DNA is a new generation material for molecular data storage, with a potential storage capacity several orders of magnitude greater than current methods. Data stored in DNA can be encoded (written) and decoded (read) using sequencing technologies. Advantages of DNA data storage are (i) high data density, (ii) high stability, (iii) ease of copy, and (iv) low energy. Current methods rely on slow, expensive, complicated synthesis of long DNA to write, followed by costly, high error rate (10%) reads. We overcome these challenges with a low-cost, enzyme-free, mix-and-detect method for high fidelity DNA data reading, writing, and rewriting using nanopore technology and universal rewritable blank medium DNA without the need for nucleic acid synthesis. This technology has applications not only in DNA data storage, but also in DNA barcoding for high throughput screening of nucleic acid secondary structure and drug/ligand binding.