feat: add sncrypto client side packages

packages/sncrypto-common/src/AES-GCM/CryptoAes256GcmInterface.ts

@@ -0,0 +1,20 @@
+import { HexString } from '../Types/HexString'
+import { Aes256GcmEncrypted } from './Aes256GcmEncrypted'
+import { Aes256GcmInput } from './Aes256GcmInput'
+
+export interface CryptoAes256GcmInterface<EncodingType> {
+  /**
+   * Encrypts a string using AES-GCM.
+   * @param input
+   * @returns An object which can be run through aes256GcmDecrypt to retrieve the input text.
+   */
+  aes256GcmEncrypt(input: Aes256GcmInput<EncodingType>): Promise<Aes256GcmEncrypted<EncodingType>>
+
+  /**
+   * Decrypts a string using AES-GCM.
+   * @param encrypted
+   * @param key - encryption key as a hex string
+   * @returns A string encoded with encoding provided in the input
+   */
+  aes256GcmDecrypt(encrypted: Aes256GcmEncrypted<EncodingType>, key: HexString): Promise<string>
+}