
Keyhole First Two Layers or Keyhole F2L, sometimes named working corner, is a method that solves, normally, the first two bottom layers of the 3x3x3 cube. It is an efficient method for inserting midlayer edges in the 3x3x3 LBL method. Its a slight advancement on the basic LBL method, because it requires fewer moves, as well as more intuition.
Basic Idea
After the bottom layer cross, only three bottom layer corners are solved. The final corner is reserved as the keyhole to be used in solving the mid layer edges efficiently. To insert a mid layer edge using the keyhole:
You start, like in normal LBL from a cross, then you fill in three of the first layer corners. From that point you solve three of the middle layer edges using the empty corner position as the keyhole. For each edge do the following:
 First position the midlayer edge in the Ulayer such that it is above the centre matching the edge's upfacing colour.
 Using a DTurn position the bottom layer so that the unsolved corner is directly below the midlayer edge's position.
 Now execute one of R U' R' or F U F' to insert the edge.
After three corners and edges are solved you complete F2L by first solving the last corner and finally the last edge using the normal LBL algorithm: R U R' U' F' U' F or the mirror F' U' F U R U R' depending on the current orientation of the edge.
Alternative Procedure
An alternative way to do keyhole F2L is to use this order:
 cross (doesn't have to match centers)
 3 corners
 4 edges
 4th corner
For that you will need three algorithms to solve the last piece depending on it's orientation:
List of algs...
F2L 32
F2L  (R U R' U')(R U R' U')(R U R') 
F2L  (U R U' R')(U R U' R')(U R U' R') 
F2L  U2 R d' R U R' d R' 
F2L  U R d' R U2 R' d R' 
F2L  R2 U R2 U R2 U2 R2 
F2L  U2 R2 U2 R2 U' R2 U' R2 
F2L 33
F2L  (U' R U' R') U2 (R U' R') 
F2L  y U' (L U' L') U2 (L U' L) 
F2L 34
F2L  U' (R U2' R') U (R U R') 
F2L  U (R U R') U2 (R U R') 
F2L  d (R' U R) U2 (R' U R) 
EdgesFirst Keyhole
Another way to approach keyhole is to start by inserting three edges, and then use the remaining unsolved edge position to insert three corners. The basic steps are as follows:
 Solve Cross
 Solve 3x Eslice edges
 Rotate cube to position remaining unsolved slot in FR
 Solve 3x Dlayer corners by:
 Position a Dlayer corner above the slot in the Ulayer
 Rotate Dlayer so that the corner's correct location is directly below the slot
 Insert the corner using one of: R U R' or F' U' F or R B U2 B' R'
If there are no corners available in the Ulayer, then rotate the Dlayer until an unsolved Dlayer corner is above the slot, and then use R U R' to swap it into the Ulayer.
Advantages
While both the corners and edges first approaches use a similar number of moves, edgesfirst does not require the solver to keep track of the working corner, which can be better for lookahead. If used in conjunction with 8355 it may also improve ease of understanding, since a similar concept is used to place the final 5 corners.
See also
External links
 Arnaud van Galen's YouTube Tutorial
 Speedsolving.com: Keyhole Method/Working Corner method
 Speedsolving.com: Edges First Keyhole
 Text Tutorial by Joël van Noort