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diff --git a/drm/libdrmframework/plugins/forward-lock/internal-format/doc/FwdLock.html b/drm/libdrmframework/plugins/forward-lock/internal-format/doc/FwdLock.html new file mode 100755 index 0000000..8f95cd2 --- /dev/null +++ b/drm/libdrmframework/plugins/forward-lock/internal-format/doc/FwdLock.html @@ -0,0 +1,1039 @@ +<html> + +<head> +<meta http-equiv=Content-Type content="text/html; charset=windows-1252"> +<meta name=Generator content="Microsoft Word 12 (filtered)"> +<title>Forward Lock Converter and Decoder</title> +<style> +<!-- + /* Font Definitions */ + @font-face + {font-family:SimSun; + panose-1:2 1 6 0 3 1 1 1 1 1;} +@font-face + {font-family:"Cambria Math"; + panose-1:2 4 5 3 5 4 6 3 2 4;} +@font-face + {font-family:Tahoma; + panose-1:2 11 6 4 3 5 4 4 2 4;} +@font-face + {font-family:"Lucida Console","DejaVu Sans Mono"; + panose-1:2 11 6 9 4 5 4 2 2 4;} +@font-face + {font-family:"\@SimSun"; + panose-1:2 1 6 0 3 1 1 1 1 1;} + /* Style Definitions */ + p.MsoNormal, li.MsoNormal, div.MsoNormal + {margin:0cm; 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+display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>3</span></a></span></p> + +<p class=MsoToc1><span class=MsoHyperlink><a href="#_Toc276471423">2<span +style='font-size:12.0pt;line-height:150%;color:windowtext;text-transform:none; +font-weight:normal;text-decoration:none'> </span>Overview<span +style='color:windowtext;display:none;text-decoration:none'>... </span><span +style='color:windowtext;display:none;text-decoration:none'>3</span></a></span></p> + +<p class=MsoToc1><span class=MsoHyperlink><a href="#_Toc276471424">3<span +style='font-size:12.0pt;line-height:150%;color:windowtext;text-transform:none; +font-weight:normal;text-decoration:none'> </span>Use Cases<span +style='color:windowtext;display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>4</span></a></span></p> + +<p class=MsoToc2><span class=MsoHyperlink><span style='font-variant:normal !important; +text-transform:uppercase'><a href="#_Toc276471425">3.1<span style='font-size: +12.0pt;line-height:150%;color:windowtext;text-transform:none;text-decoration: +none'> </span>Converter<span style='color:windowtext;display:none; +text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>4</span></a></span></span></p> + +<p class=MsoToc3><span class=MsoHyperlink><a href="#_Toc276471426">3.1.1<span +style='font-size:12.0pt;line-height:150%;color:windowtext;font-style:normal; +text-decoration:none'> </span>Convert Data (Push-Mode Conversion)<span +style='color:windowtext;display:none;text-decoration:none'> </span><span +style='color:windowtext;display:none;text-decoration:none'>4</span></a></span></p> + +<p class=MsoToc3><span class=MsoHyperlink><a href="#_Toc276471427">3.1.2<span +style='font-size:12.0pt;line-height:150%;color:windowtext;font-style:normal; +text-decoration:none'> </span>Convert File (Pull-Mode Conversion)<span +style='color:windowtext;display:none;text-decoration:none'> </span><span +style='color:windowtext;display:none;text-decoration:none'>6</span></a></span></p> + +<p class=MsoToc2><span class=MsoHyperlink><span style='font-variant:normal !important; +text-transform:uppercase'><a href="#_Toc276471428">3.2<span style='font-size: +12.0pt;line-height:150%;color:windowtext;text-transform:none;text-decoration: +none'> </span>Decoder<span style='color:windowtext;display:none; +text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>7</span></a></span></span></p> + +<p class=MsoToc3><span class=MsoHyperlink><a href="#_Toc276471429">3.2.1<span +style='font-size:12.0pt;line-height:150%;color:windowtext;font-style:normal; +text-decoration:none'> </span>Check Integrity<span style='color:windowtext; +display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>8</span></a></span></p> + +<p class=MsoToc3><span class=MsoHyperlink><a href="#_Toc276471430">3.2.2<span +style='font-size:12.0pt;line-height:150%;color:windowtext;font-style:normal; +text-decoration:none'> </span>Get Content Type<span style='color:windowtext; +display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>9</span></a></span></p> + +<p class=MsoToc3><span class=MsoHyperlink><a href="#_Toc276471431">3.2.3<span +style='font-size:12.0pt;line-height:150%;color:windowtext;font-style:normal; +text-decoration:none'> </span>Decode File<span style='color:windowtext; +display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>10</span></a></span></p> + +<p class=MsoToc1><span class=MsoHyperlink><a href="#_Toc276471432">4<span +style='font-size:12.0pt;line-height:150%;color:windowtext;text-transform:none; +font-weight:normal;text-decoration:none'> </span>Definition