A method and apparatus for encrypting data includes: acquiring a first data unit included in a media frame to be encrypted, wherein the first data unit includes a boundary portion and a content portion, the boundary portion including boundary information for identifying a starting boundary of the first data unit, and the content portion including content data of the first data unit; encrypting the content data included in the content portion of the first data unit to acquire a second data unit, wherein a boundary portion of the second data unit includes the boundary information, and a content portion of the second data unit includes a data length of the content data and encrypted data acquired by encrypting the content data.