Developing novel security devices using nanotechnology has emerged as a promising new area since they offer higher reliability, small form factor, and anti-tampering features. Single-walled carbon nanotube (CNT) is promising to replace silicon as the future transistor channel material due to its superb electrical properties and intrinsic ultrathin body. However, several imperfections of this nanomaterial such as the presence of metallic CNTs and imprecise assembly remain to be overcome to realize high-performance electronics. Here we show that by actually utilizing these inherent imperfections, an unclonable electronic random structure can be constructed at very low cost. Two-dimensional random bits array with over 2000 bits were fabricated by the ion-exchange chemistry method to assemble nanotubes into patterned HfO2 trenches, with the optimized trench width that maximizes the entropy. The low temperature, substrate agnostic processes during fabrication make CNT based crypto primitive an ideal technology for monolithic integration with both silicon and future non-silicon chips for on-chip key generation and authentication.