International Association for Cryptologic Research (IACR)
Abstract
The notion of PRO (pseudorandom oracle) is an important security notion of hash functions
because a PRO hash function inherits all properties of a random oracle up to the PRO bound (e.g., security against generic attacks, collision resistant security, preimage resistant security and so on).
In this paper, we propose a new block cipher-based double-length hash function for PROs.
Our hash function uses a single block cipher, which encrypts an n-bit string using a 2n-bit key, and maps an input of arbitrary length to a 2n-bit output.
Since many block ciphers supports a 2n-bit key (e.g. AES supports a 256-bit key),
the assumption to use the 2n-bit key length block cipher is acceptable.
We prove that our hash function is PRO up to \order(2^n) query complexity as long as the block cipher is an ideal cipher.
To our knowledge, this is the first time double-length hash function based on a single (practical size) block cipher with the birthday type PRO security