Make methods thread safe (#3)

Author: hieronymus777

android/crypto/src/main/java/com/coinbase/wallet/crypto/ciphers/AES256GCM.kt

@@ -22,7 +22,7 @@ class AES256GCM {
          *
          * @return A pair of encrypted data and authTag
          */
-        fun encrypt(data: ByteArray, key: ByteArray, iv: ByteArray): Pair<ByteArray, ByteArray> {
+        @Synchronized fun encrypt(data: ByteArray, key: ByteArray, iv: ByteArray): Pair<ByteArray, ByteArray> {
             val cipher = Cipher.getInstance(TRANSFORMATION)
             val paramSpec = GCMParameterSpec(AUTH_TAG_SIZE, iv)
             val keySpec = SecretKeySpec(key, "AES")
@@ -45,7 +45,7 @@ class AES256GCM {
          * @return A triple of iv, authTag, and encrypted data
          * @throws `EncryptionException.invalidAES256GCMData` if unable to encrypt data
          */
-        fun encrypt(data: ByteArray, secretKey: SecretKey): Triple<ByteArray, ByteArray, ByteArray> {
+        @Synchronized fun encrypt(data: ByteArray, secretKey: SecretKey): Triple<ByteArray, ByteArray, ByteArray> {
             val cipher = Cipher.getInstance(TRANSFORMATION)
 
             cipher.init(Cipher.ENCRYPT_MODE, secretKey)
@@ -68,7 +68,7 @@ class AES256GCM {
          * @return The decrypted data
          * @throws`EncryptionError.invalidAES256GCMData` if unable to decrypt data
          */
-        fun decrypt(data: ByteArray, key: ByteArray, iv: ByteArray, authTag: ByteArray): ByteArray {
+        @Synchronized fun decrypt(data: ByteArray, key: ByteArray, iv: ByteArray, authTag: ByteArray): ByteArray {
             val cipher = Cipher.getInstance(TRANSFORMATION)
             val paramSpec = GCMParameterSpec(AUTH_TAG_SIZE, iv)
             val keySpec = SecretKeySpec(key, "AES")
@@ -89,7 +89,7 @@ class AES256GCM {
          *
          * @return A triple of iv, authTag, and encrypted data
          */
-        fun decrypt(data: ByteArray, secretKey: SecretKey, iv: ByteArray, authTag: ByteArray): ByteArray {
+        @Synchronized fun decrypt(data: ByteArray, secretKey: SecretKey, iv: ByteArray, authTag: ByteArray): ByteArray {
             val cipher = Cipher.getInstance(TRANSFORMATION)
             val paramSpec = GCMParameterSpec(AUTH_TAG_SIZE, iv)
             val encryptedData = data + authTag