The former chief technology officer and chief information security officer from Andreessen Horowitz, or a16z, a venture-capital firm that has invested heavily in crypto, are starting an institution-focused cryptocurrency custody firm,according to a person familiar with the plans. Riyaz Faizullabhoy, the former CTO, and Nassim Eddequiouaq, the former chief information security officer, have the blessing and seed backing of a16z, the person said. The two men departed a16z in February.