diff --git a/src/main.zig b/src/main.zig
index 72509b6..a830a36 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const b64 = @import("base64.zig");
 const hex = @import("hex.zig");
+const xor = @import("xor.zig");
 
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
@@ -28,4 +29,23 @@ pub fn main() !void {
             try stdout.print("{s}", .{result});
         }
     }
+
+    if (std.mem.eql(u8, args[1], "xor")) {
+        const in_a = args[2];
+        const in_b = args[3];
+
+        const buf_a = try hex.decode(allocator, in_a);
+        defer allocator.free(buf_a);
+
+        const buf_b = try hex.decode(allocator, in_b);
+        defer allocator.free(buf_b);
+
+        const out = try xor.xor_buffers(allocator, buf_a, buf_b);
+        defer allocator.free(out);
+
+        const out_hex = try hex.encode(allocator, out);
+        defer allocator.free(out_hex);
+
+        try stdout.print("{s}", .{out_hex});
+    }
 }
diff --git a/src/xor.zig b/src/xor.zig
new file mode 100644
index 0000000..762a095
--- /dev/null
+++ b/src/xor.zig
@@ -0,0 +1,14 @@
+const std = @import("std");
+
+/// buf_a ^ buf_b. Caller must free result.
+pub fn xor_buffers(allocator: std.mem.Allocator, buf_a: []u8, buf_b: []u8) ![]u8 {
+    if (buf_a.len != buf_b.len) return error.UnequalLength;
+
+    var out: []u8 = try allocator.alloc(u8, buf_a.len);
+
+    for (0..buf_a.len) |i| {
+        out[i] = buf_a[i] ^ buf_b[i];
+    }
+
+    return out;
+}