The ornamental design for a key safe, as shown and described.
FIG. 1 is a front, left, top perspective view of a key safe;
FIG. 2 is a front elevation view of the key safe of FIG. 1;
FIG. 3 is a back elevation view of the key safe of FIG. 1;
FIG. 4 is a left side elevation view of the key safe of FIG. 1;
FIG. 5 is a right side elevation view of the key safe of FIG. 1;
FIG. 6 is a top plan view of the key safe of FIG. 1; and,
FIG. 7 is a bottom plan view of the key safe of FIG. 1.
Any portion of the key safe depicted in broken lines is for the purposes of illustration only and form no part of the claimed design. Additionally, broken line representations of the environment form no part of the claimed design.