In a food processor, place peppers, garlic cloves, sugar, and kosher salt. Pulse until the peppers are finely chopped, but not blended. If you don't own a food processor, you can dice the peppers and the garlic finely by hand with a pairing knife, and then stir in the sugar and salt. Just be careful with the hand eye situations.
Transfer the chopped pepper mixture to a clean jar. Seal the jar, but not too tightly. Store the mixture in a dark place, like a cabinet.
Once a day, check the jar for fermentation. Fermentation begins when you see tiny little bubbles at the bottom of the jar. This can take anywhere from 2-3 days. Stir the contents once a day until the mixture is no longer rising in volume. This step can take anywhere from 5-6 days.
Transfer the mixture to a food processor or blender and add the vinegar. Puree until completely smooth. Strain the mixture through a fine mesh strainer into a saucepan pressing on the solids to release all the liquid. The strainer should be left with seeds and any large pepper chunks. Discard the solids.
Bring the hot pepper liquid mixture to a boil and then reduce the heat to low. Allow it to simmer for 10-20 minutes until the liquid has reduced and thickened, or desired consistency has been reached. Transfer your sriracha sauce to an airtight container and store in the refrigerator. This sauce will last well over 6 months.
Some notes: Following the 5 days fermentation period, I left the mixture in the cabinet for an additional 2 days, then moved the jar to my refrigerator for about 3 more days before I blended and cooked it down. I found this gave the finished product a nice deep red color, and allowed all the ingredients to meld nicely, giving the sauce more depth in addition to a nice spicy kick.