Cohen's cryptosystem

Cohen's cryptosystem[1] is a public-key cryptosystem proposed in 1998 by Bram Cohen.

Key generation

In Cohen's cryptosystem, private key is a positive integer .

The algorithm uses public-keys defined as follows:

Generate random integers chosen randomly and uniformly between and . Where is some bound.

Let and generate random integers chosen randomly and uniformly between and .

Define .

Encrypting a bit

To encrypt a bit Alice randomly adds public keys and multiplies the result by either 1 (if she wishes to send a 0) or by 1 (if she wishes to send a 1) to obtain the ciphertext .

De-cryption

To de-crypt, Bob computes

It is easy to see that if then . However, if then . Hence Bob can read the bit sent by Alice on the most significant bit of h.

References

  1. Bram Cohen. "Simple Public Key Encryption". Archived from the original on October 7, 2011.
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