A method and system for embedding a watermark in block encrypted content, including encoding a bit string, the bit string including n bits, denoted b0-bn−1, the encoding including translating each bit, b0-bn−1, into a block of data, according to the following rule if bi=1, then translate bi into a block of data of a first type, and if bi=0, then translate bi into a block of data of a second type, thereby translating the n bits into n blocks of data corresponding to each bit b0-bn−1, arranging a composite block of data including the n blocks of data, and at least one additional block indicating the presence of the n blocks of data, and inserting the composite block of data into a content item as a watermark, wherein the watermarked content item is encrypted using an ECB mode of encryption. Related methods and apparatus are also described.