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Two New Efficient CCA-Secure Online Ciphers : MHCBC and MCBC



Mridul Nandi


Online ciphers are those ciphers whose ciphertexts can be computed in an online manner. HCBC1 and HCBC2 are two known examples of Hash Cipher Block Chaining online ciphers. HCBC1 is secure against chosen plaintext adversary (or called CPA-secure) whereas HCBC2 is secure against chosen ciphertext adver-sary (or called CCA-secure). In this paper, we have provided simple security analysis of these online ciphers. We have also proposed two new more efficient CCA-secure online ciphers, namely MHCBC (modified HCBC) and MCBC (modified CBC). MHCBC needs a universal hash function with smaller input size compared to the universal hash function of HCBC2. If one uses finite field multiplication based universal hash function then MHCBC needs one less key and one less field multiplication compared to HCBC2. MCBC does not need any universal hash function and it needs only one key for a block cipher unlike other three online ciphers where two independent keys are required (one for a hash function and one for a block cipher).
Proceedings Title
Progress in Cryptology - INDOCRYPT 2008 (Lecture Notes in Computer Science)
Conference Dates
December 14-17, 2008
Conference Location
IIT Kharagpur
Conference Title
9th International Conference on Cryptology in India (INDOCRYPT 2008)


Online cipher, Hash-CBC, Universal Hash Function, Uniform Random Permutation.


Nandi, M. (2008), Two New Efficient CCA-Secure Online Ciphers : MHCBC and MCBC, Progress in Cryptology - INDOCRYPT 2008 (Lecture Notes in Computer Science), IIT Kharagpur, -1, [online], (Accessed July 15, 2024)


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Created December 17, 2008, Updated November 10, 2018