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

Key generation

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In Cohen's cryptosystem, a 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

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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

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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

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