Patent Publication Number: US-8527750-B2

Title: System and method for generating multiple protected content formats without redundant encryption of content

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention is directed to computer systems. More particularly, it is directed to the protection of electronic content within a computing environment. 
     2. Description of the Related Art 
     To combat unauthorized consumption of content, some content owners have adopted an approach to protecting their content known as digital rights management (“DRM”), which may include various techniques for limiting access of electronic content to authorized individuals and/or enforcing other restrictions on the use of such content. Typically, clear content that is to be protected by DRM is typically encoded and packaged into an encrypted form. At packaging time, the packaging unit responsible for packaging content may utilize various types of encryption algorithms for encrypting content. In some cases, these encryption algorithms may encrypt content based on a cryptographic key, which may be selected or generated in a random fashion. At some point, the encrypted content may be provided to an electronic device associated with a content consumer. For instance, the consumer may pay a one-time fee or a recurring subscription fee to access the content electronically. To view the content in unencrypted form on the consumer&#39;s electronic device, the device may be required to obtain a respective content license that includes the correct cryptographic key for decrypting the content. 
     In some cases, decryption schemes and/or content formats may vary across consumer devices or platforms. These differences may be accommodated at packaging time. For instance multiple different encryption and formatting schemes may be applied to clear content to generate multiple different content versions that are compatible with different consumer devices or platforms. 
     SUMMARY 
     Embodiments of a system and method for generating multiple protected content formats without redundant encryption of content are described. In various embodiments, different protected (e.g., encrypted) versions of the same content may be generated without redundantly encrypting the content. For instance, embodiments may enable content to be encrypted once and assembled into various different formats while keeping the encrypted content bit compatible across such formats. In various embodiments, a first protected version of content may be generated by packetizing unencrypted content (e.g., according to a media transport stream) into multiple packets. The packetized content may include content information (e.g., actual content, such as video or audio data) as well as non-content information (e.g., packet headers). In some cases, subgroups of the packets may be further grouped into individual files (e.g., for network transport). 
     In any case, the packetized content may be chain encrypted on a block-by-block basis. For instance, block cipher encryption may be utilized to encrypt the packetized content with an encryption key and multiple initialization vectors. In various embodiments, the encryption result of this encryption process may serve as a first protected version of the content. In various embodiments, one or more different protected versions of the content may be additionally generated without re-encrypting the content that was encrypted to generate the first protected version of the content. For instance, embodiments may identify encrypted blocks of the first protected version that correspond to actual content data while discarding encrypted blocks that correspond to non-content information (e.g., packet or file headers). 
     In various embodiments, the blocks that represent encrypted content may be aggregated into samples, which may in some cases be larger than the packet payloads of the packetized content described above. During the extraction process, contiguous encryption chains may be broken (e.g., because at least some blocks corresponding to non-content information may be discarded). Accordingly, samples may include multiple different encryption chains. In various embodiments, to ensure that a second protected version of the content that includes the aforesaid samples can be decrypted properly, embodiments may include decryption information within that second protected version of the content. In various embodiments, this decryption information may specify multiple initialization vectors for decrypting each distinct encryption chain within samples. For instance, each sample may include multiple distinct encryption chains and sample header information for that sample may specify an initialization vector to be used for decrypting each of those encryption chains. As described in more detail herein, at least some of those initialization vectors may be dependent upon non-content information of the first protected version of the content (e.g., non-content information that was discarded during the extraction of content blocks during the creation of the second version of the protected content). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates block diagram of an example system in which multiple protected content formats may be generated without redundant encryption of content, according to some embodiments. 
         FIG. 2  illustrates an example flow diagram for the creation of different protected content formats without redundant encryption of content, according to some embodiments. 
         FIG. 3  illustrates one example of a chained encryption process performed on multiple blocks of content, according to some embodiments. 
         FIG. 4  illustrates a block diagram of an example client system, according to some embodiments. 
         FIG. 5  illustrates one example of a chained decryption process performed on multiple blocks of content, according to some embodiments. 
         FIG. 6  illustrates a flowchart of an example method for creating different protected content formats without redundant encryption of content, according to some embodiments. 
         FIG. 7  illustrates a flowchart of an example method for decrypting content with initialization vectors generated dependent upon a different version of that content, according to some embodiments. 
         FIG. 8  illustrates an example computer system suitable for implementing various components of the system and method for generating multiple protected content formats without redundant encryption of content, according to various embodiments. 
     
    
    
     While the system and method for generating multiple protected content formats without redundant encryption of content is described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that the system and method for generating multiple protected content formats without redundant encryption of content is not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the system and method for generating multiple protected content formats without redundant encryption of content as defined by the appended claims. Any headings used herein are for organizational purposes only and are not meant to limit the scope of the description or the claims. As used herein, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Various embodiments of a system and method for generating multiple protected content formats without redundant encryption of content are described. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, methods, apparatuses or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter. 
     Some portions of the detailed description which follow are presented in terms of algorithms or symbolic representations of operations on binary digital signals stored within a memory of a specific apparatus or special purpose computing device or platform. In the context of this particular specification, the term specific apparatus or the like includes a general purpose computer once it is programmed to perform particular functions pursuant to instructions from program software. Algorithmic descriptions or symbolic representations are examples of techniques used by those of ordinary skill in the signal processing or related arts to convey the substance of their work to others skilled in the art. An algorithm is here, and is generally, considered to be a self-consistent sequence of operations or similar signal processing leading to a desired result. In this context, operations or processing involve physical manipulation of physical quantities. Typically, although not necessarily, such quantities may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared or otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals or the like. It should be understood, however, that all of these or similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless specifically stated otherwise, as apparent from the following discussion, it is appreciated that throughout this specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining” or the like refer to actions or processes of a specific apparatus, such as a special purpose computer or a similar special purpose electronic computing device. In the context of this specification, therefore, a special purpose computer or a similar special purpose electronic computing device is capable of manipulating or transforming signals, typically represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the special purpose computer or similar special purpose electronic computing device. 
