CTRL does not actually modify the character code sent from the keyboard. For letters, the same keycode (which maps to ASCII with a constant addition of 0x3D) is always sent. Another byte in the HID report contains bit flags for modifier keys (L/R CTRL, SHIFT, etc); the OS decides what happens after that.
Not on a modern PC, but on the machine ASCII was originally developed for I could definitely see the CTRL key just pulling one bit low on the keyboard encoder.
CTRL does not actually modify the character code sent from the keyboard. For letters, the same keycode (which maps to ASCII with a constant addition of 0x3D) is always sent. Another byte in the HID report contains bit flags for modifier keys (L/R CTRL, SHIFT, etc); the OS decides what happens after that.
Note that this holds under USB HID.