1 page.title=Security and Design 2 parent.title=In-app Billing 3 parent.link=index.html 4 @jd:body 5 6 <div id="qv-wrapper"> 7 <div id="qv"> 8 <h2>In this document</h2> 9 <ol> 10 <li><a href="#billing-security">Security Best Practices</a> 11 <ol> 12 <li><a href="#unlocked">Protect Unlocked Content</a></li> 13 <li><a href="#obfuscate">Obfuscate Your Code</a></li> 14 <li><a href="#sample">Modify Sample Code</a></li> 15 <li><a href="#nonce">Use Secure Random Nonces</a></li> 16 <li><a href="#payload">Set the Developer Payload String</a></li> 17 <li><a href="#trademark">Report Trademark and Copyright Infringement</a></li> 18 <li><a href="#revocable">Implement a Revocability scheme</a></li> 19 <li><a href="#key">Protect Your Public Key</a></li> 20 </ol> 21 </li> 22 </ol> 23 <h2>See also</h2> 24 <ol> 25 <li><a href="{@docRoot}google/play/billing/billing_overview.html">Overview of In-app 26 Billing</a></li> 27 </ol> 28 </div> 29 </div> 30 31 <p>As you design your In-app Billing implementation, be sure to follow the security and design 32 guidelines that are discussed in this document. These guidelines are recommended best practices for 33 anyone who is using Google Play's In-app Billing service.</p> 34 35 <h2>Security Best Practices</h2> 36 37 <h3 id="sign">Perform signature verification tasks on a server</h3> 38 <p>If practical, you should perform signature verification on a remote server and not on a device. 39 Implementing the verification process on a server makes it difficult for attackers to break the 40 verification process by reverse engineering your .apk file. If you do offload security processing to 41 a remote server, be sure that the device-server handshake is secure.</p> 42 43 <h3 id="unlocked">Protect your unlocked content</h3> 44 <p>To prevent malicious users from redistributing your unlocked content, do not bundle it in your 45 .apk file. Instead, do one of the following:</p> 46 <ul> 47 <li>Use a real-time service to deliver your content, such as a content feed. Delivering content 48 through a real-time service allows you to keep your content fresh.</li> 49 <li>Use a remote server to deliver your content.</li> 50 </ul> 51 <p>When you deliver content from a remote server or a real-time service, you can store the unlocked 52 content in device memory or store it on the device's SD card. If you store content on an SD card, be 53 sure to encrypt the content and use a device-specific encryption key.</p> 54 55 <h3 id="obfuscate">Obfuscate your code</h3> 56 <p>You should obfuscate your In-app Billing code so it is difficult for an attacker to reverse 57 engineer security protocols and other application components. At a minimum, we recommend that you 58 run an obfuscation tool like <a 59 href="{@docRoot}tools/help/proguard.html">Proguard</a> on your 60 code.</p> 61 <p>In addition to running an obfuscation program, we recommend that you use the following techniques 62 to obfuscate your In-app Billing code.</p> 63 <ul> 64 <li>Inline methods into other methods.</li> 65 <li>Construct strings on the fly instead of defining them as constants.</li> 66 <li>Use Java reflection to call methods.</li> 67 </ul> 68 <p>Using these techniques can help reduce the attack surface of your application and help minimize 69 attacks that can compromise your In-app Billing implementation.</p> 70 <div class="note"> 71 <p><strong>Note:</strong> If you use Proguard to obfuscate your code, you must add the following 72 line to your Proguard configuration file:</p> 73 <p><code>-keep class com.android.vending.billing.**</code></p> 74 </div> 75 76 <h3 id="sample">Modify all sample application code</h3> 77 <p>The In-app Billing sample application is publicly distributed and can be downloaded by anyone, 78 which means it is relatively easy for an attacker to reverse engineer your application if you use 79 the sample code exactly as it is published. The sample application is intended to be used only as an 80 example. If you use any part of the sample application, you must modify it before you publish it or 81 release it as part of a production application.</p> 82 <p>In particular, attackers look for known entry points and exit points in an application, so it is 83 important that you modify these parts of your code that are identical to the sample application.</p> 84 85 <h3 id="nonce">Use secure random nonces</h3> 86 <p>Nonces must not be predictable or reused. Always use a cryptographically secure random number 87 generator (like {@link java.security.SecureRandom}) when you generate nonces. This can help reduce 88 replay attacks.</p> 89 <p>Also, if you are performing nonce verification on a server, make sure that you generate the 90 nonces on the server.</p> 91 92 <h3 id="payload">Set the developer payload string when making purchase requests</h3> 93 <p>With the In-app Billing Version 3 API, you can include a 'developer payload' 94 string token when sending your purchase request to Google Play. Typically, this 95 is used to pass in a string token that uniquely identifies this purchase request. 96 If you specify a string value, Google Play returns this string along with the 97 purchase response. Subsequently, when you make queries about this purchase, 98 Google Play returns this string together with the purchase details.</p> 99 <p>You should pass in a string token that helps your application to identify the user who 100 made the purchase, so that you can later verify that this is a legitimate purchase by 101 that user. For consumable items, you can use a randomly generated string, but for non- 102 consumable items you should use a string that uniquely identifies the user.</p> 103 104 <p class="note"> 105 <strong>Note:</strong> Do not use the user's 106 email address in the payload string, since that address may change. 107 </p> 108 109 <p>When you get back the response from Google Play, make sure to verify that the 110 developer payload string matches the token that you sent previously with the purchase 111 request. As a further security precaution, you should perform the verification on your 112 own secure server.</p> 113 114 115 <h3 id="trademark">Take action against trademark and copyright infringement</h3> 116 <p>If you see your content being redistributed on Google Play, act quickly and decisively. File a 117 <a href="http://support.google.com/googleplay/android-developer/bin/answer.py?hl=en&answer=141511"> 118 trademark notice of infringement</a> or a <a href="http://www.google.com/android_dmca.html"> 119 copyright notice of infringement</a>.</p> 120 121 <h3 id="revocable">Implement a revocability scheme for unlocked content</h3> 122 <p>If you are using a remote server to deliver or manage content, have your application verify the 123 purchase state of the unlocked content whenever a user accesses the content. This allows you to 124 revoke use when necessary and minimize piracy.</p> 125 126 <h3 id="key">Protect your Google Play public key</h3> 127 <p>To keep your public key safe from malicious users and hackers, do not embed it in any code as a 128 literal string. Instead, construct the string at runtime from pieces or use bit manipulation (for 129 example, XOR with some other string) to hide the actual key. The key itself is not secret 130 information, but you do not want to make it easy for a hacker or malicious user to replace the 131 public key with another key.</p> 132