     Various embodiments include various encryption and/or decryption keys, any of which may be generated via a key derivation function (KDF). Key derivation functions may include the completion of one or more iterations or instances of cryptographic operations in order to generate an encryption or decryption key. Examples of key derivation function may include but are not limited to any key derivation functions specified by Public Key Cryptography Standards (PKCS) (e.g., PKCS-5 or PKCS-12) or Adobe® Password Security. In various embodiments, KDFs may be utilized by any of the various components described herein to generate encryption keys for symmetric encryption. 
     Various portions of this detailed description may refer to “client(s)” and “server(s)” or similar terminology. For instance, various embodiments may include (among other elements) a client system or client device (or simply a “client”). It should be understood that the terms “client” and “server” do not impose any limitation on the operation, configuration, or implementation of such elements. It should be understood that these terms are used only as convenient nomenclature. Indeed, various embodiments are need not be limited by the principles of a conventional client-server architecture. 
     In various instances, this detailed description may refer to content items (which may also be referred to as “content data,” “content information” or simply “data” or “information”). In some instances, content items may include any information or data that may be licensed to one or more individuals (or other entities, such as business or group). In various embodiments, content may include electronic representations of video, audio, text and/or graphics, which may include but is not limited to electronic representations of videos, movies, or other multimedia, which may include but is not limited to data files adhering to Adobe® Flash® Video (.FLV) format or some other video file format whether such format is presently known or developed in the future. In various embodiments, the content items described herein may include electronic representations of music, spoken words, or other audio, which may include but is not limited to data files adhering to the MPEG-1 Audio Layer 3 (.MP3) format, Adobe® Sound Document (.ASND) format or some other format configured to store electronic audio whether such format is presently known or developed in the future. In some cases, content may include data files adhering to the following formats: Portable Document Format (.PDF), Electronic Publication (.EPUB) format created by the International Digital Publishing Forum (IDPF), JPEG (.JPG) format, Portable Network Graphics (.PNG) format, Adobe® Photoshop® (.PSD) format or some other format for electronically storing text, graphics and/or other information whether such format is presently known or developed in the future. In some embodiments, content items may include any combination of the above-described examples. 
     In various instances, this detailed disclosure may refer to consuming content or to the consumption of content, which may also be referred to as “accessing” content, “viewing” content, “listening” to content, or “playing” content, among other things. In some cases, the particular term utilized may be dependent on the context in which it is used. For example, consuming video may also be referred to as viewing or playing the video. In another example, consuming audio may also be referred to as listening to or playing the audio. 
     In various instances, this detailed description may refer to a devices configured to perform content consumption, such as client system  140 . In various embodiments, such a device may include but is not limited to a computing system (e.g., a desktop or laptop computer), a set-top television box, a digital audio or multimedia player (e.g., an MP3 player), a personal digital assistant (PDA), a mobile phone, a smartphone, a touchscreen phone, an e-book reader, a digital photo frame, or any other device or system configured to access, view, read, write, and/or manipulate any of the content data described herein. Any of such devices may be implemented via a computer system similar to that described with respect to  FIG. 8 . 
     Note that in various instances the description presented herein may refer to a given entity performing some action. It should be understood that this language may in some cases mean that a system (e.g., a computer) owned and/or controlled by the given entity is actually performing the action. 
     Note that in various instances the description presented herein may refer to a public key being associated with a private key or a public key corresponding to private key. It should be understood that such statements may mean that such a public key forms a public key—private key pair with such a private key. Additionally, in some cases, a public key—private key pair may be referred to as simply a “key pair.” Note that in various embodiments, public key—private key pairs may be generated via one or more key derivation functions, such as those described above. 
       FIG. 1  illustrates a flow diagram of a framework in which various embodiments of the system and method for generating multiple protected content formats without redundant encryption of content. In the illustrated embodiment, content  105  may represent a media object, which may include any type of media program that may be represented and/or stored as electronic content (e.g., electronic representations of audio, video, images, presentations or some combination thereof). In various embodiments, a media program may include prerecorded content including but not limited to movies or motion pictures, television programs, video clips or snippets, audio productions, as well as live content including but not limited to content conveying real-time or near-real time events (e.g., a live sporting event or competition). One or more encoder systems  110  may be configured to input content  105  and generate an encoded content items  115  corresponding to content  105 . In various embodiments, encoder systems may encode or compress content  105  according to one or more codecs or standards for video compression in order to generate encoded content item  115 . One non-limiting example of such a standard includes the H.264 standard. 
     For clarity of illustration, only a single encoded content item  115  is presented in the illustrated embodiment. However, it should be understood that the illustrated system may create multiple encoded content items. For instance, in various embodiments, different encoded content items may represent different temporal segments of the same media object. For example, if the media object were a movie, each encoded content item may represent a different temporal segment of that movie. Each temporal segment may be specified by a different time period of the movie, a different set of frames within the movie or a different scene within the movie, for example. 
     In the illustrated embodiment, encoded content item  115  may be processed by a packager component  125 . In various embodiments the packager component may be implemented on a packaging system  120 , which may in some cases be implemented by a computer system, such as that illustrated in  FIG. 8  described below. As illustrated, the packager component  125  may package and encrypt encoded content item  125  to generate a corresponding encrypted content item  130 . Additional details of the manner in which encrypted content items  130  are generated are described below with respect to  FIGS. 2-3 . Generally, to support different client systems, platforms or configurations, packager component  125  may be configured to generate a single encrypted content item  130  that may be assembled into multiple different content formats for different client systems without encrypting the content multiple times. As described in more detail below, the manner in which packager component  125  generates the encrypted content item may save time and/or processing resources because embodiments may require only one instance of encryption to support different content formats for different clients. In another example, the manner in which packager component  125  generates the encrypted content item may save storage resources (or reduce utilization of existing storage resources) by enabling multiple client content formats to be supported by the same encrypted content stored in a data store. 
