The diploma thesis deals with 128–bit AES data encryption and its implementation in FPGA network card using VHDL programming language. The theoretical part explains AES encryption and decryption, its individual steps and operating modes. Further was described the VHDL programming language, development environment Vivado, FPGA network card Combo–80G and configurable framework NetCOPE. The practical part is the implementation of AES–128 in VHDL. A simulation was used to eliminate errors, then the synthesis was performed. These steps were made using Vivado software. Last step of practical part was testing of synthesized firmware on COMBO–80G card. Total of 4 projects were implemented in FPGA card. Two of them were AES encryption and decryption with ECB mode and another two describe the encryption and decryption with CBC mode.