With the exponential rise in IoT networks, data transmission should be ensured to be secure and efficient as well for the integrity of maintaining communication. Most of the current cryptographic techniques fail to balance computational efficiency, memory overhead, or tamper detection in resource-constrained environments. In this paper, we present a new cryptographic framework that integrates Homomorphic Transform with Blockchain technology for secure privacy-preserving device-to-device communications in IoT ecosystems. We have implemented the HT+BC proposal with all the given metrics in terms of processing time, memory usage, entropy, hash difference, and throughput. Experimental analyses reveal that HT+BC reports a hash difference rate of 15-20% against varying scales of IoT. Contrary to other techniques, HT+BC most emphatically can detect tampering. In terms of throughput, it was observed that in large-scale IoT, the average throughput recorded by HT+BC was 28 KB/s but used much less memory of 60 KB. The hash value was slightly changed by less than 5% and had much larger memory sizes at 90-120 KB. Our approach still possesses entropy values ranging from 4.8 to 5.3 bits, thus, entropy of data unpredictability while securing communications.