diff --git a/src/crypt.c b/src/crypt.c
index 75f9cde..fb1a1a6 100644
--- a/src/crypt.c
+++ b/src/crypt.c
@@ -10,16 +10,39 @@
 
 #include "crypt.h"
 
+// Which of the two below functions is faster (find out!)
+inline int mod(int a, int b)
+{
+	return (a % b + b) % b;
+}
 
+
+inline int fast_mod(int a, int b)
+{
+	const int result = a % b;
+	return result >= 0 ? result : result + b;
+}
+
+// Below two functions do NOT work for lower case letters (fix this!)
 void caesar_encrypt(char* str, int size, int key)
 {
 	for (int i = 0; i < size && str[i] != '\n'; i++)
-		if (str[i] != ' ') str[i] += key % 26;
+		if (str[i] != ' ')
+		{
+			str[i] += key - 65;
+			str[i] %= 26;
+			str[i] += 65;
+		}
 }
 
 
 void caesar_decrypt(char* str, int size, int key)
 {
 	for (int i = 0; i < size && str[i] != '\n'; i++)
-		if (str[i] != ' ') str[i] -= key % 26;
+		if (str[i] != ' ')
+		{
+			str[i] = str[i] - key - 65;
+			str[i] = mod(str[i], 26);
+			str[i] += 65;
+		}
 }