While there is insufficient evidence to prove that North Korea is pursuing countermeasures or penetration aids (penaids), the lack of evidence certainly does not prove that they are not. The technology behind producing penaids — or still more dangerous — multiple independent reentry vehicles (MIRVs) is difficult, but not more difficult than what North Korea has already accomplished.
Open Nuclear Network News
For North Korea, the concepts of countermeasures, MIRVs, and ballistic missile defence have been long-established. It is much easier for North Korea to design for these factors from the beginning.
For every state that develops a missile there are several who want to protect against it. There are an abundance of approaches, but one of the most controversial is ballistic missile defence (BMD). The general idea of ballistic missile defence is to detect an incoming warhead and neutralize it before it hits you.