Basic Cryptology

This scroll, obtained in Castle Harmondale after the final renovation (second), explains the basic idea behind how to decode ciphered messages.  Assigning numeric values to the alphabet  makes it a little easier to understand. In the example given above, when numeric values are substituted you can see how the results are obtained:

u (21) - a (1) = t (20);
c (3) - n (14) = o (-11?); 
v (22) - g (7)  = o (15);

? since there are no zeroes or negative values one needs to add the base, in this case the total number of the alphabet (26), to the result in order to obtain a positive value.

in this equation -11 + 26 = 15 or o.
a b c d e f g h i j k l m
1 2 3 4 5 6 7 8 9 10 11 12 13

n
 o
 p
 q
 r
 s
 t
 u
 v
 w
 x
 y
 z
14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26

Scroll of Waves

Stephen Sand tells you to use the third word of this scroll as the key to unlock the following cipher:

Cipher

Applying the third word, pattern, to the first 3 words of the cipher we get the following results:

 
Y (25)
i (9)
u (21)
p (16)
j (10)
x (24)
c (3)
k (11)
o (15)
x (24)
-
p (16)
a (1)
t (20)
t (20)
e (5)
r (18)
n (14)
p (16)
a (1)
t (20)
=
i (9)
h (8)
a (1)
 (-4)
 e (5)
f (6)
 (-11)
 (-5)
n (14)
d (4)
+
      
 (26)
    
 (26)
 (26)
    
=
      
 v (22)
    
 o (15)
 u (21)
    

So the first 3 words are: I have found.... continue decoding the cipher in the scroll in the same manner to achieve the complete translation.