chore(repo): add a script to use gcm outside service (#254)

Author: jatinsandilya

.prettierignore

@@ -1,2 +1,3 @@
 node_modules
 packages/*/dist
+**/*/node_modules

scripts/backend/decrypt_email.js

@@ -0,0 +1,56 @@
+const crypto = require('crypto');
+
+const CIPHER_ALGORITHM = 'aes-256-gcm';
+const IV_LENGTH = 16;
+const TAG_LENGTH = 16;
+const SALT_LENGTH = 64;
+const ITERATIONS = 10000;
+
+const tagPosition = SALT_LENGTH + IV_LENGTH;
+const encryptedPosition = tagPosition + TAG_LENGTH;
+
+const getKey = (salt, secret) => {
+    return crypto.pbkdf2Sync(secret, salt, ITERATIONS, 32, 'sha256');
+};
+
+const gcm = {
+    encrypt: (input, secret) => {
+        const iv = crypto.randomBytes(IV_LENGTH);
+        const salt = crypto.randomBytes(SALT_LENGTH);
+
+        const AES_KEY = getKey(salt, secret);
+
+        const cipher = crypto.createCipheriv(CIPHER_ALGORITHM, AES_KEY, iv);
+        const encrypted = Buffer.concat([cipher.update(String(input), 'utf8'), cipher.final()]);
+
+        const tag = cipher.getAuthTag();
+
+        return Buffer.concat([salt, iv, tag, encrypted]).toString('hex');
+    },
+
+    decrypt: (input, secret) => {
+        const inputValue = Buffer.from(String(input), 'hex');
+        const salt = inputValue.subarray(0, SALT_LENGTH);
+        const iv = inputValue.subarray(SALT_LENGTH, tagPosition);
+        const tag = inputValue.subarray(tagPosition, encryptedPosition);
+        const encrypted = inputValue.subarray(encryptedPosition);
+
+        const key = getKey(salt, secret);
+
+        const decipher = crypto.createDecipheriv(CIPHER_ALGORITHM, key, iv);
+
+        decipher.setAuthTag(tag);
+
+        return decipher.update(encrypted) + decipher.final('utf8');
+    },
+};
+
+// Usage: `node scripts/backend/descrypt_email.js`
+// Uncomment below to use a gcm function
+// console.log(
+//     'Decrypt email',
+//     gcm.decrypt(
+//         '', //
+//         process.env.AES_ENCRYPTION_SECRET
+//     )
+// );