     In various embodiments, the encrypted content item  130  may be provided directly to content delivery system(s)  140  and/or stored in a content data store(s)  135 . In one non-limiting example, real-time or near real-time content (e.g., content for a live sporting event) may be provided to content delivery system(s)  140  whereas other content may be stored in content data store(s)  135  and retrieved by content delivery system(s)  140  at a later time. Once assembler component  145  receives the encrypted content item  130 , the assembler component may assemble the encrypted content item into any of a number of formats supported by client systems  155   a - b ; this process may be performed without re-encrypting the content. In other words, the manner in which the packaging and assembling process is performed may preserve bit compatibility among the encrypted content of different content formats. 
     In the illustrated embodiment, only two client systems  155   a - b  are presented for clarity of illustration. It should be understood that in various embodiments, any number of client systems or devices may be supported. As illustrated, each client system  155   a - b  may be provided with a different version of the encrypted content item. In the illustrated embodiment, protected content item  150   a  and protected content item  150   b  may adhere to different file formats, standards or specifications. Differences between the two versions of content items are described in more detail below. 
     To obtain the decryption key for decrypting a protected content item, each client system may perform a license acquisition  165  with license server  160 . For instance, each encrypted content item may have a metadata portion that includes an encrypted version of the content encryption key used to encrypt that content item. This encrypted content encryption key may have been encrypted with the public key of license server  160 . At  165 , the client system may submit this encrypted content encryption key to license server  160  as part of a license request. After the license server  160  positively authenticates the client system (if required), the license server may use its own private key to decrypt the encrypted content encryption key to determine the unencrypted version of the content encryption key. The license server may then re-encrypt the content encryption key with the client system&#39;s public key (or a public key of the application that is to consume the content) such that only that client system can properly decrypt that content encryption key. The result of this key re-encryption is provided within a response sent from the license server  160  to the client system. The client system may decrypt the encrypted content decryption key from that response with the corresponding private key. This content encryption key may be used to decrypt the protected content item received by that client system. In various embodiments, the client system may use this same content encryption key to decrypt subsequent ones of encrypted content items  130 . Of course, in various embodiments, decryption keys may change over time and license acquisition can be performed again when this happens. In other embodiments, other techniques for protecting the content encryption may be utilized. For instance, in some embodiments, when the client receives the content license, the content license may already include the content encryption key protected (e.g., encrypted) for that particular client. 
       FIG. 2  illustrates an example process for generating multiple protected versions of content without redundant encryption and storage of the content. In various embodiments, the illustrated process may be performed by packager component  125  and/or assembler component  145  described above. In various embodiments, the illustrated process may be implemented on a computer system, such as computer  800  of  FIG. 8 . As illustrated at packetization  250 , encoded content  200 , such as encoded content item  115  of  FIG. 1 , may be packetized into packetized content  202 . In some embodiments, packetizing may include parsing the encoded content into packets, each of which may include packet header information and a packet payload that includes content. In one non-limiting example, packetizing the encoded content may include generating a transport stream (TS) according to one or more standards, such as the MPEG-2 standard. In other cases, other standards or formats may be utilized to packetize the content. As illustrated at  252 , an aggregation process may be performed in which sets of packets may be grouped into disparate files  204 . In various embodiments, such files may be sized to provide streaming-like performance when such content is provided to a client system over one or more networks. For instance, the files may be large enough to house multiple packets but small enough such that multiple Hypertext Transfer Protocol (HTTP) requests may be submitted by a client system in order to obtain the files in a streaming-like fashion. In the illustrated embodiment, only two files  204   a - b  are presented for clarity of illustration. However, it should be understood that in various embodiments the packetized content may be grouped into any number of files. In some embodiments, grouping the packetized content into different files  204  may be optional. 
     As illustrated at  254 , a chained encryption process may be performed on files  204  to create multiple encrypted blocks  206  that represent the files. In some embodiments, encrypted blocks  206  may serve as a first protected version of the content. For example, encrypted blocks  206  may represent protected content  150   a  of  FIG. 1  described above. 
     Referring collectively to  FIGS. 2 and 3 , the chained encryption of files  204  is described in further detail.  FIG. 3  illustrates one example of chained encryption. As illustrated, files  204  may be parsed into a series of blocks. In various embodiments, these blocks may have a fixed width (e.g., 128 bits) dependent upon the type of encryption performed. In some embodiments, the encryption utilized may be Advanced Encryption Standard 128 bit Cipher-block chaining mode (AES-128 bit CBC mode) encryption. In other cases, other types of chained encryption may be utilized. In the illustrated embodiment, encryption may be generally performed in a sequential manner from the left to right of the Figure beginning with the first block B 0  and first initialization vector IV 0 . In various embodiments, the first initialization vector IV 0  may be randomly or pseudo-randomly generated. However, as described in more detail below, initialization vectors for subsequent blocks may be generated such that the encryption of each subsequent block is dependent upon the previously encrypted block. In the illustrated embodiment, initialization vector IV 0  (which may be the same width as the block to be encrypted) and the first block to be encrypted B 0  may be processed by a bit-wise exclusive-or operation. In other cases, other logic operations may be utilized in place of the exclusive-or operation. The result of the exclusive-or operation may be encrypted with a content encryption key  302  using block cipher encryption  300 . The result may be an encrypted block EB 0  having a size equal to that of the input block (e.g., 128 bits in this example). 
