For Vegans, a keto diet is possible, but harder.
If your finding protein is a bit challenging. One option I can suggest is hemp protein. This is the one I personally started using:
https://www.amazon.ca/Canada-Hemp-Foods-Natural-Protein/dp/B00E8DNRXM/ref=sr_1_5?s=hpc&ie=UTF8&qid=1514147370&sr=1-5&keywords=hemp+protein+powderI don't use it for the protein, but for the extra fiber. For myself personally I don't eat a lot of food high in fiber so I supplement with this.
If your goal is more fat, then MCT oil is an option. But don't recommend consuming too much at one time, unless you wanna be in the washroom in 5-10 minutes. 1 tbsp = ~14 grams of fat
https://www.amazon.ca/Premium-derived-only-Organic-Coconuts/dp/B00XM0Y9SE/ref=sr_1_4?s=hpc&ie=UTF8&qid=1514147577&sr=1-4&keywords=mct+oilI find MCT oil a bit expensive, so I don't use it, I just eat 1-2 tbsp of coconut oil.
My advice in starting this diet, is to lower the amount of net carbs to 20-25grams per day. I personally don't do good on more than 20 grams of carbs, but my sister can consume up to ~40 grams and still be in ketosis. The protein powder I mentioned above has 8 grams of carbs and 6 grams of dietary fiber, so my net carbs for that protein powder is 2 grams. A lot of veggies are high in fiber so you can eat a lot of veggies.