This chapter shows how cryptomodules can increase security of wireless sensor network and possibilities of biometric authentication against a node or the whole network. For secure operation of a wireless sensor network, security objectives such as confidentiality, integrity, and authentication must be implemented. These security objectives typically employ cryptography, therefore sensor nodes should be able to compute cryptographic algorithms and provide secure tamper resistant storage for cryptographic keys. Use of dedicated secure hardware for this purpose and security threats are discussed. Two scenarios where the biometric authentication would be appreciated are introduced - smart home and storehouse with medicaments. Biometric generation of cryptographic keys, biometric authentication in wireless network and possible attacks on biometrics are presented. When designing and verifying communication protocols using informal techniques, some security errors may remain undetected. Formal verification methods that provide a systematic way of finding protocol flaws are discussed.