     In various embodiments, each subsequent block may be encrypted such that it is chained to the previous block. In other words, to encrypt (and thus also to decrypt) a given block, the encryption mechanism may be required to have knowledge of the previous encrypted block, according to some embodiments. The manner in which this aspect is implemented in various embodiments includes, for a given block, using the previous encrypted block as the initialization vector for the encryption of the given block. For instance, in the illustrated embodiment, the first encrypted block EB 0  may also be used as the second initialization vector IV 1 . Similar to the encryption of the first block, an exclusive-or operation may be performed on IV 1 /EB 0  and the second block B 1 , the result of which may be encrypted by block cipher encryption  300  using content encryption key  302 . The above described processes may be repeated as illustrated in order to encrypt all blocks of files  204 . Returning to  FIG. 2 , these encrypted blocks are illustrated as encrypted blocks  206 , which may represent encrypted versions of files  204   a  and  204   b.    
     As illustrated at  256 , content samples may be generated from encrypted blocks  206 . In various embodiments, a content sample may correspond to a defined portion of content, such as an audio or video frame. However, in some embodiments, a sample may correspond to some other granularity of the content. As noted above, encrypted files  206  may be an encrypted version of files  204 , which may include both content information (e.g., data representing the actual content, such as audio or video data) as well as non-content information, such as packet header (e.g., a transport header, such as that defined by the MPEG-2 standard or another standard defining a media transport stream) or file header information. However, in various embodiments, such non-content information may serve no meaningful role within the context of a sample-based file format that is not packetized or formatted according to the format of files  204 . For various reasons (e.g., to avoid unnecessary overhead within the sample-based content  208 ), sample generation  256  may extract the encrypted blocks  206  that correspond to actual content information while disregarding non-content information. The extracted blocks may be assembled into a sample  208  as illustrated. While only one sample is presented for clarity of illustration, it should be understood that multiple samples may be generated in various embodiments. In various embodiments, this extraction process, by virtue of discarding some or all of the encrypted blocks  206  that correspond to non-content information, may break the encryption chain(s) described above. For instance, performing block-based decryption (described below with respect to  FIG. 5 ) on the blocks of a sample that omits one or more of blocks  206  may result in an incorrect determination of initialization vectors (e.g., since initialization vectors may be dependent upon previous blocks) and thus an incorrect decryption result. However, in various embodiments, this situation may be avoided by storing the appropriate initialization vectors in the illustrated sample header  210  of one or more of the samples. For example, sample  208  is illustrated as including three different sets of encrypted blocks denoted as encryption chains  260 ,  262 , and  264 . In various embodiments, while the content of these encrypted blocks may represent a contiguous (or near contiguous) portion of content, there may exist encryption boundaries where the encryption is non-continuous (e.g., due to broken chains during the extraction of content blocks from encrypted blocks  206 ). Accordingly, for the first block of each encryption chain  260 - 264  in a given sample, the sample generation process may store the initialization vectors necessary to start the chained decryption of each chain within the sample header of that given sample. In this way, when a decryption process (e.g., on the client system) encounters an encryption boundary between the encryption chains, the encryption process may access the appropriate initialization vector from the sample header and decryption may resume. 
     In various embodiments, the sample generation process may select the initialization vectors that are included in the sample header through a variety of techniques. In one example, when analyzing encrypted blocks  206 , for each content block that is immediately preceded by a non-content block (e.g., a block containing non-content information, such as packet header or file header information), the sample generation process may store that non-content block as an initialization vector within the sample header of the sample being generated. As described in more detail below, the initialization vectors stored in the sample header may be utilized to decrypt different chains of encrypted blocks in the respective sample. 
       FIG. 4  illustrates an example client system including decryption and consumption components, according to various embodiments. In the illustrated embodiment, client system  400  may be implemented by a computer system or other electronic devices, such as those described below with respect to the computer system of  FIG. 8 . In various embodiments, the client systems described above (e.g., client systems  155   a - 155   b ) may be configured in a manner similar to that of client system  400 . 
     As illustrated, client system  400  may receive one or more encrypted samples  402 , which may be configured in a manner similar to the samples described above. For example, client system  400  may receive multiple samples that represent audio and/or video frames, such as frames representing a media program (described above). For clarity of illustration, only one sample  402  is illustrated in  FIG. 4 . However, it should be understood that in various embodiments, the decryption and consumption techniques described below may be performed on multiple samples. 
     In various embodiments, decryption component  404  may be configured to perform block-based decryption on each encrypted sample. In various embodiments, to decrypt a given sample, decryption component  404  may be configured to perform the process illustrated in  FIG. 5 , which is described in more detail below. Generally, decryption component  404  may be configured to perform decryption on multiple blocks from a sample by using the initialization vectors from the sample header. The decrypted blocks are illustrated as decrypted content sample(s)  406 , which may be consumed (e.g., played) by content consumption component  408 . Content consumption component  408  may be configured to generate one or more representations of the content, such as by generating a graphical and/or audio representation of the content (e.g., on a display, speaker, and/or other device used for content consumption). 
       FIG. 5  illustrates a block diagram of the process for decrypting a given sample, according to various embodiments. The techniques of  FIG. 5  may be implemented by the client systems described above. For instance, decryption component  404  may utilize the illustrated techniques to decrypt samples received on the client system. For clarity of illustration, only one sample  500  is illustrated in  FIG. 5 . However, it should be understood that in various embodiments, the decryption and consumption techniques described below may be performed on multiple samples. Similarly, while only two different encryption chains  504  and  506  are illustrated, any number of encryption chains may be present within a given sample in various embodiments. In the illustrated example, each encryption chain includes three blocks of encrypted content. However, in various embodiments, a given encryption chain may include any quantity of blocks, which may or may not be equal to the quantity of blocks in other encryption chains of the sample. 
