Disclosed herein are methods and systems for transmitting streams of data. In one embodiment, a method comprises the steps of: receiving a stream of data; organizing the stream of data into a plurality of packets; generating a packet watermark associated with the stream of data; combining the packet watermark with each of the plurality of packets to form watermarked packets; and transmitting at least one of the watermarked packets across a network. The present invention also relates to: receiving at least one packet that has been transmitted across a network; analyzing at least one packet for a watermark; and authenticating the at least one packet using at least a portion of the watermark. The present invention also relates to generating packet watermarks and packet watermark keys.