of the +Internal Forward Lock File Format<span style='color:windowtext;display:none; +text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>11</span></a></span></p> + +<p class=MsoToc2><span class=MsoHyperlink><span style='font-variant:normal !important; +text-transform:uppercase'><a href="#_Toc276471433">4.1<span style='font-size: +12.0pt;line-height:150%;color:windowtext;text-transform:none;text-decoration: +none'> </span>Key Derivation<span style='color:windowtext;display:none; +text-decoration:none'>.. </span><span +style='color:windowtext;display:none;text-decoration:none'>11</span></a></span></span></p> + +<p class=MsoToc2><span class=MsoHyperlink><span style='font-variant:normal !important; +text-transform:uppercase'><a href="#_Toc276471434">4.2<span style='font-size: +12.0pt;line-height:150%;color:windowtext;text-transform:none;text-decoration: +none'> </span>Calculation of the Counters<span style='color:windowtext; +display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>12</span></a></span></span></p> + +<p class=MsoToc1><span class=MsoHyperlink><a href="#_Toc276471435">5<span +style='font-size:12.0pt;line-height:150%;color:windowtext;text-transform:none; +font-weight:normal;text-decoration:none'> </span>Unit Test Cases<span +style='color:windowtext;display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>12</span></a></span></p> + +<p class=MsoToc1><span class=MsoHyperlink><a href="#_Toc276471436">6<span +style='font-size:12.0pt;line-height:150%;color:windowtext;text-transform:none; +font-weight:normal;text-decoration:none'> </span>References<span +style='color:windowtext;display:none;text-decoration:none'>. </span><span +style='color:windowtext;display:none;text-decoration:none'>12</span></a></span></p> + +<p class=MsoBodyText></p> + +</div> + +<span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><br +clear=all style='page-break-before:right'> +</span> + +<div class=WordSection2> + +<h1><a name="_Toc276471422"></a><a name="_Ref263085474">1<span +style='font:7.0pt "Times New Roman"'> </span>Introduction</a></h1> + +<p class=MsoBodyText>The internal Forward Lock file format is used for encrypting +inherently unencrypted OMA DRM version 1 Forward Lock and Combined Delivery +files so they can be securely stored on externally accessible file system partitions +such as memory stick.</p> + +<p class=MsoBodyText>Our general strategy is to convert such <i>OMA DRM Message</i> +(‘.dm’) files to internal Forward Lock (‘.fl’) files as soon as they are +downloaded or otherwise transferred to the phone, and not actually provide any +decoders for ‘.dm’ files.</p> + +<h1><a name="_Toc276471423">2<span style='font:7.0pt "Times New Roman"'> +</span>Overview</a></h1> + +<p class=MsoBodyText>The <i>Forward Lock Converter</i> converts OMA DRM Message +files to the internal file format. The <i>Forward Lock Decoder</i> provides a +POSIX-level API for transparent reading and seeking through such a converted +file as if it were unencrypted. The API also includes functions for checking a +file’s integrity and getting the MIME type of its embedded content.</p> + +<p class=MsoBodyText style='margin-bottom:24.0pt'>The converter and decoder are +built into two separate libraries, which share common code for random number +generation and key encryption in a third library. For test purposes there is +also a unit test application. See Figure 1.</p> + +<p class=MsoBodyText style='page-break-after:avoid'><img width=288 height=364 +src="images/image001.gif"></p> + +<p class=MsoCaption style='margin-top:12.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm'><a name="_Ref262730885">Figure </a>1. Block diagram illustrating the dependencies between the executable modules.</p> + +<b><span style='font-size:16.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></b> + +<h1><a name="_Toc276471424">3<span style='font:7.0pt "Times New Roman"'> +</span>Use Cases</a></h1> + +<p class=MsoBodyText>This section describes all the use cases for the converter +and decoder. It shows the sequence of API calls that should be used to solve +these use cases.</p> + +<h2><a name="_Toc276471425">3.1<span style='font:7.0pt "Times New Roman"'> +</span>Converter</a></h2> + +<p class=MsoBodyText>Through the converter API, conversion can be performed in one +of two ways:</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span><i>Push-mode +conversion</i> is when the client progressively feeds data to the converter as +it arrives. This is appropriate when data arrives gradually in chunks, with +idle time in between. Consequently, push mode is used for converting files +being downloaded through HTTP. See section 3.1.1.