     In the illustrated embodiment, the first encrypted block in the sample EB 0  may be extracted and decrypted with content encryption key  510 . In various embodiments, the encrypted blocks may be symmetrically encrypted. Accordingly, content encryption key  510  may be the same as the key originally utilized to encrypt the content. In various embodiments, key  510  may be obtained through a license acquisition process, such as that described above with respect to  FIG. 1 . As illustrated, the first encrypted block EB 0  of the sample may be decrypted using the content encryption key  510 . Furthermore, in accordance with chained decryption, the appropriate initialization vector IV 0  may be applied to the decryption result to determine the first decrypted block B 0  of decrypted blocks  512 . In the illustrated embodiments, this is performed through an exclusive-or operation. The particular operation utilized will typically match the operation utilized to apply the initialization vector during the encryption process. As illustrated, the first initialization vector may be obtained from sample header  502 . The decryption of the second and third blocks EB 1  and EB 2  to generated decrypted blocks B 1  and B 2  may be performed in a similar manner with the exception being that the initialization vectors IV 1  and IV 2  used to decrypt these blocks may be equivalent to the previous encrypted block, which is consistent with the techniques used to encrypt the blocks, such as described above with respect to  FIG. 3 . However, as illustrated, encrypted block EB 3  belongs to the second encrypted chain  506 . Accordingly, block EB 2  cannot be utilized to as the initialization vector to decrypt block EB 2 . In this case, the correct initialization vector IV 3  may be extracted from sample header  502 . (As described above with respect to sample generation  256 , the initialization vectors need to start chain decryption of each chain may be stored in the sample header of each sample). In this way, the decryption process may be correctly performed across different encryption chains within the same sample. 
     In various embodiments, sample header  500  may include additional information to be used during decryption. For instance, for each set of blocks that represents a distinct encryption chain, sample header  500  may specify the size (e.g., in blocks or bits) and/or position of that set within the sample. Such information may be utilized by the client system for determining which initialization vectors apply to which blocks in the sample. In embodiments utilizing partial encryption, some sets of blocks may be unencrypted. For instance, in some embodiments, it may not be necessary for all sets of blocks to be encrypted. In one example, samples may be partially encrypted such that content consumption (e.g., playback) will be sufficiently disrupted for unauthorized clients (e.g., clients lacking the appropriate license and/or decryption keys), thus providing a deterrent to trying to consume the content without the proper license and/or decryption keys while also conserving computing resources and/or time. For instance this technique may conserve computing resources and/or time on the packaging side (because at least some sets of blocks are left unencrypted) and on the client side (e.g., because at least some sets of block do not need to be decrypted). As one example, consider an alternate configuration for sample  208  described above. If sample  208  were encrypted using partial encryption, at least some of the blocks may remain in the clear form whereas other blocks remain encrypted. For instance, instead of three encryption chains  260 ,  262 , and  264 , the sample may alternatively include encryption chain  260 , encryption  264  and the remaining set of blocks could be left unencrypted (e.g., blocks corresponding to encryption chain  262  may be left unencrypted). In various embodiments, sample header  502  may also include information that identifies unencrypted blocks. For instance, sample header  205  may identify one or more blocks or a range of blocks that are not encrypted. Such information may be utilized by the client system for determining blocks that do not require decryption, thereby saving processing resources and/or time as described above. Any of the aforesaid information may be captured during the sample generation process  256  and stored as part of a given sample&#39;s header information. 
     Example Methods 
     Embodiments may include various methods for generating different protected version of content without redundant encryption as well as methods for decrypting content generated according to the techniques described herein.  FIGS. 6 and 7  illustrate examples of such methods. In various embodiments, the illustrated Figures may be implemented by components or systems described above. In some embodiments, the methods described herein may be implemented on one or more computer systems, such as the computer system of  FIG. 8  described below. 
       FIG. 6  illustrates an example method for generating two different versions of protected content without encrypting the content multiple times. As illustrated at  600 , the method may include receiving content to be protected. Such content may include any of the content described herein, such as encoded content  115 . 
     As illustrated at  602 , the method may further include generating a first protected version of the content (e.g., encrypted blocks  206  described above) by packetizing the content into multiple packets that each include content information and non-content information. This packetization process may include any of the packetization techniques described above, such as performing packetization  250  to create packets that include non-content information (e.g., transport stream packet headers) and content information (e.g., transport stream packet payloads including content). In various embodiments, the non-content information may include a media transport packet header, such as that defined by the MPEG-2 standard or another standard defining a media transport stream. In various embodiments, packetizing content may include formatting the content according to a media transport stream according to one or more standards, such as the MPEG-2 standard. In various embodiments, this portion of the method may also include using initialization vectors to perform chained encryption on multiple blocks of the packetized content, which may include any of the techniques described above including the encryption process described above with respect to  FIGS. 2 and 3 . In various embodiments, at least some of the initialization vectors used for the encryption may be generated dependent upon non-content information (e.g., packet or file headers). For example, when performing a chained encryption on blocks of packetized content, such as described above with respect to chained encryption  254 , at least some of the blocks encrypted may represent non-content information including packet header or file header information. 
     As illustrated at  604 , the method may also include using the encrypted blocks to generate a second protected version of the content without re-encrypting the content. One example of that second protected version of the content includes sample(s)  208  described above. In various embodiments, the second protected version of the content may include multiple encrypted content samples that each include multiple encrypted blocks from the first protected version of the content. For example, as described above, sample(s)  208  and  500  may include content blocks extracted from blocks  206 . In various embodiments, for a given encrypted content sample, different sets of encrypted blocks in that sample may form different encryption chains. For instance, samples  208  and  500  are described above as including multiple different encryption chains. 
