@article {tifs08ss-security, title = {Spread spectrum watermarking security}, journal = {IEEE Transactions on Information Forensics and Security}, volume = {4}, number = {1}, year = {2009}, month = {March}, pages = {2-24}, keywords = {data-hiding, security, watermarking}, author = {Luis P{\'e}rez-Freire and Fernando P{\'e}rez-Gonz{\'a}lez} }