Abstract: Provided are a method and apparatus for providing a security mechanism guaranteeing transparency at a transport layer. The method includes: receiving a data packet from an application program, and searching key information corresponding to the data packet in key information database; determining whether to request a key exchange module of an application layer for a new key negotiation according to a result obtained by searching key information; and performing encrypting/decrypting based on key information when the key exchange module stores key negotiation information obtained by the new key negotiation in a kernel. The apparatus encrypts/decrypts the data packet at the transport layer of the kernel, thereby providing the application program with security transparency, effectively controlling and making it easily expansible.