sql_app: crypto: added crypto python helper fucntions

Idea is to isolate cryptography from database managment
	code.

Signed-off-by: HeshamTB <hishaminv@gmail.com>

sql_app/crypto.py

@@ -0,0 +1,29 @@
+
+import os
+from hashlib import pbkdf2_hmac
+
+PASS_ENCODING='utf-8'
+HASH_FUNC='sha256'
+NUM_ITIRATIONS=100000
+
+def get_new_salt(n_bytes : int = 32) -> bytes:
+    
+    if type(n_bytes) != int:
+        n_bytes = 32 # Forece in case of misuse
+    
+    return os.urandom(n_bytes)
+
+"""
+Generate a new key and salt to store.
+Returns (key, salt)
+"""
+def gen_new_key(plain_passwd : str) -> tuple:
+    salt = get_new_salt(32)
+    return (calc_key(plain_passwd, salt), salt)
+
+def verify_key(plain_passwd : str, salt : bytes, stored_key : bytes) -> bool:
+    key_tmp = calc_key(plain_passwd, salt)
+    return (stored_key == key_tmp)
+
+def calc_key(passwd: str, salt : bytes) -> bytes:
+    return pbkdf2_hmac(HASH_FUNC, passwd.encode(PASS_ENCODING), salt, NUM_ITIRATIONS)