     In various embodiments, the second protected version of the content may also include decryption information for decrypting the encrypted content samples. For example, this decryption information may include the information stored in sample header  502  described above. For instance, as described above with respect to sample generation  256 , the sample header may include the initialization vectors needed to begin the decryption of each encryption chain in the respective sample. In various embodiments, the decryption information may include at least some of the initialization vectors generated dependent upon the non-content information of the first protected version. For instance, as described above with respect to  FIG. 3 , at least some initialization vectors may be equivalent to previously encrypted blocks. Accordingly, when the previously encrypted block is an encrypted block that represents non-content information (e.g., a packet or file header), the initialization vector used to encrypt a subsequent block may be equivalent to the encrypted block that represents that non-content information. In this way, at least some of the initialization vectors of the second protected version of the content may be dependent upon information from the first protected version of the content (i.e., information not present in the second protected version of the content). By including these initialization vectors in the second protected version of the content, embodiments may prevent decryption problems associated with noncontiguous (or “broken”) encryption chains. 
     In various embodiments, while the second protected version of the content may include initialization vectors generated dependent upon non-content information (e.g., one or more media transport stream packet headers) of the first protected version, the second protected version of the content may not include at least some of that non-content information. In some embodiments, the second protected version may include none of the non-content information of the first protected version. For instance, since the second protected version of the content may be sample-based (i.e., not packetized into a media transport stream), there may be no need in the second protected version of the content for non-content information that includes media transport header information. Accordingly, some or all of this information may be excluded from the second protected version of the content. 
     Note that the media transport streams described herein (and associated header and payload information of that stream) may be different than a stream of network packets. For instance, whether content is packetized into a media transport stream (e.g., according to MPEG-2) may be independent of whether that content has been packetized according to a network protocol for transporting packets (e.g., Transmission Control Protocol (TCP), Internet Protocol (IP), etc.). For instance, in some cases, content that is packetized according to a media transport stream may or may not be additionally packetized for network transport according to a network protocol. In other cases, content that is not packetized according to a media transport stream (e.g., sample-based content) may or may not be packetized for network transport according to a network protocol. It should be understood that packetization according to media transport stream protocols and packetization according to one or more network protocols may occur at different levels of standard network models (e.g., different levels of the Open Systems Interconnection (OSI) model). 
     In some embodiments, the encrypted content samples generated at  604  may include samples that are partially encrypted. For instance, as described above with respect to an alternate version of  208 , the sample may include some sets of blocks of content that are encrypted (e.g., encryption chains) as well as one or more blocks of content that are not encrypted. As described above, using these partial encryption techniques may provide a deterrent to trying to consume the content without the proper license and/or decryption keys while also conserving computing resources and/or time. 
     In various embodiments of the method, the decryption information utilized may include additional information to be used during decryption. For instance, for each set of blocks that represents a distinct encryption chain, the decryption information may specify the size (e.g., in blocks or bits) and/or position of that set within the sample. Such information may be utilized for determining which initialization vectors apply to which blocks in the sample. In embodiments utilizing partial encryption, some sets of blocks may be unencrypted; the decryption information may also include information that identifies these blocks. Such information may be utilized for determining blocks that do not require decryption. 
     In various embodiments, by storing the initialization vectors for different encryption chains as decryption information in the second protected version of the content, embodiments may maintain bit compatibility among multiple different protected versions of the same content. In this way, embodiments avoid redundant encryption. That is, for multiple different versions of protected content, embodiments may avoid encrypting the content more than once. These characteristics may save time and or processing resources when packaging the content for different devices in accordance with different formats. Additionally, since multiple versions of the protected content may be derived from the same encrypted content, embodiments may avoid redundantly storing the encrypted content. That is, one version of the encrypted content may be stored (e.g., in memory of a computer system, such as that of  FIG. 8 ), and other protected versions may be generated from the first version as needed or “on the fly,” such as might be performed when delivering content to client systems. Even in cases where multiple protected versions of the content are stored in memory, embodiments may avoid time and processing resources associated with encrypting the same content multiple times. 
     In various embodiments of the method, multiple packets of the first protected version of the content may be part of a media transport stream and the non-content information of the first protected version of the content may include transport header information for that transport stream. For example, as described above, the packetized content may adhere to a media transport stream according to one or more standards, such as the MPEG-2 standard. 
     In various embodiments of the method one or more of the encrypted content samples may include a video or audio frame. For instance, the encrypted content samples may represent frames of any of the media programs described herein. 
     In various embodiments of the method, performing the chained encryption of block  602  may include encrypting said multiple blocks with one or more cryptographic keys (e.g., one or more content encryption keys or CEKs) distinct from said initialization vectors. In some cases, the same key may be utilized to encrypt all blocks. In other cases, different keys may be utilized for different sets of blocks. In various embodiments of the method, performing chained encryption on the multiple blocks may include sequentially encrypting each of a first block and multiple subsequent blocks with a respective initialization vector and cryptographic key where each respective initialization vector for each subsequent block is generated dependent upon a previously encrypted block. One example of such a configuration is illustrated and described with respect to the block-based encryption of  FIG. 3 . In various embodiments of the method, each block may be encrypted with a block cipher, and input to the block cipher may include a cryptographic key, an initialization vector and a block of content. The output of the block cipher may be an encrypted block, which may also be equivalent to the initialization vector for the next block to be encrypted, such as described with respect to the block-based encryption of  FIG. 3 . 
     In various embodiments of the method, the second protected version of the content additionally comprises one or more content samples that are not encrypted. For instance, embodiments may employ partial encryption to significantly protect content while at the same time preserving processing resources associated with encryption. 
