ABSTRACT

Cryptographic security-The encryption algorithm is secure against cryptographic attacks [1], e.g., ciphertext-only attack, known-plaintext attack, select-plaintext attack, etc. In the case of complete encryption, the traditional cipher or new cipher adopted is secure from a cryptographic viewpoint. In partial encryption, some parameters are encrypted with a cipher that is secure against cryptographic attacks. In compression-combined encryption, the encryption operation combined with compression operation is secure from a cryptographic viewpoint. Perceptual security-The encrypted media content is secure to human perception. For example, the encrypted image or video is unintelligible, and the encrypted audio is too chaotic to be understood. This is a special requirement of multimedia encryption. As is known, in text/binary data encryption, the encrypted content is often unintelligible. Compared with text/binary data, multimedia data often has a large redundancy. Thus, traditional encryption may lose the redundant information. For example,

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using the raw image with block cipher’s ECB mode will produce a cipherimage whose border information is still known. Additionally, in partial encryption, the perceptual security depends on the selected parameters. Thus, for multimedia encryption algorithms, perceptual security should be investigated. Parameter security in partial encryption-In partial encryption, some parameters are encrypted with a cipher and the other parameters are left unchanged. Although the adopted cipher is strong, the security of the partial encryption may not be confirmed. It depends on the relation between the encrypted parameters and unencrypted parameters. If the encrypted parameters can be replaced by or deduced from other parameters, the plaintext will be recovered under ciphertext-only attack. Thus, the parameters should be carefully selected in partial encryption.