| 摘要 |
<p>A method and a system for encrypting plaintext digital data divided into a sequence (SEQP) comprising N successive blocks (P1, P2, P3,..., PN) of a same length of x bits each and a residual plaintext block (PR) having a length of y bits lower than the length of one of the N successive blocks (P1, P2, P3,..., PN). The N successive plaintext blocks (P1, P2, P3,..., PN) are ciphered with the main encryption key (K) by using a ciphering algorithm based on a cipher block chaining mode (CBC) to obtain a sequence (SEQC) of N successive ciphered blocks (C1, C2, C3,....CN) of the same length than the plaintext blocks (P1, P2, P3,..., PN). A set of round keys (S1, S2, S3,...Sn) having a same length are generated by applying a key schedule function (KSF) on a string (ST) obtained by adding the last ciphered block (CN) to the main encryption key (K). The round keys (S1, S2, S3,...Sn) of the set are added together to obtain a resulting string (ST) having a length equal to the length of a block of the sequence (SEQP). The residual plaintext block (PR) is then added to the most left bits of the resulting string (ST) forming a string (T) having a length equal to the length of the residual block (PR) to obtain a residual ciphered block (CR). The method and the system apply also to decipher a sequence of N successive ciphered blocks (C1, C2, C3,....CN) followed by a residual ciphered block (CR).</p> |
