This paper proposes Recryptor, an energy efficient and compact ARM Cortex-M0 based reconfigurable cryptographic processor using in-memory computing. Recryptor is capable of accelerating a wide range of cryptography algorithms and standards, including public/private key cryptography and hash functions, by augmenting the memory of a commercial general purpose IoT processor resulting in a highly compact implementation. The wide bit-width of memory is ideally suited for high bitwidth (64-512b) arithmetic operations common in cryptographic functions. Recryptor (28.8 MHz at 0.7 V) achieves 6.8× average speedup and 12.8× average energy improvements over state-of-the-art software and hardware-accelerated implementations with only 0.128 mm2area overhead in 40nm CMOS.