A secured encryption algorithm must withstand all known attacks. Common attacks are Stream cipher attack, Chosen-ciphertext attack, Ciphertext-only attack, Known-plaintext attack, Cold boot attack, Brute-force attack, Man-in-the-middle attack, Meet-in-the-middle attack and Slide attack. Steam chipper attack is strong for cryptographic systems, where same key (cipher) is used twice. Chosen-ciphertext attack expects known key as a hole or as a part of ciphertext of the system. Ciphertext-only attack is also popular as known ciphertext attack where attacker assumes about a set of ciphertext. In Cold boot attack, attacker has physical access to a computer, which is able to retrieve key. Computer is shut-down at first. A light weight operating system is immediately booted from portable flash drive and content of pre-boot memory stored to a file. Attackers try to predict encryption process through analysis of pre-boot memory. Brute-force is a cryptanalytic attack, which can be used against almost all encryption system. AES is more secure against brute force attack as compared to Data Encryption Standard (DES) and A5 encryption algorithms .