Confidentiality in a very strong sense. Ciphers reaching perfect-secrecy can't be broken to disclose informations over the plaintext from the ciphertext, even with unlimited computing power. The most known example cipher reaching perfect screcy is the one-time-pad.

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What does the probability subscript mean in Shannon's secrecy definition?

Shannon's secrecy can be defined as: $$P_M (M=m) = P_{SK,M}(M=m|E(SK,m)=c)$$ What does $P_M$ means? (same question for $P_{SK,M}$) I know that is the probability space M, M being the messages; I do ...
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Perfect secrecy is maintained for other plaintext prob distributions?

Suppose a cryptosystem achieves perfect secrecy for a particular plaintext probability distribution. Prove that perfect secrecy is maintained for any other plaintext probability distribution. ...
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How we can said a crypto system have perfect secrecy?

For example: I have 3 plaintexts ($a$, $b$, $c$) and 4 keys ($K_1$, $K_2$, $K_3$, $K_4$), making a table map to the cipher text, key as row and plaintext as column $\begin{matrix} \ \ \ \ \ \ \ \ \ \ ...
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Perfect Secrecy of AES file Encryption

Why does AES file encryption not ensure perfect secrecy? I understand that $\Pr[E(K,M_1)=C_1] = \Pr[E(K,M_2)=C_2]$ given $M1\neq M2$ holds for perfect secrecy of a scheme. However, this seems to hold ...