     In various embodiments of the method, the second protected version of the content comprises unencrypted header information associated with one or more of the samples. For instance, in various embodiments of the method, for a given sample, the unencrypted header information may include one or more of information specifying whether that sample is encrypted and one or more of the initialization vectors for decryption. 
     In various embodiments of the method, the first protected version of the content and the second protected version of the content may adhere to different file format specifications. For instance, the two versions may be generated for different devices that support different file formats. As described above, this configuration may be accommodated without redundant encryption and storage of the content. 
       FIG. 7  illustrates a flowchart of an example method for content decryption, such as the decryption of sample-based content on a client system in accordance with various embodiments. In various embodiments, the illustrated method may be performed by any of the client systems described herein and/or the computer system of  FIG. 8  described below. 
     As illustrated at  702 , the method may include receiving a protected version of content that comprises multiple encrypted content samples, each encrypted content sample including multiple encrypted blocks. For instance, the method may include receiving multiple samples of content, such as samples  208  or  500  described above. In various embodiments, for a given encrypted content sample received, different sets of encrypted blocks in that sample may form different encryption chains (e.g., due to the manner in which sample generation  256  extracts content blocks and discards at least some non-content blocks). For instance, with reference to sample  500  described above, multiple different encryption chains  504 - 506  may be included in a sample. In various embodiments, the protected version of the content may also include decryption information for decrypting the encrypted content samples. For instance, the decryption information may include at least some initialization vectors generated dependent upon non-content information from a different protected version of the content. In various embodiments of the method, the decryption information may include additional information to be used during decryption. For instance, for each set of blocks that represents a distinct encryption chain, the decryption information may specify the size (e.g., in blocks or bits) and/or position of that set within the sample. Such information may be utilized for determining which initialization vectors apply to which blocks in the sample during decryption. 
     In various embodiments, while the received protected version of the content may include initialization vectors generated dependent upon non-content information (e.g., one or more media transport stream packet headers) of the different protected version, the protected version of the content may not include at least some of that non-content information. In some embodiments, the protected version may include none of the non-content information of the different protected version. For instance, since the protected version of the content may be sample-based (i.e., not packetized into a media transport stream), there may be no need in the protected version of the content for non-content information that includes media transport header information. Accordingly, some or all of this information may be excluded from the protected version of the content. 
     In some embodiments, the encrypted content samples of the protected version of the content may include samples that are partially encrypted. For instance, as described above with respect to an alternate version of  208 , the sample may include some sets of blocks of content that are encrypted (e.g., encryption chains) as well as one or more blocks of content that are not encrypted. As described above, using these partial encryption techniques may provide a deterrent to trying to consume the content without the proper license and/or decryption keys while also conserving computing resources and/or time. In these embodiments, the decryption information described above may also include information that identifies these blocks. Such information may be utilized for determining blocks that do not require decryption. As illustrated at  704 , the method may also include using the decryption information to decrypt one or more of the encrypted content samples. One example of such a decryption process includes the block-based decryption described above with respect to  FIG. 5 . In embodiments including partially encrypted samples, the method may include decrypting encrypted blocks that are not identified as being unencrypted by sample header information in accordance with the partial encryption/decryption techniques described herein (e.g., while not attempting decryption on blocks designated as being unencrypted by sample header information). 
     In various embodiments of the method, the different protected version may be a packetized version of the content comprising multiple packets, each packet comprising content information and non-content information. For instance, the different protected version may be similar to encrypted block  206  described above. In various embodiments of the method, the method may include consuming the one or more decrypted content samples in a media player application. For instance, a client system may include a media player application that is executable to playback decrypted content (e.g., on a display, speaker or other output device). In various embodiments, one or more of the decrypted content samples include a video or audio frame, such as frames of a media program as described above. In various embodiments, performing the decryption may include decrypting multiple blocks of the content with one or more cryptographic keys distinct from said initialization vectors, such as the content encryption keys of  FIG. 5  described above. 
     Secure Communication 
     In various embodiments, various elements of the illustrated framework may be associated with respective public key—private key pairs, such as key pairs utilized in Public Key Infrastructure (PKI). In the illustrated framework, a first element may securely transfer data to a second element by encrypting that data with the second element&#39;s public key. In this manner, only the second element will be able to decrypt the encrypted data to access the unencrypted data, according to various embodiments. For instance, since in various embodiments knowledge of the private key may be required to decrypt the data and since the second element may be the only element that has knowledge of its own private key, the second element may be the only element able to decrypt the data with the correct private key. Note that the aforesaid techniques may in various embodiments be utilized for any transfer of data within the system of  FIG. 1 . One example includes the “binding” of a content license to client system at license acquisition time. For example, the license server might obtain a public key for the client system and encrypt a content license with that public key prior to transferring the license to the playback device. In this example, only client system will be able to decrypt the license (since the playback device may be the only element with knowledge of the correct private key). In some embodiments, a given element may trust another element with knowledge of its private key (thereby allowing the other element to decrypt data encrypted with the given element&#39;s public key). In various embodiments, the public keys described herein may be obtained from a public key certificate, such as a certificate provided by a certificate authority (not illustrated) in PKIs. One example of such a certificate is an X.509 certificate (in other cases, other types of public key certificates may be utilized). 
     Example Computer System 
     Various embodiments of a system and method for generating multiple protected content formats without redundant encryption of content, as described herein, may be executed on one or more computer systems, which may interact with various other devices. One such computer system is computer system  800  illustrated by  FIG. 8 , which may in various embodiments implement any of the systems, devices, elements or methods illustrated in  FIGS. 1-7 . For instance, any of the functionality described above may be stored in memory as processor-executable executable program instructions  822  (e.g., program instructions executable by processor(s)  810 ). In one non-limiting example, instructions  822  may implement one or more packager components  125  or assembler components  145 , as illustrated. In the illustrated embodiment, computer system  800  includes one or more processors  810  coupled to a system memory  820  via an input/output (I/O) interface  830 . Computer system  800  further includes a network interface  840  coupled to I/O interface  830 , and one or more input/output devices  850 , such as cursor control device  860 , keyboard  870 , and display(s)  880 . In some cases, it is contemplated that embodiments may be implemented using a single instance of computer system  800 , while in other embodiments multiple such systems, or multiple nodes making up computer system  800 , may be configured to host different portions or instances of various embodiments. For example, in one embodiment some elements may be implemented via one or more nodes of computer system  800  that are distinct from those nodes implementing other elements. 
