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diff --git a/native/expo-modules/aes-crypto/android/src/main/java/app/comm/android/aescrypto/AESCryptoModule.kt b/native/expo-modules/aes-crypto/android/src/main/java/app/comm/android/aescrypto/AESCryptoModule.kt
--- a/native/expo-modules/aes-crypto/android/src/main/java/app/comm/android/aescrypto/AESCryptoModule.kt
+++ b/native/expo-modules/aes-crypto/android/src/main/java/app/comm/android/aescrypto/AESCryptoModule.kt
@@ -5,10 +5,16 @@
import expo.modules.kotlin.modules.ModuleDefinition
import expo.modules.kotlin.typedarray.Uint8Array
import java.security.SecureRandom
+import javax.crypto.Cipher
import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+import javax.crypto.spec.SecretKeySpec
private const val ALGORITHM_AES = "AES"
+private const val CIPHER_TRANSFORMATION_NAME = "AES/GCM/NoPadding"
private const val KEY_SIZE = 32 // bytes
+private const val IV_LENGTH = 12 // bytes - unique Initialization Vector (nonce)
+private const val TAG_LENGTH = 16 // bytes - GCM auth tag
class AESCryptoModule : Module() {
private val secureRandom by lazy { SecureRandom() }
@@ -17,6 +23,7 @@
Name("AESCrypto")
Function("generateKey", this@AESCryptoModule::generateKey)
+ Function("encrypt", this@AESCryptoModule::encrypt)
}
// region Function implementations
@@ -38,12 +45,85 @@
destination.write(keyBytes, position = 0, size = keyBytes.size)
}
+ /**
+ * Encrypts given [plaintext] with provided key and saves encrypted results
+ * (sealed data) into [destination]. After the encryption, the destination
+ * array will contain the following, concatenated in order:
+ * - IV
+ * - Ciphertext with GCM tag
+ *
+ * @param rawKey AES-256 key bytes. Must be of length [KEY_SIZE]
+ * @param plaintext
+ * @param destination must be of length: [plaintext]+[IV_LENGTH]+[TAG_LENGTH]
+ */
+ private fun encrypt(
+ rawKey: Uint8Array,
+ plaintext: Uint8Array,
+ destination: Uint8Array
+ ) {
+ if (destination.length != plaintext.length + IV_LENGTH + TAG_LENGTH) {
+ throw InvalidDataLengthException()
+ }
+
+ val key = rawKey.toAESSecretKey()
+ val plaintextBuffer = plaintext.toDirectBuffer()
+ val plaintextBytes = ByteArray(plaintext.byteLength)
+ .also(plaintextBuffer::get)
+ val (iv, ciphertextWithTag) = encryptAES(plaintextBytes, key)
+
+ destination.write(iv, position = 0, size = IV_LENGTH)
+ destination.write(ciphertextWithTag, IV_LENGTH, ciphertextWithTag.size)
+ }
+
// endregion
}
+// region RN-agnostic implementations
+
+/**
+ * Encrypts given [plaintext] with given [key] using AES-256 GCM algorithm
+ *
+ * @return A pair of:
+ * - IV (initialization vector) - 12 bytes long
+ * - [ByteArray] containing ciphertext with 16-byte GCM auth tag appended
+ */
+private fun encryptAES(
+ plaintext: ByteArray,
+ key: SecretKey
+): Pair<ByteArray, ByteArray> {
+ val cipher = Cipher.getInstance(CIPHER_TRANSFORMATION_NAME).apply {
+ init(Cipher.ENCRYPT_MODE, key)
+ }
+ val iv = cipher.iv.copyOf()
+ val ciphertextWithTag = cipher.doFinal(plaintext)
+ return Pair(iv, ciphertextWithTag)
+}
+
+// endregion
+
+// region Utility extension functions
+
+fun ByteArray.toSecretKey(algorithm: String = ALGORITHM_AES) =
+ SecretKeySpec(this, 0, this.size, algorithm)
+
+fun Uint8Array.toAESSecretKey(): SecretKey {
+ if (this.byteLength != KEY_SIZE) {
+ throw InvalidKeyLengthException()
+ }
+
+ return ByteArray(KEY_SIZE)
+ .also { bytes -> this.read(bytes, 0, KEY_SIZE) }
+ .toSecretKey()
+}
+
+// endregion
+
// region Exception definitions
private class InvalidKeyLengthException :
CodedException("The AES key has invalid length")
+private class InvalidDataLengthException :
+ CodedException("Source or destination array has invalid length")
+
// endregion
diff --git a/native/utils/aes-crypto-module.js b/native/utils/aes-crypto-module.js
--- a/native/utils/aes-crypto-module.js
+++ b/native/utils/aes-crypto-module.js
@@ -28,7 +28,6 @@
}
export function encrypt(key: Uint8Array, data: Uint8Array): Uint8Array {
- invariant(AESCryptoModule.encrypt, 'AESCrypto.encrypt is not implemented');
const sealedDataBuffer = new Uint8Array(data.length + IV_LENGTH + TAG_LENGTH);
AESCryptoModule.encrypt(key, data, sealedDataBuffer);
return sealedDataBuffer;

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