Android, AES algorithm encrypt and decrypt with key and IV?

Yunus, I faced with same problem, late but if someone other faces again, I'm sharing my solution. Key and IVkey already converted to base64 and ready to decode, so no need substr process. When you make substr you lose part of whole key.

for keys below I read from shared prefs.

    const val AES_KEY = "AES_KEY"
    const val AES_IV = "AES_IV"

sharedprefs returns keys as same as your keys (as encoded to base64 and as a string -not bytearray-)

{
  "key": "QaDtfPpeMW0VgMMd4XF88K6KkIPe5ZG0sitpyhuJf/E=",
  "iv": "ccp2YePjewVL9X+vCms5BQ==",
  "string": "5c2c82a6-66da-41f9-b20d-5d4ffd0c505a",
}

then just encode:

fun encrypt(message: String): String? {
    try {
        val srcBuff = message.toByteArray(charset("UTF8"))
        val skeySpec = SecretKeySpec(Base64.decode(pref.getString(Constraints.AES_KEY, null)!!, Base64.DEFAULT), "AES")
        val ivSpec = IvParameterSpec(Base64.decode(pref.getString(Constraints.AES_IV, null)!!, Base64.DEFAULT))
        val ecipher: Cipher = Cipher.getInstance("AES/CBC/PKCS7Padding")
        ecipher.init(Cipher.ENCRYPT_MODE, skeySpec, ivSpec)
        val dstBuff: ByteArray = ecipher.doFinal(srcBuff)
        return Base64.encodeToString(dstBuff, Base64.DEFAULT)
    } catch (ex: Exception) {
        context.longToast(ex.localizedMessage)
    }
    return null
}

or decode:

fun decrypt(encrypted: String): String? {
        try {
            val skeySpec = SecretKeySpec(Base64.decode(pref.getString(Constraints.AES_KEY, null)!!, Base64.DEFAULT), "AES")
            val ivSpec = IvParameterSpec(Base64.decode(pref.getString(Constraints.AES_IV, null)!!, Base64.DEFAULT))
            val ecipher: Cipher = Cipher.getInstance("AES/CBC/PKCS7Padding")
            ecipher.init(Cipher.DECRYPT_MODE, skeySpec, ivSpec)
            val raw: ByteArray = Base64.decode(encrypted, Base64.DEFAULT)
            val originalBytes: ByteArray = ecipher.doFinal(raw)
            return String(originalBytes, Charset.forName("UTF-8"))
        } catch (ex: Exception) {
            context.longToast(ex.localizedMessage)
        }
        return null
    }

I don't see much wrong, other than the fact that it is incorrectly stringified (keys and IV's should contain random byte values, including those that are not part of the printable ASCII character set).

However, the most likely culprit is this line:

 byte[] raw = Base64.decode(encrypted.getBytes(), 0, 16, Base64.DEFAULT);

As PKCS#7 always unpads, using a single block may mean that unpadding fails if it is present in one of the following blocks instead. Just decode the entire base 64, not just 16 characters.

There is absolutely no reason whatsoever why CryptoHandler should have only one instance. Your current getInstace method is not thread safe either, so you may turn up with multiple handlers anyway. Just use normal classes, and think about what should be included in them.

This is mainly a so called "wrapper class". It does nothing useful. I would recommend writing cryptography related classes that are specific to a particular use case. Trust me when I say that you may end up rewriting everything later if you don't - I've been there.

No need of any third party library for this.

private fun get16CharIv(): String {
    return UUID.randomUUID().toString().replace("-", "").substring(0, 16)
}

fun encryptTextWith16CharIv(textToEncrypt: String, key: String): String? {
    return try {
        val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
        val secretKeyByte = key.toByteArray(Charsets.UTF_8)
        val keySpec = SecretKeySpec(secretKeyByte, "AES")
        val ivSpec = IvParameterSpec(get16CharIv().toByteArray(Charsets.UTF_8))
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec)
        val encoder = BASE64Encoder()
        encoder.encode(cipher.doFinal(textToEncrypt.toByteArray(Charsets.UTF_8)))
    } catch (e: Exception) {
        null
    }
}

fun decryptTextWith16CharIv(encodedTextToDecrypt: String, key: String): String? {
    return try {
        val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
        val secretKeyByte = key.toByteArray(Charsets.UTF_8)
        val keySpec = SecretKeySpec(secretKeyByte, "AES")
        val ivSpec = IvParameterSpec(get16CharIv().toByteArray(Charsets.UTF_8))
        cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec)
        val decodedText = Base64.decode(
            encodedTextToDecrypt.toByteArray(Charsets.UTF_8), Base64.DEFAULT
        )
        String(cipher.doFinal(decodedText))
    } catch (e: Exception) {
        null
    }
}

//Another way to get IV
fun getIv(): ByteArray {
    if (IV == null) {
        val IV = ByteArray(32)
        val random: SecureRandom = SecureRandom()
        random.nextBytes(IV)
    }
    return IV!!
}

There is one more padding format called No padding. For that we have to use "AES/CBC/NoPadding"