| 摘要 |
Content items or portions of content items are made available for previewing according to various techniques. In some techniques, designated portions of content items are transmitted in plaintext, while the remaining portions are transmitted in encrypted form. In other techniques, an entire content item is transmitted in encrypted form. However, content keys for decrypting the content item may be transmitted in plaintext form for certain portions designated for previewing and in encrypted form for the remaining portions. Also, an entire content item may be transmitted in encrypted form. Similarly the content keys for decrypting the content item is transmitted in encrypted form. However, preview rights keys for decrypting the content keys may be transmitted. These rights keys have associated usage rules that limit their use. |
