I believe what you are hearing is a slightly weaker /k/ sound. The initial /s/ sound releases some of the air in your mouth and this tends to sap some of the strength of the /k/. The same thing happens in words beginning with /sp/. The /p/ sound becomes a little less explosive due to the /s/, causing many to believe it is a /b/. Contrary to every textbook in Taiwan, these are NOT /g/ and /b/ sounds, respectively. They are still /k/ and /p/ sounds, just a little weaker or less explosive.
P.S. I have never studied linguistics, so I'm sure I'll get pounded into the dirt by someone who has.
Student or Learner