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Alex123
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True asymmetric ciphers beside RSA

Is there any TRUE public key cipher beside RSA? Most people would answer Elgamal or ECC, but for what is my understanding (and I know cryptography only superficially), those are not true asymmetric ciphers (because both parties can encrypt and decrypy).

EDIT:

I realized that my question needed better explaining.

The following quote is from the Handbook of Applied Cryptography:

Definition 1.50: Consider an encryption scheme consisting of the sets of encryption and decryption transformations $\{E_e : e ∈ K\}$ and $\{D_d : d ∈ K\}$, respectively. The encryption method is said to be a public-key encryption scheme if for each associated encryption/decryption pair $(e, d)$, one key $e$ (the public key) is made publicly available, while the other $d$ (the private key) is kept secret. For the scheme to be secure, it must be computationally infeasible to compute $d$ from $e$.

Now take for instance Elgamal encryption. Bob chooses the parameters, then sends the public key to Alice, Alice computes the mask $K_M$ (the session key) and the ephemeral key $K_E$, encrypts the message $M$ with $K_M$ obtaining $C$, and sends ($C$,$K_E$) to Bob. Bob can compute $K_M$ using $K_E$ and his private key. The quoted definition is not satisfied. Alice and Bob, in the end, both have $K_M$ which is used for encryption and decryption.

EDIT2:

The reply I got from fgrieu was very satisfying, I was mistaking a shared secret key for a public key. However this made me reflect on another difference between an Elgamal scheme and an RSA scheme. I'm going start with another quote from HAC (Basic Terminology, p.12):

An encryption scheme consists of a set ${E_e : e ∈ K}$ of encryption transformations and a corresponding set ${D_d : d ∈ K}$ of decryption transformations with the property that for each $e ∈ K$ there is a unique key $d ∈ K$ such that $D_d = E_e^{−1}$; that is, $D_d(E_e(m)) = m$ for all $m ∈ M$. An encryption scheme is sometimes referred to as a cipher.

With this, Elgamal randomized E is not acceptable, because a randomized function can't be the left inverse of another function. Se we can heve $D_d(E_e(m)) = m$ for all $m ∈ M$, but we can't have $D_d = E_e^{−1}$. This is also the reason (I think) why Elgamal cipher can't be usued for digital signatures (Elgamal DS is different from the cipher).

Now my question: is the second quoted definition correct? Or $D_d = E_e^{−1}$ should be "$D_d$ is a left inverse of $E_e$"? Also unicity of $d$ is really necessary?

Alex123
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