Encryption Cryptography has two uses within DRM. The
Encryption Cryptography has two uses within DRM. The first is to encrypt content for confidentiality or protection of the owner s rights. The second is for the protection of the certificates that are used for authentication and for access control (authorization). There are two families of cryptography: shared secret and public/private key. A shared secret key (also called a symmetric) uses the same key to encrypt the content and then to decrypt it at the receiving end. In cryptography the clear file is called plaintext and the encrypted version is called ciphertext. The scrambled ciphertext feasibly can be decoded only with the key. One way to crack the encryption is to try many different keys until you chance upon the correct one. The more characters in the key, the longer it will take, on average, to find the key. This cracking can be made more difficult by changing the key at certain intervals. Shared key encryption is efficient and suited to large files just like media files. An example of a shared secret is a personal identification number (PIN) used to withdraw cash with an automated teller machine. The PIN is used to verify the physical credit card. The PIN is a secret shared by the bank computer and the authorized holder of the card. 276 The Technology of Video and Audio Streaming clear or plaintext clear or plaintext encrypted or ciphertext shared key digital video file content server media player encrypt decrypt Figure 14.7 The secret shared encryption key.
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