The paper introduces two new public-key broadcast encryption systems designed for stateless receivers, which are fully secure against any number of colluders. The first system has constant-size ciphertexts and private keys, while the public key size is linear in the total number of receivers. The second system generalizes the first, allowing a trade-off between ciphertext size and public key size. For example, it achieves a collusion-resistant broadcast system for $n$ users where both ciphertexts and public keys are of size $O(\sqrt{n})$. The paper discusses several applications, including file sharing in encrypted file systems, sending encrypted emails to large mailing lists, and content protection for DVDs. The security of the systems is based on the bilinear Diffie-Hellman Exponent (BDHE) assumption. The paper also presents a chosen ciphertext secure version of the system using a signature scheme.The paper introduces two new public-key broadcast encryption systems designed for stateless receivers, which are fully secure against any number of colluders. The first system has constant-size ciphertexts and private keys, while the public key size is linear in the total number of receivers. The second system generalizes the first, allowing a trade-off between ciphertext size and public key size. For example, it achieves a collusion-resistant broadcast system for $n$ users where both ciphertexts and public keys are of size $O(\sqrt{n})$. The paper discusses several applications, including file sharing in encrypted file systems, sending encrypted emails to large mailing lists, and content protection for DVDs. The security of the systems is based on the bilinear Diffie-Hellman Exponent (BDHE) assumption. The paper also presents a chosen ciphertext secure version of the system using a signature scheme.