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span><i>Pull-mode +conversion</i> is when the converter drives the process and consumes data from +the client as it needs it. This is appropriate when the entire file to be +converted is readily available. Hence, pull mode is used by the unit test application. +See section 3.1.2.</p> + +<p class=MsoBodyText>Internally, pull-mode conversion is implemented in terms +of the API for push-mode conversion.</p> + +<h3><a name="_Toc276471426"></a><a name="_Ref263085478">3.1.1<span +style='font:7.0pt "Times New Roman"'> </span>Convert Data +(Push-Mode Conversion)</a></h3> + +<p class=MsoBodyText>Push-mode conversion is performed as follows (see also Figure 2):</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span><span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockConv_OpenSession</span> +initializes the output parameter and returns a <i>session ID</i> to be used in +subsequent calls to the API. The output parameter is a union of return values +whose correct use at any given moment is determined by the API function last +called.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span><span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockConv_ConvertData</span> +is called repeatedly until no more input data remains. Each call converts the +maximum amount of data possible and writes it to the output buffer. The client then +writes this data to file.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>3.<span +style='font:7.0pt "Times New Roman"'> </span><span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockConv_CloseSession</span> +cleans up the session and deallocates the output buffer. If all has gone well, a +two-part cryptographic signature of the output file is calculated. The client +must go back and rewrite part of the file header with this updated signature +information.</p> + +<p class=MsoBodyText>Every time a file is being converted, the converter calls <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockGlue_GetRandomNumber</span> +to generate a new, unique session key. No two converted files look alike, even +if the original files are the same.</p> + +<p class=MsoBodyText><b>Note:</b> The random bytes cannot come from any bare-minimum +implementation of the C-library <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>rand</span> +function—they must be cryptographically secure. Otherwise, security will be +compromised.</p> + +<p class=MsoBodyText>The session key is encrypted and stored within the +converted file. Key encryption is performed using <span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockGlue_GetEncryptedKeyLength</span> and <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockGlue_EncryptKey</span>. +These two functions, together with the corresponding decryption function (<span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockGlue_DecryptKey</span>), +are the integration points where an OEM manufacturer may implement their own +key-encryption scheme.</p> + +<p class=MsoBodyText><b>Note:</b> The key-encryption key must be unique to each +device; this is what makes the files forward lock–protected. Ideally, it should +be derived from secret hardware parameters, but at the very least it should be +persistent from one master reset to the next.</p> + +<div style='margin-bottom:24.0pt;border:solid windowtext 1.0pt;padding:1.0pt 4.0pt 1.0pt 4.0pt; +background:#F2F2F2'> + +<p class=MsoBodyText style='background:#F2F2F2;border: +none;padding:0cm'><b>Note:</b> In the open-source implementation of the <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>libfwdlock-common</span> +library, a random key-encryption key is generated and stored in plaintext in +the file system, without being obfuscated in any way (doing so would be futile +since the source code is openly available). This key must be kept secret from +the user, and shouldn’t be possible to extract through backup-and-restore +functionality or the like. OEM manufacturers will probably want to implement a +truly hardware-based device-unique key.</p> + +</div> + +<p class=MsoBodyText style='page-break-after:avoid'><img width=531 height=563 +src="images/image002.gif"></p> + +<p class=MsoCaption style='margin-top:6.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm'><a name="_Ref263085187">Figure </a>2. Converter UC: Convert Data.</p> + +<b><span style='font-size:13.