diff --git a/tech/Affine.wiki b/tech/Affine.wiki
new file mode 100644
index 0000000..a6e390c
--- /dev/null
+++ b/tech/Affine.wiki
@@ -0,0 +1,13 @@
+= Affine =
+
+Affine cipher is a type of [[substitution]] cipher.
+
+The cipher is of model
+
+f(x) = ax + b mod 26
+
+Where x is some number corresponding to a letter, 0-25. a and b are variables.
+
+To decipher, the formula is of form
+
+f(y) = a^-1(y - b) mod 26
diff --git a/tech/security.wiki b/tech/security.wiki
index 9d98b1b..fd0f3de 100644
--- a/tech/security.wiki
+++ b/tech/security.wiki
@@ -9,6 +9,7 @@ Hiding information
 === Ciphers ===
 
 * [[substitution|Substitution]] 
+* [[Affine]]
 
 === Math for Crypto ===