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It all depends on how you define the machine that implements the random oracle. Consider this pseudo code random oracle that uses a hash table: def rand_oracle(input, hash_table): input_hash_key = get_hash(input) if input_hash_key in hash_table: return hash_table[input_hash_key] else: return something truly random You need to ...


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As you already mentioned, you cannot efficiently instantiate a random oracle because it would require an exponentially large description. This is the simple reason. In general, a random oracle is just a random function sampled from the set of all functions with a given domain and range. If you consider inefficient constructions, you can actually ...


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Well the idea of a cryptographically secure hash function (and often functions within them), is to mimic the Random Oracle model as closely as we can. Now, short of a little gremlin (perhaps?), some perfectly unbiased dice, a magical orb and a magic way to store all the possible outcomes from each input, we need these functions. I'm going to assume you know ...



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