Given an encryption scheme $\Pi = (G,E,D)$, either public or private, is there a name or a property to emphasize that for $c\gets \Pi.E(k,m)$, where $k$ is a key and $m$ is a message, we want $m^\prime \neq \bot$ where $m^\prime \gets \Pi.D(k^\prime, c)$ with $k\neq k^\prime$? ($\bot$ here means empty)

Schemes such as Stream-Cipher (i.e., $E(k,m) = G(k)\oplus m$ with $G$ being a pseudorandom generator), RSA, ElGamal, etc. exhibit that property. At first, I thought it might be related to the notion of malleability, but a malleable encryption scheme allows one to compute a function $f(m)$ for a message $m$ given a ciphertext $c$ that encrypts $m$. Hence, it seems with malleable encryption, the same key is used.

  • 3
    $\begingroup$ "RSA ... exhibit[s] that property"; actually, the Bleichenbacker attack on RSA PKCS #1 encryption can be viewed as exploiting the lack of that property - that is, it assumes that the attacker can distinguish a decryption that results in a padding failure (hence, $\bot$) and a decryption that results in something... $\endgroup$
    – poncho
    Commented Feb 2, 2023 at 4:27
  • $\begingroup$ The definition of deniable encryption might be of relevance here. $\endgroup$
    – tylo
    Commented Feb 2, 2023 at 18:38

1 Answer 1


If as you write "we want" this property, then I think the property is called key equivocation, which is supposed to make it harder for an attacker to distinguish the correct key from wrong ones.


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