The additions were announced after South Africa suffered a 241-run defeat in the first Test at Kingsmead.
"Following our performance and injuries in the first Test, we have recognised the need to bolster the squad," said Linda Zondi, the convener of selectors.
Apart from taking the gloves to reduce the workload of star batsman AB de Villiers, the left-handed De Kock could strengthen South Africa's fragile batting. De Kock hit a century for the Titans franchise against the Cape Cobras in a first-class match at the weekend.
South African squad: Hashim Amla (captain), Dean Elgar, Stiaan van Zyl, AB de Villiers (wkt), Faf du Plessis, Temba Bavuma, JP Duminy, Kyle Abbott, Dale Steyn, Dane Piedt, Morne Morkel, Rilee Rossouw, Quinton de Kock (wkt), Kagiso Rabada, Chris Morris.