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In which of the following cryptanalytic attacks does the attacker have access to some of the cipher text, but not the corresponding plaintext?
Known ciphertext attack [aka, ciphertext-only attack (COA)]
Chosen-ciphertext attack (CCA)
Chosen-plaintext attack (CPA)
Known plaintext attack (KPA)
Known cipher text attack is an attack model for cryptanalysis where the attacker is assumed to have access only to a set of cipher texts. The attacker has no access of the plaintext; however, a successful cryptanalysis in the COA model usually requires that the cryptanalyst must have some information on the plaintext, such as its distribution, the language in which the plaintexts are written in, standard protocol data or framing which is part of the plaintext, etc. ------------------------------------Q:) Can someone explain the difference between CCA and COA?
(ISC)2 Official Study Guide, 7th Ed. p. 259 COA: "...the only information you have at your disposal is the encrypted cipher message... in this case, one technique that proves helpful is frequency analysis..." ; CCA: "...the attacker has the ability to decrypt chosen portions of the ciphertext message and use the decrypted portion of the message to discover the key."
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