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></b> + +<h3><a name="_Toc276471427"></a><a name="_Ref263163082">3.1.2<span +style='font:7.0pt "Times New Roman"'> </span>Convert File +(Pull-Mode Conversion)</a></h3> + +<p class=MsoBodyText>Pull-mode conversion is performed by calling <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_ConvertFile</span> +with the filename, unless there is need for a specialized <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>read</span> function, in +which case <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_ConvertOpenFile</span> +should be used directly instead. See Figure 3.</p> + +<p class=MsoBodyText style='margin-bottom:24.0pt'>Internally, <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_ConvertFile</span> +calls <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_ConvertOpenFile</span>. +The latter then proceeds with the conversion using the push-mode API, acting as +the client in the previous use case; see section 3.1.1.</p> + +<p class=MsoBodyText style='page-break-after:avoid'><img width=531 height=731 +src="images/image003.gif"></p> + +<p class=MsoCaption style='margin-top:6.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm'><a name="_Ref263085208">Figure </a>3. Converter UC: Convert File.</p> + +<b><i><span style='font-size:14.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></i></b> + +<h2><a name="_Toc276471428">3.2<span style='font:7.0pt "Times New Roman"'> +</span>Decoder</a></h2> + +<p class=MsoBodyText>The decoder API allows the client to do the following:</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span>Check +the integrity of an internal Forward Lock file, i.e., detect whether it has +been manipulated in any way; see section 3.2.1.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span>Get +the MIME type of the embedded content (the “original” MIME type before DRM protection +was applied); see section 3.2.2.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>3.<span +style='font:7.0pt "Times New Roman"'> </span>Decode +the file by random access, i.e., read and seek through it in an arbitrary +manner; see section 3.2.3.</p> + +<p class=MsoBodyText>All subsequent operations on a file first require it to be +opened. Opening a file returns a <i>file descriptor</i>—a handle to be used in +these subsequent operations.</p> + +<p class=MsoBodyText>If the filename is known, an internal Forward Lock file +can be opened using <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_open</span>. +If only the file descriptor of an already open file is available, a decoding +session can instead be initialized using <span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_attach</span>.</p> + +<p class=MsoBodyText>Internally, <span style='font-size:10.0pt;font-family: +"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_open</span> calls <span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_attach</span>. For efficiency +reasons, <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_attach</span> +therefore assumes that the file position is at the beginning of the file when +the function gets called. A client who calls it directly must make sure that +this assumption holds.</p> + +<p class=MsoBodyText>When a file is being attached, the session key stored in +the file during conversion is decrypted using <span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockGlue_GetEncryptedKeyLength</span> and <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockGlue_DecryptKey</span>, +in order to set up for decoding and integrity checking.</p> + +<p class=MsoBodyText>For just getting the content type, however, retrieving the +session key would strictly speaking not be necessary, so there is an +opportunity here to optimize for that if it proves necessary later.</p> + +<p class=MsoBodyText>Symmetrical to <span style='font-size:10.0pt;font-family: +"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_open</span> and <span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_attach</span>, there are also functions +for closing a file or detaching from it:</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span>If +it was opened with <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_open</span> +it should be closed with <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_close</span>.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span>If +it was attached with <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_attach</span> +it should be detached with <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_detach</span>.</p> + +<b><span style='font-size:13.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></b> + +<h3><a name="_Ref263163099"></a><a name="_Toc276471429">3.2.1<span +style='font:7.0pt "Times New Roman"'> </span>Check Integrity</a></h3> + +<p class=MsoBodyText>There are three methods for checking the integrity of an +internal Forward Lock file, in whole or in part (see also Figure 4):</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span><span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckDataIntegrity</span>, +which checks the integrity of the encrypted content data.