Secure communication is a critical requirement for Internet of Things (IoT) devices, which are often based on Microcontroller Units (MCUs). Current cryptographic solutions, which rely on software libraries or dedicated hardware accelerators, are fundamentally limited by the performance and energy costs of data movement between memory and processing units. This paper introduces CryptoSRAM, an in-SRAM computing architecture that performs cryptographic operations directly within the MCU's standard SRAM array. By repurposing the memory array into a massively parallel processing fabric, CryptoSRAM eliminates the data movement bottleneck. This approach is well-suited to MCUs, which utilize physical addressing and Direct Memory Access (DMA) to manage SRAM, allowing for seamless integration with minimal hardware overhead. Our analysis shows that for common cryptographic kernels, CryptoSRAM achieves throughput improvements of up to 74$\times$ and 67$\times$ for AES and SHA3, respectively, compared to a software implementation. Furthermore, our solution delivers up to 6$\times$ higher throughput than existing hardware accelerators for AES. CryptoSRAM demonstrates a viable and efficient architecture for secure communication in next-generation IoT systems.