Update for 02-11-21 17:15

math/congruences.wiki

@@ -0,0 +1,12 @@
+= Congrucences =
+
+A Congruence
+
+{{{
+    ax = 1 (mod m)
+    }}}
+
+has a solution x, if and only if a and m are [[relative_prime]]s. The solution
+in the range of 1 to m-1 is denoted a^-1 or a^-1 (mod m), called the
+multiplicative inverse of a modulo m.
+

math/gcd.wiki

@@ -0,0 +1,4 @@
+= Greatest Common Denominator =
+
+A greatest common denominator or GCD is the largest number that two numbers can
+both divide into

math/index.wiki

@@ -9,3 +9,5 @@ The purest study of them all
 === Number Theory ===
 
 * [[prime]]
+* [[relative_prime]]
+* 

math/relative_prime.wiki

@@ -0,0 +1,5 @@
+= Relative Prime =
+
+Two numbers are Relative Primes if they have not common prime factors.
+Equivalently, a and b are relatively prime if their [[gcd]] is 1.:w
+

tech/security.wiki

@@ -10,6 +10,10 @@ Hiding information
 
 * [[substitution|Substitution]] 
 
+=== Math for Crypto ===
+
+* [[../math/congruences]]
+
 == Reconnaissance ==
 
 * [[nmap|nmap]] - port scanner