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span><span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckHeaderIntegrity</span>, +which checks the integrity of the file header, including the content type and +other fields not currently supported but reserved for future use.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>3.<span +style='font:7.0pt "Times New Roman"'> </span><span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckIntegrity</span>, +which internally calls first <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckHeaderIntegrity</span> +and then <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckDataIntegrity</span>.</p> + +<p class=MsoBodyText style='margin-bottom:24.0pt'><span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckHeaderIntegrity</span> is +generally much faster than <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_CheckDataIntegrity</span>, +whose running time is directly proportional to the size of the file.</p> + +<p class=MsoBodyText style='page-break-after:avoid'><img width=543 height=575 +src="images/image004.gif"></p> + +<p class=MsoCaption style='margin-top:6.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm'><a name="_Ref263163308">Figure </a>4. Decoder UC: Check Integrity.</p> + +<b><span style='font-size:13.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></b> + +<h3><a name="_Toc276471430"></a><a name="_Ref263163117">3.2.2<span +style='font:7.0pt "Times New Roman"'> </span>Get Content Type</a></h3> + +<p class=MsoBodyText style='margin-bottom:24.0pt'><span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_GetContentType</span> returns a +read-only reference to an ASCII string containing the MIME type of the +embedded content. This reference is valid as long as the file is kept open. +Clients who need access to the content type after closing the file should make +a copy of the string. See Figure 5 below.</p> + +<p class=MsoBodyText style='page-break-after:avoid'><img width=543 height=488 +src="images/image005.gif"></p> + +<p class=MsoCaption style='margin-top:6.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm'><a name="_Ref263163392">Figure </a>5. Decoder UC: Get Content Type.</p> + +<b><span style='font-size:13.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></b> + +<h3><a name="_Toc276471431"></a><a name="_Ref263163137">3.2.3<span +style='font:7.0pt "Times New Roman"'> </span>Decode File</a></h3> + +<p class=MsoBodyText>After opening an internal Forward Lock file (or attaching +to an already open one), it can be transparently read from as if it were +unencrypted. Any number of calls to read data from the current file position or +set it to a new one (which is what <span style='font-size:10.0pt;font-family: +"Lucida Console","DejaVu Sans Mono"'>lseek</span> does) can be made in any order; this is what we +call <i>random access</i>. See Figure 6.</p> + +<p class=MsoBodyText>The Forward Lock Decoder versions of the <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>read</span>, <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>lseek</span>, and <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>close</span> functions +have the exact same signatures as their POSIX counterparts. So, for example, +the call <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_lseek(fd, +0, SEEK_END)</span> returns the size of the embedded content data, i.e., the +size of the original file before DRM protection.</p> + +<p class=MsoBodyText style='margin-bottom:24.0pt'>Moreover, <span +style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>FwdLockFile_open</span> +is like regular POSIX <span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'>open</span> +except it takes only the filename as a parameter—access is always read-only.</p> + +<p class=MsoBodyText style='page-break-after:avoid'><img width=543 height=522 +src="images/image006.gif"></p> + +<p class=MsoCaption style='margin-top:6.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm'><a name="_Ref263166303">Figure </a>6. Decoder UC: Decode File.</p> + +<b><span style='font-size:16.0pt;font-family:"Arial","sans-serif"'><br +clear=all style='page-break-before:always'> +</span></b> + +<h1><a name="_Toc276471432">4<span style='font:7.0pt "Times New Roman"'> +</span>Definition of the Internal Forward Lock File Format</a></h1> + +<p class=MsoBodyText style='margin-bottom:12.0pt'>The inner structure of an internal +Forward Lock file is defined in Table 1 below.