Patent ID: 8321675

Claim:
A computer-implemented method for authenticated-encryption that encrypts a plaintext into a ciphertext without padding the plaintext, the method comprising: partitioning the plaintext into a first plaintext portion having a multiple of n bits and a second plaintext portion having n−1 or fewer bits; using a nonce to generate a sequence of offsets; computing a first ciphertext portion having the same length as the first plaintext portion from the first plaintext portion, the sequence of offsets, and an n-bit block cipher; computing a second ciphertext portion having the same length as the second plaintext portion from the second plaintext portion, an offset from the sequence of offsets, and the n-bit block cipher; computing an n-bit authentication tag by using the n-bit block cipher to encipher a value that depends on the plaintext and an offset from the sequence of offsets; and defining the ciphertext as the first ciphertext portion, the second ciphertext portion, and a portion of the n-bit authentication tag.