Tweakable block ciphers for secure data encryption

A method for encrypting a data unit plaintext into blocks of ciphertexts, said data unit plaintext being assigned a tweak value and being divided into one or more plaintext blocks, the method comprising:

• determining a tweak block value (Tj) in association with each plaintext block by applying a combinatorial function between a value derived from said tweak value and a function of a block index assigned to said plaintext block,
• wherein the method comprises, in association with each plaintext block (Pj), determining a masked value Mj(Tj) by applying a data masking algorithm to the tweak block value (Tj) determined in association with said plaintext block,
• wherein the method further comprises:
• determining (202) an encrypted tweak value by encrypting said tweak value using a block cipher and a tweak encryption key, said value derived from the tweak value being equal to said encrypted tweak value;
• determining (208) an intermediate plaintext block (IPj) by applying an XOR operation between said masked value Mj(Tj) and said plaintext block (Pj);
• determining (210) an intermediate ciphertext block (ICj) by encrypting said intermediate plaintext block using said block cipher and a data encryption key;
• determining (212) a ciphertext block (Cj) by applying an XOR operation between said masked value Mj(Tj) and said intermediate ciphertext block (ICj).

A method for decrypting a data unit ciphertext into blocks of plaintexts, said data unit ciphertext being assigned a tweak value and being divided into one or more ciphertext blocks, the decryption method comprising:

• determining a tweak block value (Tj) in association with each ciphertext block (Cj) by applying a combinatorial function between a value derived from said tweak value and a function of a block index assigned to said ciphertext block,
• wherein the method comprises, in association with each ciphertext block (Cj), determining a masked value Mj(Tj) by applying a data masking algorithm to the tweak block value (Tj) determined in association with said ciphertext block,
• wherein the method further comprises:
• determining (213) an encrypted tweak value by encrypting said tweak value using a block cipher and a tweak encryption key, said value derived from the tweak value being equal to said encrypted tweak value;
• determining (217) an intermediate ciphertext block (ICj) by applying an XOR operation between said masked value Mj(Tj) and said ciphertext block (ICj);
• determining (219) an intermediate plaintext block (IPj) by decrypting said intermediate ciphertext block (ICj) using said block cipher and a data decryption key;
• determining (221) a plaintext block (Pj) by applying an XOR operation between said masked value Mj(Tj) and said intermediate plaintext block (IPj).