Described herein are technologies pertaining to preserving privacy of users of mobile computing devices. Two users of two mobile computing devices share a quantization scheme for quantizing location data using a predefined quantization interval. The two users additionally share a private key that is utilized to encrypt locations obtained by the two computing devices that have been quantized using the shared quantization scheme. Encrypted, quantized locations are compared in a cloud computing service in connection with answering location-based queries, where the comparison is undertaken without the cloud computing service decrypting the encrypted, quantized locations.