</p> + +<table class=MsoNormalTable border=1 cellspacing=0 cellpadding=0 + style='border-collapse:collapse;border:none'> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><b>Offset [bytes]</b></p> + </td> + <td width=96 valign=top style='width:72.0pt;border:solid windowtext 1.0pt; + border-left:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><b>Size [bytes]</b></p> + </td> + <td width=361 valign=top style='width:270.85pt;border:solid windowtext 1.0pt; + border-left:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><b>Description</b></p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>0</p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>4</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>The file signature (so-called + <i>magic number</i>): a four-character code consisting of the letters + F-W-L-K.</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>4</p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>1</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>Version number (0 for the + first version).</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>5</p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>1</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>Indicates the subformat:</p> + <p class=MsoNormal style='page-break-after:avoid'><i>0x00 Forward Lock</i></p> + <p class=MsoNormal style='page-break-after:avoid'><i>0x01 Combined Delivery</i></p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>6</p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>1</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>Usage restriction flags (prohibitions + against usage as ringtone or as wallpaper and screen saver). Also indicates + if the file is bound to a specific SIM card.</p> + <p class=MsoNormal style='page-break-after:avoid'><i>0x00 No usage + restrictions</i></p> + <p class=MsoNormal style='page-break-after:avoid'><i>0x01 Ringtone usage + prohibited</i></p> + <p class=MsoNormal style='page-break-after:avoid'><i>0x02 Screen usage + prohibited</i></p> + <p class=MsoNormal style='page-break-after:avoid'><i>0x80 Bound to SIM</i></p> + <p class=MsoNormal style='page-break-after:avoid'>(Any number of these may be + OR-ed together.)</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>7</p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>1</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>Length of the MIME content + type (<i>k</i>).</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>8</p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><i>k</i></p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>The MIME content type + (ASCII-encoded without null-character termination).</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>8+<i>k</i></p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><i>l </i>= 0 or 16</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>If the subformat is + Combined Delivery, this field contains the auto-generated content ID (16 bytes). + If not, this field is zero-size.</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>8+<i>k</i>+<i>l</i></p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><i>m </i>= 0 or 9</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>If the file is bound to a + specific SIM card, this field contains the 9-byte packed IMSI number. If not, + this field is zero-size.</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>8+<i>k</i>+<i>l</i>+<i>m</i></p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><i>n</i> ≥ 16</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>The encrypted session key, the + first sixteen bytes of which are also used as the CTR-mode <i>nonce</i> (similar + to the CBC-mode <i>initialization vector</i>).</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>8+<i>k</i>+<i>l</i>+<i>m</i>+<i>n</i></p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>20</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>Data signature—the SHA-1 + HMAC of the encrypted content data.</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>28+<i>k</i>+<i>l</i>+<i>m</i>+<i>n</i></p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>20</p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>Header signature—the SHA-1 + HMAC of all the fields above, including the encrypted session key and data + signature.