Every year, millions of pupils take part in the baccalaureate examination and the examinations of entrance to Universities or Colleges in Vietnam. It is significantly necessary to keep the secrecy of the questions of these important examinations in order to keep the their fairness and to protect the legal rights of the participants. In this document we exploit the new and very secure cryptographic algorithms, especially the Advanced Encryption Standard, to devise the practical and effective method for the examination security.

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The Rijndael Block Cipher has been chosen to be Advanced Encryption Standard (AES) since October 2nd 2000. The Cipher processes blocks and keys having 128, 192, or 256 bits. The Extended Rijndael Block Cipher is proposed to process larger blocks and keys of the length 256, 384, or 512. Tom tat. Phuong phap ma h6a Rijndael vira duoc Vien Tieu Chuan va Cong Nghe Hoa Ky (NIST) chfnh tlurc chon lam chuan ma h6a AES (Advanced Encryption Standard) vao ngay 2 thang 10 narn 2000. Tren thirc te, phuong phap ma h6a Rijndael xu Iy cac khoi dir lieu va mii kh6a c6 d(J dai 128, 192 hoac 256 bit. Trong bai viet nay, cluing toi gioi thieu phien ban mo rong 256/384/5 12-bit cua thuat roan nay c6 kha nang xir Iy cac kh6i du lieu va rna kh6a c6 d(J dai 256, 384 hoac 512 bit. 7 (Ih7h6hsh4h3h2hJhoD or hexadecimal notation (lh/10D or polynomial nocation Ib;x;. ;=0 2.3. The State All operations are performed on a two-dimensional array of bytes called the State consisting of eight rows of bytes, each containing Nb bytes, where Nb is the block length divided by 64. An individual byte of the State (denoted by the symbol s