec(iv)
        cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec)
        return cipher.doFinal(message)
    }


    /**
     * Decrypt and decode ciphertext using 256-bit AES with key generated from password
     *
     * @param password                used to generated key
     * @param base64EncodedCipherText the encrpyted message encoded with base64
     * @return message in Plain text (String UTF-8)
     * @throws GeneralSecurityException if there's an issue decrypting
     */
    @Throws(GeneralSecurityException::class)
    fun decrypt(password: String, base64EncodedCipherText: String): String {

        try {
            val key = generateKey(password)
            val decodedCipherText = Base64.decode(base64EncodedCipherText, Base64.NO_WRAP)
            val decryptedBytes = decrypt(key, IV_BYTES, decodedCipherText)
            return String(decryptedBytes, charset(CHARSET))
        } catch (e: UnsupportedEncodingException) {
            throw GeneralSecurityException(e)
        }

    }

    /**
     * More flexible AES decrypt that doesn't encode
     *
     * @param key               AES key typically 128, 192 or 256 bit
     * @param iv                Initiation Vector
     * @param decodedCipherText in bytes (assumed it's already been decoded)
     * @return Decrypted message cipher text (not encoded)
     * @throws GeneralSecurityException if something goes wrong during encryption
     */
    @Throws(GeneralSecurityException::class)
    fun decrypt(key: SecretKeySpec, iv: ByteArray, decodedCipherText: ByteArray): ByteArray {
        val cipher = Cipher.getInstance(AES_MODE)
        val ivSpec = IvParameterSpec(iv)
        cipher.init(Cipher.DECRYPT_MODE, key, ivSpec)
        return cipher.doFinal(decodedCipherText)
    }
}

添加扩展方法，方便调用

private const val key: String = "Your AES Key"
    fun encrypt(input: String): String {
        return AESCrypt.encrypt(key, input)
    }

    fun decrypt(input: String): String {
        return AESCrypt.decrypt(key, input)
    }

    fun String.aesEncrypt(): String = encrypt(this)
    fun String.aesDecrypt(): String = decrypt(this)

使用方法

"明文".aesEncrypt()
"密文".aesDecrypt()