     In various embodiments, computer system  800  may be a uniprocessor system including one processor  810 , or a multiprocessor system including several processors  810  (e.g., two, four, eight, or another suitable number). Processors  810  may be any suitable processor capable of executing instructions. For example, in various embodiments processors  810  may be general-purpose or embedded processors implementing any of a variety of instruction set architectures (ISAs), such as the x96, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each of processors  810  may commonly, but not necessarily, implement the same ISA. 
     System memory  820  may be configured to store program instructions  822  and/or data  832  accessible by processor  810 . In various embodiments, program instructions  822  may be executable by the processor(s) to implement the functionality of any packaging component, assembler component, encryption component, decryption component, or client system described above. As illustrated, in various embodiments, data  832  may store one or more encrypted content items  130 , from which other protected versions of the content may be generated or assembled. In various embodiments, system memory  820  may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type of memory. In the illustrated embodiment, program instructions and data implementing any of the elements of the framework described above may be stored within system memory  820 . In other embodiments, program instructions and/or data may be received, sent or stored upon different types of computer-accessible media or on similar media separate from system memory  820  or computer system  800 . 
     In one embodiment, I/O interface  830  may be configured to coordinate I/O traffic between processor  810 , system memory  820 , and any peripheral devices in the computer system, including network interface  840  or other peripheral interfaces, such as input/output devices  850 . In some embodiments, I/O interface  830  may perform any necessary protocol, timing or other data transformations to convert data signals from one component (e.g., system memory  820 ) into a format suitable for use by another component (e.g., processor  810 ). In some embodiments, I/O interface  830  may include support for devices attached through various types of peripheral buses, such as a variant of the Peripheral Component Interconnect (PCI) bus standard or the Universal Serial Bus (USB) standard, for example. In some embodiments, the function of I/O interface  830  may be split into two or more separate components, such as a north bridge and a south bridge, for example. Also, in some embodiments some or all of the functionality of I/O interface  830 , such as an interface to system memory  820 , may be incorporated directly into processor  810 . 
     Network interface  840  may be configured to allow data to be exchanged between computer system  800  and other devices attached to a network (e.g., network  885 ), such as other computer systems (e.g., client systems  155   a - b ), or between nodes of computer system  800 . In various embodiments, network interface  840  may support communication via wired or wireless general data networks, such as any suitable type of Ethernet network, for example; via telecommunications/telephony networks such as analog voice networks or digital fiber communications networks; via storage area networks such as Fibre Channel SANs, or via any other suitable type of network and/or protocol. 
     Input/output devices  850  may, in some embodiments, include one or more display terminals, keyboards, keypads, touchpads, scanning devices, voice or optical recognition devices, or any other devices suitable for entering or accessing data by one or more computer systems  800 . Multiple input/output devices  850  may be present in computer system  800  or may be distributed on various nodes of computer system  800 . In some embodiments, similar input/output devices may be separate from computer system  800  and may interact with one or more nodes of computer system  800  through a wired or wireless connection, such as over network interface  840 . 
     In some embodiments, the illustrated computer system may implement any of the process or methods described above, such as those of  FIGS. 2-3  and  5 - 7 . In other embodiments, different elements and data may be included. 
     Those skilled in the art will appreciate that computer system  800  is merely illustrative and is not intended to limit the scope of embodiments. In particular, the computer system and devices may include any combination of hardware or software that can perform the indicated functions of various embodiments, including computers, network devices, Internet appliances, PDAs, wireless phones, set top television boxes, pagers, and/or any other electronic device described herein. Computer system  800  may also be connected to other devices that are not illustrated, or instead may operate as a stand-alone system. In addition, the functionality provided by the illustrated components may in some embodiments be combined in fewer components or distributed in additional components. Similarly, in some embodiments, the functionality of some of the illustrated components may not be provided and/or other additional functionality may be available. 
     Those skilled in the art will also appreciate that, while various items are illustrated as being stored in memory or on storage while being used, these items or portions of them may be transferred between memory and other storage devices for purposes of memory management and data integrity. Alternatively, in other embodiments some or all of the software components may execute in memory on another device and communicate with the illustrated computer system via inter-computer communication. Some or all of the system components or data structures may also be stored (e.g., as instructions or structured data) on a computer-accessible medium or a portable article to be read by an appropriate drive, various examples of which are described above. In some embodiments, instructions stored on a computer-accessible medium separate from computer system  800  may be transmitted to computer system  800  via transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a network and/or a wireless link. Generally speaking, a computer-accessible medium may include a computer-readable storage medium or memory medium such as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile or non-volatile media such as RAM (e.g. SDRAM, DDR, RDRAM, SRAM, etc.), ROM, etc. In some embodiments, a computer-accessible medium may include transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as network and/or a wireless link. 
     The methods described herein may be implemented in software, hardware, or a combination thereof, in different embodiments. In addition, the order of methods may be changed, and various elements may be added, reordered, combined, omitted, modified, etc. Various modifications and changes may be made as would be obvious to a person skilled in the art having the benefit of this disclosure. Realizations in accordance with embodiments have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of claims that follow. Finally, structures and functionality presented as discrete components in the example configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of embodiments as defined in the claims that follow.