</p> + </td> + </tr> + <tr> + <td width=111 valign=top style='width:83.4pt;border:solid windowtext 1.0pt; + border-top:none;padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>48+<i>k</i>+<i>l</i>+<i>m</i>+<i>n</i></p> + </td> + <td width=96 valign=top style='width:72.0pt;border-top:none;border-left:none; + border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'><i><to the end of the + file></i></p> + </td> + <td width=361 valign=top style='width:270.85pt;border-top:none;border-left: + none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt; + padding:0cm 5.4pt 0cm 5.4pt'> + <p class=MsoNormal style='page-break-after:avoid'>The content data encrypted + using 128-bit AES in CTR mode.</p> + </td> + </tr> +</table> + +<p class=MsoCaption style='margin-top:6.0pt;margin-right:0cm;margin-bottom: +12.0pt;margin-left:0cm;page-break-after:avoid'><a name="_Ref151269206">Table </a>1. Definition of the fields of an internal Forward Lock file.</p> + +<p class=MsoBodyText>As of now, neither Combined Delivery nor usage +restrictions (including SIM binding) are supported. These fields are reserved +for future use.</p> + +<h2><a name="_Toc276471433">4.1<span style='font:7.0pt "Times New Roman"'> +</span>Key Derivation</a></h2> + +<p class=MsoBodyText>The session key consists of sixteen bytes fetched from a +cryptographically secure random number generator. From the session key, two +separate keys are derived: one used for encryption, the other for signing.</p> + +<p class=MsoBodyText>The encryption key is the output from encrypting the +16-byte all-zero input block {0, 0, …, 0} using 128-bit AES with the random session +key as the key. The signing key is the output from encrypting the 16-byte input +block {1, 0, …, 0} the same way. The keys so derived will be cryptographically +independent from each other.</p> + +<p class=MsoBodyText>The session key is encrypted using a hardware-dependent +key-encryption key unique to each device. The encrypted session key is stored +inside the file, and its first sixteen bytes are also used as the <i>nonce</i> +for the CTR-mode encryption of the content data.</p> + +<h2><a name="_Toc276471434">4.2<span style='font:7.0pt "Times New Roman"'> +</span>Calculation of the Counters</a></h2> + +<p class=MsoBodyText>Using CTR (“counter”) mode, a block cipher such as AES can +be turned into a stream cipher. The process of encryption and decryption is +well defined in [1], except for the specifics of the calculation of the +counters. For the internal Forward Lock file format, the counters are +calculated as follows:</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span>The +nonce is interpreted as a 128-bit unsigned integer in little-endian format.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span>The +zero-based block sequence number (also a little-endian unsigned integer) is +added modulo 2<sup>128</sup> to the nonce to produce the counter for a given +block.</p> + +<h1><a name="_Toc276471435">5<span style='font:7.0pt "Times New Roman"'> +</span>Unit Test Cases</a></h1> + +<p class=MsoBodyText>Unit test cases for the converter and decoder come in two +varieties:</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>1.<span +style='font:7.0pt "Times New Roman"'> </span><i>Black-box</i> +test cases aim to verify that you get sensible results from malformed or +“tricky” input data.</p> + +<p class=MsoBodyText style='margin-left:36.0pt;text-indent:-18.0pt'>2.<span +style='font:7.0pt "Times New Roman"'> </span><i>White-box</i> +test cases aim to maximize code coverage using knowledge of code internals.</p> + +<p class=MsoBodyText>The black-box test cases are dependent on a specifically +designed set of input files found in the <span style='font-size:10.0pt; +font-family:"Lucida Console","DejaVu Sans Mono"'>forward-lock/internal-format/test/res</span> +directory in the repository. For ‘tests’ variants of the software, these input +files will be automatically installed in the file system image during build.</p> + +<p class=MsoBodyText>Run the test cases from the ADB shell command line as +follows:</p> + +<p class=MsoNormal style='margin-top:0cm;margin-right:0cm;margin-bottom:6.0pt; +margin-left:21.55pt'><span style='font-size:10.0pt;font-family:"Lucida Console","DejaVu Sans Mono"'># +gtest_fwdlock</span></p> + +<p class=MsoBodyText>If all black-box but no white-box test cases fail, the +input files probably can’t be found in the working directory.</p> + +<h1><a name="_Toc276471436">6<span style='font:7.0pt "Times New Roman"'> +</span>References</a></h1> + +<p class=MsoBodyText style='margin-left:28.9pt;text-indent:-28.9pt'>[1]<span +style='font:7.0pt "Times New Roman"'> +</span><a +href="http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf">Dworkin, +Morris: “Recommendation for Block Cipher Modes of Operation—Methods and +Techniques,” NIST Special Publication 800-38A, December 2001.</a><a +name="_Ref151269073"></a></p> + +</div> + +</body> + +</html> |