Security of sensor grids is important especially for surveillance, military and medical applications. The paper addresses methods for two security features. First, an approach for generation of very strong geographically unique identifiers is proposed that is based on cryptography hashing. Second, symmetric key establishment method for every internode communication session is presented. Implementation results are given for ARM8 and AVR32 CPU. The results show that the methods are suitable for nodes with restricted computational and memory resources. Key words: sensor networks, cryptography hashing, symmetric key management